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

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

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associatedwiththeseatoms.Inamorepracticalway,however,ametalcanbedefinedasanelementwhichhasaparticularpackageofproperties.

Metalsarecrystallineadj.晶体的

wheninthesolidstateand,withfewexceptions极少例外

（e.g.mercury）,aresolidatambient周围环境的

temperatures.Theyaregoodconductorsofheatandelectricityandareopaque不透明的

tolight.Theyusuallyhaveacomparativelyhighdensity.Manymetalsareductile柔软的；

易延展的

-thatis,theirshapecanbechangedpermanently永久地，长期不变地

bytheapplicationofaforcewithoutbreaking.Theforcesrequiredtocausethisdeformationandthoserequiredtobreakorfractureametalarecomparativelyhigh,although,thefractureforcesisnotnearly=farfrom,muchlessthan

ashighaswouldbeexpectedfromsimpleconsiderationoftheforcesrequiredtotearaparttheatomsofthemetal.

Oneofthemoresignificantofthesecharacteristicsfromourpointofviewisthatofcrystallinitycrystallinity[,kristə'

linəti]

.Acrystallinesolidisoneinwhichtheconstituentatomsarelocatedinaregularthree-dimensionalarrayasiftheywerelocatedatthecornersofthesquaresofathree-dimensionalchessboardn.棋盘

.Thespacingoftheatomsinthearrayisofthesameorderasthesizeoftheatoms,theactualspacingbeingacharacteristicoftheparticularmetal.Thedirectionsoftheaxesofthearraydefinetheorientationofthecrystalinspace.Themetalscommonlyusedinengineeringpracticearecomposedofalargenumberofsuchcrystals,calledgrains晶粒

.Inthemostgeneralcase一般情况下

thecrystalsofthevariousgrainsarerandomlyorientedinspace.Thegrainsareeverywhereinintimatecontactwithoneanotherandjoinedtogetheronanatomicscale.Theregionatwhichtheyjoinisknownasagrainboundary.

Anabsolutelypuremetal（i.e.也就是

onecomposedofonlyonetypeofatom）hasneverbeenproduced.Engineerswouldnotbeparticularlyinterestedinsuchametalevenifitweretobeproduced,becauseitwouldbesoftandweak.Themetalsusedcommerciallyinevitably不可避免地

containsmallamountsofoneormoreforeignelements,eithermetallicmetallic[mi'

tæ

lik,me-]adj.金属的，含金属的

ornonmetallic.Theseforeignelementsmaybedetrimental有害的

theymaybebeneficial,ortheymayhavenoinfluenceatallonaparticularproperty.Ifdisadvantageous,theforeignelementstendtobeknownasimpurities杂质

.Ifadvantageous,theytendtobeknownasalloyingelements合金元素

.Alloyingelementsarecommonlyaddeddeliberately故意地，蓄意地

insubstantialadj.大量的；

实质的；

内容充实的substantialevidence:

实（质）体证据|实质性证据|实质证据substantialorder:

大宗订单|大订单

amountsinengineeringmaterials.Theresultisknownasanalloy.

Thedistinctionbetweenthedescriptors“metal”and“alloy”isnotclear-cut.Theterm“metal”maybeusedtoencompassbothacommerciallypuremetalanditsalloys.Perhapsitcanbesaidthatthemoredeliberatelyanalloyingadditionhasbeenmadeandthelargertheamountoftheaddition,themorelikelyitisthattheproductwillspecificallybecalledanalloy.Inanyevent无论如何，不管怎样

thechemicalcompositionofametaloranalloymustbeknownandcontrolledwithincertainlimitsifconsistent一致的

performanceistobeachievedinservice.Thuschemicalcompositionhastobetakenintoaccountwhendevelopinganunderstandingofthefactorswhichdeterminethepropertiesofmetalsandtheiralloys.

Ofthe50orsometallicelements,onlyafewareproducedandusedinlargequantitiesinengineeringpractice.Themostimportantbyfarisiron铁

onwhicharebasedtheubiquitous普遍的，无处不在的

steelsandcastirons（basicallyalloysofironandcarbon）.Theyaccountforabout98%byweightofallmetalsproduced.Nextinimportanceforstructuraluses（thatis,forstructuresthatareexpectedtocarryloads）arealuminum铝

copper,nickel,andtitanium[tai'

teiniəm,ti-]n.[化]钛（金属元素）

.Aluminumaccountsforabout0.8%byweightofallmetalsproduced,andcopperabout0.7%,leavingonly0.5%forallothermetals.Asmightbeexpected,theremaindersareallusedinrather相当

specialapplications.Forexample,nickelalloysareusedprincipally主要地

incorrosion-andheat-resistantapplications,whiletitaniumisusedextensively广泛地

intheaerospaceindustrybecauseitsalloyshavegoodcombinationsofhighstrengthandlowdensity.Bothnickelandtitaniumareusedinhigh-cost,high-qualityapplications,and,indeed,itistheirhighcostthatten