材料专业词汇

材料专业词汇!(全)希望有用 - 化学元素(elements) 化学元素,简称元素,是化学元素周期表中的基本组成,现有113种元素,其中原子序数从93到113号的元素是人造元素。 物质(matter) 物质是客观实在,且能被人们通过某种方式感知和了解的东西,是元素的载体。 材料(materials) 材料是能为人类经济地、用于制造有用物品的物质。 化学纤维(man-made fiber, chemical fiber) 化学纤维是用天然的或合成的高聚物为原料,主要经过化学方法加工制成的纤维。可分为再生纤维、合成纤维、醋酯纤维、无机纤维等。 芯片(COMS chip) 芯片是含有一系列电子元件及其连线的小块硅片,主要用于计算机和其他电子设备。 光导纤维(optical waveguide fibre) 光以波导方式在其中传输的光学介质材料,简称光纤。 激光(laser) (light amplification by stimulated emission of radiation简写为:laser) 激光是利用辐射计发光放大原理而产生的一种单色(单频率)、定向性好、干涉性强、能量密度高的光束。 超导(Superconduct) 物质在某个温度下电阻为零的现象为超导,我们称具有超导性质的材料为超导体。 仿生材料(biomimetic matorials) 仿生材料是模仿生物结构或功能,人为设计和制造的一类材料。 材料科学(materials science) 材料科学是一门科学,它从事于材料本质的发现、分析方面的研究,它的目的在于提供材料结构的统一描绘,或给出模型,并解释这种结构与材料的性能之间的关系。 材料工程(materials engineering) 材料工程属技术的范畴,目的在于采用经济的、而又能为社会所接受的生产工艺、加工工艺控制材料的结构、性能和形状以达到使用要求。 材料科学与工程(materials science and engineering) 材料科学与工程是研究有关材料的成份、结构和制造工艺与其性能和使用性能间相互关系的知识及这些知识的应用,是一门应用基础科学。材料的成份、结构,制造工艺,性 能及使用性能被认为是材料科学与工程的四个基本要素。 成份(composition) 成分是指材料的化学组成及其所占比例。 组织、结构(morphology 、structure) 组织结构是表示材料微观特征的。组织是相的形态、分布的图象,其中用肉眼和放大镜观察到的为宏观组织,用显微镜观察到的为显微组织,用电子显微镜观察到的为电子显微组织。结构是指材料中原子或分子的排列方式。 性能(property) 性能是指材料所具有的性质与效用。 工艺(process) 工艺是将原材料或半成品加工成产品的方法、技术等。 使用性能(performance) 材料在具体的使用条件和环境下所表现出来的行为。 上一页下一页 电负性( electro negativity ) 周期表中各元素的原子吸引电子能力的一种相对标度为电负性,又称负电性。元素的电负性愈大,吸引电子的倾向愈大,非金属性也愈强。电负性的定义和计算方法有多种,每一种方法的电负性数值都不同,比较有代表性的有3种:①LC鲍林提出的标度。根据热化学数据和分子的键能,指定氟的电负性为3.98,计算其他元素的相对电负性。②RS密立根从电离势和电子亲合能计算的绝对电负性。③AL阿莱提出的建立在核和成键原子的电子静电作用基础上的电负性。利用电负性值时,必须是同一套数值进行比较。 元素的电负性值(鲍林标度) 元素电负性氢 2.20 钪 1.36 锂0.98 钛 1.54 钠0.93 钒 1.63 钾0.82 铬 1.66 铷0.82 锰 1.55 铯0.79 铁 1.83 铍 1.57 钴 1.88 镁 1.31 镍 1.91 钙 1.00 铜 1.90 锶0.95 锌 1.65 钡0.89 硼 2.04 铝 1.61 砷 2.18 镓 1.81 锑 2.05 铟 1.78 铋 2.02 铊 2.04 氧 3.44 碳 2.55 硫 2.58 硅 1.90 硒 2.55 锗 2.01 氟 3.98 锡 1.96 氯 3.16 铅 2.33 溴 2.96 氮 3.04 碘 2.66 磷 2.19 离子键(ionic bond ) 离子键是通过异性电荷之间的吸引产生的化学结合作用,又称电价键。电离能小的金属原子(如碱金属)和电子亲合能大的非金属原子(如卤素)接近时,前者将失去电子形成正离子,后者将获得电子形成负离子,正负离子通过库仑作用相互吸引。当这种吸引力与离子的电子云之间的排斥力达到平衡时,形成稳定的以离子键结合的体系。 离子键的特征是作用力强,而且随距离的增大减弱较慢;作用不受方向性和饱和性的限制,一个离子周围能容纳多少个异性离子及其配置方式,由各离子间的库仑作用决定。以离子键结合的体系倾向于形成晶体,以便在一个离子周围形成尽可能多的离子键,例如NaCl分子倾向于聚集为NaCl晶体,使每个钠(或氯)离子周围的离子键从1个变为6个。 共价键(covalent bond) 共价键是原子之间通过共享电子而产生的化学结合作用。典型的共价键存在于同核双原子分子中,由每个原子提供一个电子构成成键电子对。这对电子的自旋方向相反,集中在中间区域,并吸引带正电的两个原子的核心部分而把它们结合起来。在异核双原子分子中,2个原子的核心部分对成键电子的吸引力不同,成键电子偏向一方,例如在氟化氢分子中电子偏向氟,这种化学键称为极性键。共价键的特征是有饱和性、方向性和作用的短程性。一个原子能形成的典型共价键的数目等于该原子的价电子数,称为它的原子价。共价键之间有特定的相对取向,例如水分子呈弯曲形,而二氧化碳分子是直线形的。共价键的方向性使分子具有特定的几何形状。 金属键(metallic bond ) 使金属原子结合成金属的相互作用。金属原子的电离能低,容易失去电子而形成正离子和自由电子,正离子整体共同吸引自由电子而结合在一起。金属键可看作高度离域的共价键,但没有饱和性和方向性。金属键的显著特征是成键电子可在整个聚集体中流动,这使金属呈现出特有的属性:良好的导热性和导电性、高的热容和熵值、延展性和金属光泽等。 分子键(molecule bond) 惰性气体分子间是靠分子键结合的,其实质是分子偶极矩间的库仑相互作用,这种结合键较弱。其分子间相互作用力为范德华力。 氢键(hydrogen bond) 一个与电负性高的原子X共价结合的氢原子(X-H)带有部分正电荷,能再与另一个电负性高的原子(如Y)结合,形成一个聚集体X-H…Y的化学结合作用。X、Y原子的电负性越大、半径越小, 则形成的氢键越强。例如,F-H…F是最强的氢键。氢键表面上有饱和性和方向性:一个H原子只能与两个其他原子结合,X-H…Y要尽可能成直线。但氢键H…Y 之间的作用主要是离子性的,呈现的方向性和饱和性主要是由X和Y之间的库仑斥力决定的。氢键可以在分子内形成,称为内氢键;也可以在两个分子之间形成。分子间的氢键可使很多分子结合起来,形成链状、环状、层状或立体的网络结构。 氢键的键能比较小,通常只有17~25千焦/摩尔。但氢键的形成对物质的性质有显著影响,例如使熔点和沸点升高;溶质与溶剂之间形成氢键,使溶解度增大;在核磁共振谱中氢键使有关质子的化学位移移向低场;在红外光谱中氢键X-H…Y的形成使X-H的特征振动频率变小并伴有带的加宽和强度的增加;氢键的形成决定蛋白质分子的构象,在生物体中起重要的作用。 晶体(crystal) 微粒(原子、分子或离子) 在空间呈三维周期性规则排列的固体。自然界的物质有3种存在形态,即气体、液体和固体, 固体物质又有晶体和非晶态之分,例如玻璃是非晶态物质。固体物质中绝大多数都是晶体,如金属、合金、硅酸盐,大多数无机化合物和一些有机化合物,甚至植物纤维都是晶体。有些晶体具有规则的多面体外形,如水晶,称为单晶体;有些则没有规则整齐的外形,如金属,整个固体是由许多取向随机的微小单晶颗粒组合而成,这样的固体称为多晶体。 晶体的一切性质无不与其内部结构有三维周期性这个特征密切相关,如晶体具有固定的熔点、各向异性、对称性、能使X射线发生衍射。固体物质是否为晶体,一般用X射线 衍射法予以鉴定。另外,晶体还具有对称性。 准晶(Quasicrystal) 准晶是同时具有长程准周期平移性和非晶体学旋转对称性的固态有序相。准周期性和非晶体学对称性构成了准晶结构的核心特征。 非晶(amorphism) 与晶体不同,非晶体原子排列是短程有序、长程无序,固体的性能是各向同性的。 液晶(liquid crystal) 液晶态是介于三维有序晶态与无序晶态之间的一种中间态。在热力学上是稳定的,它既具有液体的易流动性,又具有晶体的双折射等各向异性的特征。处于液晶态的物质,其分子排列存在位置上的无序性,但在取向上仍有一维或二维的长程有序性,因此液晶又可称为―位置无序晶体‖或―取向有序液体‖。液晶材料都是有机化合物,有小分子也有高分子,其数量已近万种,通常将其分为二大类,热致液晶和溶致液晶。热致液晶只在一定温度范围内呈现液晶态,即这种物质的晶体在加热熔化形成各向同性的液体之前形成液晶相。热致液晶又有许多类型,主要有向列型、近晶型和胆甾型。溶致液晶是一种只有在溶于某种溶质中才呈现液晶态的物质。 基元(element) 组成晶体的原子、离子、分子或原子团统称称为晶体的基本结构单元,简称基元。点阵(lattice) 晶体基元周期性排列的点的集合,它就称为―晶格‖(或点阵),这些点被称为格点。因此,可以说晶体的结构是由组成晶体的基元加上空间点阵来决定的。 晶胞(crystal cell) 晶胞是晶体的基本结构单位。反映晶体结构三维周期性的晶格将晶体划分为一个个彼此互相并置而等同的平行六面体,即为晶胞。晶胞包括两个要素:一是晶胞的大小、型式;另一是晶胞的,前者主要指晶胞参数的大小,即平行六面体的边长a 、b、c和夹角α、β、γ的大小, 以及与晶胞对应的空间点阵型式,即属于简单格子P还是带心格子I、F或C 等;后者主要指晶胞中有哪些原子、离子以及它们在晶胞中的分布位置等。 面心立方结构(fcc——face-centered-cubic),体心立方结构(bcc——body-centered-cubic)和密排六方结构(hcp——hexagonal close-packed) 金属所具有的典型晶体结构为面心立方结构(fcc)(图2-27),体心立方结构(bcc) (图2-28)和密排六方结构(hcp)(图2-29),皆属于立方结构晶系。 具有面心立方结构的常见金属有: γ-Fe 、Al、Ni、Cu、Ag、Au、Pt,等 具有体心立方结构的常见金属有:β-Ti、V、Cr、α-Fe、β-Zr、Nb、Mo、Ta、W等具有密排六方结构的常见金属有:α-Ti、α-Zr、Co、Mg、Zn等 离子键(ionic bond ) 离子键是通过异性电荷之间的吸引产生的化学结合作用,又称电价键。电离能小的金属原子(如碱金属)和电子亲合能大的非金属原子(如卤素)接近时,前者将失去电子形成正离子,后者将获得电子形成负离子,正负离子通过库仑作用相互吸引。当这种吸引力与离子的电子云之间的排斥力达到平衡时,形成稳定的以离子键结合的体系。 离子键的特征是作用力强,而且随距离的增大减弱较慢;作用不受方向性和饱和性的限制,一个离子周围能容纳多少个异性离子及其配置方式,由各离子间的库仑作用决定。以 离子键结合的体系倾向于形成晶体,以便在一个离子周围形成尽可能多的离子键,例如NaCl分子倾向于聚集为NaCl晶体,使每个钠(或氯)离子周围的离子键从1个变为6个。 上一页下一页 硅酸盐结构(silicate structure) 硅酸盐结构是一种共价晶体的结构,硅酸盐的基本结构单元就是四面体(图2-33),硅原子位于氧原子四面体间隙中,每个氧原子外层只有7个电子,为-1价,还能和其他金属离子键合,其中Si的配位数是4,氧的配位数是2,Si-O-Si的结合键间键角接近145°。这种硅氧四面体可以孤立地在结构中存在,如镁橄榄石Mg2SiO4 ,锆英石ZrSiO4等;也可以通过其顶点互相连接;除可以连成骨架状外,还可以连成链状和层状(图2-34)。莫莱石就是链状硅酸盐,高岭土和滑石则是层状硅酸盐。 离子晶体结构(ion crystal structure) 离子晶体是由正负离子通过离子键,按一定方式堆积起来而形成的,也就是说,离子晶体的基元是离子而不是原子了,这些离子化合物的晶体结构必须确保电中性,而又能使不同尺寸的离子有效地堆积在一起。多数盐类,碱类(金属氢氧化物)及金属氧化物都形成离子晶体。 周期性(periodicity) 对空间点阵,可以看成是由几何点沿空间三个不共面的方向各按一定距离无限重复地平移构成(图2-20),每个方向的一定平移距离称为该点阵在该方向的周期,故周期性也可以称之为平移对称性。理想晶体的内部结构是组成晶体的原子、分子或原子团等在三维空间中有规则地周期性重复排列,这种周期性排列是晶体最基本的特点,也是研究晶体各种物理性质的重要基础。 对称性(symmetry) 晶体的对称性是指晶体经过某种几何变换(平移、旋转等操作)仍能恢复原状的特性。 配位数(CN——coordination number) 对于简单晶格,配位数CN为晶格中任一原子周围最近邻且等距离的原子数; 致密度(堆积因子)(Packing factor) 原子体积占总体积的百分数。若以一个晶胞来计算,致密度就是晶胞中原子体积与晶胞体积之比,即k=nv/V,其中v为单个原子的体积,V为晶胞体积,n为一个晶胞中的原子数。 离子半径(ionic radius) 离子半径是反映离子大小的一个物理量。离子可近似视为球体,离子半径的导出以正、负离子半径之和等于离子键键长这一原理为基础,从大量X射线晶体结构分析实测键长值中推引出离子半径。离子半径的大小主要取决于离子所带电荷和离子本身的电子分布,但还要受离子化合物结构型式(如配位数等)的影响。 负离子配位多面体(Anion coordination polyhedron) 负离子配位多面体指的是离子晶体结构中,与某一个正离子成配位关系而且相邻的各个负离子中心线所构成的多面体。 空位(vacancy) 如果晶格中某格点上的原子空缺了,则称为空位,这是晶体中最重要的点缺陷。 间隙原子(interstice) 脱位原子有可能挤入格点的间隙位置,形成间隙原子。 色心(color center) 离子晶体的某些点缺陷是有效电荷的中心,他们可能束缚电子,这种缺陷的电子结构能吸收可见光而使该晶体着色,故称这种能吸收可见光的晶体缺陷为色心。 刃位错、螺位错(edge dislocation、screw dislocation) 晶体中由于滑移或晶体失配,原子或离子排列的点阵结构发生畸变的线型缺陷轨道称为位错线,简称位错(dislocation)。晶体中位错的基本类型为刃型位错和螺型位错。图2-47是刃型位错模型,可以看到,与完整晶格相比,它多了一个半原子面,而且这个半原子面象个"劈"一样,楔入完整晶体,终止于晶体中,面的边缘是一条线,这条线周围若干个原子距离内的原子的规则排列遭到破坏,这就形成了刃位错。如果让晶体中的一部分在切应力作用下滑移,如图2-47所示,可以发现,发生滑移与未发生滑移的交界处也是一条直线,其附近原子的规则排列也被破坏了,如图2-48所示,这些原子呈螺旋状分布,称这种位错为螺型位错。 晶界(grain boundary) 不同取向的晶粒之间的界面。 孪晶界(twin boundary) 孪晶间的界面叫孪晶界,其界面两侧的原子排列成镜面对称。 相(phase) 相是指系统中的物质结构均匀的部分。气体在平衡条件下,不论有多少组分,都是均匀的,因此气相只有一种,固体内部就比较复杂了,在固体材料中,具有同样聚集状态,同样原子排列特征性质,并以界面相互隔开的均匀组成部分称之为―相‖。相可以是单质,也可以是化合物。材料的性能与各组成相的性质、形态、分布和数量直接有关。 组织(morphology) 组织是相的形态、分布的图象,其中用肉眼和放大镜观察到的为宏观组织,用显微镜观察到的为显微组织,用电子显微镜观察到的为电子显微组织。 相图(phase diagram) 平衡状态下物系的组分、物相和外界条件间相互关系的几何描述,也称状态图或平衡图。凝聚体系的相图多数是恒压下的温度-组分关系图。 杠杆定律(lever law) 确定某种成份的合金在二相区中各相的相对含量的法则。首先要确定各单相的成份。在一定温度下,两单相的成份是确定的,就是温度水平线与相界线的交点所对应的成份。如图2-58所示,现在我们考虑成份为C %(wt)的A合金在t1温度下液、固二相的相对含 量。从图中可以看出,液相浓度为CL %(wt),固相浓度为Cα%(wt),假设合金的质量为1,液相质量为WL,固相质量为Wα,则WL+Wα=1,另外合金A中的含Ni量应该等于液相含Ni量和固相合Ni量之和,即WL CL + Wα Cα= 1xC,由这二式可以得出WL/ Wα=( Cα- C)/(C- CL)= rb /ar ,再变换一下可得WL?ar = Wα?rb ,这个关系式与以r为支点,以a、b二点为受力端点的杠杆平衡时的关系类似,故称其为杠杆定律。 匀晶相图(somorphous) 这种相图的特点是两组元不但在液态无限互溶,而且在固态也无限互溶。结晶时,都是从液相中结晶出单相固溶体。我们把从液相结晶出单相固溶体的结晶过程称为匀晶转变。具有这类相图的二元合金系有Cu-Ni、Ag-Au、Fe-Ni、Cr-Mo、Cu-Au等,有些硅酸盐材料如镁橄榄石(Mg2 SiO4)-铁橄榄石(Fe2SiO2)等也具有此类特征。 共晶反应(eutectic reaction) 在共晶相图上有单相区。两单相区之间为双相区。另外还都有一条水平线,如Pb-Sn 相图上MEN,这表示在水平线所对应的这个特定温度下有三相共存。E点是二条液相线AE和BE的交点,在E点的上方是液相,其下方是α、β二相共存区。这说明,相当于E 点成份的液相在冷却至三相共存线的温度时,会同时结晶出成份为M的α相和成份为N 的β相,这种反应可以写成如下形式: 这种由某一成份液相在恒温下同时结晶出二个成份不同的固相的反应称为共晶反应,发生共晶反应的温度TE为共晶温度,成份为E点的合金为共晶合金。共晶组织为α相和β相的机械混合物,它们通常呈层片状相间分布。 共晶相图(eutectic phase diagram) 两组元在液态无限互溶,固态有限互溶或完全不互溶,冷却过程中发生共晶反应的相图为共晶相图。具有共晶相图的合金系有Pb-Sn、Al-Si、Pb-Bi等,一些硝酸盐也具有共晶相图。 包晶反应(peritectic reaction) 包晶反应是由一固定成份的液相和一固定成份的固相相互作用生成另一个固定成份的固相,其反应式可表示为,包晶反应的产物是单相固溶体。 包晶相图(peritectic phase diagram) 两组元在液态无限固溶,固态下有限互溶(或不互溶)并发生包晶反应的二元系相图称为包晶相图,Pb-Ag就形成包晶相图,陶瓷ZrO2-CaO也形成包晶相图。在包晶相图上也存在单相区、双相区、三相区,也是只有在特定的温度下才能三相共存。 Fe-C相图(Fe-C phase diagram) Fe-C相图是Fe-C合金的二元相图,是材料科学尤其是金属热处理最重要的相图之一。 共析反应(eutectoid reaction) 共析反应是由一固定成份的固相在特定温度下同时析出两种固相的反应,其反应式可表示为,共析反应的产物是两种固相的机械混合物。 铁素体α (ferrite) 铁或其内固溶有一种或数种其他元素所形成的、晶体点阵为体心立方的固溶体。 奥氏体γ(austenite) 铁内固溶有碳和〔或〕其他元素的、晶体结构为面心立方的固溶体。它是以英国冶金学家R.Austen的名字命名的。 珠光体(pearlite) 本意是奥氏体从高温缓慢冷却时发生共析转变所形成的产物,其立体形态为铁素体薄层和碳化物(包括渗碳体)薄层交替重叠的层状复相物。广义则包括过冷奥氏体发生珠光体转变所形成的层状复相物。这种组织是以其金相形态酷似珍珠母甲壳外表面的光泽而得名。 固溶体(solid solution) 固态条件下,一种组分(溶剂)内―溶解‖了其他组分(溶质)而形成的单一、均匀的晶态固体。固溶体有置换型(替位型)和间隙型(填隙型)两种:溶质原子位于溶剂晶格中某些结点位置时形成置换型固溶体;溶质原子位于溶剂晶格中某些间隙位置时形成间隙型固溶体。 能带(energy band) 能带是描述晶体中电子能量状态的一个物理概念。晶体是由大量原子规则排列组成的,在晶体中原子的外层电子运动已不再局限在该原子附近,而是可以在整个晶体中运动。这种情况称为电子运动的共有化。其结果是:N个孤立原子有N个相同的能级,在晶体中变成N个能量略有差别的不同等级,构成能带。 空带(vacancy band) 没有被电子或空穴填充的能带。 导带(conduction band) 金属的价带之上的最低能带有大量电子,但没有占满所有的能带,这些电子在电场作用下,可以在晶体中运动,引起电流,因此这种能带称为导带。 价带(valence band) 一系列能带中,能量最高的满带被称为价带。 禁带(forbidden band) 有些晶体中,能带和能带之间有一定的间隔,这个间隔中的能量一般是该晶体电子不能具有的,所以称此间隔为禁带。禁带往往表示价带和最低导带之间的能量间隔。 能隙(energy gap) 固体中电子两相邻能带相隔的能量范围称为能隙,亦称为禁带宽度。 弹性(elastic property) 弹性是反映晶格中原子在外力作用下自平衡位置产生可逆位移的力学性能之一。 虎克定律(Hooke's law) 当材料发生弹性变形的时候,应力与应变呈线性关系,即σ=Eε,这就是著名的虎克定律,E为杨氏模量,σ为应力,既单位面积所受的力,ε为应变,既单位长度的伸长。 塑性(plasticity) 塑性是指材料断裂前发生塑性变形的能力。 延伸率(percentage of elongation) 延伸率指的是试样拉断后标距的伸长和原始标距的百分比。 断面收缩率(percentage reduction of area) 断面收缩率是试样拉断后,缩颈处横截面积的最大缩减量与原始横截面积的百分比。强度(strength) 强度是材料或物件经得起变形的能力。 屈服强度(yield strength) 屈服强度是试样在拉伸过程中,开始产生塑性变形所须的应力。通常用标距部分残余伸长达到原标距长度的规定数值时之力除以原横截面积所得的应力来表示,一般取残余应变0.2%。 抗拉强度(tensile strength) 抗拉强度是在拉伸试验中,试样所能承受的最大负荷除以原横截面积所得的应力值。 韧性(toughness) 韧性是材料在外力作用下,在塑性形变过程中吸收能量的能力。吸收能量愈大,韧性愈好。 断裂韧性fracture toughness 断裂韧性是断裂力学中,量度裂纹扩展阻力的主要指标之一,它反映具有裂纹的材料对外界作用的一种抵抗能力。 硬度(hardness) 硬度是指材料表面上不大的体积内抵抗变形或破裂的能力。 布式硬度(Brinell hardness ) 用一定直径的球体(钢球或硬质合金球)以相应的试验力压入试样表面,经规定保持时间后卸除试验力,用测量的表面压痕直径计算的一种压痕硬度值。 洛式硬度(Rockwell hardness) 在初始试验力及总试验力先后作用下,将压头(金刚石圆锥或钢球)压入试样表面,经规定保持时间后卸除主试验力,用测量的残余压痕深度增量计算的一种压痕硬度值。 维式硬度(Vickers hardness) 将相对面夹角为136°的正四棱锥体金刚石压头以选定的试验力(49.03~980.7N)压入试样表面,经规定保持时间后卸除试验力,用测量的压痕对角线长度计算的一种压痕硬 度值 显微硬度(microhardness) 显微硬度主要用于确定很薄的材料、细金属丝、小型精密零件(如钟表和仪表零件)的硬度,测定淬硬表面的硬度变化率,研究小面积内硬度的变化以及在金相学中研究金属中不同相体的硬度等。测量方法与维氏硬度基本相同,但载荷很小,以克力计数;压痕的特征尺寸也很小,需要用读数显微镜测出,故得名。 固溶强化(solid solution strengthening) 在纯金属中加入溶质原子(间隙型或置换型)形成固溶合金(或多相合金中的基体相),将显著提高屈服强度,此即为固溶强化。 形变强化(strain strengthening) 从图3-2的应力-应变曲线上可以看出,材料屈服以后,随着塑性变形量的增加,所需的应力是不断增加的,这种现象叫形变强化,也叫加工硬化。形变强化是金属强化的重要方法之一,它能为金属材料的应用提供安全保证,也是某些金属塑性加工工艺所必须具备的条件,如拔制。 晶界强化(grain size strengthening) 随着晶粒细化,晶界所占体积增加,金属的强度和塑性是同时提高的。这种强化工艺称为晶界强化。 弥散强化(第二相强化)(dispersion strengthening) 所谓第二相强化是指在金属基体(通常是固溶体)中还存在另外的一个或几个相,这些相的存在使金属的强度得到提高。 择优取向(preferred orientation) 在一般多晶体中,每个晶粒有不同于相邻晶粒的结晶学取向,从整体看,所有晶粒的取向是任意分布的。但某些情况下,晶体的晶粒在不同程度上围绕某些特殊的取向排列,就称为择优取向或简称织构。 再结晶(recrystallization) 金属塑性变形后,被拉长了的晶粒重新生核、结晶,变为等轴晶粒这种现象称为再结晶。 再结晶温度(recrystallization temperature) 再结晶温度是开始产生再结晶现象的最低温度。对纯金属,再结晶温度约为0.4Tm,式中Tm为金属的熔点。 热处理(heat treatment) 热处理是对固体金属或合金进行加热、保温和冷却处理以便得到所需性质的一种加工工艺。其原理是利用扩散、晶核化、沉积和晶体增长等现象,使金属或合金的组织发生变化,进而获得均匀的或改性的机械和物理性质。 扩散型相变、非扩散型相变(transformation involving diffusion、diffusionless transformation) 根据冷却速度的不同,存在着二大类固态相变,一类是相变时存在原子扩散,为扩散 型相变,如珠光体、贝氏体转变;还有一类是不存在原子的扩散,但原子也发生了重排,为非扩散型相变,如马氏体相变。 马氏体(martensite) 马氏体是高温相以很快的速度冷却,以非扩散转变形成的产物。钢在高温奥氏体化后淬火得到马氏体。 贝氏体(bainite) 贝氏体是在奥氏体化后被过冷到珠光体转变温度区间以下,马氏体转变温度区间以上这一中温区间(所谓―贝氏体转变温度区间‖)转变而成的由铁素体及其内分布着弥散的碳化物所形成的亚稳组织。 退火(annealing) 将组织偏离平衡态的钢加热到适当温度,保温一段时间,然后缓慢冷却(炉冷)以获得接近平衡态组织的热处理工艺叫退火 正火(normalizing) 将钢件加热到Ac3以上30-50℃,保温后取出在空气中冷却,这是正火 淬火(quenching) 将钢件加热到奥氏体化温度并保温后,急冷(油冷或水冷)至室温,从而使奥氏体变成马氏体的处理为淬火。 回火(tempering) 回火指将经过淬火的工件重新加热到低于下临界温度的适当温度,保温一段时间后在空气或水、油等介质中冷却的金属热处理。回火的作用在于:①提高组织稳定性,使工件在使用过程中不再发生组织转变,从而使工件几何尺寸和性能保持稳定。②消除内应力,以便改善工件的使用性能并稳定工件几何尺寸。③调整材料的力学性能以满足使用要求。 时效(ageing) 时效是指合金经固溶处理或冷塑性变形后,在室温或一定温度保温,以达到沉淀硬化目的的工艺。 人工时效(artifical aging) 人工时效是在高于室温以上,通过过饱和固溶体中可溶组分的脱溶,使合金强化的热处理。 自然时效(natural aging) 自然时效是在室温下,通过过饱和固溶体中可溶组分自发的脱溶,使合金强化的处理。 控制轧制(controlled rolling) 把金属材料压力加工和热处理工艺相结合,同时利用形变强化与相变强化的一种形变热处理工艺。 铝-锂合金(Al-Li alloy) 铝-锂合金是一种新型铝合金材料,具有较高的强度和弹性模量,是航空航天工业理想的结构材料,用于飞机上,可减轻飞机重量8~16%。铝锂合金还具有良好的抗辐照特性和 较高的电阻率,经受中子辐照后残留放射性低,可用作核聚变装置中的真空容器。此外,铝锂合金在一定温度和应变速率下具有很好的超塑性,可用以制造超塑性/扩散焊接结构,应用于航空和车辆等各个领域。 紫铜(red copper) 紫铜即纯铜。 黄铜(brass) 黄铜是以锌为主要添加元素的铜合金。 青铜(bronze) 最早使用的青铜是Cu-Sn合金,现在把除黄铜以外的铜合金都称为青铜。 α型钛合金(α - titanium alloy) 金属钛有两种异构体,一种是密排六方结构的α相,是低温稳定相;另一种是体心立方结构的β相,是高温稳定相。成分中含有α相稳定元素,在室温稳定状态基本为α相的钛合金为α型钛合金。 β型钛合金(β - titanium alloy) 成分中含有β相稳定元素,在室温稳定状态基本为β 相的钛合金为β型钛合金。 α+β型钛合金(α+β titanium alloy) 成分中含有较多的β 稳定剂,在室温稳定状态由α及β 相所组成的钛合金为α+β型钛合金。 钛铝化合物为基的钛合金(Ti-Al intermetallic compound) 钛铝化合物是指Ti3Al,TiAl,TiAl3这些金属间化合物。钛铝化合物为基的钛合金是一种新型钛合金。钛铝化合物为基的高温钛合金与普通钛合金及镍基高温合金比较,高温性能明显优于普通钛合金,已与镍基高温合金相近。 结构陶瓷(structure ceramics) 结构陶瓷是指作为工程结构材料使用的陶瓷材料,主要利用其高机械强度、耐高温、耐腐蚀、耐摩擦,以及高硬度等性能。陶瓷虽然抗压强度相当高,但抗拉强度却很小,是一种脆性材料。结构陶瓷按其组份可分为氧化物陶瓷和非氧化物陶瓷,有些结构陶瓷也具有功能陶瓷的性能如ZrO2陶瓷等。 相变增韧(phase transformation toughening) 相变增韧是一种有效的增强、增韧方法,利用多晶多相陶瓷中某些相组分在不同温度的相变,从而达到增强、增韧的效果,这统称为相变增韧。例如,利用ZrO2的马氏体相变可以改善陶瓷材料的力学性能。 ZrO2相变增韧又分为应力诱导相变增韧、微裂纹增韧和表面压应力三种。相变增韧不但存在于ZrO2陶瓷中,将ZrO2相颗粒加入其它陶瓷材料中也能产生相变增韧的效果。 ZrO2相变增韧(zirconium oxide phase transfotmation toughening) ZrO2存在三种晶型,立方、四方、单斜。 其中四方相向单斜相的相变伴随有较大的体积变化~7%,这种相变体积变化是相变增韧的基础。 应力诱导相变增韧(stress-induced phase transformation toughening) 分散于陶瓷基体内的四方ZrO2相颗粒,从高温向低温变化,当温度低于1100℃时,由于陶瓷基体的约束,不能发生四方向单斜的相变,四方ZrO2相颗粒以亚稳态的形式存在于室温,当陶瓷基体受到外力的作用,解除了对四方ZrO2相颗粒的约束,四方ZrO2相颗粒就发生相变,降低裂纹尖端的应力场强度,达到增强、增韧的目的。 微裂纹增韧(microcrack toughening) 分散于陶瓷基体内的四方ZrO2相颗粒,在降温过程或受力后相变,在裂纹尖端产生多条微裂纹,从而增大了断裂表面能,达到增韧的效果。 表面增韧(surface toughening) 分散于陶瓷基体表面的四方ZrO2相颗粒,由于在一个面上没有受到约束,相对于基体内的四方ZrO2相颗粒,比较容易相变,在降温或受力后,表面的四方ZrO2相颗粒发生相变,产生体积膨胀,使得陶瓷材料的表面受到压应力,达到增强、增韧的效果。 弥散增韧(dispersion toughening) 陶瓷基体中渗入具有一定颗粒尺寸的微细粉末,达到增韧的效果,这称为弥散增韧。这种细粉料可以是金属粉末,加入陶瓷基体之后,以其塑性变形,来吸收弹性应变的释放能,从而增加了断裂表面能,改善了韧性。细粉料也可以是非金属颗粒,在与基体生料颗粒均匀混合之后,烧结时,多存在于晶界相中,以其高弹性模量和高温强度增加了整体的断裂表面能,特别是高温断裂韧性。 纤维增韧(fibre toughening) 在陶瓷中加入高弹性模量的纤维,纤维均布于陶瓷基体中,受力时,由于纤维的强度及弹性模量高,大部分应力由纤维承受,减轻了陶瓷的负担,而且纤维还可以阻止裂纹扩展,起到增韧的作用。 层状化增韧(lamellar toughening) 将陶瓷材料层状化,增加裂纹扩展时的阻力,也能达到增强、增韧的效果。层状结构可以使裂纹扩展时发生偏转。 纳米陶瓷(nanocrystalline ceramics) 具有纳米级晶粒尺寸的陶瓷材料为纳米陶瓷。纳米级晶粒尺寸使得陶瓷材料的性能得到改善,目前已有纳米Al2O3、ZrO2、TiO2、Si3N4、SiC等陶瓷粉料和陶瓷制品。 硅酸盐水泥(portland cement) 硅酸盐水泥在建筑上主要用于配制砂浆和混凝土,作为大量应用的工程材料,其最重要的性质是强度、体积变化以及与环境相互作用的耐久性。其中,水泥的强度是评比水泥质量的重要指标,是划分标号的依据。影响水泥强度的因素很多,主要有浆体组成、熟料矿物组成、水灰比、水化程度、温度与压力等。 硬化水泥浆体(hard cement ingredient) 硬化水泥浆体是由无数钙矾石的针状晶体和多种形貌的C-S-H,再夹杂着六方板状的氢氧化钙和单硫型水化硫铝酸钙等晶体交织在一起而形成的,它们密集连生交叉结合,又受到颗粒间的范德华力或化合键的影响,硬化水泥浆就成为由无数晶体编织而成的―毛毡‖而具有强度。 玻璃(glass) 玻璃是无机氧化物的熔融混合物,它们并没有特有的固定的组成。玻璃按组分可分为三种主要类型:钠钙硅、硼硅酸以及铅硅酸玻璃。 钢化玻璃(lempered glass) 如果能在玻璃表面层中产生―永久性‖压应力,就可以使生产的玻璃制品的强度比常规状态高。要使这样的制品发生断裂,就需要较高的张应力,这是因为在使这类表面缺陷承受张应力之前,必须先克服表面的压应力。经过处理而使表面处于压应力状态的玻璃被称为钢化玻璃。 大分子链(macromolecules) 大分子链是组成高分子材料(也称为聚合物)的基本单元。大分子链的分子量很大(通常几万,再大者可达数百万),主要是由C、H、O、N、P、S等原子以共价键方式成链。这种分子链被称为大分子链。按其主链所包含原子的种类,可分为:①碳链高分子化合物,主链全部为碳原子、如聚烯烃、聚二烯烃等(表3-1-1);②杂键高分子化合物,主链除碳原子外,还可有O、N、P、S等元素, 这类高分子化合有聚酯、聚醚、聚酰胺等(表3-1-2); ③元素有机聚合物,主链是由Si、Ti、Al、B等原子和O原子构成, 侧基一般为有机基团,如有机硅树脂、有机硅橡胶等。 分子量(molecular weight) 分子量是分子中各原子量的总和。 单体(monomer) 单体是能自身聚合或与其他类似的化合物共聚而生成聚合物的简单化合物。 聚合物(polymer) 聚合物是由聚合生成的具有重复链节的化合物 链节(monomeric unit) 链节是聚合物分子链上,含与真实单体或假想单体相同原子种类和原子数目的重复单元。 聚合度(degree of polymerization) 大分子链中链节的重复次数, 称之为聚合度。 分子量的多分散性(distribution of molecular weight) 高分子化合物是由大量的大分子链组成的。各个大分子链的链节数不同,大分子链的长短不同、分子量也不同,高分子化合物中大分子链分子量不等的现象称为分子质量的多 分散性。这是高分子化合物的一大特点,这种分子量的分散性决定了高分子化合物的物理、力学性能的大分散度。 官能度(functionality) 官能度是指在一个链节上能接上新分子的位置数。 加聚反应(addition reaction) 加聚反应是指由一种或多种单体相互加成而连接成聚合物的反应。 缩聚反应(condensation reaction) 缩聚反应是指由一种或多种单体相互混合而连接成聚合物的同时析出(缩出)某种低分子物质(如水、氨、醇、卤化氢等)的反应。 构型(configuration) 分子链中各种基团的空间分布称为分子链的构型。 线型(linear) 大分子链的形状有三种: 线型,支化型,体型(或网型)(图3-55)。 线型高分子的结构是整个分子链呈细长线条状,通常卷曲成不规则的线团,但受拉时可以伸展为直线。 支化型(branched) 大分子链的形状有三种: 线型,支化型,体型(或网型)(图3-55)。支化型大分子链的结构是在大分子主链节上有一些或长或短的小支链,整个大分子呈树枝状。 体型(或网型)(network) 大分子链的形状有三种: 线型,支化型,体型(或网型)(图3-1-6)。体型高分子的结构是大分子链之间通过支链或化学键连接成一体的所谓交联结构,在空间呈网状。 构象(conformation) 由于单键内旋引起的原子在空间占据不同位置所构成的分子链的各种形象,即为大分子链的构象。 单键内旋(rotation of single chain bonds) 组成大分子链的每个单键,都有一定的键长和键角,并且能在保持键长和键角不变的情况下任意旋转。每个单键围绕相邻单键按一定角度进行的旋转运动称为单键的内旋转。 柔顺性(flexibility) 大分子链由于构象变化,获得不同卷曲程度的特性为大分子链的柔顺性。柔顺性与大分子链中单键内旋的难易程度有关。 无定型(noncrystalline) 无定型结构也称为非晶态结构。 结晶度(degree of crystallinity) 高分子化合物中结晶区所占的重量百分数即为结晶度 玻璃化转变温度(glass transition temperature) 高分子化合物在玻璃态和橡胶态之间的转变温度。 玻璃态(glass state0 在Tg温度以下,高聚物的弹性模量较高,较刚、硬,称之为玻璃态。 橡胶态(rubber state) 在Tg温度以上,高聚物表现出柔软而富有弹性,如橡胶,故这一阶段称之为高弹态或橡胶态。 粘流态(viscous flow state) 当温度高于Tf后, 变形量随温度升高进一步迅速增加, 高聚物开始产生粘性流动, 处于所谓粘流态。 粘流温度(软化温度)(viscous flow temperature) Tf为高弹态与粘流态间的转变温度,叫做粘流温度或软化温度。 熔点[melting point] 熔点是固体熔化的温度。 老化(aging) 材料在环境作用下逐步失效的过程。 降解(degradation) 降解是由气候、热、光、氧、射线等作用引起的大分子链断裂或化学结构发生失效的过程。 交联(cross link) 交联是在橡胶分子链之间或同一分子链内嵌入交联键,形成网状结构的过程 热固性塑料(thermosetting plastics) 热固性塑料为体型结构,其成型加工是用相对低分子量的粘稠体和固化剂混合,在一定温度和压力下发生聚合反应,在成型时产生强烈地交联,形成三维网状结构。网状结构一旦形成后不能改变,所以不可循环使用 热塑性塑料(thermoplastics) 热塑性塑料是线型链状结构,加热时是软的,可注射入模子成型,在取出前需冷却,成型过程中不发生进一步聚合,可反复多次成型。 橡胶(rubber) 橡胶是在线型链状结构中形成少量的交联,具有较好弹塑性的一类高分子材料。 拉拔强化(drawing strenghtening) 和金属冷拉可以造成强烈的加工硬化类似,一些高分子材料在Tg温度附近冷拉,也可使其强度和弹性模量大幅度提高,称之为拉拔强化。 