Microstructure and mechanical properties at room and elevated temperature of crack-free Hastelloy X fabricated by laser powder bed fusion

Abstract

In this study, dense and crack-free specimens were fabricated from the solid-solution strengthened nickel-based superalloy Hastelloy X (HX) through laser powder bed fusion (LPBF) in both horizontal and vertical build orientations. Samples were subjected to one of three conditions: as-built (AB), hot isostatic pressing treatment (HIP), and conventional heat treatment (HT). Tensile testing was carried out for every orientation and condition at room temperature (RT) and an elevated temperature of 750 °C (ET). AB samples showed columnar grains and a partial fiber texture aligned with the build direction, which is reduced after HIP and HT, where partial recrystallization occurred. Mo and Cr carbides, as well as Al–O enriched precipitates were found in the RT microstructures, and were seen to increase in size after ET exposure. AB samples displayed high strength (up to 924 ± 10 MPa ultimate tensile strength), while HIP and HT samples maintained strength values close to a reference HX wrought alloy. Although lower ductility was observed for the AB samples when testing at ET, the elongation was improved after HIP and HT. Strength and elongation comparable to that of the wrought alloy at RT can be obtained by performing just HT, without the need of HIPing.