Influence of heat treatments on the microstructure and mechanical properties of Inconel 625 fabricated by directed energy deposition

Usually, the laser additive manufactured nickel-based superalloys require subsequent heat treatment to modify their microstructure and mechanical properties. In present work, the solution treatment (ST), solution + aging treatment (SA) and hot isostatic pressing (HIP) treatment were used to investigate the effect of different heat treatments on microstructural evolution and tensile properties of Inconel 625 prepared by directed energy deposition (DED). The microstructure of as-deposited Inconel 625 was mainly composed of epitaxially grown columnar grains, the chain-like Laves phase was formed in the inter-dendritic regions. During high temperature heat treatment process, the initial columnar grains were replaced by equiaxed grains since the occurrence of static recrystallization, and the Laves phase dissolved into matrix completely. The nanoscale γ″ phase was formed after aging treatment, the yield strength and ultimate strength was larger than other samples. However, the steady working hardening stage of SA treated samples was shorter than that of other samples, and its ductility was the lowest. Considering the strength and ductility comprehensively, the HIP treatment was a better heat treatment for Inconel 625 fabricated by DED.