洛阳理工专业英语课件.ppt

1、1,2.1.3 Cast Irons 铸铁,As stated earlier 如前所述=as discussed earlier, as mentioned, we define cast irons as the ferrous alloys with greater than 2% (w) carbon. They also generally contain up to 多达 3% (w) silicon for control of carbide formation kinetics kinetiks 动力学. Cast irons have relatively low melt

2、ing temperatures and liquid phase viscosities visksiti 粘度, do not form undesirable surface films 膜 when poured, and undergo 经历 moderate 适度的 shrinkage 收缩 during solidification and cooling. ,ENGLISH IN MATERIALS SCIENCE AND ENGINEERING II,2,2.1.3 Cast Irons,The cast irons must balance good formability

3、 成型性能 of complex shapes against inferior infiri 较差的 mechanical properties compared to wrought 精细的；锻 造的 alloys 形变合金. A cast iron is formed into a final 最终的 shape by pouring molten metal into a mold 铸模. The shape of the mold is retained 保持 by the solidified metal. Inferior mechanical properties result

4、 from 导致 a less uniform microstructure, including some porosity 多孔.,ENGLISH IN MATERIALS SCIENCE AND ENGINEERING II,3,2.1.3 Cast Irons,Wrought alloys 形变合金 are initially 起初 cast but are rolled 轧制 or forged 锻造 into final, relatively simple shapes (in fact, “wrought” simply means “worked” 处理 过的，加工过的 ).

5、 There are four general 一般的 types of cast irons. White iron 白口铸铁 has a characteristic 特有的 white, crystalline 晶体的 fracture surface 断面. Large amounts of Fe3C are formed during casting, giving 产生 a hard, brittle material.,ENGLISH IN MATERIALS SCIENCE AND ENGINEERING II,4,2.1.3 Cast Irons,Gray iron 灰口铸铁

6、 has a gray fracture surface with a finely 细微地 faceted fsitid 有小面的 structure. A significant silicon content (wsi=2%3%) promotes graphite (C) precipitation 沉淀、析出=deposition rather than cementite (Fe3C). The sharp, pointed graphite 石墨 flakes 薄片 contribute to 促进，有助于 characteristic brittleness 脆性 in gra

7、y iron. By adding a small amount (w=0.05%) of magnesium mgni:zim 镁 to the molten metal of the gray iron composition 成分,ENGLISH IN MATERIALS SCIENCE AND ENGINEERING II,5,2.1.3 Cast Irons,spheroidal sfiridl 球状的 graphite precipitates rather than flakes are produced. This resulting ductile iron derives

8、its name from the improved mechanical properties. Ductility is increased by a factor of 20 20倍, and strength is doubled. A more traditional form of cast iron with reasonable 合理的 ductility is malleable mlibl可锻的 iron, which is first cast as white iron and then heat treated to produce nodular ndjul 球状

9、的 graphite precipitates.,ENGLISH IN MATERIALS SCIENCE AND ENGINEERING II,6,2.1.3 Cast Irons,Key words: viscosity 粘性 shrinkage 收缩 porosity 多孔,magnesium 镁 malleable 可锻的 nodular 球状的,ENGLISH IN MATERIALS SCIENCE AND ENGINEERING II,7,2.2 Non-ferrous Alloys,Although ferrous alloys are used in the majority

10、 大多数的 of metallic mtlk 金属的 applications in current engineering designs, non-ferrous alloys play a large and indispensable ,indispensbl 不可缺少的 role in our technology. As for 至于 ferrous alloys, the list 列表，名单 of non-ferrous alloys is, of course, long and complex. We shall briefly list the major familie

11、s of non-ferrous alloys and their key attributes 特性，属性. Aluminum lju:minm alloys are best known for low density and corrosion resistance.,ENGLISH IN MATERIALS SCIENCE AND ENGINEERING II,8,2.2 Non-ferrous Alloys,Electrical conductivity, ease 容易 of fabrication 制造, and appearance are also attractive fe

12、atures. Because of these, the world production of aluminum roughly 粗略的 doubled in one recent 10 year period. Ore reserves 储量 for aluminum are large (representing 8% of the earths crust) and aluminum can be easily recycled.,ENGLISH IN MATERIALS SCIENCE AND ENGINEERING II,9,2.2 Non-ferrous Alloys,Magn

13、esium alloys have even lower density than aluminum and, as a result, appear in numerous structural applications such as aerospace 航空航天学 designs. Aluminum is a fcc (face centered crystal structure) material and therefore has numerous (12) slip systems, leading to good ductility. By contrast 相比较而言, ma

14、gnesium is hcp (close-packed hexagonal crystal structure) with only three slip systems and characteristic 特有的 brittleness.,ENGLISH IN MATERIALS SCIENCE AND ENGINEERING II,10,2.2 Non-ferrous Alloys,Titanium alloys have become widely used since World War II. Before that time, a practical method of sep

15、arating titanium metal from reactive 易反应的 oxides 氧化物 and nitrides naitraid 氮化物 was not available. Once formed 一旦形成, titaniums reactivity 反应性 works to its advantage. A thin, tenacious tineis 坚韧的oxide coating 层 forms on its surface, giving excellent resistance to corrosion.,ENGLISH IN MATERIALS SCIENC

16、E AND ENGINEERING II,11,2.2 Non-ferrous Alloys,This “passivation” 钝化 will be discussed in detail 详细地 later. Titanium alloys, like Al and Mg, are of lower density than iron. Although more dense 密实地 than Al or Mg, Titanium alloys have a distinct 明显的 advantage of retaining strength at moderate service

17、temperatures, leading to numerous aerospace design applications. Titanium shares the hcp structure with magnesium leading to characteristically 特有的 low ductility. However, a high temperature bcc structure can be stabilized at room temperature by certain alloy additions such as vanadium.,ENGLISH IN M

18、ATERIALS SCIENCE AND ENGINEERING II,12,2.2 Non-ferrous Alloys,Copper alloys possess a number of superior sju:piri优越的 properties. Their excellent electrical conductivity makes copper alloys the leading 最重要的 material for electrical wiring. Their excellent thermal conductivity leads to applications for

19、 radiators 散热器 and heat exchangers 交换器. Superior corrosion resistance is exhibited in marine and other corrosive environments. The fcc structure contributes to their generally high ductility and formability.,ENGLISH IN MATERIALS SCIENCE AND ENGINEERING II,13,2.2 Non-ferrous Alloys,Their coloration 着

20、色 is frequently used for architectural 建筑的 appearance. Widespread uses of copper alloy through history has led to a somewhat confusing 混淆collection 收藏品 of descriptive 描述的terms. The mechanical properties of these alloys rival raivl 匹敌the steels in their variability 变化性. High purity copper is an exceptionally 异常地 soft material. The addition of 2 w beryllium berilim 铍 fo