強(qiáng)化機(jī)制英文

WritingasanEngineerHomework1,Spring2012PRACTICINGTHESTEPSOFTHEWRITINGPROCESSPickonefromthefollowingsituationsandwriteaparagraphusingthestepsofthewritingprocess.Youareaskedtodescribehowtomakeametallicmaterialstronger.Describeascientificorengineeringresearchprojectyouworkedonwithyoursignificantfindings.Tellperspectivestudentswhyhaveselectedyourdegreeprogramorwhyyouhavechosentheschoolyouareattending.Youwanttotellotherpeopleabouttheprocessorstepsneededtoregisterforclasses,byacar,installawindowssystemtoyourcomputer,orseekemployment.Describeavehicle,avacationspot,orafavoritewebsiteandlookatitfromsixperspectives,andargueitspositivesandnegatives.Youarewritingarecommendationreportforthepurchaseofcomputerprinters.PrewritingBrainstormalist(ormakeaclusterdiagram)ofideasaboutwhattobeincludedinyourwriting.WritingWriteaparagraphofyourchoice.Usetheinformationfromyourprewritingasaguide.Remembertobeginwithagoodtopicsentenceandtoorganizeyoursentencesinalogicalorder.1Youareaskedtodescribehowtomakeametallicmaterialstronger.Fundamentallyspeaking,thestrengthofametallicmaterialderivesfromtheatomicbindingforce.Consequently,therearebasicallytwowaystostrengthenametallicmaterial:oneistoincreasetheatomicbindingbondo"analloysoastoimproveitstheoreticalstrengthandobtainperfectnon-defectcrystal;Theotheristointroducemassivecrystaldefectsintothematerial,suchasdislocationandpointdefect.Currentlyforengineeringmaterials,combinedstrengtheningmethodsareusuallyadoptedtoachievebettercomprehensivecharacteristics.Specificallytherearefiveapproachestomakeametallicmaterialstronger:solidsolutionstrengthening,deformationstrengthening(workhardening),precipitationstrengthening,grainsizestrengtheningandphasetransformationtoughening.Abriefexplanationofthestrengtheningmechanismsisofferednext.SolidsolutionstrengtheningThephenomenonthatthestrengthandhardnessofpuremetalsincreasewhentheyaretransformedintosolidsolutionsbyappropriatealloying(byaddingalloyingelements)iscalledsolidsolutionstrengthening,whoseesseneeisthattheinteractionbetweendislocationsandtheIong-termstressfieldofsoluteatomshindersthemovementofdislocations.DeformationstrengtheningWhenmetalsgothroughplasticdeformation,increasedstressisdemandedsoastoacquirefurtherdeformation,andthisphenomenonisdefinedasdeformationstrengthening(orwork-hardening),whichpresentsanotableimprovementinthecrystalstrengthandapparentdeclineinplasticity.PrecipitationstrengtheningWiththefallingofthetemperatureorduringtheIong-timethermalinsulationprocess,supersaturatedsolidsolutionwouldprecipitategradually.Precipitationstrengtheningisalsocalledageingstrengthening,whoseprocessisoftencomplicated.Itsstrengtheningmechanismfunctionsassmall-sizeprecipitations,whicharedistributedoverthematrix,hinderthemovementofdislocationsandthereforethematerialbecomesstronger.GrainsizestrengtheningSmall-sizedcrystalgrainsleadtomoregrainboundariesinthemicrostructureofmetals,whichcanhamperslipdeformationandthusstrengthenthemetallicmaterial.Atthesametime,thetoughnessofthematerialisimproved,whichisimpossibletoachievewithotherstrengtheningapproaches.PhasetransformationtougheningSolidstatephasetransformationcanoccurinalloyedmetallicmaterialsbymeansofheattreatment,sothatexpectedmicrostructurescanbeacquiredandthematerialsgetstrengthened.RevisingReadoveryourparagraph.Thinkaboutwaystoimproveit.Usetherevisingchecklistgiveninthelecturetohelpyou.Reviseyourparagraphandthenrewriteitusingthe“trackchange”featureinMicrosoftWord?.Thehomeworksubmittedtotheinstructorhastodemonstratesuchrevisionsinthefile.1Youareaskedtodescribehowtomakeametallicmaterialstronger.Fundamentallyspeaking,thestrengthofametallicmaterialderivesfromtheatomicbindingforce.Consequently,therearebasicallytwowaystostrengthenametallicmaterial:oneistoincreasetheatomicbindingbondo"analloysoastoimproveitstheoreticalstrengthandabtainperfectnon-defectcrystal;Theotheristointroducemassivecrystaldefectsintothematerial,suchasdislocationandpointdefect.Currentlyforengineeringmaterials,combinedstrengtheningmethodsareusuallyadoptedtoachievebettercomprehensivecharacteristics.Specificallytherearefiveapproachestomakeametallicmaterialstronger:solidsolutionstrengthening,deformationstrengthening(workhardening),precipitationstrengthening,grainsizestrengtheningandphasetransformationtoughening.Abriefexplanationofthestrengtheningmechanismsisofferednext.SolidsolutionstrengtheningThephenomenonthatthestrengthandhardnessofpuremetalsincreasewhentheyaretransformedintosolidsolutionsbyappropriatealloying(byaddingalloyingelements)iscalledsolidsolutionstrengthening,whoseesseneeisthattheinteractionbetweendislocationsandtheIong-termstressfieldofsoluteatomshindersthemovementofdislocations.DeformationstrengtheningWhenmetalsgothroughplasticdeformation,increasedstressisdemandedsoastoacquirefurtherdeformation,andthisphenomenonisdefinedasdeformationstrengthening(orwork-hardening),whichpresentsanotableimprovementinthecrystalstrengthandapparentdeclineinplasticity.PrecipitationstrengtheningWiththefallingofthetemperatureorduringtheIong-timethermalinsulationprocess,supersaturatedsolidsolutionwouldprecipitategradually.Precipitationstrengtheningisalsocalledageingstrengthening,whoseprocessisoftencomplicated.Itsstrengtheningmechanismfunctionsassmall-sizeprecipitations,whicharedistributedoverthematrix,hinderthemovementofdislocationsandthereforethematerialbecomesstrongerGrainsizestrengtheningSmall-sizedcrystalgrainsleadtomoregrainboundariesinthemicrostructureofmetals,whichcanhamperslipdeformationandthusstrengthenthemetallicmaterial.Atthesam