去应力退火SLM成形Inconel 738合金组织和性能演变

Evolution of Microstructure and Properties of SLM Formed Inconel 738 Alloy During Stress Relief Annealing

由于选区激光熔化(SLM)制备Inconel738合金过程中快速熔化凝固的特点,成形合金中存在较高的残余应力,影响合金的服役。主要研究了不同退火温度(700~900℃)下保温24h后合金中残余应力、析出相行为、组织和性能演变。结果表明:退火过程中,组织演变机制为静态回复,发生位错迁移和晶界类型转变;形成短棒状γ’相(240~440nm)和球状γ’相(50~250 nm);晶界碳化物分布由点状向连续状转变,类型由MC向M23C6转变;800℃退火后,残余应力由380.94 MPa(沉积态)下降至–66.7 MPa,残余应力得到释放;随着退火温度升高,硬度和抗拉强度先增大后减小,延伸率逐渐增大,800℃退火后,合金具有最高的硬度(HV)和抗拉强度(5812 MPa、1330 MPa),分别为铸造合金(4100 MPa、945 MPa)的1.42和1.41倍。

Due to the characteristics of rapid melting and solidification of selective laser melting(SLM)process in preparing Inconel 738 alloy,there is residual stress in alloy,so the alloy cannot be directly used.Thus,stress relief annealing is required.The evolution of residual stress,precipitation behavior,microstructure and properties of the alloy after annealing at different temperatures(700~900℃)for 24 h was studied.The results show that the microstructure evolution mechanism is static recovery,while dislocation migration,rearrangement and grain boundary style change occur and a bimodal distribution of sphericalγ’phase(50~250 nm)and short rod-shapedγ’phase(240~440 nm)are formed.The grain boundary carbides change from a dotted state to a continuous one and the type of carbides changes from MC to M23C6;after annealing at 800℃,the residual stress decreases from 380.94 MPa(as-SLMed)to–66.7 MPa,indicating the residual stress is eliminated.With the annealing temperature increasing,the microhardness and tensile strength first increase and then decrease,and the elongation increases gradually.The alloy annealed at 800℃has the highest microhardness(HV)and tensile strength(5812,1330 MPa),which are 1.42 and 1.41 times of those of as-cast alloy(4100,945 MPa),respectively.