γTiAl基合金铸锭的制备技术及其缺陷分析

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1、.~二一一~选型汪些笠E赶驻丝卑L一一一-一一一一-摘要本文采用理论分析和实验研究相结合的方法，对比研究了ISM重力浇铸工艺、离心浇铸工艺、ISM-VAR联合工艺制备的Y-TiAl基合金铸锭内部存在的气孔、缩孔、缩松、偏析等缺陷及其内部组织。实验结果表明，ISM重力浇铸条件下采用上大下小钢锭模由于增大了“补缩通道扩张角”，增强了对“补缩困难区”的补缩力，从而提高了集中缩孔的高度。但是由于铸型结构限制和浇注工艺不合理，缩孔附近存在较大尺寸的卷入性气孔。采用陶瓷模壁和金属模壁相结合的混合模壁锭模，利于集中缩孔_L移，但延长了凝固时间，使得锭内出现分散缩孔。ISM

2、重力浇铸铸锭的组织均匀，铸态组织晶粒粗大，铸锭内A1.Ti的成分偏析主要为正常偏析，偏析量小。离心浇铸条件下铸锭内部不存在大的集中缩孔，但分布有肉眼可见的偏中心线缩孔缩松。根据实验结果及理论分析，表明离心力场下偏中心线缩孔缩松的偏移量随正向和反向填充时间的增加而增大，表现为随着距入口端长度的减小而增加。金属型离心浇铸所得的铸锭具有典型的三晶区，晶粒大小随凝固顺序的进行而增大，但是由于熔体充型过程存在反向填充的特殊性，使金属液流动增强，合金元素的成分偏析较大。采用ISM-VAR联合工艺所得铸锭内部几乎无气孔出现，集中缩孔位置上升到顶面附近。与上两类工艺相比，采

3、用联合工艺所得到的铸锭利用率高，Al和Ti的成分偏析大大减小，晶内多为粗大柱状晶。关键词Y一Ti人I基合金:铸锭缺陷;熔铸哈尔滨工业大学工学硕士学位论文AbstractInthispaper,defectsappearedintheingotproducedwiththreedifferentprocessingincludinggravitycasting,centrifugalcastingandISM-VARunidirectionalsolidifyingwereinvestigated.Theexperimentresultsshowedthatu

4、nderISMgravitycastingconditionfeedingcapacityto"difficult-to-feedingarea"couldbeincreasedthroughenlargethefeedingangle,thusmovedthecentralizedshrinkagecavityfromthecentertotheupoftheingot.Butthiscastingprocesscausedsomebig-sizeinvolvedgaseousporesneartheshrinkagecavity.Usingaduplex

5、mouldofceramicswallandmetallicwallcanraisethelocationofshrinkagecavityandprolongthetimeofsolidificationwhichcausedispersedshrinkage.IngotobtainedbyISMgravitycastinghasahomogeneousbutcoarsemicrostructure.Segregationintheingotismainlyasmallamountofnormalsegregation.Forcentrifugalcast

6、ingingot,thereisnocentralizedshrinkagebutmicro-dispersedshrinkage,whichdistributedoffthecenterlineoftheingot.Experimentresultsandtheoreticalanalysisshowedthattheofsetofofcenteringshrinkageandporosityincreasedwiththetimediferencebetweenonwardsandback-fillingmeltanddecreasewiththedis

7、tancefromentrance.Ingotproducedbymetallicmouldcentrifugalcastinghasatypicalthreecrystallineregionsandgrainsizeincreasewithsolidification.Meltflowisreinforcedsothatalloyelementsegregationwasratherseverebecauseoftheparticularityofback-fillingmelt.IntheingotproducedbyISM-VARprocessing

8、,almostnotanygaseousporesc