1、1,Unit 6,An Introduction to Metallic Materials,2,We should grasp,What is a metal? What is an alloy? What are the differences between their properities? Explain solid solution and intermetallic compound.,3,New Words & Expressions from Part1,roamrumgraphitegrfait malleablemlibl ductiledktail solublesl
2、jubl chromiumkrumjm transitiontrnzin shellel,v.漫游，闲逛，徜徉 ； n.漫步，漫游，徘徊 n.石墨 a.有伸延性的，可锻的 a.易延展的，柔软的 a.可溶解的，可溶的 n.铬 n.转换，跃迁，过渡 n.壳，外壳,4,Translation I,The outmost layer of electrons最外层电子 Free election gas自由电子气 Electrical conductivity电导率，电导性 Plain-carbon steel普通碳素钢 Solid solution固溶体，固溶液，固体溶液,5,Translation
3、 II,Intermetallic compound金属互化物 Metallic material金属材料 Strainless steel不锈钢 Solute溶质 Solvent溶剂,Periodic table元素周期表 Electronegativity电负性 Transition metal过渡金属 Crystal structure晶体结构,6,What is a Metal?,Q: What is a Metal? A: Metal is consisted of positive centers (or ions) sitting in a “gas ” of free-elec
4、tros.It tends to be good electrical conductors.,7,What is an Alloy?,Consist of a mixture of a pure and one or more other elements. 由两种或两种以上的金属或金属与非金属经一定方法所合成的具有金属特性的物质。,8,Its some properties: less malleable and ductile than pure metals and tend to have lower to melting points. 合金的一些性质：延展性较差，低熔点。,9,S
5、omething else,1、合金根据组成元素的数目，可分为二元合金、三元合金和多元合金。 2、根据结构的不同，合金主要类型是： (1)混合物合金：当液态合金凝固时，构成合金的各组分分别结晶而成的合金，如焊锡； (2)固熔体合金当液态合金凝固时形成固溶体的合金，如金银合金； (3)金属互化物合金：各组分相互形成化合物的合金，如铜、锌组成的黄铜。,10,3、合金的一些性质： (1)多数合金熔点低于其组分中任一种组成金属的熔点； (2)硬度比其组分中任一金属的硬度大； (3)合金的导电性和导热性低于任一组分金属。利用合金的这一特性，可以制造高电阻和高热阻材料。还可制造有特殊性能的材料。 (4)有
6、的抗腐蚀能力强(如不锈钢) 4、常见合金： 球墨铸铁、锰钢、不锈钢、黄铜、青铜、白铜、焊锡、硬铝、18K黄金、18K白金。,11,What is an Alloy?,Q: What is an Alloy? A: An alloy consists of a mixture of a pure metal and one or more other elements which can be metals or non-metal. Q: What are the differences between their properties? A:Alloys are usually less m
7、alleable and ductile than pure metals and the tend to have lower melting points.,12,Think about,Give examples to explain soild solution and intermetallic compound?,13,Solid Solutions,In many cases ,metals are quite soluble in other metals .For example ,solid copper and soild nickel are fully soluble
8、 in each other . This type of perfect soild solubility is a side effect of having free electrons.Since the electrons are free to move ,the exact number of valence electrons possessed by any given atom shouldnt matter .,14,So a “solid-solution” is that one metal serves as the solvent and the other as
9、 the other as the solute ,althought in a case like copper and nickel where these are mutually soluble at all compositions the terms solvent and solute can be a little misleading .,15,For example,the figure in the right is Au-Ag phasediagram，below fusiform area is solid solutions,，,16,Intermetallic C
10、ompounds,Not all metals are soluble in other metals,thus, produced another new phase called “intermetallic compounds”,such as nickel will dissolve some aluminum, so that at low aluminum contents a solid solution is produced. But if larger amounts of aluminum are added, then produce intermetallic com
