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Unit 1 Metals

金属

The use of metals has always been a key factor 在人类社会的发展中，金属的应用起着关键性的in the development of the social systems of man. Of 作用。构成物质的大约100种基本元素中，大约有一半为金the roughly 100 basic elements of which all matter 属。金属和非金属之间的区别不是特别明显。最基本的定义is composed, about half are classified as metals. The 集中在元素原子间存在的连接形式和与这些原子相关联的distinction between a metal and a nonmetal is not 电子的某些特性。然而，在实际应用中，可以将具有某些特always clear-cut. The most basic definition centers 性集合金属定义为某种元素。 around the type of bonding existing between the atoms of the element, and around the characteristics of certain of the electrons associated with these atoms. In a more practical way, however, a metal can be defined as an element which has a particular package of properties. ------------------------------------------- -------------------------------------------- 除了少数例外金属在常温下是固态的。它们是热Metals are crystalline when in the solid state and, with few exceptions (e.g. mercury), are solid 和电的良导体，不透光。它们往往具有较高的密度。许多金at ambient temperatures. They are good conductors of 属具有延展性，也就是说，在不被破坏的情况下它们的形状heat and electricity and are opaque to light. They 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usually have a comparatively high density. Many 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metals are ductile-that is, their shape can be 有像所预期的撕开金属原子所需的力那么大。 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 required to tear apart the atoms of the metal. 从我们的观点来看，在所有的特性中结晶性是最重要------------------------------------------------- ------------------------------------------------- One of the more significant of these characteristics from our point of view is that of 的。结晶体是这样一种结构，组成它的原子定位在规则的三crystallinity. A crystalline solid is one in which 维排列中，仿佛位于三维棋盘的方格的角上。原子间距随着the constituent atoms are located in a regular 原子大小呈规律性变化，原子间距是金属的一种特性。三维three-dimensional array as if they were located at 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the corners of the squares of a three-dimensional 的金属由大量的晶体组成，这些晶体称之为晶粒。在大多数chessboard. The spacing of the atoms in the array is 情况下，晶粒在空间中是自由排列的。在原子范围内，晶粒of the same order as the size of the atoms, the actual 之间相互接触紧密结合。晶粒之间连接区域被称为晶界。 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 engineering practice are composed of a large number of such crystals, called grains. In the most general case, the crystals of the various grains are randomly oriented in space. The grains are everywhere in intimate contact with one another and joined together on an atomic scale. The region at which they join is known as a grain boundary. 绝对纯净的金属从来也没有被生产出来过。即使绝对------------------------------------------------- ------------------------------------------------- An absolutely pure metal (i.e. one composed of only one type of atom) has never been produced. 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Engineers would not be particularly interested in 兴趣，因为它们很柔软、脆弱。实际应用中的金属往往都包such a metal even if it were to be produced, because 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it would be soft and weak. The metals used 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commercially inevitably contain small amounts of one 的属性没有影响。如果是有害的，这些外来元素被认为是杂or more foreign elements, either metallic or 质。如果是有益的，它们被认为是合金元素。在工程材料中nonmetallic. These foreign elements may be 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detrimental, they may be beneficial, or they may have 合金。 no 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 金属和合金区别不大。金属这个词可以包括工业用纯------------------------------------------------- ------------------------------------------------- “metal” and “alloy” is not clear-cut. The term 金属和它的合金。也许可以这样说，合金元素越故意的被添“metal” may be used to encompass both a 加，被添加的合金元素的量越大，那么生产出来的产品越倾commercially pure metal and its alloys. Perhaps it 向于被称之为合金。不管怎样，如果想使一种金属或合金在can be said that the more deliberately an alloying 使用中表现出稳定一致的特性，在其中添加何种化学成分，addition has been made and the larger the amount of 它的量多大都应该在控制范围之内。因此，当想了解决定金the addition, the more likely it is that the product 属和合金性质的因素时，应充分考虑它们的化学组成。 will specifically be called an alloy. In any event, the chemical composition of a metal or an alloy must be known and controlled within certain limits if consistent performance is to be achieved in service. Thus chemical composition has to be taken into account when developing an understanding of the factors which determine the properties of metals and their alloys. ------------------------------------------------- ------------------------------------------------- Of the 50 or so metallic elements, only a few 在50种左右的金属元素里，工程实践中只有少数金属are produced and used in large quantities in engineering practice. The most important by far is 被大量生产和使用。到目前为止最重要的是铁，以它为基础iron, on which are based the ubiquitous steels and 构成了处处可见的钢和铸铁。（主要由铁和碳构成的合金）cast irons (basically alloys of iron and carbon). 它们的重量占所有生产出来的金属重量的98%。在结构应用They account for about 98% by weight of all metals （也就是说，可以承受载荷的结构）中居于其次位置的是铝、produced. Next in importance for structural uses 铜、镍和钛。在所有的金属产量中，铝占0.8％，铜占0.7％，(that is, for structures that are expected to carry 剩下的占0.5％。剩下的金属用于相对特殊的用途。例如，loads) are aluminum, copper, nickel, and titanium. 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Aluminum accounts for about 0.8% by weight of all 强度和低密度的综合特性，钛被广泛应用于航空工业中。镍metals produced, and copper about 0.7%, leaving only 合钛有高成本和高质量的使用特性，事实上，它们高的成本0.5% for all other metals. As might be expected, the 限制了它们的应用。 remainders are all used in rather special applications. For example, nickel alloys are used principally in corrosion-and heat-resistant applications, while titanium is used extensively in the aerospace industry because its alloys have good combinations of high strength and low density. Both nickel and titanium are used in high-cost, high-quality applications, and, indeed, it is their high cost that tends to restrict their application. ------------------------------------------------- ------------------------------------------------- We cannot discuss these more esoteric 我们不能在这里讨论这些深奥的特性。在合金材料被properties here. Suffice it to say that a whole complex of properties in addition to structural 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strength is required of an alloy before it will be 质就够了。举例来说，它可以强度很高，并且有好的耐磨性；accepted into, and survive in, engineering practice. 它可以被例如拉伸加工，机械加工，或焊接等特殊工艺来加It may, for example, have to be strong and yet have 工出来；它可以被循环利用；它的成本和实用性是首要的。 reasonable corrosion resistance; it may have to be able to be fabricated by a particular process such as deep drawing, machining, or welding; it may have to be readily recyclable; and its cost and availability may be of critical importance.