Tailored ductility and strength for enhanced impact toughness of laser powder fusion built Alloy 718
Magnus Neikter, D.C. Raja, Arun Ramanathan Balachandramurthi, Peter Harlin
Abstract
Impact toughness of Alloy 718 built via laser powder bed fusion (LPBF) in as-built and thermally post-treated conditions were investigated. The effect of various stages in the thermal post-treatment, including stress relief, hot isostatic pressing, solution treatment, and aging on the microstructure, texture, ductility, hardness, and impact toughness were studied. The greatest impact toughness was found in the as-built Alloy 718 material, associated with the high ductility of the material. The ductility results were also inversely related to the hardness of the investigated materials. Where the material with the highest ductility had the lowest hardness etc. Anisotropy in the impact toughness behavior was present in the as-built and post-heat treated specimens, which was explained by the presence of texture in all of the investigated material. With the applied heat treatments, recrystallization occurred and the preferential crystal orientations were randomized, decreasing the texture. The thermal post-treating conditions rendered different types of microstructures, with various grain sizes. The carbide content remained the same for the three investigated thermal post-treating conditions.