橡胶增韧(rubber toughening) 橡胶增韧是指在塑料等高分子材料中掺入橡胶粒子以达到增韧目的的一类工艺。 聚乙烯(polyethylene) 聚乙烯是以乙烯为单体聚合制得的聚合物。英文缩写PE。聚乙烯在塑料总产量中居首位。聚乙烯具有优良的力学性能,绝缘性、耐寒性、化学稳定性、吸水性和低透气性,无毒,易于加工成型。 聚氯乙烯( polyvinyl chloride) 聚氯乙烯是氯乙烯的聚合物。英文缩写PVC。聚氯乙烯是仅次于聚乙烯的第二大塑料品种。玻璃化温度80~85°C,密度1.35~1.45克/厘米3 ,使用温度-15~60°C。PVC 具有优良的耐酸碱、耐磨、耐燃及绝缘性能,与大多数增塑剂的混合性好,因此可大幅度改变材料的力学性能。加工性能优良,价格便宜,但对光、热稳定性差,100°C以上或光照下性能迅速下降。 聚苯乙烯(polystyrene) 聚苯乙烯是苯乙烯的聚合物。英文缩写PS。聚苯乙烯结构式为 , 是典型的线型无定型高聚物, 由于有取代基苯环, 结晶度低, 柔顺性差,所以具有较大的刚度。它比重小,几乎不吸水,具有优良的耐蚀性,电阻大,是很好的隔热、防震、防潮和高频绝缘材料。聚苯乙烯添加发泡剂后可制成泡沫塑料,比重只有0.033g/cm3, 是隔音、包装、救生的极好材料。 ABS塑料(ABS plastics) ABS塑料是丙烯腈(A)、丁二烯(B)、苯乙烯(S),3种单体的接枝共聚物。实际上往往是含丁二烯的接枝共聚物与丙烯腈、苯乙烯共聚物(AS或SAN)的混合物。ABS 是一种强度高,韧性好,耐油,耐酸、碱、盐及化学试剂,综合性能优良,易于加工成型的高分子材料。 聚酰胺(polyamide) 聚酰胺俗称尼龙, 英文缩写PA,这种热塑性塑料或由二元胺和二元酸缩聚而成,或由氨基酸脱水成内酰胺再聚合而成。结构式分别为 根据胺与酸中的碳原子数或氨基酸中的碳原子数,分别命名为尼龙66, 尼龙6等品种。 氟塑料(fluoric plastics) 氟塑料是含氟塑料的总称。机械工业中应用最多的是聚四氟乙烯(F-4), 其结构式为[-CF2-CF2-]n 。 聚甲基丙烯酸甲脂(polymethacrylates) 聚甲基丙烯酸甲脂,俗称有机玻璃, 英文缩写PMMA,结构式为 , 是典型的无定形结构,取代基为极性集团。 酚醛塑料(novalac plastics) 酚醛塑料,英文缩写PF是由酚类和醛类在酸或碱的催化下缩聚而成的酚醛树脂,再加入添加剂而制得的高聚物,应用最多的酚醛树脂是苯酚和甲醛的缩聚物。 环氧塑料(epoxy plastics) 环氧塑料,英文缩写EP,是环氧树脂加固化剂后形成的热固性塑料,常用固化剂为胺 类和酸酐类。 复合材料(composite materials) 复合材料是由两种或两种以上的组分材料通过适当的制备工艺复合在一起的新材料,其既保留原组分材料的特性,又具有原单一组分材料所无法获得的或更优异的特性。 基体(matrix) 复合材料中占主要组分的材料称为基体。 增强材料(reinforced materials) 增强材料是复合材料的重要组成部分,相对基体而言,主要起到增强作用。复合材料中的增强材料就其形态而言,主要有纤维及其织物、晶须和颗粒。就其组成的性质而言又可分为有机增强材料、金属增强材料和无机非金属增强材料(见图3-80)。 混合法则(Rule of Mixtures) 在复合材料中,在已知各组分材料的力学性能、物理性能的情况下,复合材料的力学性能(如强度、弹性模量)和物理性能(密度、电导率、热导率、热膨胀系数等)主要取决于组成复合材料的材料组分的体积百分比(vol.%),可用下式表示: 式中Pc 表示复合材料的某性能,如强度、弹性模量、密度、电导率、热导率、热膨胀系数等;Pi 表示各组分材料的对应复合材料的某性能;V表示组成复合材料各组分的体积百分比(vol.%);下标i表示组成复合材料的组分数(包括基体、若干增强材料)。上式称之为混合法则。 复合材料增韧机制(toughening meehanism of composite materials) 复合材料在受冲击载荷时材料发生破坏(断裂),其韧性大小取决于材料吸收冲击能量大小和抵抗裂纹扩展的能力。以纤维增强复合材料为例,主要有纤维的拔出、纤维与基体的脱粘、纤维搭桥等增韧机制。除了上述增韧机制外,在颗粒、短纤维和晶须增强复合材料中,由于增强材料的存在,阻碍了裂纹在基体中的扩展,在增韧方面,还存在有裂纹偏转、微裂纹增韧等机制。此外,在陶瓷基复合材料中,利用氧化锆的相变产生的体积效应,引起基体产生微裂纹,从而增加陶瓷基复合材料的韧性,这种方法称之为相变增韧机制。 复合材料中界面作用(interface effect of composite materials) 在复合材料中,界面往往起到把载荷由基体传递到纤维的传递作用。此外,复合材料的界面还起到诱导作用、阻断作用、散射及吸收作用等。为了保证界面的作用,纤维与基体之间要有一定的粘结,并且两者之间的结合与增强材料及基体的性质有关。除此之外,复合材料界面的结合方式、界面结构和性质会直接影响和控制复合材料的性能。 玻璃纤维(glass fibre) 玻璃纤维是纤维增强材料中的一种。玻璃纤维具有耐高温、耐腐蚀(除碱外)、热膨胀系数小等特点,但不耐磨、脆而易折。玻璃纤维与其它纤维相比,其价格便宜,品种多,适合编织制成各种玻璃织物,因而广泛应用于航空航天领域,尤其是民用领域,如建筑材料、交通工具、体育用品等玻璃纤维增强复合材料中。 芳纶纤维(kevlar fibre) 芳纶纤维是目前主要用于聚合物基复合材料的一种有机纤维,是美国杜邦公司(Dupont)在1968年研制成功的,并在1973年正式以Kevlar作为其商品名。芳纶纤维的密度仅为1.44 g/cm3,其抗拉强度高达3.4GPa,模量为59~190GPa,因此其比强度和模量均优于玻璃纤维,特别是比强度甚至高于一般碳纤维和硼纤维。和其它的有机纤维(如聚乙烯、尼龙和聚酯纤维)相比,耐热性较高,象Kevlar49纤维的抗拉强度长期在150℃下几乎不变,在427℃下不分解,在-190℃低温下不变脆,并且在高温下不易变形,尺寸稳定,特别是其柔韧性好,抗冲击,耐酸、碱。但芳纶纤维制成的聚合物基复合材料层间抗剪强度较低。 碳纤维(carbon fibre) 碳纤维是纤维增强材料中的一种。根据原材料不同分为人造丝(粘胶纤维)、聚丙烯腈(PAN)碳纤维和沥青基碳纤维。经过碳化和石墨化后,可以分别得到高强度碳纤维、超高强度碳纤维、高模量碳纤维、超高模量碳纤维、高强度高模量碳纤维等。 与玻璃纤维相比,碳纤维比强度和比模量有明显提高。此外,碳纤维导热、导电,耐化学腐蚀性好,但仍然较脆,且抗氧化性差。碳纤维不仅作为玻璃纤维的代用品,用于聚合物基复合材料,而且适用于金属基复合材料。因此,碳纤维成为航空航天领域所用先进复合材料中不可缺少的增强材料。 硼纤维(boron fibre) 硼纤维是在金属丝上沉积硼而形成的无机纤维。通常用氢和三氯化硼在炽热的钨丝上反应,置换出无定形的硼沉积于钨丝表面获得。属脆性材料,抗拉强度约3500MPa,弹性模量400 GPa,密度只有钢材的1/4,抗压缩性能好;在惰性气体中,高温性能良好;在空气中超过500°C时,强度显著降低。是良好的增强材料,可与金属、塑料或陶瓷复合,制成高温结构用复合材料。由于其高的比强度和比模量,在航空、航天和军工领域获得广泛应用。 碳化硅纤维(silicon carbide fibre) 碳化硅纤维是陶瓷纤维,具有陶瓷特征,抗氧化、耐腐蚀,与金属基体一般不发生反应,湿润性好,且价格便宜,可用作聚合物基、金属基和陶瓷基复合材料的增强材料。碳化硅纤维增强复合材料主要可用于航空航天、汽车结构部件和运动器械(滑雪板、网球拍) 晶须(whisker) 晶须是一种直径为零点几至几个微米的针状单晶体纤维材料。在单晶体中的原子排列非常整齐,几乎没有多晶材料中存在的各种缺陷,如杂质、空穴和位错等,因此从强度而言,晶须的强度接近理论极限。 功能材料(functional materials) 功能材料是与结构材料相对应的另一大类材料,主要利用材料的光学、电学、磁学等性能。 一次功能(primary function) 当向材料输入的能量和从材料输出的能量属于同一种形式时,材料仅起能量传递的作用,材料的此种功能为一次功能。 二次功能(secondary function) 当向材料输入的能量和从材料输出的能量不属于同一种形式时,材料起能量转换作用,材料的此种功能为二次功能。 导电性(conductivity) 导电性是评价材料所具有的传导电流的性质。 电阻率(electric resistivity) 电阻率是单位横截面积、单位长度的物质的电阻值,表征材料对电流的阻碍能力的物理量。 电导率(conductivity) 电导率是电阻率的倒数,表征材料导电能力的物理量。 载流子(carrier ) 简单地说, 材料能导电是由于在电场作用下材料中产生了电荷的定向运动,而电荷的运动是通过一定的微观粒子来实现的。将带电荷的微观粒子统称为载流子,可以是自由电子或空穴;也可以是正、负离子或空位。前者为电子电导,后者为离子电导。 迁移率(mobility) 电导率的大小应该与载流子的数目有关系,还应该与载流子的运动速度有关。为了表征这个关系,人们定义了迁移率的概念,,物理薏义是在单位电场作用下载流子的运动速度,这样可得到的关系,为载流子所带电荷。 本征半导体(intrinsic semiconductor) 具有禁带宽度小于2ev能带结构的材料为半导体。无掺杂的单质半导体为本征半导体。 n型半导体(n-type semiconductor) 以电子为主要导电载流子的半导体材料被称为N型半导体,也叫做施主型半导体,因为在本征半导体中添加了施主杂质。 P型半导体(P-type semiconductor) 以空穴为主要导电载流子的半导体材料被称为P型半导体,也叫受主半导体,因为在本征半导体中添加了受主杂质。 固体电解质(solid electrolyte) 固体电解质是具有离子导电性的固态物质。这些物质或因其晶体中的点缺陷或因其特殊结构而为离子提供快速迁移的通道,在某些温度下具有高的电导率(1~106西门子/厘米),故又称为快离子导体。 超导性(superconductivity) 某些物质在一定温度条件下电阻降为零的性质被称为超导性。材料表现超导性的条件实际有三个: ①超导体进入超导态时,其电阻率等于零。从电阻不为零的正常态转变为超导态的温 度称为超导转变温度或超导临界温度,用Tc表示。 ②外磁场可破坏超导态。只有当外加磁场小于某一量值Hc时才能维持超导电性,否则超导态将转变为正常态,Hc 称为临界磁场强度。Hc与温度的关系为Hc≈H0〔1-(T/T c )2 〕,H0是T=0K时的临界磁场强度。 ③超导体内的电流强度超过某一量值Ic 时,超导体转变为正常导体,Ic 称为临界电流。 超导体变为超导态后,除电阻为零外,体内的磁感应强度也恒为零,即超导体能把磁力线全部排斥到体外,具有完全的抗磁性。另外,超导体具有能隙。 低温超导材料(low temperature superconducting material) 具有低临界转变温度,在液氦温度条件下工作的超导材料。 高温超导材料(high temperature superconducting material) 具有高临界转变温度,能在液氮温度条件下工作的超导材料。 绝缘体(insulator) 绝缘性通常是指材料阻滞热、电或声通过的能力。 极化率(polarizability) 极化率是衡量原子、离子、分子在电场作用下极化强度的微观参数, 通常用α表示,α为原子、离子、分子在电场作用下形成的偶极矩与作用于原子、离子、分子上的有效内电场之比。 极化强度(polarization) 极化强度是电介质单位体积中电偶极矩的矢量和。 介质极化系数(polarization coeffecient of dielectric materials) 为了将极化强度P和宏观实际有效电场E相联系, 人们定义, 式中为真空介电常数,F/m(法/米), 为电介质的极化系数,是个无量纲的数。 绝对介电常数、相对介电常数 (ablolute-dielectric constant、relative-dielectric constant) 电介质在电场E中极化后产生的电场可用电感应强度D 表征, , 式中为电介质的绝对介电常数, 为电介质的相对介电常数, 也是一个无量纲的数, ,可见。绝对介电常数、相对介电常数都是物理学中讲平板电容时引入的参数, 表征电介质极化并储存电荷的能力,是个宏观物理量。 电子位移极化(也叫形变极化)(electronic polarization) 在外电场作用下,原子外围的电子云相对于原子核发生位移形成的极化叫电子位移极化,也叫形变极化。 离子位移极化(ionic polarization) 离子晶体在电场作用下离子间的键合被拉长, 导致电偶极矩的增加, 被称为离子位移极化,象Nacl在电场作用下就会发生位移极化。 偶极子取向极化(dipole orientation polarization) 偶极子取向极化是极性电介质的一种极化方式。组成极性电介质中的极性分子具有恒 定的偶极矩。无外加电场时,这些极性分子的取向在各个方向的几率是相等的,就介质整体来看,偶极矩等于零。在电场作用下,这些极性分子除贡献电子极化和离子极化外,其固有的偶极矩将沿外电场方向有序化,沿外场方向取向的偶极子比和它反向的偶极子的数目多,所以介质整体出现宏观偶极矩。这种极化现象为偶极子取向极化。 松弛极化(relaxation) 当材料中存在着弱联系电子、离子和偶极子等松弛质点时,热运动使这些松弛质点分布混乱,而电场力图使这些质点按电场规律分布,最后在一定温度下,电场的作用占主导,发生极化。这种极化具有统计性质,叫作松驰极化。松驰极化是一种不可逆的过程,多发生在晶体缺陷处或玻璃体内。 电介质的击穿(breakdown of dielectric medium) 电介质只能在一定的电场强度以内保持绝缘的特性。当电场强度超过某一临界值时,电介质变成了导体,这种现象称为电介质的击穿,相应的临界电场强度称为介电强度或击穿电场强度。 介质损耗(dielectric loss) 将电介质在电场作用下,单位时间消耗的电能叫介质损耗。 氧化铝、氧化铍、碳化硅及氮化铝(alumina、beryllium oxide、silicon carbide、aluminum nitride) 氧化铝、氧化铍、碳化硅及氮化铝是几种新型高性能介电陶瓷材料。可作为集成电路基板材料。其中的氧化铝应用最为普通。氧化铝陶瓷介电损耗低,电性能与温度的关系不大,机械强度高,化学稳定性好,已被广泛应用于基板材料。氧化铍的最大优点是导热系数高,介电常数较低,但由于其毒性大,价格高而限制了其应用。碳化硅的导热性优于氧化铝,但烧结困难。近年来,氮化铝基板由于其得天独厚的优点,已引起国内外的普遍关注。日本商品化AlN的热传导率已达260W/m.k, 是目前普遍使用的氧化铝的10倍,而其他电性能与Al2O3相当。目前氮化铝作为基板使用要解决的是其金属化技术的可靠性,多层布线技术及降低成本等问题。 光透射(transmittance) 光透射是指光对介质的穿透现象。 吸收(absorption of light) 光的吸收是光在介质中传播时部分能量被介质吸收的现象 反射(reflection) 光反射是指光被表面折回的现象,遵循光的反射定律,既反射角等于入射角。这种反射为镜反射。 折射(refraction) 当光从一种介质1进入另一种介质2时, 其速度和传播方向发生变化,即发生了折射。与界面法向形成入射角和折射角(图3-2-17), 与间关系与两种材料的折射率有关。 ,式中、分别为光在材料1和材料2中的传播速度, 为材料2相对于材料1的折射率。 折射率还与入射光的频率有关,随频率的减小(或波长的增加)而减小,这种性质称为折射率的色散。 光子(photons) 光具有波动和微粒二重性,当考虑光与电子之间的能量转换时,把光当成粒子来看待,称为光子。光子是最早发现的构成物质的基本粒子之一。光子所具有的能量不是连续的,而是与其频率v 有关,光子能量,式中v 为光的频率,为光的波长,h为普朗克常数, 选择吸收(selectire absorption) 材料对不同波长的光的吸收能力不同,对某种波长的光吸收率很高,而对另外一些波长的光吸收率很低,这种现象被称为选择吸收。 漫反射(diffuse reflection) 当光线照射到一粗糙不平的表面,则在局部位置入射角的实际大小并不一样,因而反射光的方向也不一致,形成了漫反射。 光泽(luster) 光泽是材料表面在光照条件下所显现出的色泽,光泽与镜反射和漫反射的相对含量密切相关,当镜反射光带宽度窄但强度高时,可以获得高的表面光泽。 透光性(transmittance) 透光性是指光对介质的穿透能力。 荧光材料(fluorescence) 荧光材料是一类发光材料。由于当外界任一形式的能量将电子由价带激发至导带后,该电子又返回到价带时发出的光子频率在可见光范围内,所以材料发光。如果在激发除去之后的内,电子跳回价带时,同时发光。这种光为荧光,该发光材料为荧光材料。 磷光材料(phosphorescent materials) 磷光材料是一类发光材料。发磷光的材料含有杂质,并在禁带中建立施主能级。当激发的电子从导带跳回价带时,首先跳到施主能级上并被捕获。当电子再从捕获陷阱溢出返回价带时,才会发光,因而延迟了发光的时间(图3-2-25c)。通常人们把这种激发停止后一定时间内能够发光的材料称为磷光材料。 粒子数反转(turning electron numbers over) 粒子数反转是产生激光的必要条件, 即通过使高能级上的电子数多于低能级的电子数,从而实现受激辐射几率大于吸收几率。 光导纤维(optical waveguide fibre) 光以波导方式在其中传输的光学介质材料,简称光纤。光导纤维由纤芯和包层两部分组成。有两种纤维结构可以形成波导传输,即阶跃(折射率)型和梯度(折射率)型。阶跃型光导纤维的纤芯与包层间折射率是阶梯状的,纤芯的折射率大于包层,入射光线在纤芯和包层间界面产生全反射,因此呈锯齿状曲折前进。梯度型光导纤维的纤芯折射率从中心轴线开始向着径向逐渐减小。因此,入射光线进入光纤后,偏离中心轴线的光将呈曲线路径向中心集束传输,光束在梯度型光导纤维中传播时,形成周期性的会聚和发散,呈波浪式曲线前进。 故梯度型光导纤维又称聚焦型光导纤维。 全反射(total reflection) 全反射是光从光密介质射向光疏介质且当入射角大于临界角时,光被界面全部反射回原介质不再进入光疏介质中的现象。 光存储材料(optical memory materials) 光存储材料是通过调制激光束,以光点的形式把信息编码记录在镀膜介质中的一类功能材料。根据存储方式不同,光存储材料可分为三种类型,①只读式,②一次写入多次读出,③可擦重写方式。 光电转换材料(photoelectric conversion material) 光电转换材料是将太阳能转换为电能的一类材料。主要用于制作太阳能电池。 磁感应强度(magnetic intensity) 任何物质在外磁场作用下,除了外磁场外,由于物质内部原子磁矩的有序排列,还要产生一个附加磁场。在物质内部,外磁场和附加磁场的总和称之为磁感应强度,是矢量,常用符号B表示。在国际单位制(SI)中,磁感应强度的单位是特斯拉,简称特(T)。 介质磁导率(magnetic permeability) 磁导率是描述磁介质磁性的物理量之一。常用符号μ表示,等于磁介质中磁感应强度B与磁场强度H之比。 相对磁导率(relative magnetic permeability) 相对磁导率是描述磁介质磁性的物理量之一,其定义为磁导率μ与真空磁导率μ0 之比。 磁化强度(magnatization) 描述磁介质磁化状态的物理量,常用符号M表示。定义为单位体积内分子磁矩m 的矢量和。在国际单位制(SI)中,磁化强度M的单位是安培/米(A/m)。 磁化率(magnetic susceptibility) 表征磁介质属性的物理量。常用符号χm 表示,等于磁化强度M与磁场强度H之比,即M= χm H 抗磁性(diamagnetism) 根据磁化强度的大小、正负,可将磁性分为抗磁性、顺磁性、铁磁性和反铁磁性四类(图3-2-32)。 当磁化强度为负值时,物质表现出抗磁性。抗磁性一般较弱,磁化率为负值,在量级。金属等具有这种性质。周期表中前18种元素的单质表现为抗磁性,而且这些元素构成了陶瓷材料中几乎所有的阴离子,故陶瓷材料的大多数原子是抗磁性的。 顺磁性(paramagnetism) 当磁化强度与外磁场方向一致,为正值且与磁场强度成正比时,物质为顺磁性。顺磁性的大小还与温度有关,温度越高,顺磁磁化率越小。顺磁物质的磁化率一般也很小,室温下约。一般含有奇数个电子的原子或分子,电子未填满壳层的原子或离子如过渡族 单质、稀土、锕系及铝、铂等金属都属于顺磁物。 铁磁性(ferromagnetism) 对于铁、钴、镍这几种金属,磁化率均为正,且可达量级,属于强磁性物质,这种磁性称为铁磁性。铁磁体的铁磁性只在某一温度以下才表现出来,超过这一温度,铁磁性转变为强顺磁性。这个温度称之为居里点。 反铁磁性(antiferromagnetism) 反铁磁性物质磁性特征是磁化率几乎为零。这种现象的存在与温度有关,只在某个温度以下存在,这个温度称为尼尔点。当,反铁磁体与顺磁体有相同的磁化行为。反铁磁性物质大都是非金属化合物,如。 磁滞回线(hysteresis loop) 磁滞回线是显示磁滞现象的闭合磁化曲线。 剩磁(residual magnetism) 剩磁是移去外加磁场,仍保留在试件中的磁性。 矫顽力(coercive field) 铁磁体磁化到饱和后,使他的磁化强度或磁感应强度降低到零所需要的反向磁场称为矫顽力。 磁致伸缩(magnetostriction) 当铁磁体磁化状态改变时,磁体的尺寸及形状会变化,这种现象叫磁致伸缩。定义沿磁化方向单位长度发生的变化为磁致伸缩系数,磁化强度饱和时的磁致伸缩系数是材料常数。 磁矩(magnetic moment) 描述载流线圈或微观粒子磁性的物理量。平面载流线圈的磁矩定义为式中i为电流强度;S为线圈面积;n为与电流方向成右手螺旋关系的单位矢量。 交换作用(exchange effect) 交换作用是指处于不同原子的、未被填满壳层上的电子之间发生的特殊相互作用。由这种交换作用所产生的交换能J与晶格的原子间距有密切关系(图3-2-36)。当原子间距离很大时,J接近于零,随着距离的减小,相互作用增加。当原子间距a与未被填满的电子壳层的直径D之比大于3时,交换能为正值,材料呈现铁磁性;当时,交换能为负值,材料呈现反铁磁性 磁畴(domains) 磁畴是磁矩方向一致的小区域,含有个原子,体积约。磁畴的形成是由于近邻原子间的交换作用。 自发磁化(spontaneous magnetization) 铁磁体内部自发地形成了磁化到饱和的小区域-磁畴。铁磁体的这种作用不是依赖外磁场的作用,因此称为自发磁化。自发磁化是铁磁物质的一个基本特性,是其与顺磁物质的区别所在。 软磁材料(soft magnet materials) 软磁材料是具有低矫顽力和高磁导率的磁性材料。软磁材料易于磁化,也易于退磁,广泛用于电工设备和电子设备中。应用最多的软磁材料是铁硅合金(硅钢片)以及各种软磁铁氧体等。 硬磁材料(permanent magnetic material) 硬磁材料也称为永磁材料,具有宽磁滞回线、高矫顽力、高剩磁,一经磁化即能保持恒定磁性的材料。 磁记录材料(magnetic recording materials) 磁记录材料是主要被用于磁记录的一类材料,其原理是利用磁头气隙中随信息变化的磁场将磁记录介质磁化,即将随时间变化的信息磁场转变为磁记录介质按空间变化的磁化强度分布,经过相反的过程,可将记录的信息经磁头重放出来(图?3-2-43)。磁记录材料是作为硬磁材料来应用的,但它与传统硬磁材料不同,它往往不是以块状形态使用。 铁氧体(ferrites) 铁氧体是含铁酸盐的陶瓷磁性材料,按材料结构分,铁氧体有尖晶石型、石榴石型、磁铅石型、钙钛矿型、钛铁矿型和钨青铜型等六种。 亚铁磁性(ferrimagnetism) 铁氧体磁性与铁磁性相同之处在于有自发磁化和磁畴,因此有时也被统称为铁磁性物质。但其也有与铁磁物质不同之处,表现在铁氧体一般都是多种金属氧化物复合而成,因此铁氧体中有两种取向不同的磁矩,它们方向相反,大小不等,两种磁矩之差就产生了自发磁化现象,所以严格地说,铁氧体磁性称为亚铁磁性。 材料工艺(material technics) 制造材料本身,以及把材料制造成为人类所能利用的产品的过程,都必须通过一定的工艺才能实现,这一系列工艺称为材料工艺。材料工艺包含两个方面的内容,一是材料的生产工艺,一是材料的加工工艺。 材料生产工艺(material production technics) 材料的生产工艺就是把天然原料(包括初级人造原料)经过物理和化学变化而变成工程上有用的原材料的工艺技术,如钢铁厂冶炼生产钢材、化工厂合成塑料颗粒的过程。 材料加工工艺(material process technics) 材料的加工就是把材料制备成具有一定形状尺寸和性能的制品的过程。主要指材料的成形加工、内部组织结构的控制以及表面处理等,如制罐厂把薄金属带制造成易拉罐、塑料厂生产出塑料制品的过程。 工艺性能(process properties) 通常指材料可被加工的能力,也称加工性能。根据特定的制造方法要求,材料的加工性能包括可焊接性、可铸造性、可切削性、可成型性和可变形性等等。它是材料能否大量工业应用的一个重要因素。 冶金(metallurgy) 金属材料一般从矿石中提取,往往涉及到冶炼过程,因此金属材料的生产通称为冶金。根据工艺特点的不同可分为:火法冶金、湿法冶金、电冶金以及粉末冶金等。 火法冶金(fire metallurgy) 火法冶金是指利用高温(超过金属熔点温度)从矿物中提取金属或其他化合物的方法,典型的例子是钢铁材料的冶炼。 湿法冶金( wet metallurgy) 利用溶剂,借助于氧化、还原、中和、水解、络合等化学作用,对原料中金属进行提取和分离,得到金属或其化合物的过程,称为湿法冶金。其优点是环境污染少,并且能提炼低品位的矿石,但成本较高。主要用于生产锌、氧化铝、氧化铀及一些稀有金属。 电冶金(electricity metallurgy) 电冶金是指应用电能从矿石或其它原料中提取、回收、精炼金属的冶金过程,一般仅指电解(电化学)冶金,包括水溶液电解和熔盐电解冶金。电冶金通常用于获得高纯度金属,如高纯铝、镁、钠等金属的生产。 粉末冶金(powder metallurgy) 把原料粉末在固态条件下压制成型,通过加热烧结的方式得到制品的过程称粉末冶金。与陶瓷产品的生产工艺非常相近。多用于制造切削用的硬质合金(碳化钨、碳化钛等难熔碳化物的混合物)刀头,钨、铌、钽、钛等高熔点致密合金零件等。 陶瓷生产工艺(ceramic production technics) 陶瓷生产工艺就是以相图和高温物理化学为理论基础的矿物合成工艺。主要步骤为:配料、压制成型、坯块烧结和后处理。陶瓷制品的生产工艺和加工工艺是通常是合二为一的,烧结成型之后除了磨削和抛光以外,几乎不进行任何加工,因此陶瓷的生产工艺直接影响到制品的性能。 陶瓷成型(ceramic forming) 陶瓷成型就是把准备好的原材料加工成一定形状和尺寸的半成品的过程。根据坯料(可塑泥料、粉料、浆料)的不同,成型的方法主要有以下几种:湿塑成型、注浆成型、干压成型、注射成型、热压成型等。 陶瓷烧结(ceramic sinter) 将干燥好的坯体放到窑或炉内加热到高温,通过一系列物理化学变化,成瓷并获得所要求的性能的过程就是烧结。日用瓷的烧结温度一般在1250-1450 ℃烧结。在烧结过程中会发生膨胀、气体产生、收缩、液相出现、晶相的长大和转变等变化,随着这些变化,气孔率降低,体积密度增大,坯体转变成具有一定尺寸形状和强度的制品。 玻璃成型(glass forming) 熔融的玻璃在固化时,没有明显的凝固点,也没有体积的突变,材料的粘度连续变化,在液态流动性很好,可以进行吹制成型,也可以象金属一样进行铸造、轧制、拉丝和挤压。 单晶制备(single crystal making) 单晶材料的制备关键使是避免多余晶核的形成,保证唯一晶核的长大,因此,要求材料纯度高,凝固过程过冷度低。目前单晶制备已发展成为一种重要的专门技术。按照单晶材料原子的来源,可以分为液相法、气相法和固相法,其中液相法应用较多,如单晶硅的制备。 铸造(casting) 铸造是将金属材料由液态直接凝固成型的一种通用方法,即将熔融金属浇注到型腔内,凝固后得到一定形状的铸件。成本低廉,能大批制造出内腔形状复杂的零件,但铸件的机械性能较差。 压力加工(pressure process) 对固态金属施加外力,通过塑性变形得到一定形状尺寸和性能的制品的过程就是压力加工。根据加工方式的不同,压力加工可分为锻造、轧制、挤压、拉拔、冲压等过程。压力加工的一个重要特点是可改善金属材料的机械性能,可以提高材料的强度和韧性。根据加工温度的不同,通常分为热加工和冷加工。 热加工(thermo-process) 热加工是指在再结晶温度以上进行的加工过程(再结晶温度可近似用熔点的0.4倍来估计(以绝对温度表示),如纯铁为450℃)。锻造和热轧就是典型的热加工。热加工可以改善材料的内部组织结构,缺点是表面的氧化不可避免,影响表面质量,同时尺寸精度也较低,常常用于成形毛坯。 冷加工(cold work) 冷加工是指低于再结晶温度下进行的加工过程。由于温度较低,冷加工过程不能产生回复和再结晶现象。冷加工过程中工件将不断受到加工硬化,使工件成形同时也得到强化。冷加工可以获得较精密的尺寸和良好的表面质量,多用于加工比较薄的产品。 焊接(weld) 焊接是使两个分离的固态物质借助于原子间结合力而连接在一起的连接方法,通过压结、熔合、扩散、合金化、再结晶等现象,而使金属零件永久地结合。焊接是一种高速高效的连接方法,广泛地用于制造桥梁、船舶、车辆、压力容器、建筑物等大型工程结构。焊接过程对材料的影响很大,是一个很重要的工艺过程。包括电弧焊、气焊、气体保护焊、电渣焊、压力焊和钎焊等等。 切削加工(cutting process) 切削加工是指利用各种刀具,单纯改变零件的外形和尺寸的物理加工过程。切削加工一般不引起材料内部组织和性能的变化(少量的加工硬化除外),可提高零件尺寸精度和表面光洁度,或者获得其它手段不易得到的特殊的形状。金属的切削加工可分为车、铣、刨、钻和磨五种基本的方法。切削过程生产效率较低,成本较高。 注射成型(注塑)(inject forming) 利用注塑机将熔化的塑料快速注入闭合的模具内,使之冷却固化,开模得到定型的塑料制品的方法。注塑过程包括加料、塑化、注射、冷却和脱模等工序。 挤出成型(挤塑)(pressing forming)) 利用挤出机,借助柱塞或螺杆的挤压作用,使受热熔化的塑料连续通过口模成型的过程。挤塑主要用于生产各种热塑性的塑料板材、棒材、管材、异型材、薄膜、电缆护层等,具有生产效率高、用途广、适应性强等特点。 模压成型(压塑)(coining forming) 将原料放入加热的模具型腔内,加压加热使塑料发生交联化学反应而固化,得到塑料制品的过程。模压通常在油压机或水压机上进行,整个工艺包括:加料、闭模、排气、固化、脱模和清理模具等工序。 吹制成型(吹塑)(blow-moulding forming) 吹塑类似于吹制玻璃器皿,是制造塑料中空制品或薄膜等的常用工艺。通常是把挤塑、注塑得到的管状坯料,加热软化,置于对开的模具中,将压缩空气通入使其吹胀,紧紧贴于模具的内壁,冷却后脱模即得到制品。 浇铸成型(铸塑)(casting forming) 类似于金属的铸造,将处于流动状态的高分子材料注入特定的模具,使之固化并得到与模具型腔一致的制品的过程。其特点是铸模的成本低,可以把塑料与其它材料包封在一起,但生产效率低,尺寸精度差。浇铸成型还可以用于橡胶制品的生产。 压延成型(drawing forming) 压延成型是生产橡胶片材(胶片)的主要成型方法,类似于金属材料的轧制。压延成型就是使材料在相对旋转的加热辊之间被压延,而连续形成一定厚度和宽度的薄板材的过程。压延之后可以趁热通过压花辊,得到压花薄膜。 表面改性(surface modification) 为获得材料表面与内部不同的性能,可以借助许多特殊方法改变材料表面的化学成分、物理结构和相应的性能,或者获得新的薄膜材料,这就是表面改性。表面改性包括:离子注入、离子束沉积、物理气相沉积、化学气相沉积、等离子体化学气相沉积和激光表面改性等等。 离子注入(ion injecting) 离子注入就是在真空中把气体或固体蒸汽源离子化,通过加速后把离子直接注入到固体材料表面,从而改变材料表面(包括近表面数十到数千埃的深度)的成分和结构,达到改善性能之目的。 物理气相沉积(physical vapor diposition) 用热蒸发或电子束、激光束轰击靶材等方式产生气相物质,在真空中向基片表面沉积形成薄膜的过程称为物理气相沉积。包括:蒸发镀膜、溅射沉积和离子镀膜等物理方法。 化学气相沉积(chemical vapor diposition) 利用气态物质在固体表面上进行化学反应,生成固态沉积物的过程,称为化学气相沉积。包括常压化学气相沉积、低压化学气相沉积、激光化学气相沉积、金属有机化合物化学气相沉积和等离子体化学气相沉积等。 激光表面改性(laser surface improving) 利用激光产生的热量对工件表面进行处理的过程就是激光表面改性。激光表面改性包括:激光相变硬化、激光表面熔融、激光涂敷、激光表面合金化等。其优点是:非接触式的处理,热变形小;可以局部加热,能量密度高,处理时间短,可以在线加工,能精确控制处理条件,便于自动化过程。缺点是:设备费用较贵,成本高;处理效率低,不适宜大面积处理等等。 金属雾化喷射沉积(Spray atomization and deposition of Metals) 金属雾化喷射沉积是指将金属熔化成液态后,雾化为熔滴颗粒,然后直接沉积在具有一定形状的收集器上,从而获得大块整体致密度接近理论密度的金属实体的过程。 金属半固态加工(semi-solid processing) 在金属凝固过程中,进行剧烈搅拌,或控制固-液态温度区间,得到一种液态金属母液中均匀地悬浮着一定固相组分的固-液混合浆料,这种浆料具有某种流变特性,可以方便地进行成型加工。利用这种金属浆料加工成型的方法,称为金属的半固态加工。半固态加工的主要流程包括:金属浆料制备、半固态铸造、半固态压力加工等。 自蔓延高温合成技术(self-propagation hige-temperature synthesizing technology) 自蔓延高温合成技术也称燃烧合成,是一种利用化学反应(燃烧)本身放热制备材料的新技术。其过程为把原料按一定比例混合成型,然后通过点火引燃,使其局部发生燃烧反应,并得到所需要的反应产物。同时,燃烧反应放出的热量足以使其它部分原料逐步燃烧,使整个坯料完全发生反应,获得具有所需的一定成分和结构的材料。 失效(failure) 所谓失效就是产品失去了规定的功能,而这规定的功能是指国家有关法规、质量标准以及规定的对产品适用、安全和其他特性的要求。 失效分析( failure analysis) 失效分析就是判断失效产品的失效模式、查找产品的失效机理和原因,提出预防再失效的对策这样一系列的技术活动和管理活动。失效分析的对象是失效产品及其相关的失效过程,因此它是一种全过程全方位的分析。 失效模式(failure mode) 失效模式是指失效的外在宏观表现形式、过程规律和失效机理。 失效机理( failure mechanism) 失效机理是指失效的物理、化学变化的本质和微观过程。既要分析微观上原子、分子尺度和结构的变化,也要涉及宏观的性能。根据机械失效过程中材料发生变化的物理、化学的本质不同和过程特征的差异,可作如下分类:变形、断裂、磨损、腐蚀等,对于具体的失效问题,往往是几种不同的材料变化机理引起的。 淬透性(hardenability) 淬透性表示奥氏体化后的钢在淬火时获得马氏体的能力,其大小是用钢在一定条件下淬火获得的淬透层深度来表示的。淬透性是钢的重要工艺性能。是选材和确定热处理工艺 的重要依据。 脆性断裂(brittle fracture) 脆性断裂是几乎不伴随塑性变形而形成脆性断口(断裂面通常与拉应力垂直,宏观上由具有光泽的亮面组成)的断裂。脆性断裂一般包括沿晶脆性断裂、解理断裂、准解理断裂、疲劳断裂、腐蚀疲劳断裂、应力腐蚀断裂、氢脆断裂等。 塑性断裂(ductile fracture) 与脆性断裂不同,塑性断裂是材料断裂前产生明显宏观塑性变形的断裂方式。 穿晶断裂(transgranular fracture)/font> 穿晶断裂又称晶内断裂,裂纹穿过晶粒内部。 沿晶断裂(intergranular fracture) 沿晶断裂又称晶间断裂,它是多晶体沿不同取向晶粒间晶界分离的现象。 疲劳断裂(fatigue fracture) 疲劳断裂指金属在循环载荷作用下产生疲劳裂纹萌生和扩展而导致的断裂,其断口在宏观上由疲劳源、扩展区和最后破断区三个区域构成,在微观上可出现疲劳条纹。 解理断裂(cleavage fracture) 解理断裂是金属在正应力作用下,由于原子结合键破坏而造成的沿一定的晶体学平面(即解理面)快速分离的过程,是一种脆性断裂。 准解理断裂(quasicleavage) 准解理断裂是介于解理断裂和韧窝断裂之间一种过渡断裂形式,准解理的形成过程是首先在许多不同部位同时产生许多解理裂纹核,然后按解理方式扩展成解理小刻面,最后以塑性方式撕裂,与相邻的解理小刻面相连,形成撕裂岭。 韧窝断口(dimple fracture) 韧窝是金属塑性断裂的主要微观特征。它是材料在微区范围内塑性变形产生的显微空洞,经形核、长大、聚集最后相互连接而导致断裂后,在断口表面上所留下的痕迹。韧窝的大小包括平均直径和深度。影响韧窝大小的主要因素从材料方面讲为第二相的大小、密度、基体的塑性变形能力、形变硬化指数等,从外界条件讲与应力大小和加载速率有关。一般在断裂条件相同时,韧窝尺寸越大,表示材料的塑性越好。 纤维区,放射区,剪切唇(radiation region,fibrous region,shear lip) 金属断裂的宏观断口通常可分为三个宏观特征区,即中间的纤维区,然后是放射区和剪切唇区,这就是所谓的断口宏观特征三要素。纤维区的宏观平面与拉伸应力轴垂直,呈粗糙的纤维状,断裂从这一区开始。放射区是裂纹由缓慢扩展向快速的不稳定扩展转化的标志,其特征是放射线花样,放射线方向为裂纹扩展方向。剪切唇区是最后断裂区,表面较光滑,与拉伸应力轴的交角约45°。对于不同的材料,不同的温度和受力状态,三个区域的位置、形状、大小及分布有所不同,有时在断口上也可能只出现一种或二种形貌特征。 磨损失效(wear failure) 磨损失效是物体表面相接触并作相对运动时,材料自该表面逐渐损失以致构件失效的现象。 粘着磨损(additive wear) 粘着磨损是一种严重的磨损方式,是相对运动的物体接触表面发生了固相粘着,使材料从一个表面转移到另一表面的现象 磨粒磨损(abrasire wear) 磨粒磨损也称为磨料磨损或研磨磨损,它是当磨擦偶件一方的硬度比另一方硬度大得多时,或者在接触面之间存在着硬质粒子时,所产生的一种磨损。 疲劳磨损(fatigue wear) 疲劳磨损是指两接触面作滚动,或滑动,或是滑动与滚动复合的磨擦状态,同时在高交变接触应力的作用下,使材料表面疲劳而产生物质流失的过程,也称表面疲劳磨损或接触疲劳磨损。 