Characterization of the microstructure and mechanical properties of highly textured and single crystal Hastelloy X thin struts fabricated by laser powder bed fusion

Abstract

In the present study, dense and crack-free Hastelloy X (HX) thin cylindrical struts with diameters ranging from 0.25 mm to 2 mm were fabricated through laser powder bed fusion (LPBF). Their crystallographic texture was found to transition from a<110> || building direction (BD) fiber texture in the 2 mm strut, to a single crystal in the 0.25 mm strut with<110> || BD. The size of the cellular sub-grain microstructure increased as the strut diameter decreased and was linked with an inverse trend in microhardness, which was the highest in the 2 mm strut due to a smaller cell size. Lower hardness measurements in the regions close to the strut edges was also related to larger cell size observed in these regions. From tensile testing, elongation to fracture values were measured in the range of 35–50%. Deformation twinning and lattice rotation after testing were observed. Differences in strength from between different struts of different diameter are also discussed. Finally, fractography analysis further confirmed the ductile fracture behavior.