Unit 1 Metals
金属
The use of metals has always bee n a key factor in the 在人类社会的发展中，金属 的应用起着关键性的作用。构成物质 的大约100种基本元素中，大约有一 半为金属。金属和非金属之间的区别 不是特别明显。最基本的定义集中在 are The 兀素原子间存在的连接形式和与这 些原子相关联的电子的某些特性。然 而，在实际应用中，可以将具有某些 特性集合金属疋义为某种兀素。 除了少数例外金属在常温下 是固态的。它们是热和电的良导体， 不透光。它们往往具有较咼的密度。 许多金属具有延展性，也就是说，在 不被破坏的情况下它们的形状在外 力的作用下可以发生变化。引起永久 变形所需的力和最终使金属断裂所 需的力相当大，尽管发生断裂所需的 力远没有像所预期的撕幵金属原子 of 所需的力那么大。 development of the social systems of man. Of the roughly 100 basic eleme nts of which all matter is composed, classified about half as metals. distinction between a metal and a nonmetal is not always clear-cut . The most basic definition centers around the type of bonding existing between the atoms of the eleme nt, and around of certa in the characteristics of the electro ns associated with these atoms. In a more practical way, however, a metal can be defined as an element which has a particular package
properties. 从我们的观点来看，在所有的特 性
Metals are crystalline when in the 中结晶性是最重要的。结晶体是这 样
solid state and, with few excepti ons (e.g. mercury), are solid at ambient temperatures. They are good con ductors of heat and electricity and are 一种结构，组成它的原子定位在规 则的三维排列中，仿佛位于三维棋盘 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 一定数量的一种或多种外来金属或 非金属元素，这些外来元素可能是有 害的也可能是有益的或者它们对某 种特定的属性没有影响。如果是有害
opaque to light. They usually have a comparatively high density. Many metals are ductile -that is, their shape can be cha nged perma nen tly by the application without required break ing. to of a force The forces cause this deformati on and those break or fracture a comparatively high, required to metal are although, not nearly the fracture forces is as high as would be expected from simple con siderati on of the forces required to tear apart the atoms of the metal.
Oneof the more significant these characteristics point of view is that of A crystalli ne of 的，这些外来兀素被认为是杂质。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 疋数量的合金兀素。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 致的特性，在其中添加何种化学 from our crystalli ni ty. solid is one in which the con stitue nt atoms are located in a regular three-dime nsio nal array as if they were located at the cor ners of the squares of a three-dime nsional chessboard. The spac ing of the atoms in the array is of the same order as the size of the atoms, the actual spacing being a characteristic the particular metal. of The 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。 在50种左右的金属兀素里，工 程实践中只有少数金属被大量生产 和使用。到目前为止最重要的是铁， 以它为基础构成了处处可见的钢和 铸铁。（主要由铁和碳构成的合金） directions of the axes of the array define the orientation of the crystal in space. The metals commonly used in engineering practice are composed of a large nu mber of such crystals, called grains. In the most general case,
the crystals of the various grains are ran domly orie nted in space. The gra ins are everywhere in in timate con tact
with one
another and joined together on an atomic scale. The region at which they join is known as a grain boun dary.
An absolutely pure metal (i.e. one
composed of only one type of atom)
has never been produced. Engin eers would not be particularly in terested in such a metal even if it were to be produced, because it would be soft and weak. The metals used commercially in evitably con ta in small amounts of one or more foreig n
eleme nts, either
metallic or nonmetallic. These foreig n
eleme nts may be
detrimental , they may be 它们的重量
占所有生产出来的金属 重量的98%在结构应用（也就是说， 可以承受载荷的结构）中居于其次位 置的是铝、
铜、镍和钛。在所有的金 属产量中，铝占0.8 %，铜占0.7 %, 剩下的占0.5 %。剩下的金属用于相 对特殊的用途。例如，镍合金主要用 于抗磨损和耐高温的用途，由于钛合 金具有高强度和低密度的综合特性， 钛被广泛应用于航空工业中。镍合钛 有高成本和
高质量的使用特性，事实 上，它们高
的成本限制了它们的应 用。
我们不能在这里讨论这些深奥 的特性。在合金材料被采用和应用于 工程实际之前，掌握其结构强度和它 的综合性质就够了。举例来说，它可 以强度很高，并且有好的耐磨性；它 可以被例如拉伸加工，机械加工，或 焊接等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。
ben eficial, or they may have no in flue nee at all on a particular property. If disadva ntageous, the foreig n eleme nts tend to be known as impurities . If advantageous, they tend to be known as Alloying added substa ntial engin eeri ng allo ying eleme nts. elements are commonly deliberately amounts materials. in in The result is known as an alloy. The distinction descriptors between the and “ metal” “ alloy ” is not clear -cut. The term “metal” may be used to encompass both a commercially pure metal and its alloys. Perhaps it can be more deliberately an alloving the additi on has bee n made and larger the amount of the
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