腐蚀磨损(corrosion wear) 腐蚀磨损是由于外界环境引起金属表层的腐蚀产物(主要是氧化物)剥落,及与金属磨面之间的机械磨损相结合而出现的现象。 应力腐蚀(stress corrosion) 金属构件在静应力和特定的腐蚀环境共同作用下所导致的脆性断裂为应力腐蚀。断裂前没有预兆,不易预防,危害性极大。 氢脆(hydrogen embrittlement) 由于氢渗入金属内部导致损伤,从而使金属零件在低于材料屈服极限的静应力作用下产生的失效称为氢脆。 氢致延迟断裂(hydrogen induced delay cracking) 金属材料在加工、制造及使用环境下很容易受到氢的侵入,而且随后在静应力作用下,会向应力高的部位扩散聚集,当聚集的氢含量达到一定的临界浓度时,使金属原子间结合力下降而导致断裂。由于氢的扩散聚集需要一定的时间,所以断裂的发生是在加载后的某个时间,故称之为氢致延迟断裂。 腐蚀疲劳(corrosion fatigue) 腐蚀疲劳是在交变载荷和腐蚀环境协同、交互作用下发生的材料破坏过程。 电极电位(electrode potential) 某电极与标准氢电极组成一特殊的原电池,其中标准氢电极规定为负极,所测得的这种电池的电动势,称为该电极的电极电位或称氢标电极电位。各种电极的氢标电极可以表示出电极与溶液界面间电位差的相对大小 化学腐蚀(chemical corrosion) 化学腐蚀是金属在非电化学作用下的腐蚀(氧化)过程。通常指在非电解质溶液及干燥气体中,由纯化学作用引起的腐蚀。 电化学腐蚀(electrochemical corrosion) 电化学腐蚀是在电解质溶液中或金属表面的液膜中,服从于电化学反应规律的金属腐蚀(氧化)过程。 点蚀(pitting corrosion) 产生点状的腐蚀,且从金属表面向内部扩展,形成孔穴。 晶间腐蚀(intercrystalline corrosion) 晶间腐蚀是指金属材料或构件沿晶界产生并沿晶界扩展导致金属材料或物件的损伤。 缝隙腐蚀(crevice corrosion) 由于狭缝或间隙的存在,在狭缝内或近旁发生的腐蚀 老化(aging) 高分子材料在加工储存和使用过程中由于对一些环境因素较为敏感而导致性能逐渐下降的现象称为高分子材料的老化。 热老化(thermal aging) 高分子材料在热环境因素作用下而导致性能逐渐下降的现象称为高分子材料的热老化。高分子材料在真空中加热30分后损失一半重量所需要的温度称为半分解温度,常用这个参量来表示高分子材料的热稳定性。 光老化(light aging) 高分子材料在光线作用下而导致性能逐渐下降的现象称为高分子材料的光老化。 辐照老化(radiation aging) 高分子材料在辐射线(α、β、γ、χ射线、快中子、慢中子、离子)辐照下而导致性能逐渐下降的现象称为高分子材料的辐照老化。 氧化老化(oxidation aging) 高分子材料与空气中氧(臭氧)发生反应而引起高分子降解或交联称为氧化老化。 生物降解(biodegradation) 生物降解是在环境介质中,通过生物的复杂作用,将有机物分子分解的过程。 b b s . k aoy a n . c om 转载请注明出自bbs.kaoyan.com,本贴地址:转发给QQ/MSN好友 bbs.kaoyan.com/t2057006p1 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UID 2352318 阅读权限 100 在线时间622 小时 最后登录2010-5-22 查看详细资料引用回复TOP 点燃一支烟 版主 忠诚的稻草人帖子 6156 精华 30 积分 48206 威望 40861 K币 11399 元 注册时间沙发大中小发表于2007-11-20 18:52 只看该作者 A Abrasive. A hard and wear-resistant material (commonly a ceramic) that is used to wear, grind, or cut away other material. Absorption. The optical phenomenon whereby the energy of a photon of light is assimilated within a substance, normally by electronic polarization or by an electron excitation event. Acceptor level. For a semiconductor or insulator, an energy level lying within yet near the bottom of the energy band gap, which may accept electrons from the valence band, leaving behind holes. The level is normally introduced by an 2007-9-30 个人空间发短消息加为好友当前离线impurity atom. Activation energy (Q). The energy required to initiate a reaction, such as diffusion. Activation polarization. The condition wherein the rate of an electrochemical reaction is controlled by the one slowest step in a sequence of steps that occur in series. Addition (or chain reaction) polymerization. The process by which bifunctional monomer units are attached one at a time, in chainlike fashion, to form a linear polymer macromolecule. Adhesive. A substance that bonds together the surfaces of two other materials (termed adherends). Age hardening. See Precipitation hardening. Allotropy. The possibility of existence of two or more different crystal structures for a substance (generally an elemental solid). Alloy. A metallic substance that is composed of two or more elements. 480 Alloy steel. A ferrous (or ironbased) alloy that contains appreciable concentrations of alloying elements (other than C and residual amounts of Mn, Si, S, and P). These alloying elements are usually added to improve mechanical and corrosion resistance properties. Alternating copolymer. A copolymer inwhich two different mer units alternate positions along the molecular chain. Amorphous. Having a noncrystalline structure. Anelastic deformation. Time-dependent elastic (nonpermanent) deformation. Anion. A negatively charged, nonmetallic ion. Anisotropic. Exhibiting different values of a property in different crystallographic directions. Annealing. A generic term used to denote a heat treatment wherein the microstructure and, consequently, the properties of amaterial are altered. ??Annealing‘‘ frequently refers to a heat treatment whereby a previously cold-worked metal is softened by allowing it to recrystallize. Annealing point (glass). That temperature at which residual stresses in a glass are eliminated within about 15 min; this corresponds to a glass viscosity of about 1012 Pa-s (1013 P). Anode. The electrode in an electrochemical cell or galvanic couple that experiences oxidation, or gives up electrons. Antiferromagnetism. A phenomenon observed in some materials (e.g., MnO); complete magnetic moment cancellation occurs as a result of antiparallel coupling of adjacent atoms or ions. The macroscopic solid possesses no net magnetic moment. Artificial aging. For precipitation hardening, aging above room temperature. Atactic. A type of polymer chain configuration wherein side groups are randomly positioned on one side of the chain or the other. Athermal transformation. A reaction that is not thermally activated, and usually diffusionless, as with the martensitic transformation. Normally, the transformation takes place with great speed (i.e., is independent of time), and the extent of reaction depends on temperature. Atomic mass unit (amu). A measure of atomic mass; one twelfth of the mass of an atom of C12. Atomic number (Z). For a chemical element, the number of protons within the atomic nucleus. Atomic packing factor (APF). The fraction of the volume of a unit cell that is occupied by ??hard sphere‘‘atoms or ions. Atomic vibration. The vibration of an atom about its normal position in a substance. Atomic weight (A). The weighted average of the atomic masses of an atom‘s naturally occurring isotopes. It may be expressed in terms of atomic mass units (on an atomic basis), or the mass per mole of atoms. Atom percent (at%). Concentration specification on the basis of the number of moles (or atoms) of a particular element relative to the Glossary ● 481 total number of moles (or atoms) of all elements within an alloy. Austenite. Face-centered cubic iron; also iron and steel alloys that have the FCC crystal structure. Austenitizing. Forming austenite by heating a ferrous alloy above its upper critical temperature—to within the austenite phase region from the phase diagram. B Bainite. An austenitic transformation product found in some steels and cast irons. It forms at temperatures between those at which pearlite and martensite transformations occur. The microstructure consists of -ferrite and a fine dispersion of cementite. Band gap energy (Eg). For semiconductors and insulators, the energies that lie between the valence and conduction bands; for intrinsic materials, electrons are forbidden to have energies within this range. Bifunctional. Designating monomer units that have two active bonding positions. Block copolymer. A linear copolymer in which identical mer units are clustered in blocks along the molecular chain. Body-centered cubic (BCC). A common crystal structure found in some elemental metals. Within the cubic unit cell, atoms are located at corner and cell center positions. Bohr atomic model. An early atomic model, in which electrons are assumed to revolve around the nucleus in discrete orbitals. Bohr magneton ( B). The most fundamental magnetic moment, of magnitude 9.27 10 24 A-m2. Boltzmann‘s constant (k). A thermal energy constant having the value of 1.38 10 23 J/atom-K (8.62 10 5 eV/atom-K). See also Gas constant. Bonding energy. The energy required to separate two atoms that are chemically bonded to each other. It may be expressed on a peratom basis, or per mole of atoms. Bragg‘s law. A relationship (Equation 3.10) which stipulates the condition for diffraction by a set of crystallographic planes. Branched polymer. A polymer having a molecular structure of secondary chains that extend from the primary main chains. Brass. A copper-rich copper–zinc alloy. Brazing. A metal joining technique that uses a molten filler metal alloy having a melting temperature greater than about 425 C (800 F). Brittle fracture. Fracture that occurs by rapid crack propagation and without appreciable macroscopic deformation. Bronze. A copper-rich copper–tin alloy; aluminum, silicon, and nickel bronzes are also possible. Burgers vector (b). A vector that denotes the magnitude and direction of lattice distortion associated with a dislocation. C Calcination. A high-temperature reaction whereby one solid material dissociates to form a gas and another solid. It is one step in the production of cement. Capacitance (C). The charge-storing ability of a capacitor, defined as the magnitude of charge stored on either plate divided by the applied voltage. Carbon-carbon composite. A composite that is composed of continuous fibers of carbon that are imbedded in a carbon matrix. The matrix was originally a polymer resin that was subsequently pyrolyzed to form carbon. Carburizing. The process by which the surface carbon concentration of a ferrous alloy is increased by diffusion from the surrounding environment. Case hardening. Hardening of the outer surface (or ??case‘‘) of a steel component by a carburizing or nitriding process; used to improve wear and fatigue resistance. Cast iron. Generically, a ferrous alloy, the carbon content of which is greater than the maximum solubility in austenite at the eutectic temperature. Most commercial cast irons contain between 3.0 and 4.5 wt%C, and between 1 and 3 wt%Si. Cathode. The electrode in an electrochemical cell or galvanic couple at which a reduction reaction occurs; thus the electrode that receives electrons from an external circuit. Cathodic protection. A means of corrosion prevention whereby electrons are supplied to the structure to be protected from an external source such as another more reactive metal or a dc power supply. Cation. A positively charged metallic ion. Cement. A substance (often a ceramic) that by chemical reaction binds particulate aggregates into a cohesive structure. With hydraulic cements the chemical reaction is one of hydration, involving water. Cementite. Iron carbide (Fe3C). Ceramic. A compound of metallic and nonmetallic elements, for which the interatomic bonding is predominantly ionic. Ceramic-matrix composite (CMC). A composite for which both matrix and dispersed phases are ceramic materials. The dispersed phase is normally added to improve fracture toughness. Cermet. Acomposite material consisting of a combination of ceramic and metallic materials. The most common cermets are the cemented carbides, composed of an extremely hard ceramic (e.g., WC, TiC), bonded together by a ductile metal such as cobalt or nickel. Chain-folded model. For crystalline polymers, a model that describes the structure of platelet crystallites. Molecular alignment is accomplished by chain folding that occurs at the crystallite faces. Charpy test. One of two tests (see also Izod test) that may be used to measure the impact energy or notch toughness of a standard notched 482 ● Glossary specimen. An impact blow is imparted to the specimen by means of a weighted pendulum. Cis. For polymers, a prefix denoting a type of molecular structure. For some unsaturated carbon chain atoms within amer unit, a side atom or group may be situated on one side of the chain or directly opposite at a 180 rotation position. In a cis structure, two such side groups within the same mer reside on the same side (e.g., cis-isoprene). Coarse pearlite. Pearlite for which the alternating ferrite and cementite layers are relatively thick. Coercivity (or coercive field, Hc). The applied magnetic field necessary to reduce to zero the magnetic flux density of a magnetized ferromagnetic or ferrimagnetic material. Cold working. The plastic deformation of a metal at a temperature below that at which it recrystallizes. Color. Visual perception that is stimulated by the combination of wavelengths of light that are transmitted to the eye. Colorant. An additive that imparts a specific color to a polymer. Component. A chemical constituent (element or compound) of an alloy, which may be used to specify its composition. Composition (Ci). The relative content of a particular element or constituent (i) within an alloy, usually expressed in weight percent or atom percent. Concentration. See Composition. Concentration gradient (dC/dx). The slope of the concentration profile at a specific position. Concentration polarization. The condition wherein the rate of an electrochemical reaction is limited by the rate of diffusion in the solution. Concentration profile. The curve that results when the concentration of a chemical species is plotted versus position in a material. Concrete. A composite material consisting of aggregate particles bound together in a solid body by a cement. Condensation (or step reaction) polymerization. The formation of polymer macromolecules by an intermolecular reaction involving at least two monomer species, usually with the production of a by-product of low molecular weight, such as water. Conduction band. For electrical insulators and semiconductors, the lowest lying electron energy band that is empty of electrons at 0 K. Conduction electrons are those that have been excited to states within this band. Conductivity, electrical ( ). The proportionality constant between current density and applied electric field; also ameasure of the ease with which a material is capable of conducting an electric current. Congruent transformation. Atransformation of one phase to another of the same composition. Continuous cooling transformation (CCT) diagram. Aplot of temperature versus the logarithm of time for a steel alloy of definite composition. Used to indicate when transformations occur as the initially austenitized material is continuously cooled at a specified rate; in addition, the final microstructure and mechanical characteristics may be predicted. Coordination number. The number of atomic or ionic nearest neighbors. Copolymer. A polymer that consists of two or more dissimilar mer units in combination along its molecular chains. Corrosion. Deteriorative loss of a metal as a result of dissolution environmental reactions. Corrosion fatigue. Atype of failure that results from the simultaneous action of a cyclic stress and chemical attack. Corrosion penetration rate (CPR). Thickness loss of material per unit of time as a result of corrosion; usually expressed in terms of mils per year or millimeters per year. Coulombic force. A force between charged particles such as ions; the force is attractive when the particles are of opposite charge. Covalent bond. A primary interatomic bond that is formed by the sharing of electrons between neighboring atoms. Creep. The time-dependent permanent deformation that occurs under stress; for most materials it is important only at elevated temperatures. Crevice corrosion. A form of corrosion that occurs within narrow crevices and under deposits of dirt or corrosion products (i.e., in regions of localized depletion of oxygen in the solution). Critical resolved shear stress ( crss). That shear stress, resolved within a slip plane and direction, which is required to initiate slip. Crosslinked polymer. Apolymer in which adjacent linear molecular chains are joined at various positions by covalent bonds. Crystalline. The state of a solid material characterized by a periodic and repeating three-dimensional array of atoms, ions, or molecules. Crystallinity. For polymers, the state wherein a periodic and repeating atomic arrangement is achieved by molecular chain alignment. Crystallite. A region within a crystalline polymer in which all the molecular chains are ordered and aligned. Crystal structure. For crystalline materials, the manner in which atoms or ions are arrayed in space. It is defined in terms of the unit cell geometry and the atom positions within the unit cell. Crystal system. A scheme by which crystal structures are classified according to unit cell geometry. This geometry is specified in terms of the relationships between edge lengths and interaxial angles. There are seven different crystal systems. Curie temperature (Tc). That temperature above which a ferromagGlossary ● 483 netic or ferrimagnetic material becomes paramagnetic. D Defect structure. Relating to the kinds and concentrations of vacancies and interstitials in a ceramic compound. Degradation. A term used to denote the deteriorative processes that occur with polymeric materials. These processes include swelling, dissolution, and chain scission. Degree of polymerization. The average number of mer units per polymer chain molecule. Design stress ( d). Product of the calculated stress level (on the basis of estimated maximum load) and a design factor (which has a value greater than unity). Used to protect against unanticipated failure. Devitrification. The process in which a glass (noncrystalline or vitreous solid) transforms to a crystalline solid. Diamagnetism. A weak form of induced or nonpermanent magnetism for which the magnetic susceptibility is negative. Dielectric. Any material that is electrically insulating. Dielectric constant ( r). The ratio of the permittivity of a medium to that of a vacuum. Often called the