机械设计制造及其自动化专业英语翻译超级大全Word文件下载.doc

1、 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.Metals are crystallineadj.晶体的 when in the solid state and, with few exceptions极少例外 （e.g. mercury）, are solid at ambient周围环境的 temperatures. They are good c

2、onductors of heat and electricity and are opaque不透明的 to light. They usually have a comparatively high density. Many metals are ductile柔软的；易延展的-that is, their shape can be changed permanently永久地，长期不变地 by the application of a force without breaking. The forces required to cause this deformation and th

3、ose required to break or fracture a metal are comparatively high, although, the fracture forces is not nearly =far from,much less than as high as would be expected from simple consideration of the forces required to tear apart the atoms of the metal.One of the more significant of these characteristi

4、cs from our point of view is that of crystallinitycrystallinity ,kristlinti. 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 chessboardn. 棋盘. The spacing of the ato

5、ms 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 engineering practice are composed of a large number of

6、 such crystals, called grains晶粒. In the most general case一般情况下, 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.An abso

7、lutely pure metal （i.e.也就是 one composed of only one type of atom） has never been produced. Engineers would not be particularly interested in such a metal even if it were to be produced, because it would be soft and weak. The metals used commercially inevitably不可避免地 contain small amounts of one or mo

8、re foreign elements, either metallicmetallic mitlik, me-adj. 金属的，含金属的 or nonmetallic. These foreign elements may be detrimental有害的, they may be beneficial, or they may have no influence at all on a particular property. If disadvantageous, the foreign elements tend to be known as impurities杂质. If adv

9、antageous, they tend to be known as alloying elements合金元素. Alloying elements are commonly added deliberately故意地，蓄意地 in substantialadj. 大量的；实质的；内容充实的substantial evidence:实（质）体证据|实质性证据|实质证据substantial order:大宗订单|大订单 amounts in engineering materials. The result is known as an alloy.The distinction betw

10、een the descriptors “metal” and “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 said that the more deliberately an alloying addition has been made and the larger the amount of the addition, the more likely it is tha

11、t the product will specifically be called an alloy. In any event无论如何，不管怎样, the chemical composition of a metal or an alloy must be known and controlled within certain limits if consistent一致的 performance is to be achieved in service. Thus chemical composition has to be taken into account when develop

12、ing an understanding of the factors which determine the properties of metals and their alloys.Of the 50 or so metallic elements, only a few are produced and used in large quantities in engineering practice. The most important by far is iron铁, on which are based the ubiquitous普遍的，无处不在的 steels and cas

13、t irons （basically alloys of iron and carbon）. They account for about 98% by weight of all metals produced. Next in importance for structural uses （that is, for structures that are expected to carry loads） are aluminum铝, copper, nickel, and titanium taiteinim, ti-n. 化钛（金属元素）. Aluminum accounts for a

14、bout 0.8% by weight of all metals produced, and copper about 0.7%, leaving only 0.5% for all other metals. As might be expected, the remainders are all used in rather相当 special applications. For example, nickel alloys are used principally主要地 in corrosion-and heat-resistant applications, while titanium is used extensively广泛地 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 ten