Revealing deformation mechanisms in additively manufactured Alloy 718: Cryogenic to elevated temperatures

Tensile behavior of Alloy 718, fabricated through laser powder directed energy deposition, was examined over a wide temperature range (-195, 25, 200, 425, 650, 870, and 980 ?C). The tensile properties, deformation mechanisms, and their temperature dependence were specifically investigated. The microstructure and me-chanical properties were characterized in fully heat treated condition; i.e., first stress relieved, then homoge-nized, then solution annealed, and finally 2-step-aged. Tensile results showed thermally stable behavior from room temperature up to 650 ?C, similar to other additively manufactured and wrought counterparts. Rapid reductions of strength with increasing test temperature were observed at-195 to 25 ?C and 650-870 ?C ranges, which were respectively ascribed to a significant reduction in deformation twinning density and the coarsening of gamma ''-precipitates as confirmed by electron microscopy. The fully heat treated microstructure also contained populous Mo/Nb-rich carbides within grain interior which were observed to be the dominant mechanism of fracture and responsible for the temperature insensitive ductility up to 650 ?C. At 870 and 980 ?C, sliding be-tween dynamically recrystallized grains became significant resulting in an increased ductility.