材料科學基礎 課件8

Chapter8

Deformationand

Strengtheningmechanism第八章(固體材料的)變形和強化機制吉林大學材料科學與工程學院曹占義10/15/20231Chapter8DeformationandStrengtheningmechanism8.1INTRODUCTIONDeformation:PlasticdeformationElasticdeformation變形塑性變形彈性變形10/15/20232Chapter8DeformationandStrengtheningmechanism8-ADEFORMATIONMECHANISMSFORMETALS8.2HISTORICALtheoreticalstrengthsofperfectcrystals完整晶體的理論強度10/15/20233Chapter8DeformationandStrengtheningmechanism8-ADEFORMATIONMECHANISMSFORMETALS位錯模型來源于人們對塑性變形抗力的探索1926年Frank利用理想晶體模型提出晶體理論強度模型,但是遠遠高于實際材料的強度1934年G.I.Taylor、M.Polanyi、E.Orowan三人幾乎同時提出了晶體中位錯的概念1939年Burgers提出柏氏矢量來表征位錯特性，同時提出螺型位錯模型1947年A.H.Corttrell用位錯和溶質原子交互作用解釋了低碳鋼的屈服現(xiàn)象1950年Frank、Read同時提出了位錯增殖機制（F-R位錯源）1950年人們用透射電子顯微鏡觀察到了位錯的存在、運動、增殖和消亡等現(xiàn)象。至此位錯理論得到廣泛承認。DislocationTheoryofCrystalDeformation10/15/20234Chapter8DeformationandStrengtheningmechanism8-ADEFORMATIONMECHANISMSFORMETALS8.3BASICCONCEPTSOFDISLOCATIONSDislocationTheoryofCrystalDeformation10/15/20235Chapter8DeformationandStrengtheningmechanism8-ADEFORMATIONMECHANISMSFORMETALS8.3BASICCONCEPTSOFDISLOCATIONSDislocationTheoryofCrystalDeformation10/15/20236Chapter8DeformationandStrengtheningmechanism8-ADEFORMATIONMECHANISMSFORMETALS8.3BASICCONCEPTSOFDISLOCATIONSDislocationTheoryofCrystalDeformation10/15/20237Chapter8DeformationandStrengtheningmechanism8-ADEFORMATIONMECHANISMSFORMETALS8.4CHARACTERISTICSOFDISLOCATIONSDislocationTheoryofCrystalDeformation10/15/20238Chapter8DeformationandStrengtheningmechanism8-ADEFORMATIONMECHANISMSFORMETALS8.4CHARACTERISTICSOFDISLOCATIONSDislocationTheoryofCrystalDeformation10/15/20239Chapter8DeformationandStrengtheningmechanism8-ADEFORMATIONMECHANISMSFORMETALS8.5SLIPSYSTEMSThecombinationofacrystallographicplaneand,withinthatplane,acrystallographicdirectionalongwhichslip(i.e.,dislocationmotion)occurs.DislocationTheoryofCrystalDeformationSlipsystemofaFCCcell10/15/202310Chapter8DeformationandStrengtheningmechanism10/15/202311Chapter8DeformationandStrengtheningmechanism8-ADEFORMATIONMECHANISMSFORMETALS8.7PLASTICDEFORMATIONOFPOLYCRYSTALLINEMETALSDislocationTheoryofCrystalDeformationSliplinesonthesurfaceofPCCu10/15/202312Chapter8DeformationandStrengtheningmechanism8-B

MECHANISMSOFSTRENGTHENINGINMETALS8.9STRENGTHENINGBYGRAINSIZEREDUCTIONDislocationTheoryofCrystalDeformationtheabilityofametaltoplasticallydeformdependsontheabilityofdislocationstomove.restrictingorhinderingdislocationmotionrendersamaterialharderandstronger.illustratinghowtheboundaryactsasabarriertocontinuedslip.晶粒細化強化10/15/202313Chapter8DeformationandStrengtheningmechanism8-B

MECHANISMSOFSTRENGTHENINGINMETALS8.9STRENGTHENINGBYGRAINSIZEREDUCTIONHall-Petchequationillustratinghowtheboundaryactsasabarriertocontinuedslip.Notes:notvalidforbothverylargegrainandextremelyfinegrainpolycrystallinematerials.improvesnotonlystrength,butalsothetoughness10/15/202314Chapter8DeformationandStrengtheningmechanism8-B

