On the Orientation Dependent Microstructure and Mechanical Behavior of Hastelloy X Superalloy Fabricated by Laser Powder Bed Fusion

Ni-based superalloys fabricated by laser powder bed fusion (LPBF) have shown great potentials in various industrial sectors with demanding environment, but limited understanding in the microstructure-property relationship of the LPBF fabricated alloys hinders their practical applications. In this study, Ni-based superalloy Hastelloy X (HX) was manufactured by LPBF, and the resulting microstructure was characterized using multiscale correlative microscopy and its relationships with mechanical behaviors were investigated. A typical cellular structure formed in the HX alloy during LPBF, and cell walls are enriched with Cr and Mo elements and contain a high density of dislocations, and misorientation accumulation across cell walls leads to the formation of low and high angle boundaries in the alloy. Correlative microscopic characterizations demonstrate that epitaxial cell growth across molten pool boundaries between adjacent layers and side-branching between neighboring tracks result in the formation of a strong Goss texture. Mechanical testing shows that the fabricated HX alloy exhibits a lower strength and a higher tensile ductility along the building direction, compared to those along transverse directions. The governing mechanism for the strength anisotropy is the anisotropic columnar grain structure, and the ductility anisotropy is mainly caused by the orientation-dependent capability in mechanical twining. Moreover, a very pronounced anisotropy in plasticity was found, where macroscopic shape change from circular to highly elliptical was observed in the sample after tensioning along the building direction. It is demonstrated that an orientation-dependent dislocation activity which results in a planar strain during tensioning is account for the anisotropic plastic deformation