relative dielectric constant or relative permittivity. Dielectric displacement (D). The magnitude of charge per unit area of capacitor plate. Dielectric (breakdown) strength. The magnitude of an electric field necessary to cause significant current passage through a dielectric material. Diffraction (x-ray). Constructive interference of x-ray beams that are scattered by atoms of a crystal. Diffusion. Mass transport by atomic motion. Diffusion coefficient (D). The constant of proportionality between the diffusion flux and the concentration gradient in Fick‘s first law. Its magnitude is indicative of the rate of atomic diffusion. Diffusion flux (J). The quantity of mass diffusing through and perpendicular to a unit cross-sectional area of material per unit time. Diode. An electronic device that rectifies an electrical current—i.e., allows current flow in one direction only. Dipole (electric). A pair of equal yet opposite electrical charges that are separated by a small distance. Dislocation. A linear crystalline defect around which there is atomic misalignment. Plastic deformation corresponds to the motion of dislocations in response to an applied shear stress. Edge, screw, and mixed dislocations are possible. Dislocation density. The total dislocation length per unit volume of material; alternately, the number of dislocations that intersect a unit area of a random surface section. Dislocation line. The line that extends along the end of the extra half-plane of atoms for an edge dislocation, and along the center of the spiral of a screw dislocation. Dispersed phase. For composites and some two-phase alloys, the discontinuous phase that is surrounded by the matrix phase. Dispersion strengthening. Ameans of strengthening materials wherein very small particles (usually less than 0.1 m) of a hard yet inert phase are uniformly dispersed within a load-bearing matrix phase. Domain. A volume region of a ferromagnetic or ferrimagnetic material in which all atomic or ionic magnetic moments are aligned in the same direction. Donor level. For a semiconductor or insulator, an energy level lying within yet near the top of the energy band gap, and from which electrons may be excited into the conduction band. It is normally introduced by an impurity atom. Doping. The intentional alloying of semiconducting materials with controlled concentrations of donor or acceptor impurities. Drawing (metals). A forming technique used to fabricate metal wire and tubing. Deformation is accomplished by pulling the material through a die by means of a tensile force applied on the exit side. Drawing (polymers). A deformation technique wherein polymer fibers are strengthened by elongation. Driving force. The impetus behind a reaction, such as diffusion, grain growth, or a phase transformation. Usually attendant to the reaction is a reduction in some type of energy (e.g., free energy). Ductile fracture. A mode of fracture that is attended by extensive gross plastic deformation. Ductile iron. A cast iron that is alloyed with silicon and a small concentration of magnesium and/or cerium and in which the free graphite exists in nodular form. Sometimes called nodular iron. Ductile-to-brittle transition. The transition from ductile to brittle behavior with a decrease in temperature exhibited by BCC alloys; the temperature range over which the transition occurs is determined by Charpy and Izod impact tests. Ductility. A measure of a material‘s ability to undergo appreciable plastic deformation before fracture; it may be expressed as percent elongation (%EL) or percent reduction in area (%RA) from a tensile test. E Edge dislocation. A linear crystalline defect associated with the lattice distortion produced in the vicinity of the end of an extra halfplane of atoms within a crystal. The Burgers vector is perpendicular to the dislocation line. Elastic deformation. Deformation that is nonpermanent, that is, totally recovered upon release of an applied stress. Elastic recovery. Nonpermanent deformation that is recovered or regained upon the release of a mechanical stress. Elastomer. A polymeric material that may experience large and reversible elastic deformations. 484 ● Glossary Electrical conductivity. See Conductivity, electrical. Electric dipole. See Dipole (electric). Electric field (E ). The gradient of voltage. Electroluminescence. The emission of visible light by a p–n junction across which a forward-biased voltage is applied. Electrolyte. A solution through which an electric current may be carried by the motion of ions. Electromotive force (emf) series. A ranking of metallic elements according to their standard electrochemical cell potentials. Electron configuration. For an atom, the manner in which possible electron states are filled with electrons. Electronegative. For an atom, having a tendency to accept valence electrons. Also, a term used to describe nonmetallic elements. Electron energy band. A series of electron energy states that are very closely spaced with respect to energy. Electroneutrality. The state of having exactly the same numbers of positive and negative electrical charges (ionic and electronic), that is, of being electrically neutral. Electron state (level). One of a set of discrete, quantized energies that are allowed for electrons. In the atomic case each state is specified by four quantum numbers. Electron volt (eV). A convenient unit of energy for atomic and subatomic systems. It is equivalent to the energy acquired by an electron when it falls through an electric potential of 1 volt. Electropositive. For an atom, having a tendency to release valence electrons. Also, a term used to describe metallic elements. Endurance limit. See Fatigue limit. Energy band gap. See Band gap energy. Engineering strain. See Strain, engineering. Engineering stress. See Stress, engineering. Equilibrium (phase). The state of a system where the phase characteristics remain constant over indefinite time periods. At equilibrium the free energy is a minimum. Erosion–corrosion. A form of corrosion that arises from the combined action of chemical attack and mechanical wear. Eutectic phase. One of the two phases found in the eutectic structure. Eutectic reaction. A reaction wherein, upon cooling, a liquid phase transforms isothermally and reversibly into two intimately mixed solid phases. Eutectic structure. A two-phase microstructure resulting from the solidification of a liquid having the eutectic composition; the phases exist as lamellae that alternate with one another. Eutectoid reaction. A reaction wherein, upon cooling, one solid phase transforms isothermally and reversibly into two new solid phases that are intimately mixed. Excited state. An electron energy state, not normally occupied, to which an electron may be promoted (from a lower energy state) by the absorption of some type of energy (e.g., heat, radiative). Extrinsic semiconductor. A semiconducting material for which the electrical behavior is determined by impurities. Extrusion. A forming technique whereby a material is forced, by compression, through a die orifice. F Face-centered cubic (FCC). A crystal structure found in some of the common elemental metals. Within the cubic unit cell, atoms are located at all corner and face-centered positions. Fatigue. Failure, at relatively low stress levels, of structures that are subjected to fluctuating and cyclic stresses. Fatigue life (Nf ). The total number of stress cycles that will cause a fatigue failure at some specified stress amplitude. Fatigue limit. For fatigue, the maximum stress amplitude level below which a material can endure an essentially infinite number of stress cycles and not fail. Fatigue strength. The maximum stress level that a material can sustain, without failing, for some specified number of cycles. Fermi energy (Ef ). For a metal, the energy corresponding to the highest filled electron state at 0 K. Ferrimagnetism. Permanent and large magnetizations found in some ceramic materials. It results from antiparallel spin coupling and incomplete magnetic moment cancellation. Ferrite (ceramic). Ceramic oxide materials composed of both divalent and trivalent cations (e.g., Fe2 and Fe3 ), some of which are ferrimagnetic. Ferrite (iron). Body-centered cubic iron; also iron and steel alloys that have the BCC crystal structure. Ferroelectric. A dielectric material that may exhibit polarization in the absence of an electric field. Ferromagnetism. Permanent and large magnetizations found in some metals (e.g., Fe, Ni, and Co), which result from the parallel alignment of neighboring magnetic moments. Ferrous alloy. A metal alloy for which iron is the prime constituent. Fiber. Any polymer, metal, or ceramic that has been drawn into a long and thin filament. Fiber-reinforced composite. Acomposite in which the dispersed phase is in the form of a fiber (i.e., a filament that has a large length-todiameter ratio). Fiber reinforcement. Strengthening or reinforcement of a relatively weak material by embedding a strong fiber phase within the weak matrix material. Fick‘s first law. The diffusion flux is proportional to the concentration gradient. This relationship is emGlossary ● 485 ployed for steady-state diffusion situations. Fick‘s second law. The time rate of change of concentration is proportional to the second derivative of concentration. This relationship is employed in nonsteady-state diffusion situations. Filler. An inert foreign substance added to a polymer to improve or modify its properties. Fine pearlite. Pearlite for which the alternating ferrite and cementite layers are relatively thin. Firing. A high temperature heat treatment that increases the density and strength of a ceramic piece. Flame retardant. A polymer additive that increases flammability resistance. Flexural strength ( fs). Stress at fracture from a bend (or flexure) test. Fluorescence. Luminescence that occurs for times much less than a second after an electron excitation event. Foam. A polymer that has been made porous (or spongelike) by the incorporation of gas bubbles. Forging. Mechanical forming of a metal by heating and hammering. Forward bias. The conducting bias for a p–n junction rectifier such that electron flow is to the n side of the junction. Fracture mechanics. A technique of fracture analysis used to determine the stress level at which preexisting cracks of known size will propagate, leading to fracture. Fracture toughness (Kc). Critical value of the stress intensity factor for which crack extension occurs. Free electron. An electron that has been excited into an energy state above the Fermi energy (or into the conduction band for semiconductors and insulators) and may participate in the electrical conduction process. Free energy. A thermodynamic quantity that is a function of both the internal energy and entropy (or randomness) of a system. At equilibrium, the free energy is at a minimum. Frenkel defect. In an ionic solid, a cation–vacancy and cation–interstitial pair. Full annealing. For ferrous alloys, austenitizing, followed by cooling slowly to room temperature. G Galvanic corrosion. The preferential corrosion of the more chemically active of two metals that are electrically coupled and exposed to an electrolyte. Galvanic series. A ranking of metals and alloys as to their relative electrochemical reactivity in seawater. Gas constant (R). Boltzmann‘s constant per mole of atoms. R 8.31 J/mol-K (1.987 cal/mol-K). Gibbs phase rule. For a system at equilibrium, an equation (Equation 10.16) that expresses the relationship between the number of phases present and the number of externally controllable variables. Glass–ceramic. Afine-grained crystalline ceramic material that was formed as a glass and subsequently devitrified (or crystallized). Glass transition temperature (Tg). That temperature at which, upon cooling, a noncrystalline ceramic or polymer transforms from a supercooled liquid to a rigid glass. Graft copolymer. A copolymer wherein homopolymer side branches of one mer type are grafted to homopolymer main chains of a different mer. Grain. An individual crystal in a polycrystalline metal or ceramic. Grain boundary. The interface separating two adjoining grains having different crystallographic orientations. Grain growth. The increase in average grain size of a polycrystalline material; for most materials, an elevated- temperature heat treatment is necessary. Grain size. The average grain diameter as determined from a random cross section. Gray cast iron. A cast iron alloyed with silicon in which the graphite exists in the form of flakes. A fractured surface appears gray. Green ceramic body. A ceramic piece, formed as a particulate aggregate, that has been dried but not fired. Ground state. A normally filled electron energy state from which electron excitation may occur. H Hall effect. The phenomenon whereby a force is brought to bear on a moving electron or hole by a magnetic field that is applied perpendicular to the direction of motion. The force direction is perpendicular to both the magnetic field and the particle motion directions. Hardenability. A measure of the depth to which a specific ferrous alloy may be hardened by the formation of martensite upon quenching from a temperature above the upper critical temperature. Hard magnetic material. A ferrimagnetic or ferromagnetic material that has large coercive field and remanence values, normally used in permanent magnet applications. Hard ness. The measure of a material‘s resistance to deformation by surface indentation or by abrasion. Heat capacity (Cp , Cv). The quantity of heat required to produce a unit temperature rise per mole of material. Hexagonal close-packed (HCP). A crystal structure found for some metals. The HCP unit cell is of hexagonal geometry and is generated by the stacking of close-packed planes of atoms. High polymer. A solid polymeric material having a molecular weight greater than about 10,000 g/mol. High-strength, low-alloy (HSLA) steels. Relatively strong, low-carbon steels, with less than about 10 wt% total of alloying elements. Hole (electron). For semiconductors and insulators, a vacant elec486 ion. Anisotropic. Exhibiting different values of a property in different crystallographic directions. Annealing. A generic term used to denote a heat treatment wherein the microstructure and, consequently, the properties of amaterial are altered. ??Annealing‘‘ frequently refers to a heat treatment whereby a previously cold-worked metal is softened by allowing it to recrystallize. Annealing point (glass). That temperature at which residual stresses in a glass are eliminated within about 15 min; this corresponds to a glass viscosity of about 1012 Pa-s (1013 P). Anode. The electrode in an electrochemical cell or galvanic couple that experiences oxidation, or gives up electrons. Antiferromagnetism. A phenomenon observed in some materials (e.g., MnO); complete magnetic moment cancellation occurs as a result of antiparallel coupling of adjacent atoms or ions. The macroscopic solid possesses no net magnetic moment. Artificial aging. For precipitation hardening, aging above room temperature. Atactic. A type of polymer chain configuration wherein side groups are randomly positioned on one side of the chain or the other. Athermal transformation. A reaction that is not thermally activated, and usually diffusionless, as with the martensitic transformation. Normally, the transformation takes place with great speed (i.e., is independent of time), and the extent of reaction depends on temperature. Atomic mass unit (amu). A measure of atomic mass; one twelfth of the mass of an atom of C12. Atomic number (Z). For a chemical element, the number of protons within the atomic nucleus. Atomic packing factor (APF). The fraction of the volume of a unit cell that is occupied by ??hard sphere‘‘atoms or ions. Atomic vibration. The vibration of an atom about its normal position in a substance. Atomic weight (A). The weighted average of the atomic masses of an atom‘s naturally occurring isotopes. It may be expressed in terms of atomic mass units (on an atomic basis), or the mass per mole of atoms. Atom percent (at%). Concentration specification on the basis of the number of moles (or atoms) of a particular element relative to the Glossary ● 481 total number of moles (or atoms) of all elements within an alloy. Austenite. Face-centered cubic iron; also iron and steel alloys that have the FCC crystal structure. Austenitizing. Forming austenite by heating a ferrous alloy above its upper critical temperature—to within the austenite phase region from the phase diagram. B Bainite. An austenitic transformation product found in some steels and cast irons. It forms at temperatures between those at which pearlite and martensite transformations occur. The microstructure consists of -ferrite and a fine dispersion of cementite. Band gap energy (Eg). For