Tensile deformation behavior of laser powder direct energy deposited Inconel 625: Cryogenic to elevated temperatures

This study investigated the tensile behavior of laser powder direct energy deposited (LP-DED) Inconel 625 at temperatures ranging from cryogenic (−195 °C) to an elevated temperature of 980 °C. The tensile properties and deformation mechanisms at different temperatures were revealed. The tensile strength of the material, i.e., yield strength (YS) and ultimate tensile strength (UTS), was observed to decrease with increasing test temperature. Sudden decreases in YS were observed from −195 °C to 20 °C and above 870 °C, and in UTS from −195 °C to 20 °C and above 650 °C. The sudden decline in tensile strengths from −195 °C to 20 °C was attributed to the reduction in deformation twin density in the material. In contrast, softening caused by the dynamic recrystallization (DRX) resulted in a rapid decline in YS and UTS above 870 °C and 650 °C, respectively. The ductility of the material was observed to decrease with increasing test temperature until 650 °C, where the tensile fractures were governed by the decohesion of carbides. Above 650 °C, DRX was observed in the microstructure and the grain boundary (GB) sliding of the DRX grains governed the tensile fracture. At 870 °C, a lower degree of GB sliding improved the ductility, while at 980 °C an excessive GB sliding induced fracture significantly deteriorated the ductility.