中英文翻译、外文文献翻译——浇铸钛和金的显微结构和机械性能

附录一浇铸钛和金的显微结构和机械性能摘要通过感应熔化的方法而获得的TI21523合金，研究热处理和冷却凝固率对其显微结构和机械性能的影响和作用。结果表明通过增加冷却凝固率，可以使TI21523合金的显微结构从单一化特征及大尺寸的粒状结构变成了具有优良性能的小尺寸粒状结构。通过采用不同的方法和对不同时期的合金进行处理，合金相位逐渐在粒状晶体的内部和粒状晶体的边界上沉淀。由于沉淀物晶相的改变，合金承受拉力的性能和伸长率同时被改良。在B1406GPA、45时，将会获得一种具有良好性能的合金,在临界区域里使用这种合金会让我们收到满意的效果。关键字浇铸TI21523合金；冷却凝固率；机械性能1介绍钛合金以其优良的机械性能，在飞机、航空航天和其它领域中，受到了人们的关注和认可，尤其是在较高特殊作用力的环境之下。在降低航天器的质量并改进的它的运输适宜性上，该合金受到了关注。为了满足以上两种情况，一种被叫做贝它钛的重要钛合金逐渐得到发展和优化。由于其具有高抗力、弹性系数和伸长率等良好的综合性能，合金TI215V23CR23SN23ALTI21523已经变成了潜在的选择材料被用于在那些贝它类型合金之中。从以上的论述中我们可以知道，TI21523合金在室温有较好的可使用性，同时也适用于寒冷的工作环境之下。不幸地是，由于合金的高处理成本以及诸如低可塑性和高刚度等缺点，使其在制造复杂的联合体和薄壁件时存在许多问题，成为影响其在航空航天业中广泛应用的关键所在。为了降低其合成成本并达到其易于重新塑造的弹性，精密铸造技术被引入到了这个领域中。但是由于铸造出来的合金其贝它晶粒较大且机械性能很低，故此TI21523合金的使用受到了极大的限制。由于热处理对TI21523合金的力有影响，因此TI21523合金还是可以改善其伸长率并提高它的机械性能的。关于热处理对TI21523合金的影响的研究首先在美国和前苏联开展。他们指出在热处理之后，在阿尔法晶相的内部和边界上均出现了矩阵式的沉淀物，阿尔法相的出现与分布戏剧性地改善了合金的机械性能。这篇文章的目地就是要找出在不同的冷却凝固率和热处理条件下钛合金的机械性能和微观结构的变化，以找到一个科学合理的方法来测量和进一步提高合金的机械性能。2实验实验的原料来自海棉状的钛,矾和铝的合金，高纯净的铝块，铬粉和锡块。然后他们在一起在感应炉里被融化，依照合金名义上的组成成份，其组成成份有15V、3AL、3CR、3SN，其余的全部是TI。装料的总重量是18千克。我们设置旋转式喷灌器工作转速为200转/分，分布的温度大约是1750。为了研究合金不同的冷却凝固率对于其机械性能和微观结构的影响，熔化的合金离心后被浇注到一个长235MM，宽100MM，厚度分别为50MM、25MM、10MM的一系列金属模具内。用于分析合金的微观结构和机械性能的样品就来自于其中。热处理的试样在800下被加热20分钟，然后水冷。其他用空气冷却的试样也是如此。合金的显微结构被放在高倍显微镜下和TEM机上进行研究。拉伸试验后的物理断面也被放在SEM机下进行研究。它的机械特性是在INSTRON1186电子拉伸机上进行测试的。3结果及讨论31冷却凝固率对合金微观结构的影响合金在冷却凝固后的微观结构如图1所示带有少许气体和热力孔的等轴晶粒在合金晶粒的内部和边界上均有分布。带有黑色的第二幅图被认为是一个不平衡的冷却凝固结构。随着冷却凝固率的不断增加，晶粒的尺寸变得越来越小。越靠近模型的内表面晶粒的尺寸越小，越小的铸造尺寸结果也是如此。这是因为在模型的内表面以及较小的铸造尺寸时，激冷作用对合金的晶粒尺寸并没有多少不同之处32冷却凝固率对合金机械性能的影响下表1列出了不同的冷却凝固率对合金延展性的影响。随着冷却凝固率的增加，合金承受的拉力也随之增加，与此同时，合金的延伸率也逐渐升高。延展率的增加主要归因于较小的晶粒尺寸。比较较薄的部分而言，中等厚度及较厚区域在延展性方面并没有太大的不同之处。33热处理后的合金微观结构在正常情况下，通过空冷和小冷的合金单是可以区分开的。经过不同时期和不同方法的处理之后，针状的相出现在了晶粒的内部以及边界上，良好的拉伸和延伸率的结合是可以通过恰当地热处理来达到的。图2的（A）和（B）中展示了TEM假想的在450到650时加热8小时后的合金显微结构。随着温度的逐渐升高，针状的相变得粗糙。相与其基体之间存在着互不相干的相互关系。图2（C）中显示出相析出于晶粒的边界上，相与晶粒边界所成的角度估计30。相之所以很容易在晶粒的边界上析出的原因可以归结为较低的成核能量以及不完全处理后在晶粒的边界上所产生的元素相互排斥作用。在晶粒的边界上大量的析出相将导致合金的脆性。