semiconductors and insulators, the energies that lie between the valence and conduction bands; for intrinsic materials, electrons are forbidden to have energies within this range. Bifunctional. Designating monomer units that have two active bonding positions. Block copolymer. A linear copolymer in which identical mer units are clustered in blocks along the molecular chain. Body-centered cubic (BCC). A common crystal structure found in some elemental metals. Within the cubic unit cell, atoms are located at corner and cell center positions. Bohr atomic model. An early atomic model, in which electrons are assumed to revolve around the nucleus in discrete orbitals. Bohr magneton ( B). The most fundamental magnetic moment, of magnitude 9.27 10 24 A-m2. Boltzmann‘s constant (k). A thermal energy constant having the value of 1.38 10 23 J/atom-K (8.62 10 5 eV/atom-K). See also Gas constant. Bonding energy. The energy required to separate two atoms that are chemically bonded to each other. It may be expressed on a peratom basis, or per mole of atoms. Bragg‘s law. A relationship (Equation 3.10) which stipulates the condition for diffraction by a set of crystallographic planes. Branched polymer. A polymer having a molecular structure of secondary chains that extend from the primary main chains. Brass. A copper-rich copper–zinc alloy. Brazing. A metal joining technique that uses a molten filler metal alloy having a melting temperature greater than about 425 C (800 F). Brittle fracture. Fracture that occurs by rapid crack propagation and without appreciable macroscopic deformation. Bronze. A copper-rich copper–tin alloy; aluminum, silicon, and nickel bronzes are also possible. Burgers vector (b). A vector that denotes the magnitude and direction of lattice distortion associated with a dislocation. C Calcination. A high-temperature reaction whereby one solid material dissociates to form a gas and another solid. It is one step in the production of cement. Capacitance (C). The charge-storing ability of a capacitor, defined as the magnitude of charge stored on either plate divided by the applied voltage. Carbon-carbon composite. A composite that is composed of continuous fibers of carbon that are imbedded in a carbon matrix. The matrix was originally a polymer resin that was subsequently pyrolyzed to form carbon. Carburizing. The process by which the surface carbon concentration of a ferrous alloy is increased by diffusion from the surrounding environment. Case hardening. Hardening of the outer surface (or ??case‘‘) of a steel component by a carburizing or nitriding process; used to improve wear and fatigue resistance. Cast iron. Generically, a ferrous alloy, the carbon content of which is greater than the maximum solubility in austenite at the eutectic temperature. Most commercial cast irons contain between 3.0 and 4.5 wt%C, and between 1 and 3 wt%Si. Cathode. The electrode in an electrochemical cell or galvanic couple at which a reduction reaction occurs; thus the electrode that receives electrons from an external circuit. Cathodic protection. A means of corrosion prevention whereby electrons are supplied to the structure to be protected from an external source such as another more reactive metal or a dc power supply. Cation. A positively charged metallic ion. Cement. A substance (often a ceramic) that by chemical reaction binds particulate aggregates into a cohesive structure. With hydraulic cements the chemical reaction is one of hydration, involving water. Cementite. Iron carbide (Fe3C). Ceramic. A compound of metallic and nonmetallic elements, for which the interatomic bonding is predominantly ionic. Ceramic-matrix composite (CMC). A composite for which both matrix and dispersed phases are ceramic materials. The dispersed phase is normally added to improve fracture toughness. Cermet. Acomposite material consisting of a combination of ceramic and metallic materials. The most common cermets are the cemented carbides, composed of an extremely hard ceramic (e.g., WC, TiC), bonded together by a ductile metal such as cobalt or nickel. Chain-folded model. For crystalline polymers, a model that describes the structure of platelet crystallites. Molecular alignment is accomplished by chain folding that occurs at the crystallite faces. Charpy test. One of two tests (see also Izod test) that may be used to measure the impact energy or notch toughness of a standard notched 482 ● Glossary specimen. An impact blow is imparted to the specimen by means of a weighted pendulum. Cis. For polymers, a prefix denoting a type of molecular structure. For some unsaturated carbon chain atoms within amer unit, a side atom or group may be situated on one side of the chain or directly opposite at a 180 rotation position. In a cis structure, two such side groups within the same mer reside on the same side (e.g., cis-isoprene). Coarse pearlite. Pearlite for which the alternating ferrite and cementite layers are relatively thick. Coercivity (or coercive field, Hc). The applied magnetic field necessary to reduce to zero the magnetic flux density of a magnetized ferromagnetic or ferrimagnetic material. Cold working. The plastic deformation of a metal at a temperature below that at which it recrystallizes. Color. Visual perception that is stimulated by the combination of wavelengths of light that are transmitted to the eye. Colorant. An additive that imparts a specific color to a polymer. Component. A chemical constituent (element or compound) of an alloy, which may be used to specify its composition. Composition (Ci). The relative content of a particular element or constituent (i) within an alloy, usually expressed in weight percent or atom percent. Concentration. See Composition. Concentration gradient (dC/dx). The slope of the concentration profile at a specific position. Concentration polarization. The condition wherein the rate of an electrochemical reaction is limited by the rate of diffusion in the solution. Concentration profile. The curve that results when the concentration of a chemical species is plotted versus position in a material. Concrete. A composite material consisting of aggregate particles bound together in a solid body by a cement. Condensation (or step reaction) polymerization. The formation of polymer macromolecules by an intermolecular reaction involving at least two monomer species, usually with the production of a by-product of low molecular weight, such as water. Conduction band. For electrical insulators and semiconductors, the lowest lying electron energy band that is empty of electrons at 0 K. Conduction electrons are those that have been excited to states within this band. Conductivity, electrical ( ). The proportionality constant between current density and applied electric field; also ameasure of the ease with which a material is capable of conducting an electric current. Congruent transformation. Atransformation of one phase to another of the same composition. Continuous cooling transformation (CCT) diagram. Aplot of temperature versus the logarithm of time for a steel alloy of definite composition. Used to indicate when transformations occur as the initially austenitized material is continuously cooled at a specified rate; in addition, the final microstructure and mechanical characteristics may be predicted. Coordination number. The number of atomic or ionic nearest neighbors. Copolymer. A polymer that consists of two or more dissimilar mer units in combination along its molecular chains. Corrosion. Deteriorative loss of a metal as a result of dissolution environmental reactions. Corrosion fatigue. Atype of failure that results from the simultaneous action of a cyclic stress and chemical attack. Corrosion penetration rate (CPR). Thickness loss of material per unit of time as a result of corrosion; usually expressed in terms of mils per year or millimeters per year. Coulombic force. A force between charged particles such as ions; the force is attractive when the particles are of opposite charge. Covalent bond. A primary interatomic bond that is formed by the sharing of electrons between neighboring atoms. Creep. The time-dependent permanent deformation that occurs under stress; for most materials it is important only at elevated temperatures. Crevice corrosion. A form of corrosion that occurs within narrow crevices and under deposits of dirt or corrosion products (i.e., in regions of localized depletion of oxygen in the solution). Critical resolved shear stress ( crss). That shear stress, resolved within a slip plane and direction, which is required to initiate slip. Crosslinked polymer. Apolymer in which adjacent linear molecular chains are joined at various positions by covalent bonds. Crystalline. The state of a solid material characterized by a periodic and repeating three-dimensional array of atoms, ions, or molecules. Crystallinity. For polymers, the state wherein a periodic and repeating atomic arrangement is achieved by molecular chain alignment. Crystallite. A region within a crystalline polymer in which all the molecular chains are ordered and aligned. Crystal structure. For crystalline materials, the manner in which atoms or ions are arrayed in space. It is defined in terms of the unit cell geometry and the atom positions within the unit cell. Crystal system. A scheme by which crystal structures are classified according to unit cell geometry. This geometry is specified in terms of the relationships between edge lengths and interaxial angles. There are seven different crystal systems. Curie temperature (Tc). That temperature above which a ferromagGlossary ● 483 netic or ferrimagnetic material becomes paramagnetic. D Defect structure. Relating to the kinds and concentrations of vacancies and interstitials in a ceramic compound. Degradation. A term used to denote the deteriorative processes that occur with polymeric materials. These processes include swelling, dissolution, and chain scission. Degree of polymerization. The average number of mer units per polymer chain molecule. Design stress ( d). Product of the calculated stress level (on the basis of estimated maximum load) and a design factor (which has a value greater than unity). Used to protect against unanticipated failure. Devitrification. The process in which a glass (noncrystalline or vitreous solid) transforms to a crystalline solid. Diamagnetism. A weak form of induced or nonpermanent magnetism for which the magnetic susceptibility is negative. Dielectric. Any material that is electrically insulating. Dielectric constant ( r). The ratio of the permittivity of a medium to that of a vacuum. Often called the relative dielectric constant or relative permittivity. Dielectric displacement (D). The magnitude of charge per unit area of capacitor plate. Dielectric (breakdown) strength. The magnitude of an electric field necessary to cause significant current passage through a dielectric material. Diffraction (x-ray). Constructive interference of x-ray beams that are scattered by atoms of a crystal. Diffusion. Mass transport by atomic motion. Diffusion coefficient (D). The constant of proportionality between the diffusion flux and the concentration gradient in Fick‘s first law. Its magnitude is indicative of the rate of atomic diffusion. Diffusion flux (J). The quantity of mass diffusing through and perpendicular to a unit cross-sectional area of material per unit time. Diode. An electronic device that rectifies an electrical current—i.e., allows current flow in one direction only. Dipole (electric). A pair of equal yet opposite electrical charges that are separated by a small distance. Dislocation. A linear crystalline defect around which there is atomic misalignment. Plastic deformation corresponds to the motion of dislocations in response to an applied shear stress. Edge, screw, and mixed dislocations are possible. Dislocation density. The total dislocation length per unit volume of material; alternately, the number of dislocations that intersect a unit area of a random surface section. Dislocation line. The line that extends along the end of the extra half-plane of atoms for an edge dislocation, and along the center of the spiral of a screw dislocation. Dispersed phase. For composites and some two-phase alloys, the discontinuous phase that is surrounded by the matrix phase. Dispersion strengthening. Ameans of strengthening materials wherein very small particles (usually less than 0.1 m) of a hard yet inert phase are uniformly dispersed within a load-bearing matrix phase. Domain. A volume region of a ferromagnetic or ferrimagnetic material in which all atomic or ionic magnetic moments are aligned in the same direction. Donor level. For a semiconductor or insulator, an energy level lying within yet near the top of the energy band gap, and from which electrons may be excited into the conduction band. It is normally introduced by an impurity atom. Doping. The intentional alloying of semiconducting materials with controlled concentrations of donor or acceptor impurities. Drawing (metals). A forming technique used to fabricate metal wire and tubing. Deformation is accomplished by pulling the material through a die by means of a tensile force applied on the exit side. Drawing (polymers). A deformation technique wherein polymer fibers are strengthened by elongation. Driving force. The impetus behind a reaction, such as diffusion, grain growth, or a phase transformation. Usually attendant to the reaction is a reduction in some type of energy (e.g., free energy). Ductile fracture. A mode of fracture that is attended by extensive gross plastic deformation. Ductile iron. A cast iron that is alloyed with silicon and a small concentration of magnesium and/or cerium and in which the free graphite exists in nodular form. Sometimes called nodular iron. Ductile-to-brittle transition. The transition from ductile to brittle behavior with a decrease in temperature exhibited by BCC alloys; the temperature range over which the transition occurs is determined by Charpy and Izod impact tests. Ductility. A measure of a material‘s ability to undergo appreciable plastic deformation before fracture; it may be expressed as percent elongation (%EL) or percent reduction in area (%RA) from a tensile test. E Edge dislocation. A linear crystalline defect associated with the lattice distortion produced in the vicinity of the end of an extra halfplane of atoms within a crystal. The Burgers vector is perpendicular to the dislocation line. Elastic deformation. Deformation that is nonpermanent, that is, totally recovered upon release of an applied stress. Elastic recovery. Nonpermanent deformation that is recovered or regained upon the release of a mechanical stress. Elastomer. A polymeric material that may experience large and reversible elastic deformations. 