11、pounds.,17,Some of these compounds have a very well defined composition ,such as Ni3AlOthers have quite a wide range of composition,such as NiAl,18,Three types of circumstances of intermetallic compounds forming,The first circumstance:size differenence The second circumstance:a large differenence in
12、 electronegativity The third circumstance:certain ratios of the number of valence electrons to the number of atoms in a structure,19,Hume-Rothery Rule,Hume-Rothery Rule 1:Atomic Size Factor (the 15%) Rule. Extensive substitutional solid solution occurs only if the relative difference between the ato
13、mic diameters (radii) of the two species is less than 15%. If the difference 15%, the solubility is limited.Comparing the atomic radii of solids that form solid solutions, theempirical rule given by Hume-Rothery is given as：,Mismatch=,20,Hume-Rothery Rule 2:Crystal Structure Rule :For appreciable so
14、lid solubility, the crystal structures of the two elements must be identical. Hume-Rothery Rule 3: Valency Rule :A metal will dissolve a metal of higher valency to a greater extent than one of lower valency. The solute and solvent atoms should typically have the same valence in order to achieve maxi
15、mum solubility. Hume-Rothery Rule 4: The Electronegativity Rule :Electronegativity difference close to 0 gives maximum solubility. The more electropositive one element and the more electronegative the other, the greater is the likelihood that they will form an intermetallic compound instead of a sub
16、stitutional solid solution. The solute and the solvent should lie relatively close in the electrochemical series.,21,休姆罗瑟里（HumeRothery）规律,（1）形成合金的元素原子半径之差超过1415，则固溶度极为有限；若尺寸差小于15，尺寸因素成为次要的影响因素，固溶度由其他影响因素确定，这就是知名的15规律。 （2）如果合金组元的负电性相差很大，固溶度就极小； （3）两元素的固溶度与它们的原子价有关，高价元素在低价元素中的固溶度大于低价元素在高价元素中的固溶度； （4）B
17、B族溶质元素在B族溶剂元素中的固溶度都相同(e/a=1.36)，与具体的元素种类无关； （5）两组元只有具有相同的晶体结构才能形成无限(或连续)固溶体。,22,各式各样的合金,磁 性 合 金镍铬合金烤瓷牙 铜中间合金,23,金属外壳,锆石合金 铜乌合金,24,1. Given that many of the compounds formed in alloys are size factor or electron compounds,these do not follow the rules of valency. 在合金中，许多化合物是按比例组合或是电子化合物，不能很好的遵循价键理论。,
18、25,2.Whereas the chemical formula of an ionic compound , like NaCl or Al2O3 can be predicted easily from the compounds position in the periodic table ,this is not the case for many intermetallic compounds. 换句话说，尽管像氯化钠，氧化铝的价键可以通过他们在元素周期表的位置进行预测，但却不能解释合金中金属元素的成健方式。,26,3.Thus,knowing from their positio
19、n in the periodic table that Na wants to from Na+ ions and chlorine wants to from Cl- ions explans why an ionic compound with a formula NaCl is observed.从元素周期表可以知道，钠有变成钠离子的趋势，氯有变成氯离子的趋势，这就解释了氯化钠的形成。,27,4.In contrast,this dosent explain why a carbide with a formula Cr23C6 is formed in stainless steel
20、s.然而，这却解释不了Cr23C6在钢铁中的成健方式。,28,5.The precipitation of Cr23C6 is a big problem when stainless steels are welded.这样 Cr23C6 成为钢铁焊接的大问题高铬高碳冷作钢,29,6.Cr23C6 forms in the “heat affected zone”around the weld (this region is heated but not melted during welding). 在“受热区”的Cr23C6遍布在焊接点周围（这个区域在焊接的时候受热但不熔化）,30,7.
