An investigation into the temperature-dependent tensile behavior of Hastelloy-X: The effect of additive manufacturing processes

This study investigated the tensile behavior of Hastelloy-X produced by two additive manufacturing processes, i.e., laser powder bed fusion and laser powder directed energy deposition, across a wide temperature range from cryogenic (−195°C) to elevated (982°C). Prior to the tensile tests, a multi-step heat treatment resulted in partial dissolution of dendritic microstructures in laser powder bed fused (L-PBF) specimens and complete dissolution in laser powder directed energy deposited (LP-DED) ones, along with the formation of some Cr-rich/Mo-rich carbides in both specimen sets. The yield strengths between both sets were comparable across all test temperatures except at cryogenic condition (i.e . , −195°C). However, the ultimate tensile strength had some variation, with the L-PBF specimens having higher values from −195°C to 649°C. The tensile strengths of L-PBF specimens were higher than those of LP-DED in cryogenic condition due to heightened deformation twinning activities. At elevated temperatures up to 649°C, the deformation twinning reduced, and dislocation activity increased more in L-PBF specimens than in LP-DED ones. Below 649°C, the L-PBF specimens showed higher percentage elongation to failure and more necking due to delayed fracture caused by fewer carbide particles serving as void nucleation sites than LP-DED. Above 649°C, ductility of L-PBF specimens deteriorated due to easier fracture from grain boundary sliding in their fine grain microstructure.