Investigation of Microstructure and Mechanical Properties of SLM-Produced Inconel 718 and Hastelloy-X Alloys

Inconel 718 (IN718) and Hastelloy-X (HX) samples were manufactured by utilizing the selective laser melting (SLM) method in two different specimen orientations: parallel and perpendicular to the build direction; moreover, IN718 samples were subjected to precipitation hardening treatment. Microstructural investigation, densification behavior, and hardness values were studied along with an examination of uniaxial tensile properties at room temperature and 649°C. Microstructural investigations showed that grain orientations strictly depended on heat flow direction where the columnar grains were formed perpendicular to the base plate. A subsequent heat treatment led to the disappearance of melt pool boundaries while laser tracks were still visible for IN718. Hardness properties were not affected considerably by build direction for both IN718 and HX materials in as-built and heat-treated conditions. Yield and ultimate tensile strengths (UTS) were improved ~84% and ~43%, respectively, for IN718 samples after subsequent precipitation hardening heat treatment along with a remarkable decrease of ~43% in elongation at room temperature. A consistent increase in yield and UTS for heat-treated samples was observed when the uniaxial tensile tests were carried out at an elevated temperature. The room temperature and elevated temperature tensile properties were also investigated for HX samples in as-built condition within this study. It was found that HX is a very promising alloy, particularly for high-temperature aerospace applications.