484 ● Glossary Electrical conductivity. See Conductivity, electrical. Electric dipole. See Dipole (electric). Electric field (E ). The gradient of voltage. Electroluminescence. The emission of visible light by a p–n junction across which a forward-biased voltage is applied. Electrolyte. A solution through which an electric current may be carried by the motion of ions. Electromotive force (emf) series. A ranking of metallic elements according to their standard electrochemical cell potentials. Electron configuration. For an atom, the manner in which possible electron states are filled with electrons. Electronegative. For an atom, having a tendency to accept valence electrons. Also, a term used to describe nonmetallic elements. Electron energy band. A series of electron energy states that are very closely spaced with respect to energy. Electroneutrality. The state of having exactly the same numbers of positive and negative electrical charges (ionic and electronic), that is, of being electrically neutral. Electron state (level). One of a set of discrete, quantized energies that are allowed for electrons. In the atomic case each state is specified by four quantum numbers. Electron volt (eV). A convenient unit of energy for atomic and subatomic systems. It is equivalent to the energy acquired by an electron when it falls through an electric potential of 1 volt. Electropositive. For an atom, having a tendency to release valence electrons. Also, a term used to describe metallic elements. Endurance limit. See Fatigue limit. Energy band gap. See Band gap energy. Engineering strain. See Strain, engineering. Engineering stress. See Stress, engineering. Equilibrium (phase). The state of a system where the phase characteristics remain constant over indefinite time periods. At equilibrium the free energy is a minimum. Erosion–corrosion. A form of corrosion that arises from the combined action of chemical attack and mechanical wear. Eutectic phase. One of the two phases found in the eutectic structure. Eutectic reaction. A reaction wherein, upon cooling, a liquid phase transforms isothermally and reversibly into two intimately mixed solid phases. Eutectic structure. A two-phase microstructure resulting from the solidification of a liquid having the eutectic composition; the phases exist as lamellae that alternate with one another. Eutectoid reaction. A reaction wherein, upon cooling, one solid phase transforms isothermally and reversibly into two new solid phases that are intimately mixed. Excited state. An electron energy state, not normally occupied, to which an electron may be promoted (from a lower energy state) by the absorption of some type of energy (e.g., heat, radiative). Extrinsic semiconductor. A semiconducting material for which the electrical behavior is determined by impurities. Extrusion. A forming technique whereby a material is forced, by compression, through a die orifice. F Face-centered cubic (FCC). A crystal structure found in some of the common elemental metals. Within the cubic unit cell, atoms are located at all corner and face-centered positions. Fatigue. Failure, at relatively low stress levels, of structures that are subjected to fluctuating and cyclic stresses. Fatigue life (Nf ). The total number of stress cycles that will cause a fatigue failure at some specified stress amplitude. Fatigue limit. For fatigue, the maximum stress amplitude level below which a material can endure an essentially infinite number of stress cycles and not fail. Fatigue strength. The maximum stress level that a material can sustain, without failing, for some specified number of cycles. Fermi energy (Ef ). For a metal, the energy corresponding to the highest filled electron state at 0 K. Ferrimagnetism. Permanent and large magnetizations found in some ceramic materials. It results from antiparallel spin coupling and incomplete magnetic moment cancellation. Ferrite (ceramic). Ceramic oxide materials composed of both divalent and trivalent cations (e.g., Fe2 and Fe3 ), some of which are ferrimagnetic. Ferrite (iron). Body-centered cubic iron; also iron and steel alloys that have the BCC crystal structure. Ferroelectric. A dielectric material that may exhibit polarization in the absence of an electric field. Ferromagnetism. Permanent and large magnetizations found in some metals (e.g., Fe, Ni, and Co), which result from the parallel alignment of neighboring magnetic moments. Ferrous alloy. A metal alloy for which iron is the prime constituent. Fiber. Any polymer, metal, or ceramic that has been drawn into a long and thin filament. Fiber-reinforced composite. Acomposite in which the dispersed phase is in the form of a fiber (i.e., a filament that has a large length-todiameter ratio). Fiber reinforcement. Strengthening or reinforcement of a relatively weak material by embedding a strong fiber phase within the weak matrix material. Fick‘s first law. The diffusion flux is proportional to the concentration gradient. This relationship is emGlossary ● 485 ployed for steady-state diffusion situations. Fick‘s second law. The time rate of change of concentration is proportional to the second derivative of concentration. This relationship is employed in nonsteady-state diffusion situations. Filler. An inert foreign substance added to a polymer to improve or modify its properties. Fine pearlite. Pearlite for which the alternating ferrite and cementite layers are relatively thin. Firing. A high temperature heat treatment that increases the density and strength of a ceramic piece. Flame retardant. A polymer additive that increases flammability resistance. Flexural strength ( fs). Stress at fracture from a bend (or flexure) test. Fluorescence. Luminescence that occurs for times much less than a second after an electron excitation event. Foam. A polymer that has been made porous (or spongelike) by the incorporation of gas bubbles. Forging. Mechanical forming of a metal by heating and hammering. Forward bias. The conducting bias for a p–n junction rectifier such that electron flow is to the n side of the junction. Fracture mechanics. A technique of fracture analysis used to determine the stress level at which preexisting cracks of known size will propagate, leading to fracture. Fracture toughness (Kc). Critical value of the stress intensity factor for which crack extension occurs. Free electron. An electron that has been excited into an energy state above the Fermi energy (or into the conduction band for semiconductors and insulators) and may participate in the electrical conduction process. Free energy. A thermodynamic quantity that is a function of both the internal energy and entropy (or randomness) of a system. At equilibrium, the free energy is at a minimum. Frenkel defect. In an ionic solid, a cation–vacancy and cation–interstitial pair. Full annealing. For ferrous alloys, austenitizing, followed by cooling slowly to room temperature. G Galvanic corrosion. The preferential corrosion of the more chemically active of two metals that are electrically coupled and exposed to an electrolyte. Galvanic series. A ranking of metals and alloys as to their relative electrochemical reactivity in seawater. Gas constant (R). Boltzmann‘s constant per mole of atoms. R 8.31 J/mol-K (1.987 cal/mol-K). Gibbs phase rule. For a system at equilibrium, an equation (Equation 10.16) that expresses the relationship between the number of phases present and the number of externally controllable variables. Glass–ceramic. Afine-grained crystalline ceramic material that was formed as a glass and subsequently devitrified (or crystallized). Glass transition temperature (Tg). That temperature at which, upon cooling, a noncrystalline ceramic or polymer transforms from a supercooled liquid to a rigid glass. Graft copolymer. A copolymer wherein homopolymer side branches of one mer type are grafted to homopolymer main chains of a different mer. Grain. An individual crystal in a polycrystalline metal or ceramic. Grain boundary. The interface separating two adjoining grains having different crystallographic orientations. Grain growth. The increase in average grain size of a polycrystalline material; for most materials, an elevated- temperature heat treatment is necessary. Grain size. The average grain diameter as determined from a random cross section. Gray cast iron. A cast iron alloyed with silicon in which the graphite exists in the form of flakes. A fractured surface appears gray. Green ceramic body. A ceramic piece, formed as a particulate aggregate, that has been dried but not fired. Ground state. A normally filled electron energy state from which electron excitation may occur. H Hall effect. The phenomenon whereby a force is brought to bear on a moving electron or hole by a magnetic field that is applied perpendicular to the direction of motion. The force direction is perpendicular to both the magnetic field and the particle motion directions. Hardenability. A measure of the depth to which a specific ferrous alloy may be hardened by the formation of martensite upon quenching from a temperature above the upper critical temperature. Hard magnetic material. A ferrimagnetic or ferromagnetic material that has large coercive field and remanence values, normally used in permanent magnet applications. Hard ness. The measure of a material‘s resistance to deformation by surface indentation or by abrasion. Heat capacity (Cp , Cv). The quantity of heat required to produce a unit temperature rise per mole of material. Hexagonal close-packed (HCP). A crystal structure found for some metals. The HCP unit cell is of hexagonal geometry and is generated by the stacking of close-packed planes of atoms. High polymer. A solid polymeric material having a molecular weight greater than about 10,000 g/mol. High-strength, low-alloy (HSLA) steels. Relatively strong, low-carbon steels, with less than about 10 wt% total of alloying elements. Hole (electron). For semiconductors and insulators, a vacant elec486 ● Glossary tron state in the valence band that behaves as a positive charge carrier in an electric field. Homopolymer. A polymer having a chain structure in which all mer units are of the same type. Hot working. Any metal forming operation that is performed above a metal‘s recrystallization temperature. Hybrid composite. A composite that is fiber reinforced by two or more types of fibers (e.g., glass and carbon). Hydrogen bond. A strong secondary interatomic bond that exists between a bound hydrogen atom (its unscreened proton) and the electrons of adjacent atoms. Hydrogen embrittlement. The loss or reduction of ductility of a metal alloy (often steel) as a result of the diffusion of atomic hydrogen into the material. Hydroplastic forming. The molding or shaping of clay-based ceramics that have been made plastic and pliable by adding water. Hypereutectoid alloy. For an alloy system displaying a eutectoid, an alloy for which the concentration of solute is greater than the eutectoid composition. Hypoeutectoid alloy. For an alloy system displaying a eutectoid, an alloy for which the concentration of solute is less than the eutectoid composition. Hysteresis (magnetic). The irreversible magnetic flux densityversus- magnetic field strength (B-versus-H) behavior found for ferromagnetic and ferrimagnetic materials; a closed B–H loop is formed upon field reversal. I Impact energy (notch toughness). A measure of the energy absorbed during the fracture of a specimen of standard dimensions and geometry when subjected to very rapid (impact) loading. Charpy and Izod impact tests are used to measure this parameter, which is important in assessing the ductileto- brittle transition behavior of a material. Imperfection. A deviation from perfection; normally applied to crystalline materials wherein there is a deviation from atomic/molecular order and/or continuity. Index of refraction (n). The ratio of the velocity of light in a vacuum to the velocity in some medium. Inhibitor. A chemical substance that, when added in relatively low concentrations, retards a chemical reaction. Insulator (electrical). A nonmetallic material that has a filled valence band at 0 K and a relatively wide energy band gap. Consequently, the room-temperature electrical conductivity is very low, less than about 10 10 ( -m) 1. Integrated circuit. Thousands of electronic circuit elements (transistors, diodes, resistors, capacitors, etc.) incorporated on a very small silicon chip. Interdiffusion. Diffusion of atoms of one metal into another metal. Intergranular corrosion. Preferential corrosion along grain boundary regions of polycrystalline materials. Intergranular fracture. Fracture of polycrystalline materials by crack propagation along grain boundaries. Intermediate solid solution. A solid solution or phase having a composition range that does not extend to either of the pure components of the system. Intermetallic compound. A compound of two metals that has a distinct chemical formula. On a phase diagram it appears as an intermediate phase that exists over a very narrow range of compositions. Interstitial diffusion. A diffusion mechanism whereby atomic motion is from interstitial site to interstitial site. Interstitial solid solution. A solid solution wherein relatively small solute atoms occupy interstitial positions between the solvent or host atoms. Intrinsic semiconductor. A semiconductor material for which the electrical behavior is characteristic of the pure material; that is, electrical conductivity depends only on temperature and the band gap energy. Invariant point. A point on a binary phase diagram at which three phases are in equilibrium. Ionic bond. A coulombic interatomic bond that exists between two adjacent and oppositely charged ions. Isomerism. Thephenomenonwhereby two or more polymer molecules or mer units have the same composition but different structural arrangements and properties. Isomorphous. Having the same structure. In the phase diagram sense, isomorphicity means having the same crystal structure or complete solid solubility for all compositions (see Figure 10.2a). Isotactic. A type of polymer chain configuration wherein all side groups are positioned on the same side of the chain molecule. Isothermal. At a constant temperature. Isothermal transformation (T– T–T) diagram. A plot of temperature versus the logarithm of time for a steel alloy of definite composition. Used to determine when transformations begin and end for an isothermal (constant-temperature) heat treatment of a previously austenitized alloy. Isotopes. Atoms of the same element that have different atomic masses. Isotropic. Having identical values of a property in all crystallographic directions. Izod test. One of two tests (see also Charpy test) that may be used to measure the impact energy of a standard notched specimen. An impact blow is imparted to the specimen by a weighted pendulum. Glossary ● 487 J Jominy end-quench test. A standardized laboratory test that is used to assess the hardenability of ferrous alloys. Junction transistor. A semiconducting device composed of appropriately biased n–p–n or p–n–p junctions, used to amplify an electrical signal. K Kinetics. The study of reaction rates and the factors that affect them. L Laminar composite. A series of two-dimensional sheets, each having a preferred high-strength direction, fastened one on top of the other at different orientations; strength in the plane of the laminate is highly isotropic. Large-particle composite. A type of particle-reinforced composite wherein particle-matrix interactions cannot be treated on an atomic level; the particles reinforce the matrix phase. Laser. Acronym for light amplification by stimulated emission of radiation—a source of light that is coherent. Lattice. The regular geometrical arrangement of points in crystal space. Lattice parameters. The combination of unit cell edge lengths and interaxial angles that defines the unit cell geometry. Lattice strains. Slight displacements of atoms relative to their normal lattice positions, normally imposed by crystalline defects such as dislocations, and interstitial and impurity atoms. Lever rule. Mathematical expression, such as Equation 10.1b or Equation 10.2b, whereby the relative phase amounts in a two-phase alloy at equilibrium may be computed. Linear coefficient of thermal expansion. See Thermal expansion coefficient, linear. Linear polymer. A polymer in which each molecule consists of bifunctional mer units joined end to end in a single chain. Liquid crystal polymer (LCP). A group of polymeric materials having extended and rod-shaped molecules, which, structurally, do not fall within traditional liquid, amorphous, crystalline, or semicrystalline classifications. They are used in digital displays and a variety of applications in electronics and medical equipment industries. Liquidus line. On a binary phase diagram, that line or boundary separating liquid and liquid solid phase regions. For an alloy, the liquidus temperature is that temperature at which a solid phase first forms under conditions of equilibrium cooling. Longitudinal direction. The lengthwise dimension. For a rod or fiber, in the direction of the long axis. Lower critical temperature. For a steel alloy, the temperature below which, under equilibrium conditions, all austenite has transformed to ferrite and cementite phases. Luminescence. The emission of visible light as a result of electron decay from an excited state. M Macromolecule. A huge molecule made up of thousands of atoms. Magnetic field strength (H). The intensity of an externally applied magnetic field. Magnetic flux density (B). The magnetic field produced in a substance by an external magnetic field. Magnetic induction (B). See Magnetic flux density. Magnetic susceptibility ( m). The proportionality constant between the magnetization M and the magnetic field strength H. Magnetization (M). The total magnetic moment per unit volume of material. Also, a measure of the contribution to the magnetic flux by some material within an H field. Malleable cast iron. White cast iron that has been heat treated to convert the cementite into graphite clusters; a relatively ductile cast iron. Martensite. A metastable iron phase supersaturated in carbon that is the product of a diffusionless (athermal) transformation from austenite. Matrix phase. The phase in a composite or two-phase alloy microstructure that is continuous or completely surrounds the other (or dispersed) phase. Matthiessen‘s rule. The total electrical resistivity of a metal is equal to the sum of temperature-, impurity-, and cold work-dependent contributions. Melting point (glass). The temperature at which the viscosity of a glass material is 10 Pa-s (100 P). Mer. The group of atoms that constitutes a polymer chain repeat unit. Metal. The electropositive elements and alloys based on these elements. The electron band structure of metals is characterized by a partially filled electron band. Metallic bond. A primary