Effect of solid-solution treatment on high-temperature properties and creep fracture mechanism of laser powder bed fused Inconel 625 alloy

Abstract

Laser powder bed fusion (LPBF) has been widely used for fabricating Inconel 625 (IN625) alloy, and it is widely regarded as a promising manufacturing technology. However, during high-temperature service, the γ″ strengthening phase of LPBFed IN625 gradually transforms into the detrimental δ phase. Controlling the morphology and distribution of precipitates is necessary for optimizing high-temperature performance. This study compared the as-built and 1090°C solution-treated LPBFed IN625 alloy and investigated the microstructure evolution, tensile properties, and creep fracture behavior at a high temperature of 815°C. The results show that the solid-solution treatment improves the creep ductility of LPBFed IN625 alloys at 815°C by forming a high percentage of twinned boundaries and eliminating dislocations. The formation of coarsened needle-like δ phases and carbides during creep reduces the strength of the grain boundaries and is responsible for creep fracture failure. During creep of the as-built samples, the irregular Laves phase between the columnar dendrites gradually transforms into plate-like δ phases and M6C carbides uniformly and densely distributed within the columnar grains. The precipitation-strengthening effect of these fine precipitates, combined with the initial high density of dislocations and strong texturing effect, brings favorable high-temperature strength and creep fracture life but consequently leads to low creep ductility.