选区激光熔化TiAl合金裂纹产生机制及工艺优化试验研究

Crack Initiation Mechanism and Experiment Study of Process Optimization of TiAl Alloy Formed by Selective Laser Melting

TiAl合金具有优良的整体性能而获得广泛应用,但传统加工工艺容易出现缺陷,制约了该材料的进一步应用,采用增材制造技术即选区激光熔化(SLM)技术成形TiAl合金,分析总结了裂纹产生的机制,即温度梯度和残余应力导致了裂纹的出现,并研究了减少裂纹出现的工艺方法。首先总结了TiAl合金的发展及成形现状,针对SLM技术成形TiAl合金过程中裂纹产生的原因,采用不同温度的基板预热、预烧结、重熔等辅助工艺及其组合研究了成形中各种工艺过程对裂纹抑制的效果,进行了单熔道和块体的3D打印实验研究。实验结果表明:不使用任何辅助工艺的效果最差,单独采用一种优化工艺方案,基板预热改善效果最好,预烧结和重熔次之;组合工艺中,采用基板预热辅助预烧结或重熔工艺的效果有利于裂纹的消除,其中最优的工艺组合为基板预热200℃与预烧结工艺,预热使残余应力减少,预烧结降低了温度梯度,工艺组合的综合作用延缓了裂纹的出现,取得了最好的截面质量。

TiAl alloy was widely used because of its excellent overall properties.However,the traditional processing technology was prone to defects,so the further application of TiAl alloy was restricted.As an advanced technology,selective laser melting (SLM) was used to form TiAl alloy.Firstly,the development and forming technology of TiAl alloys were summarized.The crack initiation mechanism such as the temperature gradient and residual stress was studied in the process of forming TiAl alloys by SLM and the technology of how to lease the crack was also proposed and used in the experiment.Then the effects of various forming processes on crack suppression were studied by using auxiliary processes such as substrate preheating,pre-sintering,remelting and combination technology.The experiment of single melting channel and block was studied and the results showed that the effect without any auxiliary process was the worst,the best technology was the preheating on the substrate,and followed by pre-sintering.The best combination technology was presintering process and substrate preheating at 200 ℃ although the effect of auxiliary pre-sintering or remelting process was beneficial to the elimination of cracks,and the combination of pre-sintering process and substrate preheating at 200 ℃ obviously delayed the occurrence of cracks because the residual stress was reduced by substrate preheating,and the temperature gradient was reduced by pre sintering.