图3（A）和（B）中展示出了TEM机假想的在450下加热6小时和24小时时的合金相图。随着加热时间的增加，相变得越来越粗糙。同时，相也会部分的增加。图3（）中展示出了TEM机假想的双期处理后的合金的对比。双期处理后的相变得更加粗糙，在相的析出物上有很长一段的距离。34热处理后合金的机械性能图4（A）中表示了在不同的加热温度下加热8小时后合金机械性能的变化。随着加热温度的逐渐增加，伸长率和屈服强度下降而伸展率增加。导致合金机械性能变化的主要原因是晶粒的大小，数量以及基体上的相。随着加热温度的不断增加，相变得越来越粗糙，从而导致了该相越来越容易析出并附着在原有的晶粒上。在进行机械性能测试的过程中，相最终导致了合金的低强度和高的延展性。当加热温度为450时，等于1406GPA,当加热B温度为650时，等于905MPA。对比于强度而言，合金延展率的变化有不同的倾向，延展率从45（450）变为144（650）。图4（B）中展示出了在450下加热不同时间后合金机械性能的变化。随着加热时间的不断增加，合金的伸长率和屈服强度稍有增加而延伸率却下降了。随着加热时间的继续增加，析出物的距离变得特别小，从而很难再析出，以致于导致了在测试的过程中，金属的强度升高而延伸率下降。图5显示出了在450和650下加热8小时后的合金破碎形态。结果显示出破碎是在内部出现的表现出涟漪的特性。虽然破碎是内部的微粒，但是相对较小的微粒尺寸也许是高延展性的最好解释，合金二期加热后，强度增加而延展性下降，下降到了386兆B帕。延展率提高到35个百分点，二期处理之后，析出物之间较长的距离是导致合金低强度和高延展性的主要原因。35热处理后冷却凝固率对合金机械性能的影响图6显示出了热处理之后合金中等厚度和较厚部分的机械性能，试样在800摄氏度下完全处理20分钟之后在不同的温度下加热8小时。随着加热温度的逐渐增加，中等厚度和较厚区域合金的拉伸力下降而延展率升高，总的来说，合金中部的伸长率和延展率都比较厚部分的高，但是当温度厚度部分高于510摄氏度时加热8小时后，合金中等厚度部分的伸长率和延展率却都比较厚部分的低。这个不期望的后果可以由晶粒从边界向晶粒内部逐渐混合，从而导致了内部应力起作用而获得解释SIKLD1/21其中I是断层混乱运动中磨擦力的反作用力。KL是一个常量，D是晶粒直径。晶粒内部应力可以由ASHBY的OROWAN公式来描述。GB/2DLLNL/R02其中G是剪切模量，B是伯格斯向量，R04B,D是析出物之间的距离，L是析出物的厚度。当考虑到拉伸屈服作用力的时候，我们便可以推断出多晶材料时1/2晶粒边界应力和内部应力的混合作用关系式可以表示为SIKLB1/2GB/DLLNL/R03增加晶粒的尺寸将会导致屈服强度的下降，但同样可以导致在晶粒内部的析出物的密度变大，从而使析出物之间的距离减小，比较较小尺寸的晶粒而言，较大尺寸的晶粒在晶粒内部的析出物在对伸长率的影响与作用上占有优势。当在510摄氏度下加热8小时后，大尺寸晶粒的伸长率在晶体内部的析出物中要远远超过小尺寸的晶粒。4结论（1）凝固后的合金的微观结构是由各方等大的晶粒和在晶体边界和内部的一些气泡和热力孔所组成。随着冷却凝固的增加，合金的晶粒尺寸变小，伸长率和屈服强度增加。同时，合金的延展率升高。（2）随着加热温度的升高和加热时间的增加，针状的相变得粗糙。同时，相的碎片数量也随之增加，二期处理后相变得更加粗糙。（3）随着加热温度的升高，伸长率和屈服强度下降而延展率升高，随着加热时间的升高，伸长率和屈服强度稍有升高而延展率下降而伸长率下降。（4）总体来说，中等厚度部分的合金的伸长率和延展率均比较厚部分的高，各项性能的最好结合是在等于1406GPA,为45时获得的。它可以满B足临界领域这种合金的使用要求。附录2MICROSTRUCTUREANDMECHANICALPROPERTIESOFHIGHSTRENGTHASCASTTI21523ALLOYABSTRACTTHEEFFECTSOFHEATTREATMENTANDSOLIDIFICATIONCOOLINGRATEONTHEMICROSTRUCTUREANDMECHANICALPROPERTIESOFASCASTTI21523ALLOYPREPAREDBYINDUCTIONSKULLMELTINGMETHODWEREINVESTIGATEDRESULTSSHOWTHATTHEMICROSTRUCTUREOFAS2CASTTI21523ALLOYCHANGESFROMTHEFEATURESOFSIMPLIFIEDANDLARGERSIZEOFBETAGRAINSTOFINERGRAINSIZEWITHINCREASINGSOLIDIFICATIONCOOLINGRATEAFTERSOLUTIONTREATMENTANDDIFFERENTAGEINGTREATMENT,ALPHAPHASEPRECIPITATESINGRAINSINTERIORASWELLASINGRAINBOUNDARIESDUETOTHEMODIFICATIONOFTHEPRECIPITATEPHASE,THETENSILESTRENGTHANDELONGATIONOFTHEALLOYAREIMPROVEDSIMULTANEOUSLYAGOODCOMBINATIONOFTHEVALUESOFOFAND45OFWASOBTAINED,WHICHWILLBESATISFIEDTHEUSEOFTHISKINDOFALLOYINCRITICALAREASKEYWORDSCASTTI21523ALLOYSOLIDIFICATIONCOOLINGRATEMECHANICALPROPERTIES1INTRODUCTIONTITANIUMALLOYSHAVERECEIVEDAPPRECIATEDATTENTIONSINTHEFIELDSOFAIRCRAFT,AEROSPACE,ANDOTHERSOWINGTOTHEIREXCELLENTMECHANICALPROPERTIES,ESPECIALLYTHEHIGHSPECIFICSTRENGTHWITHREGARDSTOLOWERTHEMASSOFAIRCRAFTANDIMPROVINGTHEIRSUITABILITYFORTRANSPORTATION,ANIMPORTANTCLASSNAMEDBETATITANIUMALLOYSAREDEVELOPEDTOMEETTHEREQUIREMENTOFTHEABOVESITUATIONS1,2ASTHERESULTSOFGOODPROPERTIESCOMBINATIONOFHIGHEREMITICSTRENGTH,ELASTICMODULUSANDELONGATION,THEALLOYTI215V23CR23SN23ALTI21523HASBECOMEAPOTENTIALLYSELECTIVEMATERIALTOBEUSEDAMONGTHOSEBETATYPEALLOYS3FROMREF4,ITISKNOWNTHATTHEALLOYTI21523HASGOODWORKABILITYATROOMTEMPERATUREANDSUITABLEFORCOLDWORKINGUNFORTUNATELY,THEHIGHPROCESSINGCOSTANDDRAWBACKSOFLOWPLASTICITYANDHIGHDEFORMATIONFORCEOFTHEALLOYHAVEMADEITDIFFICULTTOPRODUCECOMPLEXANDTHINWALLEDCOMPONENTSTHATAREBEINGTHEKEYNOTESFORAEROAPPLICATIONS5INORDERTOREDUCETHEPROCESSINGCOSTANDREACHTHEFLEXIBILITYOFSHAPINGTI21523ALLOY,THETECHNIQUEOFPRECISIONCASTINGHASBEENINVOLVEDINTHEFIELDBUTDUETOTHELARGEBETAGRAINSIZEANDLOWERMECHANICALPROPERTIESUNDERCASTINGCONDITION,THEUSAGEOFTHEAS2CASTTI21523ALLOYISLIMITEDBECAUSEOFTHESTRENGTHENEFFECTSOFHEATTREATMENTONTHEBETATYPETITANIUMALLOYS,THETI21523ALLOYCANSOMEWHATBESTRENGTHENEDTOTHEEXTENTOFHIGHLEVELOFTHEMECHANICALPROPERTIESTHEINVESTIGATIONSONTHEEFFECTSOFHEATTREATMENTONTITANIUMALLOYSHAVEBEENCARRIEDOUTBYAMERICAANDTHEFORMERSOVIETUNION6,7ASITISPOINTEDOUTTHATAFTERHEATTREATMENT,THEMATRIXPRECIPITATESALPHAPHASEINGRAININTERIORANDATGRAINBOUNDARIESASWELLTHEAPPEARANCEANDDISTRIBUTIONOFALPHAPHASEIMPROVETHEMECHANICALPROPERTIESOFTHEALLOYDRAMATICALLY8THEPURPOSEOFTHISARTICLEISTOINVESTIGATETHEEFFECTOFDIFFERENTSOLIDIFICATIONCOOLINGRATESANDHEATTREATMENTONTHEMICROSTRUCTUREANDMECHANICALPROPERTIESOFTHEALLOYINORDERTOFINDANEFFICIENTMEASUREMENTTOFURTHERIMPROVETHEMECHANICALPROPERTIESOFTHEALLOY2EXPERIMENTALTHEEXPERIMENTALRAWMATERIALSCAMEFROMSPONGYTITANIUM,VANADIUMALUMINIUMMASTERALLOY,HIGHPURITYALUMINUMBLOCK,CHROMEPOWDERANDTINBLOCKTHENTHEYWEREMELTEDINANINDUCTIONSKULLMELTINGFURNACEACCORDINGTOTHENOMINALCOMPOSITIONOFTHEALLOYWHICHCOMPOSEDOF15V,3AL,3CR,3SN,ANDTHEBALANCETITHETOTALMASSOFTHECHARGEWAS18KGTHEPOURINGPARAMETERSWERESETASTHESPEEDOF200R/MINFORROTATINGTABLEANDTHEPOURINGTEMPERATUREOFABOUT1750INORDERTOSTUDYTHEEFFECTOFDIFFERENTSOLIDIFICATIONCOOLINGRATESONTHESOLIDIFICATIONMICROSTRUCTUREANDMECHANICALPROPERTIESOFTHEALLOY,THEMOLTENALLOYWERECENTRIFUGALLYPOURINGINTOASTEPMETALMOULDWITHTHEGAUGEOF235MMINLENGTH,100MMINWIDTH,AND50MM,25MM,AND10MMINTHICKNESSRESPECTIVELYTHESAMPLESFORTHEANALYSESOFMICROSTRUCTUREANDMECHANICALPROPERTIESOFTHEALLOYCAMEFROMTHESTEPSPECIMENTHESAMPLESFORHEATTREATMENTWASSOLUTETREATEDAT800FOR20MINANDTHENWATERCOOLINGASWELLASTHETREATMENTOFDIFFERENTAGEINGTEMPERATURESANDTIMESWITHAIRCOOLINGTHEMICROSTRUCTUREOFTHEALLOYWASSTUDIEDWITHOPTICALMICROSCOPEANDTEMTHEMORPHOLOGYOFFRACTURESAFTERTENSILETESTWASALSOINVESTIGATEDBYSEMTHEMECHANICALPROPERTIESWERETESTEDINMODELINSTRON1186ELECTRICTENSILEMACHINE3RESULTSANDDISCUSSION31EFFECTOFSOLIDIFICATIONCOOLINGRATEONMICROSTRUCTUREOFALLOYTHEMICROSTRUCTUREOFTHEALLOYAFTERSOLIDIFICATIONISSHOWNINFIG1THEEQUIAXEDBETAGRAINISFOUNDWITHAFEWOFGASANDSHRINKINGHOLESINGRAININTERIORANDATGRAINBOUNDARIESASWELLTHESECONDARYPHASESWITHBLACKCOLORWERECONFIRMEDASANONEQUILIBRIUMSOLIDIFICATIONSTRUCTUREWITHINCREASINGSOLIDIFICATIONCOOLINGRATE,THEGRAINSIZEBECOMESSMALLERTHEGRAINSIZEISSMALLWHEREATTACHEDTOTHEINNERSURFACEOFMOULDORPOSITIONSWITHSMALLERCASTINGSIZEBECAUSEOFTHEACTIONOFCHILLINGEFFECTOFMOULDINNERSURFACEANDSMALLERCASTINGSIZEONTHEALLOYCOMPAREDWITHTHETHINSECTION,THEMIDDLEANDTHICKSECTIONHAVELESSDIFFERENCEINGRAINSIZE32EFFECTOFSOLIDIFICATIONCOOLINGRATEONMECHANICALPROPERTIESOFALLOYTABLE1HASSHOWNTHEEFFECTSOFDIFFERENTSOLIDIFICATIONCOOLINGRATESONTHETENSILEPROPERTIESOFTHEALLOYWITHINCREASINGSOLIDIFICATIONCOOLINGRATE,THETENSILESTRENGTHOFTHEALLOYINCREASESATTHESAMETIMETHEELONGATIONOFTHEALLOYISIMPROVEDTHEINCREASEOFSTRENGTHANDELONGATIONATTRIBUTESTOSMALLGRAINSIZE9COMPAREDWITHTHETHINSECTION,THEMIDDLEANDTHICKSECTIONHASLESSDIFFERENCEINTENSILEPROPERTIES33MICROSTRUCTUREOFALLOYAFTERHEATTREATMENTATTHENORMALCONDITIONTHESINGLEBETAMICROSTRUCTUREFORTHEALLOYCANBEOBTAINEDBYAIRCOOLINGANDWATERCOOLINGAFTERSOLUTIONTREATMENTANDDIFFERENTAGEINGTREATMENTS,ACICULARALPHAPHASEISOBSERVEDATGRAINSINTERIORASWELLASINGRAINBOUNDARIESAGOODCOMBINATIONOFSTRENGTHANDELONGATIONCANBEACHIEVEDWITHPROPERHEATTREATMENTFIGS2AANDBSHOWTEMIMAGEOFTHEALLOYAGEDAT450AND650FOR8HWITHINCREASINGAGEINGTEMPERATURE,THEACICULARALPHAPHASESBECOMECOARSETHEREEXISTSINCOHERENTCORRESPONDINGRELATIONSHIPBETWEENTHEALPHAPHASEANDMATRIX10FIG2CSHOWSALPHAPHASESPRECIPITATEATGRAINBOUNDARIESTHEANGLESBETWEENTHEGRAINBOUNDARIESANDALPHAPHASESWEREESTIMATEDABOUT30THEREASONSFORTHEEASYPRECIPITATIONOFALPHAPHASESATGRAINBOUNDARIESCANBEINTERPRETEDASLOWNUCLEATIONENERGYANDTHESEGREGATIONOFALLOYINGELEMENTATGRAINBOUNDARIESDUETOTHEINADEQUATESOLUTIONTREATMENTTHELARGEQUANTITYOFPRECIPITATESATGRAINBOUNDARIESWASRESPONSIBLEFORTHEBRITTLENESSOFTHEALLOYFIGS3AANDBPRESENTTEMIMAGEOFTHEALLOYAGEDAT450FOR6HAND24HWITHINCREASINGAGEINGTIME,THEALPHAPHASESBECOMECOARSERTHEVOLUMEFRACTIONOFTHEALPHAPHASEINCREASESSIMULTANEOUSLYFIG3CPRESENTTHECOMPARISONOFTEMIMAGEOFTHEALLOYWITHDUPLEXAGEINGTREATMENTTHEALPHAPHASESBECAMECOARSERWITHALONGERDISTANCEBETWEENALPHAPRECIPITATESAFTERDUPLEXAGED34MECHANICALPROPERTIESOFALLOYAFTERHEATTREATMENTFIG4ADEMONSTRATESTHECHANGEOFMECHANICALPROPERTIESOFTHEALLOYAGEDATDIFFERENTTEMPERATURESFOR8HWITHINCREASINGAGEINGTEMPERATURE,THETENSILESTRENGTHANDYIELDSTRENGTHDECREASEANDELONGATIONINCREASESTHEDIRECTREASONSFORTHECHANGEOFMECHANICALPROPERTIESOFTHEALLOYISTHESIZE,QUANTITYANDDISTRIBUTIONOFALPHAPHASESINTHEMATRIXWITHRAISINGAGEINGTEMPERATURE,THEALPHAPHASESBECOMECOARSETHATLEADSTOTHEMOREEASINESSFORDISLOCATIONSTOCROSSTHEPRECIPITATIONDURINGTHETESTPROCESSSOTHATTHESTRENGTHENINGACTIONOFTHEALPHAPHASELESSENSWHICHWILLCAUSETHELOWERSTRENGTHANDHIGHERELONGATIONOFTHEALLOYWHENTHEAGEINGTEMPERATUREIS450,BEQUALSTO1406GPAWHILETHEAGEINGTEMPERATUREIS650,BEQUALSTO905MPACOMPAREDWITHTHESTRENGTH,THEELONGATIONOFTHEALLOYHASDIFFERENTCHANGETRENDSTHEELONGATIONISFROM45450TO144650FIG4BDEMONSRATESTHECHANGEOFMECHANICALPROPERTIESOFTHEALLOYAGEDAT450FORDIFFERENTTIMESWITHINCREASINGAGEINGTIME,THETENSILESTRENGTHANDYIELDSTRENGTHINCREASEALITTLEWITHTHEDECREASEOFELONGATIONWITHPROLONGINGTHEAGEINGTIME,THEDISTANCEBETWEENTHEPRECIPITATIONSBECOMENEARLYTHATLEADSTOTHEMOREDIFFICULTYFORDISLOCATIONSTOCROSSTHEPRECIPITATIONSDURINGTHETESTPROCESS,WHICHCAUSETHEHIGHERSTRENGTHANDLOWERELONGATIONFIG5SHOWSTHEFRACTUREMORPHOLOGYOFTHEALLOYAGEDAT450AND650FOR8HITHASSHOWNTHATTHEFRACTUREISINTERGRANULARCHARACTERIZEDBYDIMPLESALTHOUGHTHEFRACTURESAREINTERGRANULAR,THERELATIVELYSMALLERGRAINSIZESMAYBETHEBETTEREXPLANATIONOFTHEHIGHELONGATIONWHENTHEALLOYISDUPLEXAGED,THESTRENGTHDECREASESWITHINCREASEOFELONGATIONBHASBEENCUTDOWNBY386MPATHEELONGATIONHASBEENIMPROVEDBY35THELONGERDISTANCEBETWEENTHEPRECIPITATIONSAFTERDUPLEXAGINGISRESPONSIBLEFORTHELOWERSTRENGTHANDHIGHERELONGATION35EFFECTOFSOLIDIFICATIONCOOLINGRATEONMECHANICALPROPERTIESOFALLOYAFTERHEATTREATMENTFIG6PRESENTSSTHEMECHANICALPROPERTIESOFTHEALLOYWHICHLOCATEINTHEMIDDLEANDTHICKSECTIONAFTERHEATTREATMENTTHESAMPLESWERESOLUTETREATEDAT800FOR20MINANDTHENAGEINGATDIFFERENTTEMPERATURESFOR8HTHETENSILESTRENGTHOFTHEALLOYFROMBOTHTHEMIDDLEANDTHICKSECTIONDECREASESWITHTHEINCREASEOFELONGATIONWHENTHEAGEINGTEMPERATUREINCREASESASAWHOLE,THETENSILESTRENGTHANDELONGATIONOFTHEALLOYFROMMIDDLESECTIONAREHIGHERTHANTHATFROMTHETHICKSECTIONBUTAGEDATORABOVE510FOR8H,THETENSILESTRENGTHOFTHEALLOYFROMMIDDLESECTIONISLOWERTHANTHATOFTHETHICKSECTIONTHISUNEXPECTEDBEHAVIORCANBEEXPLAINEDBYMEANSOFMODELWHICHINCORPORATETHECONTRIBUTIONOFTHEGRAINBOUNDARIESTOANDTHEGRAININTERIORTOTHETENSILESTRENGTH8THECONTRIBUTIONOFTHEGRAINBOUNDARIESTOSCANBEEXPRESSEDBYTHEWELLKNOWNHALLPETCHRELATIONSHIPSIKLD1/21WHEREIISTHEFRICTIONSTRESSOPPOSINGTODISLOCATIONMOTION,KLISACONSTANT,ANDDISTHEGRAINDIAMETERTHECONTRIBUTIONOFTHEGRAININTERIORTOPRECIPITATESMAYBEEXPRESSEDBYTHEOROWANEQUATIONMODIFIEDBYASHBY11GB/2DLLNL/R02WHEREGISTHESHEARMODULUS,BISTHEBURGERSVECTORANDR04B,DISTHEDISTANCEBETWEENPRECIPITATES,LISTHETHICKNESSOFTHEPRECIPITATESWHENCONSIDERINGTHETENSILEYIELDSTRENGTHITISPOSSIBLETOASSUMETHATFORAPOLYCRYSTALLINEMATERIAL1/2THECOMBINEDCONTRIBUTIONOFGRAINBOUNDARIESANDTHEPRECIPITATESINTHEGRAININTERIORISSIKLB1/2GB/DLLNL/R03INCREASINGTHEGRAINSIZEWOULDDECREASETHEYIELDSTRENGTH,BUTWOULDALSOCAUSELARGERPRECIPITATEDENSITYINTHEGRAININTERIOR,WHICHRESULTINASMALLERDISTANCEBETWEENPRECIPITATESCOMPAREDWITHTHESMALLGRAINSIZE,THECONTRIBUTIONOFPRECIPITATESINTHEGRAININTERIORTOTHETENSILESTRENGTHISTHEDOMINATINGFACTORFORTHELARGEGRAINSIZEWHENAGEDATORABOVE510FOR8H,THETENSILESTRENGTHOFLARGEGRAINSIZEHASEXCEEDEDTHESMALLONEDUETOTHERELATIVELYSTRONGERSTRENGTHENINGACTIONOFTHEPRECIPITATESINTHEGRAININTERIOR4CONCLUSIONS1THEMICROSTRUCTUREOFTHEALLOYAFTERSOLIDIFICATIONISTHEEQUIAXEDBETAGRAINWITHAFEWOFGASANDSHRINKINGHOLESINGRAININTERIORANDGRAINBOUNDARIESASWELLWITHINCREASINGSOLIDIFICATIONCOOLINGRATE,THESIZEOFGRAINBECOMESSMALLER,THETENSILESTRENGTHANDYIELDSTRENGTHOFTHEALLOYINCREASEATTHESAMETIME,THEELONGATIONOFTHEALLOYISIMPROVED2WITHINCREASINGAGEINGTEMPERATUREANDALSOPROLONGINGOFAGEINGTIME,THEACICULARALPHAPHASEBECOMESCOARSETHEVOLUMEFRACTIONOFTHEALPHAPHASEINCREASESSIMULTANEOUSLYTHEALPHAPHASEBECOMESCOARSEAFTERDUPLEXAGED3WITHINCREASINGAGEINGTEMPERATURE,THETENSILESTRENGTHANDYIELDSTRENGTHDECREASEANDTHEELONGATIONINCREASESWITHINCREASINGAGEINGTIMETHETENSILESTRENGTHANDYIELDSTRENGTHINCREASEALITTLEANDTHEELONGATIONDECREASESAFTERTHEALLOYISDUPLEXAGED,THESTRENGTHDECREASESANDTHEELONGAT