MECHANISMSOFSTRENGTHENINGINMETALS8.9STRENGTHENINGBYGRAINSIZEREDUCTIONStrengtheningeffectivenessofvariesboundariesSmall-anglegrainboundariesarenoteffectiveininterferingwiththeslipprocessbecauseoftheslightcrystallographicmisalignmentacrosstheboundary.Ontheotherhand,twinboundarieswilleffectivelyblockslipandincreasethestrengthofthematerial.Boundariesbetweentwodifferentphasesarealsoimpedimentstomovementsofdislocations;thisisimportantinthestrengtheningofmorecomplexalloys.Thesizesandshapesoftheconstituentphasessignificantlyaffectthemechanicalpropertiesofmultiphasealloys.晶粒細化強化10/15/202315Chapter8DeformationandStrengtheningmechanism8-B

MECHANISMSOFSTRENGTHENINGINMETALS8.10SOLID-SOLUTIONSTRENGTHENINGSolid-solutionstrengthening:Hardeningandstrengtheningofmetalsthatresultfromalloyinginwhichasolidsolutionisformed.Thepresenceofimpurityatomsrestrictsdislocationmobility.10/15/202316Chapter8DeformationandStrengtheningmechanism8-B

MECHANISMSOFSTRENGTHENINGINMETALS8.10SOLID-SOLUTIONSTRENGTHENINGSolid-solutionstrengthening:PuremetalsLarge-dun10/15/202317Chapter8DeformationandStrengtheningmechanism8-B

MECHANISMSOFSTRENGTHENINGINMETALS8.10SOLID-SOLUTIONSTRENGTHENINGSolid-solutionstrengthening:Small-dunInter-dun10/15/202318Chapter8DeformationandStrengtheningmechanism8-B

MECHANISMSOFSTRENGTHENINGINMETALS8.11STRAINHARDENINGStrainhardening：Theincreaseinhardnessandstrengthofaductilemetalasitisplasticallydeformedbelowitsrecrystallizationtemperature.形變強化，加工硬化Coldworking：Theplasticdeformationofametalatatemperaturebelowthatatwhichitrecrystallizes.冷變形率percentcoldwork10/15/202319Chapter8DeformationandStrengtheningmechanism8-B

MECHANISMSOFSTRENGTHENINGINMETALS10/15/202320Chapter8DeformationandStrengtheningmechanism8-CRECOVERY,RECRYSTALLIZATION,

ANDGRAINGROWTHRecovery.Thereliefofsomeoftheinternalstrainenergyofapreviouslycold-workedmetal,usuallybyheattreatment.Recrystallization.Theformationofanewsetofstrain-freegrainswithinapreviouslycold-workedmaterial;normallyanannealingheattreatmentisnecessary.Graingrowth.Theincreaseinaveragegrainsizeofapolycrystallinematerial;formostmaterials,anelevated-temperatureheattreatmentisnecessary.10/15/202321Chapter8DeformationandStrengtheningmechanism8-CRECOVERY,RECRYSTALLIZATION,

ANDGRAINGROWTH8.12RECOVERYthestoredinternalstrainenergyisrelievedThenumberofdislocations,anddislocationconfigurations.Physicalproperties.8.13RECRYSTALLIZATIONnewsetofstrain-freeandequiaxedgrainsdrivingforce8.14GRAINGROWTH10/15/202322Chapter8DeformationandStrengtheningmechanism8-CRECOVERY,RECRYSTALLIZATION,

ANDGRAINGROWTH8.12RECOVERYthestoredinternalstrainenergyisrelievedThereissomereductioninthenumberofdislocations,anddislocationconfigurationsareproducedhavinglowstrainenergies.Physicalpropertiessuchaselectricalandthermalconductivitiesandthelikearerecoveredtotheirprecold-workedstates.10/15/202323Chapter8DeformationandStrengtheningmechanism8-CRECOVERY,RECRYSTALLIZATION,

ANDGRAINGROWTH8.13RECRYSTALLIZATIONtheformationofanewsetofstrain-freeandequiaxedgrainsThedrivingforce:thedifferenceininternalenergybetweenthestrainedandunstrainedmaterial.Thenewgrainsformasverysmallnucleiandgrowuntiltheycompletelyreplacetheparentmaterial,processesthatinvolveshort-rangediffusion.themechanicalpropertiesarerestoredtotheirprecold-workedvaluesRecrystallizationisdependsonbothtimeandtemperatureRecrystallizationtemperature10/15/202324Chapter8DeformationandStrengtheningmechanism8-CRECOVERY,RECRYSTALLIZATION,

ANDGRAINGROWTHColdworkingandHotworking10/15/202325Chapter8DeformationandStrengtheningmechanism8-CRECOVERY,RECRYSTALLIZATION,

ANDGRAINGROWTH8.14GRAINGROWTHDrivingforceforgraingrowth:boundaryenergy.Graingrowthoccursbythemigrationofg