Effect of heat treatment on microstructure and small punch creep property of selective laser melted Inconel 718 alloy

Abstract

In present study, the Inconel 718 alloys fabricated by selective laser melting (SLM) were subjected to traditional homogenization plus double aging heat treatment (HT1), and a novel heat treatment (HT2). The effect of heat treatment on the anisotropic microstructure and the small punch creep (SPC) property of Inconel 718 samples was investigated. The experimental results show that the general high-angle grain boundaries with stress concentration, and the equiaxed and columnar grains are observed in the HT1 samples. Compared with the traditional solution treatment at 1065 °C for the HT1 samples, a higher solution performed at 1150 °C can efficiently eliminate the stress concentration and lead to the transformation of columnar grains to equiaxed grains in the HT2 samples by introducing complete recrystallization. The recrystallization is accompanied by the formation of annealing twins with high proportion Σ3n (n = 1, 2, 3) twin boundaries. The larger γ″ phases, less grain boundaries perpendicular to the load direction and smaller Laves phases in the HT1-Z (Z represents parallel to the building direction) sample result in a longer creep life. Microcracks distributed along the general high-angle grain boundaries rather than twin boundaries promote the final intergranular fracture. The anisotropy in creep rupture time of SLMed Inconel 718 alloy can be obviously alleviated by applying higher temperature solution treatment.