Unit 1
金属
Metals
The use of metals has always 在人类社会的发展中，金been a key factor in the 属的应用起着关键性的作用。构development of the social 成物质的大约100种基本元素中，systems of man. Of the roughly 大约有一半为金属。金属和非金100 basic elements of which all 属之间的区别不是特别明显。最matter is composed, about half 基本的定义集中在元素原子间存are classified as metals. The 在的连接形式和与这些原子相关
distinction between a metal 联的电子的某些特性。然而，在
and a nonmetal is not always 实际应用中，可以将具有某些特
clear-cut. The most basic 性集合金属定义为某种元素。
definition centers around the 除了少数例外金属在常温type of bonding existing 下是固态的。它们是热和电的良between the atoms of the 导体，不透光。它们往往具有较element, and around the 高的密度。许多金属具有延展性，
characteristics of certain of 也就是说，在不被破坏的情况下the electrons associated with 它们的形状在外力的作用下可以
these atoms. In a more 发生变化。引起永久变形所需的practical way, however, a 力和最终使金属断裂所需的力相metal can be defined as an 当大，尽管发生断裂所需的力远element which has a particular 没有像所预期的撕开金属原子所
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package of properties. 需的力那么大。
Metals are crystalline when 从我们的观点来看，在所有的in the solid state and, with 特性中结晶性是最重要的。结晶few exceptions (e.g. mercury), 体是这样一种结构，组成它的原are
solid
at
ambient 子定位在规则的三维排列中，仿
temperatures. They are good conductors
of
heat
and electricity and are opaque to light. They usually have a comparatively high density. Many metals are ductile-that is, their shape can be changed permanently by the application of a force without breaking. The forces required to cause this deformation and those required to break or fracture a metal are comparatively high, although, the fracture forces is not nearly as high as would be expected from simple consideration of the forces 谢谢欣赏
佛位于三维棋盘的方格的角上。原子间距随着原子大小呈规律性
变化，原子间距是金属的一种特性。三维排列的轴线决定了晶体在空间中的方向。在工程实践中应用的金属由大量的晶体组成，这些晶体称之为晶粒。在大多数情况下，晶粒在空间中是自由排列的。在原子范围内，晶粒之间相互接触紧密结合。晶粒之间连接区域被称为晶界。
绝对纯净的金属从来也没有被生产出来过。即使绝对纯净的金属可以生产出来，工程师们对它们也并不会特别感兴趣，因为它们很柔软、脆弱。实际应用中的金属往往都包含着一定数量的
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required to tear apart the 一种或多种外来金属或非金属元atoms of the metal.
素，这些外来元素可能是有害的
One of the more significant 也可能是有益的或者它们对某种of these characteristics from 特定的属性没有影响。如果是有our point of view is that of 害的，这些外来元素被认为是杂crystallinity. A crystalline solid is one in which the constituent atoms are located in a regular three-dimensional array as if they were located at the corners of the squares of
a
three-dimensional chessboard. The spacing of the atoms in the array is of the same order as the size of the atoms, the actual spacing being a characteristic of the particular
metal.
The directions of the axes of the array define the orientation of the crystal in space. The metals commonly used in 谢谢欣赏
质。如果是有益的，它们被认为是合金元素。在工程材料中往往被特意地加入一定数量的合金元素。得到的物质被叫做合金。 金属和合金区别不大。金属这个词可以包括工业用纯金属和它的合金。也许可以这样说，合金
元素越故意的被添加，被添加的合金元素的量越大，那么生产出来的产品越倾向于被称之为合金。不管怎样，如果想使一种金属或合金在使用中表现出稳定一致的特性，在其中添加何种化学
成分，它的量多大都应该在控制范围之内。因此，当想了解决定金属和合金性质的因素时，应充分考虑它们的化学组成。
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engineering practice are 在50种左右的金属元素里，
composed of a large number of 工程实践中只有少数金属被大量such crystals, called grains. 生产和使用。到目前为止最重要In the most general case, the 的是铁，以它为基础构成了处处crystals of the various grains 可见的钢和铸铁。（主要由铁和are randomly oriented in 碳构成的合金）它们的重量占所space.
The
grains
are 有生产出来的金属重量的98%。在
everywhere in intimate contact 结构应用（也就是说，可以承受with one another and joined 载荷的结构）中居于其次位置的together on an atomic scale. 是铝、铜、镍和钛。在所有的金The region at which they join 属产量中，铝占0.8％，铜占0.7is known as a grain boundary. ％，剩下的占0.5％。剩下的金属 An absolutely pure metal 用于相对特殊的用途。例如，镍(i.e. one composed of only one 合金主要用于抗磨损和耐高温的type of atom) has never been 用途，由于钛合金具有高强度和produced. Engineers would not 低密度的综合特性，钛被广泛应be particularly interested in 用于航空工业中。镍合钛有高成such a metal even if it were to 本和高质量的使用特性，事实上，be produced, because it would 它们高的成本限制了它们的应be soft and weak. The metals 用。
used commercially inevitably 我们不能在这里讨论这些深contain small amounts of one or 奥的特性。在合金材料被采用和
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more foreign elements, either 应用于工程实际之前，掌握其结
metallic or nonmetallic. These 构强度和它的综合性质就够了。
foreign elements may be 举例来说，它可以强度很高，并
detrimental, they may be 且有好的耐磨性；它可以被例如
beneficial, or they may have no 拉伸加工，机械加工，或焊接等influence at all on a particular
property.
If disadvantageous, the foreign elements tend to be known as
impurities. If advantageous,
they tend to be known as
alloying elements. Alloying
elements are commonly added
deliberately in substantial
amounts
in
engineering
materials. The result is known as an alloy.
The distinction between the descriptors “metal” and “alloy” is not clear-cut. The term “metal” may be used to
encompass
both
a
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特殊工艺来加工出来；它可以被循环利用；它的成本和实用性是
首要的。
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