interatomic bond involving the nondirectional sharing of nonlocalized valence electrons (??sea of electrons‘‘) that are mutually shared by all the atoms in the metallic solid. Metal-matrix composite (MMC). A composite material which has a metal or metal alloy as the matrix phase. The dispersed phase may be particulates, fibers, or whiskers that normally are stiffer, stronger, and/ or harder than the matrix. Metastable. Nonequilibrium state that may persist for a very long time. Microconstituent. An element of the microstructure that has an identifiable and characteristic structure. It may consist of more than one phase such as with pearlite. Microscopy. The investigation of microstructural elements using some type of microscope. Microstructure. The structural features of an alloy (e.g., grain and 488 ● Glossary phase structure) that are subject to observation under a microscope. Miller indices. A set of three integers (four for hexagonal) that designate crystallographic planes, as determined from reciprocals of fractional axial intercepts. Mixed dislocation. A dislocation that has both edge and screw components. Mobility (electron, e , and hole, h ). The proportionality constant between the carrier drift velocity and applied electric field; also, a measure of the ease of charge carrier motion. Modulus of elasticity (E). The ratio of stress to strain when deformation is totally elastic; also a measure of the stiffness of a material. Molarity (M). Concentration in a liquid solution, in terms of the number of moles of a solute dissolved in 106 mm3 (103 cm3) of solution. Molding (plastics). Shaping a plastic material by forcing it, under pressure and at an elevated temperature, into a mold cavity. Mole. The quantity of a substance corresponding to 6.023 1023 atoms or molecules. Molecular chemistry (polymer). With regard only to composition, not the structure of a mer. Molecular structure (polymer). With regard to atomic arrangements within and interconnections between polymer molecules. Molecular weight. The sum of the atomic weights of all the atoms in a molecule. Molecule. A group of atoms that are bound together by primary interatomic bonds. Monomer. A molecule consisting of a single mer. MOSFET. Metal-oxide-siliconfield effect transistor, an integrated circuit element. Nn -Type semiconductor. Asemiconductor for which the predominant charge carriers responsible for electrical conduction are electrons. Normally, donor impurity atoms give rise to the excess electrons. Natural aging. For precipitation hardening, aging at room temperature. Network polymer. Apolymer composed of trifunctional mer units that form three-dimensional molecules. Nodular iron. See Ductile iron. Noncrystalline. The solid state wherein there is no long-range atomic order. Sometimes the terms amorphous, glassy, and vitreous are used synonymously. Nonferrous alloy. Ametal alloy for which iron is not the prime constituent. Nonsteady-state diffusion. The diffusion condition for which there is some net accumulation or depletion of diffusing species. The diffusion flux is dependent on time. Normalizing. For ferrous alloys, austenitizing above the upper critical temperature, then cooling in air. The objective of this heat treatment is to enhance toughness by refining the grain size. Nucleation. The initial stage in a phase transformation. It is evidenced by the formation of small particles (nuclei) of the new phase, which are capable of growing. O Octahedral position. The void space among close-packed, hard sphere atoms or ions for which there are six nearest neighbors. An octahedron (double pyramid) is circumscribed by lines constructed from centers of adjacent spheres. Ohm‘s law. The applied voltage is equal to the product of the current and resistance; equivalently, the current density is equal to the product of the conductivity and electric field intensity. Opaque. Being impervious to the transmission of light as a result of absorption, reflection, and/or scattering of incident light. Overaging. During precipitation hardening, aging beyond the point at which strength and hardness are at their maxima. Oxidation. The removal of one or more electrons from an atom, ion, or molecule. P Paramagnetism. A relatively weak form of magnetism that results from the independent alignment of atomic dipoles (magnetic) with an applied magnetic field. Particle-reinforced composite. A composite for which the dispersed phase is equiaxed. Passivity. The loss of chemical reactivity, under particular environmental conditions, by some active metals and alloys. Pauli exclusion principle. The postulate that for an individual atom, at most two electrons, which necessarily have opposite spins, can occupy the same state. Pearlite. A two-phase microstructure found in some steels and cast irons; it results from the transformation of austenite of eutectoid composition and consists of alternating layers (or lamellae) of -ferrite and cementite. Periodic table. The arrangement of the chemical elements with increasing atomic number according to the periodic variation in electron structure. Nonmetallic elements are positioned at the far right-hand side of the table. Peritectic reaction. A reaction wherein, upon cooling, a solid and a liquid phase transform isothermally and reversibly to a solid phase having a different composition. Permeability (magnetic, ). The proportionality constant between B and H fields. The value of the permeability of a vacuum ( 0) is 1.257 10 6 H/m. Permittivity ( ). The proportionality constant between the dielectric displacement D and the electric field E. The value of the permittivity 0 for a vacuum is 8.85 10 12 F/m. Glossary ● 489 Phase. A homogeneous portion of a system that has uniform physical and chemical characteristics. Phase diagram. A graphical representation of the relationships between environmental constraints (e.g., temperature and sometimes pressure), composition, and regions of phase stability, ordinarily under conditions of equilibrium. Phase equilibrium. See Equilibrium (phase). Phase transformation. A change in the number and/or character of the phases that constitute the microstructure of an alloy. Phonon. A single quantum of vibrational or elastic energy. Phosphorescence. Luminescence that occurs at times greater than on the order of a second after an electron excitation event. Photoconductivity. Electrical conductivity that results from photoninduced electron excitations in which light is absorbed. Photomicrograph. Thephotograph made with a microscope, which records a microstructural image. Photon. Aquantum unit of electromagnetic energy. Piezoelectric. A dielectric material in which polarization is induced by the application of external forces. Pilling–Bedworth ratio (P–B ratio). The ratio of metal oxide volume to metal volume; used to predict whether or not a scale that forms will protect a metal from further oxidation. Pitting. A form of very localized corrosion wherein small pits or holes form, usually in a vertical direction. Plain carbon steel. A ferrous alloy in which carbon is the prime alloying element. Planck‘s constant (h). A universal constant that has a value of 6.63 10 34 J-s. The energy of a photon of electromagnetic radiation is the product of h and the radiation frequency. Plane strain. The condition, important in fracture mechanical analyses, wherein, for tensile loading, there is zero strain in a direction perpendicular to both the stress axis and the direction of crack propagation; this condition is found in thick plates, and the zero-strain direction is perpendicular to the plate surface. Plane strain fracture toughness (KIc). The critical value of the stress intensity factor (i.e., at which crack propagation occurs) for the condition of plane strain. Plastic. A solid material the primary ingredient of which is an organic polymer of high molecular weight; it may also contain additives such as fillers, plasticizers, flame retardants, and the like. Plastic deformation. Deformation that is permanent or nonrecoverable after release of the applied load. It is accompanied by permanent atomic displacements. Plasticizer. Alow molecular weight polymer additive that enhances flexibility and workability and reduces stiffness and brittleness. Point defect. A crystalline defect associated with one or, at most, several atomic sites. Poisson‘s ratio ( ). For elastic deformation, the negative ratio of lateral and axial strains that result from an applied axial stress. Polar molecule. A molecule in which there exists a permanent electric dipole moment by virtue of the asymmetrical distribution of positively and negatively charged regions. Polarization (P). The total electric dipole moment per unit volume of dielectric material. Also, a measure of the contribution to the total dielectric displacement by a dielectric material. Polarization (corrosion). The displacement of an electrode potential from its equilibrium value as a result of current flow. Polarization (electronic). For an atom, the displacement of the center of the negatively charged electron cloud relative to the positive nucleus, which is induced by an electric field. Polarization (ionic). Polarization as a result of the displacement of anions and cations in opposite directions. Polarization (orientation). Polarization resulting from the alignment (by rotation) of permanent electric dipole moments with an applied electric field. Polycrystalline. Referring to crystalline materials that are composed of more than one crystal or grain. Polymer. A solid, nonmetallic (normally organic) compound of high molecular weight the structure of which is composed of small repeat (or mer) units. Polymer-matrix composite (PMC). A composite material for which the matrix is a polymer resin, and having fibers (normally glass, carbon, or aramid) as the dispersed phase. Polymorphism. The ability of a solid material to exist in more than one form or crystal structure. Powder metallurgy (P/M). The fabrication of metal pieces having intricate and precise shapes by the compaction of metal powders, followed by a densification heat treatment. Precipitation hardening. Hardening and strengthening of a metal alloy by extremely small and uniformly dispersed particles that precipitate from a supersaturated solid solution; sometimes also called age hardening. Precipitation heat treatment. A heat treatment used to precipitate a new phase from a supersaturated solid solution. For precipitation hardening, it is termed artificial aging. Prepreg. Continuous fiber reinforcement preimpregnated with a polymer resin that is then partially cured. Prestressed concrete. Concrete into which compressive stresses have been introduced using steel wires or rods. 490 ● Glossary Primary bonds. Interatomic bonds that are relatively strong and for which bonding energies are relatively large. Primary bonding types are ionic, covalent, and metallic. Primary phase. A phase that exists in addition to the eutectic structure. Principle of combined action. The supposition, often valid, that new properties, better properties, better property combinations, and/or a higher level of properties can be fashioned by the judicious combination of two or more distinct materials. Process annealing. Annealing of previously cold-worked products (commonly steel alloys in sheet or wire form) below the lower critical (eutectoid) temperature. Proeutectoid cementite. Primary cementite that exists in addition to pearlite for hypereutectoid steels. Proeutectoid ferrite. Primary ferrite that exists in addition to pearlite for hypoeutectoid steels. Property. A material trait expressed in terms of the measured response to a specific imposed stimulus. Proportional limit. The point on a stress–strain curve at which the straight line proportionality between stress and strain ceases. p-Type semiconductor. Asemiconductor for which the predominant charge carriers responsible for electrical conduction are holes. Normally, acceptor impurity atoms give rise to the excess holes. Q Quantum mechanics. A branch of physics that deals with atomic and subatomic systems; it allows only discrete values of energy that are separated from one another. By contrast, for classical mechanics, continuous energy values are permissible. Quantum numbers. A set of four numbers, the values of which are used to label possible electron states. Three of the quantum numbers are integers, which also specify the size, shape, and spatial orientation of an ele ctron‘s probability density; the fourth number designates spin orientation. R Random copolymer. A polymer in which two different mer units are randomly distributed along the molecular chain. Recovery. The relief of some of the internal strain energy of a previously cold-worked metal, usually by heat treatment. Recrystallization. The formation of a new set of strain-free grains within a previously cold-worked material; normally an annealing heat treatment is necessary. Recrystallization temperature. For a particular alloy, the minimum temperature at which complete recrystallization will occur within approximately one hour. Rectifying junction. A semiconductor p–n junction that is conductive for a current flow in one direction and highly resistive for the opposite direction. Reduction. The addition of one or more electrons to an atom, ion, or molecule. Reflection. Deflection of a light beam at the interface between two media. Refraction. Bending of a light beam upon passing from one medium into another; the velocity of light differs in the two media. Refractory. A metal or ceramic that may be exposed to extremely high temperatures without deteriorating rapidly or without melting. Reinforced concrete. Concretethat is reinforced (or strengthened in tension) by the incorporation of steel rods, wires, or mesh. Relative magnetic permeability ( r ). The ratio of the magnetic permeability of some medium to that of a vacuum. Relaxation frequency. The reciprocal of the minimum reorientation time for an electric dipole within an alternating electric field. Relaxation modulus [Er (t)]. For viscoelastic polymers, the time-dependent modulus of elasticity. It is determined from stress relaxation measurements as the ratio of stress (taken at some time after the load application—normally 10 s) to strain. Remanence (remanent induction, Br ). For a ferromagnetic or ferrimagnetic material, the magnitude of residual flux density that remains when a magnetic field is removed. Residual stress. A stress that persists in a material that is free of external forces or temperature gradients. Resilience. The capacity of a material to absorb energy when it is elastically deformed. Resistivity ( ). The reciprocal of electrical conductivity, and a measure of a material‘s resistance to the passage of electric current. Resolved shear stress. An applied tensile or compressive stress resolved into a shear component along a specific plane and direction within that plane. Reverse bias. The insulating bias for a p–n junction rectifier; electrons flow into the p side of the junction. Rolling. A metal-forming operation that reduces the thickness of sheet stock; also elongated shapes may be fashioned using grooved circular rolls. Rule of mixtures. The properties of amultiphase alloy or composite material are a weighted average (usually on the basis of volume) of the properties of the individual constituents. Rupture. Failure that is accompanied by significant plastic deformation; often associated with creep failure. S Sacrificial anode. An active metal or alloy that preferentially corrodes and protects another metal or alloy to which it is electrically coupled. Glossary ● 491 Safe stress ( w). A stress used for design purposes; for ductile metals, it is the yield strength divided by a factor of safety. Sandwich panel. A type of structural composite consisting of two stiff and strong outer faces that are separated by a lightweight core material. Saturated. A term describing a carbon atom that participates in only single covalent bonds with four other atoms. Saturation magnetization, flux density (Ms , Bs ). The maximum magnetization (or flux density) for a ferromagnetic or ferrimagnetic material. Scanning electron microscope (SEM). A microscope that produces an image by using an electron beam that scans the surface of a specimen; an image is produced by reflected electron beams. Examination of surface and/or microstructural features at high magnifications is possible. Scanning probe microscope (SPM). Amicroscope that does not produce an image using light radiation. Rather, a very small and sharp probe raster scans across the specimen surface; out-of-surface plane deflections in response to electronic or other interactions with the probe are monitored, from which a topographical map of the specimen surface (on a nanometer scale) is produced. Schottky defect. In an ionic solid, a defect consisting of a