21、The formation of this chromium-rich phase pulls chromium out of solution in the surrounding iron. 富铬相的结构，使铬在离子溶液的氛围之外。,31,8. This in turn,prevents the formation of a protective layer of Cr2O3 on the surface of the stainless steel and so the stainless steel is no longer stainless,but instead suffers
22、from catastrophic localized corrosion. 这样，就保护了钢铁表面氧化铬保护层的结构，从而钢铁不再是单纯的铁，而是可以抗局部严重腐蚀的物质。,Cr2O3,32,9.Consider a different example,NiAl is an electron compound which froms due to having a “magic” 1.5 valence electrons per atom (this magic number isnt really magic , but is a results of deviations from t
23、he free electron model). 另外一个不同的例子，NiAl是具有“魔法”的化合物因为其中每个原子都是1.5价的（神奇的不是数字本身，而是1.5价不符合自由电子模型）。,33,10.There is one nickel atom and one aluminum atom in NiAl and the valency of nickel is two and that of aluminum is three.given that (2+3)/2=2.5 this doesnt seem like 1.5 valence electons per atom . 一个镍原子
24、和一个铝原子构成了NiAl，从价键理论看，镍是二价，铝是三价。照这样，应该平均每个原子有2.5个价电子，与实际上每个原子1.5个价电子不同。,34,11.However ,as a transition metal ,nickel is able to act as if it does nor have a valency by “hiding”electrons in the emply states in the shell.thus , effectively ,there are (0+3)/2=1.5 valence electrons per atom in NiAl. 镍作为一
25、种过渡金属，可以将外层电子“隐藏”在次外电子层的空轨道，看起来没有价电子。所以，铝镍合金中，每个原子有1.5个价电子。,35,合金的组成多种多样，可分为混合物合金，固溶体合金和金属化合物合金等类型。 铋镉合金是一种混合物合金，合金由两种金属的晶粒相互间混合，紧密作用而得。这种合金有低共熔点的特征，类似于某些盐的水溶液使水在低于零度时才结冰一样。 铜镍合金是固溶体合金，由一种金属原子进入另一种金属的晶胞空隙而形成的。 我们上面所讲的铝镍合金是金属化合物合金，这类合金原子以金属键相互作用，不遵守化合价规则。这类合金比任意组分的纯金属硬度都要强，但却降低了可塑性。,36,12.Even in cas
26、es where intermetallic formation does not occur ,there may not be perfect solid-solubility ,if tow metals have different crystal structures then at some intermediate composition there will have to be a change from the crystal structure of one metal to that of the other . 即使两种金属形成的晶体没有缺陷，也不能说明它们能形成完美
27、的固溶体，如果两种金属有不同的晶格结构，必须在介质中改变一种金属的晶格结构，使其与另外一种金属的晶格结构相适应,37,13.In such a case the result would be ,on gradually changing the composition of an alloy from pure metal A(froming the a-phase )to pure metal B (froming the b-phase) 为了形成这种晶格，逐渐将合金从A（相）变到B（相）。,38,Single-phase a soild-solution; Two-phase mixt
28、ure of a soild-solution and b soild-sulition; Single-phase b solid-solution. 单相固溶体 单相固溶体与单相固溶体混合 单相固溶体,39,Think about.,Q: Give examples to explain soild solution and intermetallic compound? A: For example, nickel will dissolve some aluminum,so that at low aluminum contents a solid solution is produc
29、ed.However,if larger amounts of aluminum are added,then a series of intermetallic compounds(for example Ni3Al and NiAl) are produced.,40,Do you still remember?,roamrumgraphitegrfait malleablemlibl ductiledktail solublesljubl chromiumkrumjm transitiontrnzin shellel,v.漫游，闲逛，徜徉 ； n.漫步，漫游，徘徊 n.石墨 a.有伸延性
30、的，可锻的 a.易延展的，柔软的 a.可溶解的，可溶的 n.铬 n.转换，跃迁，过渡 n.壳，外壳,41,New Words from Part2 I,phase plasma precipitate ferrite austenite lattice interstitial cuboid orthorhombic tetragonal crystallography,n.相 n.等离子体，等离子区 n.沉淀物；vt.沉淀 n.铁盐酸，铁素体 n.体，奥氏体，碳丙铁 n.格子 a.空隙的，裂缝的 a.立方体的，立方形的 a.正方晶的 a.四方晶的 n.结晶学，晶体学,42,New Words
31、 from Part2 II,turbine blade polygonal gemstone spherical amorphous transparent pit coaster viscous interfacial,n.涡轮 n.刀刃，刀片 a.多角形的，多边形的 n.宝石 a.球形的 a.无定形的，无晶形的 a.透明的 n.坑，槽 n.垫子，银盘 a.粘性的，粘滞的，胶粘的 a.界面的，分界面的,43,Central Content of Part 2,The text is about structures of metals and alloys, the most famili
32、ar phases are solid, liquid, vapor and plasma. Explain crystal structure, atoms are arranged in a different pattern, the pattern is made up of a repeating unit. Because of the lattice parameter and the atoms are arranged differently within the cube, the metals and alloys have different structures-property. And the size of the atom can affect its structures-property. The differences between crystalline and amorphous metals.,44,What is a Phase?,45,Crystal Structures,46,Crystalline and Amorphous Metals,
