Synergic effects of scanning pattern and heat treatment on the microstructure-hot tensile behavior relationships of powder bed fusion-laser beam manufactured Hastelloy X.

The synergic effects of scanning pattern types and subsequent heat treatment on the room- and elevated-temperature tensile properties of powder bed fusion-laser beam additively manufactured Hastelloy X Ni-based superalloy are investigated. The samples were built via bi-directional and chessboard scanning patterns. The as-built microstructures comprised dislocation and solidification cells embedded within the columnar grains. After applying heat treatment at 1175 °C for various soaking times, the as-built microstructures were gradually modified via recrystallization resulting from the residual stresses. The recrystallization kinetics equations for both bi-directional and chessboard samples were derived. It was found that the recrystallization occurred via the twinning-assisted nucleation mechanism and was promoted through bulging. The chessboard and bi-directional samples had similar driving forces; however, the recrystallization fraction in the chessboard sample was higher than that of the bi-directional sample due to differences in the grain's micro-texture. It was observed that the heat treatment cycle had no significant influence on the room- and high-temperature strength; by contrast, it interestingly improved the room- and high-temperature ductility due to reduced dislocation density and formation of twin boundaries. In addition, the heat-treated chessboard sample displayed superior hot tensile ductility than the bi-directional ones, owing to more promotion in recrystallization. [ABSTRACT FROM AUTHOR]