cation– vacancy and anion–vacancy pair. Scission. A polymer degradation process whereby molecular chain bonds are ruptured by chemical reactions or by exposure to radiation or heat. Screw dislocation. A linear crystalline defect associated with the lattice distortion created when normally parallel planes are joined together to form a helical ramp. The Burgers vector is parallel to the dislocation line. Secondary bonds. Interatomic and intermolecular bonds that are relatively weak and for which bonding energies are relatively small. Normally atomic or molecular dipoles are involved. Secondary bonding types are van der Waals and hydrogen. Selective leaching. A form of corrosion wherein one element or constituent of an alloy is preferentially dissolved. Self-diffusion. Atomic migration in pure metals. Self-interstitial. A host atom or ion that is positioned on an interstitial lattice site. Semiconductor. Anonmetallic material that has a filled valence band at 0 K and a relatively narrow energy band gap. The room temperature electrical conductivity ranges between about 10 6 and 104 ( - m) 1. Shear. A force applied so as to cause or tend to cause two adjacent parts of the same body to slide relative to each other, in a direction parallel to their plane of contact. Shear strain ( ). The tangent of the shear angle that results from an applied shear load. Shear stress ( ). The instantaneous applied shear load divided by the original cross-sectional area across which it is applied. Single crystal. A crystalline solid for which the periodic and repeated atomic pattern extends throughout its entirety without interruption. Sintering. Particle coalescence of a powdered aggregate by diffusion that is accomplished by firing at an elevated temperature. Slip. Plastic deformation as the result of dislocation motion; also, the shear displacement of two adjacent planes of atoms. Slip casting. A forming technique used for some ceramic materials. A slip, or suspension of solid particles in water, is poured into a porous mold. A solid layer forms on the inside wall as water is absorbed by the mold, leaving a shell (or ultimately a solid piece) having the shape of the mold. Slip system. The combination of a crystallographic plane and, within that plane, a crystallographic direction along which slip (i.e., dislocation motion) occurs. Softening point (glass). The maximum temperature at which a glass piece may be handled without permanent deformation; this corresponds to a viscosity of approximately 4 106 Pa-s (4 107 P). Soft magnetic material. A ferromagnetic or ferrimagnetic material having a small B versus H hysteresis loop, which may be magnetized and demagnetized with relative ease. Soldering. A technique for joining metals using a filler metal alloy that has a melting temperature less than about 425 C (800 F). Lead–tin alloys are common solders. Solid solution. A homogeneous crystalline phase that contains two or more chemical species. Both substitutional and interstitial solid solutions are possible. Solid-solution strengthening. Hardening and strengthening of metals that result from alloying in which a solid solution is formed. The presence of impurity atoms restricts dislocation mobility. Solidus line. On a phase diagram, the locus of points at which solidification is complete upon equilibrium cooling, or at which melting begins upon equilibrium heating. Solubility limit. The maximum concentration of solute that may be added without forming a new phase. Solute. One component or element of a solution present in aminor concentration. It is dissolved in the solvent. Solution heat treatment. The process used to form a solid solution by dissolving precipitate particles. Often, the solid solution is supersaturated and metastable at ambient conditions as a result of rapid 492 ● Glossary cooling from an elevated temperature. Solvent. The component of a solution present in the greatest amount. It is the component that dissolves a solute. Solvus line. The locus of points on a phase diagram representing the limit of solid solubility as a function of temperature. Specific heat (cp , cv ). The heat capacity per unit mass of material. Specific modulus (specific stiffness). The ratio of elastic modulus to specific gravity for a material. Specific strength. The ratio of tensile strength to specific gravity for a material. Spheroidite. Microstructure found in steel alloys consisting of spherelike cementite particles within an - ferrite matrix. It is produced by an appropriate elevated-temperature heat treatment of pearlite, bainite, or martensite, and is relatively soft. Spheroidizing. For steels, a heat treatment carried out at a temperature just below the eutectoid in which the spheroidite microstructure is produced. Spherulite. An aggregate of ribbonlike polymer crystallites radiating from a common center, which crystallites are separated by amorphous regions. Spinning. The process by which fibers are formed. A multitude of fibers are spun as molten material is forced through many small orifices. Stabilizer. A polymer additive that counteracts deteriorative processes. Stainless steel. A steel alloy that is highly resistant to corrosion in a variety of environments. The predominant alloying element is chromium, which must be present in a concentration of at least 11 wt%; other alloy additions, to include nickel and molybdenum, are also possible. Standard half-cell. An electrochemical cell consisting of a pure metal immersed in a 1M aqueous solution of its ions, which is electrically coupled to the standard hydrogen electrode. Steady-state diffusion. The diffusion condition for which there is no net accumulation or depletion of diffusing species. The diffusion flux is independent of time. Stereoisomerism. Polymer isomerism in which side groups within mer units are bonded along the molecular chain in the same order, but in different spatial arrangements. Stoichiometry. For ionic compounds, the state of having exactly the ratio of cations to anions specified by the chemical formula. Strain, engineering ( ). The change in gauge length of a specimen (in the direction of an applied stress) divided by its original gauge length. Strain hardening. The increase in hardness and strength of a ductile metal as it is plastically deformed below its recrystallization temperature. Strain point (glass). The maximum temperature at which glass fractures without plastic deformation; this corresponds to a viscosity of about 3 1013 Pa-s (3 101 4 P). Strain, true. See True strain. Stress concentration. The concentration or amplification of an applied stress at the tip of a notch or small crack. Stress corrosion (cracking). Aform of failure that results from the combined action of a tensile stress and a corrosion environment; it occurs at lower stress levels than are required when the corrosion environment is absent. Stress, engineering ( ). The instantaneous load applied to a specimen divided by its cross-sectional area before any deformation. Stress intensity factor (K). Afactor used in fracture mechanics to specify the stress intensity at the tip of a crack. Stress raiser. A small flaw (internal or surface) or a structural discontinuity at which an applied tensile stress will be amplified and from which cracks may propagate. Stress relief. A heat treatment for the removal of residual stresses. Stress, true. See True stress. Structural clay products. Ceramic products made principally of clay and used in applications where structural integrity is important (e.g., bricks, tiles, pipes). Structural composite. A composite the properties of which depend on the geometrical design of the structural elements. Laminar composites and sandwich panels are two subclasses. Structure. The arrangement of the internal components of matter: electron structure (on a subatomic level), crystal structure (on an atomic level), and microstructure (on a microscopic level). Substitutional solid solution. A solid solution wherein the solute atoms replace or substitute for the host atoms. Superconductivity. A phenomenon observed in some materials: the disappearance of the electrical resistivity at temperatures approaching 0 K. Supercooling. Cooling to below a phase transition temperature without the occurrence of the transformation. Superheating. Heating to above a phase transition temperature without the occurrence of the transformation. Syndiotactic. A type of polymer chain configuration in which side groups regularly alternate positions on opposite sides of the chain. System. Two meanings are possible: (1) a specific body of material that is being considered, and (2) a series of possible alloys consisting of the same components. T Temper designation. Aletter–digit code used to designate the mechanical and/or thermal treatment to which a metal alloy has been subjected. Tempered martensite. The microstructural product resulting from a Glossary ● 493 tempering heat treatment of a martensitic steel. The microstructure consists of extremely small and uniformly dispersed cementite particles embedded within a continuous -ferrite matrix. Toughness and ductility are enhanced significantly by tempering. Tempering (glass). See Thermal tempering. Tensile strength (TS). The maximum engineering stress, in tension, that may be sustained without fracture. Often termed ultimate (tensile) strength. Terminal solid solution. A solid solution that exists over a composition range extending to either composition extremity of a binary phase diagram. Tetrahedral position. The void space among close-packed, hard sphere atoms or ions for which there are four nearest neighbors. Thermal conductivity (k). For steady-state heat flow, the proportionality constant between the heat flux and the temperature gradient. Also, a parameter characterizing the ability of a material to conduct heat. Thermal expansion coefficient, linear ( l). The fractional change in length divided by the change in temperature. Thermal fatigue. A type of fatigue failure wherein the cyclic stresses are introduced by fluctuating thermal stresses. Thermal shock. The fracture of a brittle material as a result of stresses that are introduced by a rapid temperature change. Thermal stress. A residual stress introduced within a body resulting from a change in temperature. Thermal tempering. Increasing the strength of a glass piece by the introduction of residual compressive stresses within the outer surface using an appropriate heat treatment. Thermally activated transformation. A reaction that depends on atomic thermal fluctuations; the atoms having energies greater than an activation energy will spontaneously react or transform. The rate of this type of transformation depends on temperature according to Equation 11.3. Thermoplastic (polymer). A polymeric material that softens when heated and hardens upon cooling. While in the softened state, articles may be formed by molding or extrusion. Thermoplastic elastomer (TPE). A copolymeric material that exhibits elastomeric behavior yet is thermoplastic in nature. At the ambient temperature, domains of one mer type form at molecular chain ends that act as physical crosslinks. Thermosetting (polymer). A polymeric material that, once having cured (or hardened) by a chemical reaction, will not soften or melt when subsequently heated. Tie line. A horizontal line constructed across a two-phase region of a binary phase diagram; its intersections with the phase boundaries on either end represent the equilibrium compositions of the respective phases at the temperature in question. Time–temperature–transformation (T–T–T) diagram. See Isothermal transformation diagram. Toughness. A measure of the amount of energy absorbed by a material as it fractures. Toughness is indicated by the total area under the material‘s tensile stress–strain curve. Trans. For polymers, a prefix denoting a type of molecular structure. To some unsaturated carbon chain atoms within a mer unit, a single side atom or group may be situated on one side of the chain, or directly opposite at a 180 rotation position. In a trans structure, two such side groups within the same mer reside on opposite chain sides (e.g., trans-isoprene). Transformation rate. The reciprocal of the time necessary for a reaction to proceed halfway to its completion. Transgranular fracture. Fracture of polycrystalline materials by crack propagation through the grains. Translucent. Having the property of transmitting light only diffusely; objects viewed through a translucent medium are not clearly distinguishable. Transmission electron microscope (TEM). A microscope that produces an image by using electron beams that are transmitted (pass through) the specimen. Examination of internal features at high magnifications is possible. Transparent. Having the property of transmitting light with relatively little absorption, reflection, and scattering, such that objects viewed through a transparent medium can be distinguished readily. Transverse direction. A direction that crosses (usually perpendicularly) the longitudinal or lengthwise direction. Trifunctional mer. Designating mer units that have three active bonding positions. True strain ( T). The natural logarithm of the ratio of instantaneous gauge length to original gauge length of a specimen being deformed by a uniaxial force. True stress ( T). The instantaneous applied load divided by the instantaneous cross-sectional area of a specimen. U Ultimate (tensile) strength. See Tensile strength. Ultrahigh molecular weight polyethylene (UHMWPE). A polyethylene polymer that has an extremely high molecular weight (approximately 4 106 g/mol). Distinctive characteristics of this material include high impact and abrasion resistance, and a low coefficient of friction. Unit cell. The basic structural unit of a crystal structure. It is generally defined in terms of atom (or ion) positions within a parallelepiped volume. 494 ● Glossary Unsaturated. A term describing carbon atoms that participate in double or triple covalent bonds and, therefore, do not bond to a maximum of four other atoms. Upper critical temperature. For a steel alloy, the minimum temperature above which, under equilibrium conditions, only austenite is present. V Vacancy. A normally occupied lattice site from which an atom or ion is missing. Vacancy diffusion. The diffusion mechanism wherein net atomic migration is from lattice site to an adjacent vacancy. Valence band. For solid materials, the electron energy band that contains the valence electrons. Valence electrons. The electrons in the outermost occupied electron shell, which participate in interatomic bonding. van der Waals bond. A secondary interatomic bond between adjacent molecular dipoles, which may be permanent or induced. Viscoelasticity. A type of deformation exhibiting the mechanical characteristics of viscous flow and elastic deformation. Viscosity ( ). The ratio of the magnitude of an applied shear stress to the velocity gradient that it produces; that is, a measure of a noncrystalline material‘s resistance to permanent deformation. Vitrification. During firing of a ceramic body, the formation of a liquid phase that upon cooling becomes a glass-bonding matrix. Vulcanization. Nonreversible chemical reaction involving sulfur or other suitable agent wherein crosslinks are formed between molecular chains in rubber materials. The rubber‘s modulus of elasticity and strength are enhanced. W Wave-mechanical model. Atomic model in which electrons are treated as being wavelike. Weight percent (wt%). Concentration specification on the basis of weight (or mass) of a particular element relative to the total alloy weight (or mass). Weld decay. Intergranular corrosion that occurs in some welded stainless steels at regions adjacent to the weld. Welding. A technique for joining metals in which actual melting of the pieces to be joined occurs in the vicinity of the bond. A filler metal may be used to facilitate the process. Whisker. A very thin, single crystal of high perfection that has an extremely large length-to-diameter ratio. Whiskers are used as the reinforcing phase in some composites. White cast iron. A low-silicon and very brittle cast iron, in which the carbon is in combined form as cementite; a fractured surface appears white. Whiteware. A clay-based ceramic product that becomes white after high-temperature firing; whitewares include porcelain, china, and plumbing sanitary ware. Working point (glass). The temperature at which a glass is easily deformed, which corresponds to a viscosity of 103 Pa-s (104 P). Wrought alloy. A metal alloy that is relatively ductile and amenable to hot working or cold working during fabrication. Y Yielding. The onset of plastic deformation. Yield strength ( y). The stress required to produce a very slight yet specified amount of plastic strain; a strain offset of 0.002 is commonly used. Young‘s modulus. See Modulus