金属材料专业介绍(英文版)(ppt-47页)

1Unit6AnIntroductiontoMetallicMaterials2Weshouldgrasp…Whatisametal?Whatisanalloy?Whatarethedifferencesbetweentheirproperities?Explainsolidsolutionandintermetalliccompound.3NewWords&ExpressionsfromPart1roam[rəum]graphite['græfait]malleable['mæliəbl]ductile[‘dʌktail]soluble[‘sɔljubl]chromium[‘krəumjəm]transition[træn‘ziʒən]shell[ʃel]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4TranslationITheoutmostlayerofelectrons最外层电子Freeelectiongas自由电子气Electricalconductivity电导率，电导性Plain-carbonsteel普通碳素钢Solidsolution固溶体，固溶液，固体溶液5TranslationIIIntermetalliccompound金属互化物Metallicmaterial金属材料Strainlesssteel不锈钢Solute溶质Solvent溶剂Periodictable元素周期表Electronegativity电负性Transitionmetal过渡金属Crystalstructure晶体结构6WhatisaMetal?Q:WhatisaMetal?A:Metalisconsistedofpositivecenters(orions)sittingina“gas”offree-electros.Ittendstobegoodelectricalconductors.7WhatisanAlloy?Consistofamixtureofapureandoneormoreotherelements.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Itssomeproperties:lessmalleableandductilethanpuremetalsandtendtohavelowertomeltingpoints.合金的一些性质：延展性较差，低熔点。9Somethingelse…..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。11WhatisanAlloy?Q:WhatisanAlloy?A:Analloyconsistsofamixtureofapuremetalandoneormoreotherelementswhichcanbemetalsornon-metal.Q:Whatarethedifferencesbetweentheirproperties?A:Alloysareusuallylessmalleableandductilethanpuremetalsandthetendtohavelowermeltingpoints.12Thinkabout…..Giveexamplestoexplainsoildsolutionandintermetalliccompound?13SolidSolutionsInmanycases,metalsarequitesolubleinothermetals.Forexample,solidcopperandsoildnickelarefullysolubleineachother.Thistypeofperfectsoildsolubilityisasideeffectofhavingfreeelectrons.Sincetheelectronsarefreetomove,theexactnumberofvalenceelectronspossessedbyanygivenatomshouldn’tmatter.14Soa“solid-solution”isthatonemetalservesasthesolventandtheotherastheotherasthesolute,althoughtinacaselikecopperandnickelwherethesearemutuallysolubleatallcompositionsthetermssolventandsolutecanbealittlemisleading.15Forexample,thefigureintherightisAu-Agphasediagram，belowfusiformareaissolidsolutions，16IntermetallicCompoundsNotallmetalsaresolubleinothermetals,thus,producedanothernewphasecalled“intermetalliccompounds”,suchasnickelwilldissolvesomealuminum,sothatatlowaluminumcontentsasolidsolutionisproduced.Butiflargeramountsofaluminumareadded,thenproduceintermetalliccompounds.17Someofthesecompoundshaveaverywelldefinedcomposition,suchasNi3AlOthershavequiteawiderangeofcomposition,suchasNiAl18ThreetypesofcircumstancesofintermetalliccompoundsformingThefirstcircumstance:sizedifferenenceThesecondcircumstance:alargedifferenenceinelectronegativityThethirdcircumstance:certainratiosofthenumberofvalenceelectronstothenumberofatomsinastructure19Hume-RotheryRuleHume-RotheryRule1:AtomicSizeFactor(the15%)Rule.Extensivesubstitutionalsolidsolutionoccursonlyiftherelativedifferencebetweentheatomicdiameters(radii)ofthetwospeciesislessthan15%.Ifthedifference15%,thesolubilityislimited.Comparingtheatomicradiiofsolidsthatformsolidsolutions,theempiricalrulegivenbyHume-Rotheryisgivenas：Mismatch=%15100solventsolventsoluterrr20Hume-RotheryRule2:CrystalStructureRule:Forappreciablesolidsolubility,thecrystalstructuresofthetwoelementsmustbeidentical.Hume-RotheryRule3:ValencyRule:Ametalwilldissolveametalofhighervalencytoagreaterextentthanoneoflowervalency.Thesoluteandsolventatomsshouldtypicallyhavethesamevalenceinordertoachievemaximumsolubility.Hume-RotheryRule4:TheElectronegativityRule:Electronegativitydifferencecloseto0givesmaximumsolubility.Themoreelectropositiveoneelementandthemoreelectronegativetheother,thegreateristhelikelihoodthattheywillformanintermetalliccompoundinsteadofasubstitutionalsolidsolution.Thesoluteandthesolventshouldlierelativelycloseintheelectrochemicalseries.21休姆－罗瑟里（Hume－Rothery）规律（1）形成合金的元素原子半径之差超过14％～15％，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）ⅡB～ⅤB族溶质元素在ⅠB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.Giventhatmanyofthecompoundsformedinalloysaresizefactororelectroncompounds,thesedonotfollowtherulesofvalency.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。252.Whereasthechemicalformulaofanioniccompound,likeNaClorAl2O3canbepredictedeasilyfromthecompound’spositionintheperiodictable,thisisnotthecaseformanyintermetalliccompounds.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,knowingfromtheirpositionintheperiodictablethatNawantstofromNa+ionsandchlorinewantstofromCl-ionsexplanswhyanioniccompoundwithaformulaNaClisobserved.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。274