Investigation of deformation mechanisms in Hastelloy X superalloy manufactured via laser powder-bed fusion: Insights into effects of carbides and cellular structure at elevated temperatures

Abstract

Hastelloy X (HX) is an important nickel-based superalloy used to manufacture heat-resistant components for aerospace engines. To understand the failure mechanisms of laser powder-bed fusion (LPBF)-manufactured HX (LPBF HX) at high temperature, the effects of carbides and cellular structures on the stress rupture life of LPBF HX at 815 °C are investigated. Different heat treatment conditions, including 1100 °C solution treatment (ST1100) and 1180 °C solution treatment (ST1180, which involves the standard heat treatment temperature), as well as the as-built state, are implemented to control the carbides and recrystallization degree. The stress rupture life of the ST1100 specimen is three times longer than that of the ST1180 specimen. Coarsened carbides are formed at the grain boundaries of the ST1100 specimen during the stress rupture test, which restrained wedge-shaped cracks. In addition, the cellular structure of the ST1100 specimen contributes to both continuous dynamic recrystallization and discontinuous dynamic recrystallization at high temperatures, thus providing additional plastic deformation ability. Therefore, a lower heat treatment temperature leads to better stress rupture performance of the LPBF HX because of the combined effect of the larger carbide size and cellular structures.