Investigation of microstructure-tensile behavior relationship in Hastelloy X Ni-based superalloy processed by laser powder-bed fusion: Insights into the elevated temperature ductility loss

The microstructure-tensile response correlation in a crack-free laser powder-bed fusion (LPBF) Hastelloy X Ni-based superalloy is investigated. The LPBF process parameters in terms of volumetric energy density were optimized to obtain the maximum relative densities, as well as the lowest defect size. The microstructure and tensile behavior of samples were evaluated. Microstructural characterizations showed that the columnar grains of the austenite phase consisted of a submicron cellular microstructure with a weak texture along direction. The as-built sample had an acceptable tensile behavior at the ambient temperature, as compared to the AMS 5536 N standard specification. However, at 760 °C, it was observed that the plastic deformation of the as-built sample was influenced by an intergranular brittle fracture, leading to the elevated temperature ductility loss. The results of fractography investigations, performed by means of electron backscatter diffraction analysis, indicated that grain boundaries were precipitation-free and the cracks were formed in the areas with a high Taylor factor value. The investigations also demonstrated that a high degree of grain-to-grain incompatibilities, especially in the grains having parallel to the building direction orientation, resulted in the stress concentration in the grain boundaries, leading to inferior elevated temperature tensile properties. © 2021