Microstructural evolution and hot tensile deformation behaviors below δ-solvus temperature of IN718 alloy fabricated by plasma arc additive manufacturing

Plasma arc additive manufacturing (PAAM) stands out for its remarkable efficient utilization and good performance reliability, making it a highly favored additive manufacturing technique. This study delves into the tensile deformation below δ-solvus temperature of PAAM IN718 alloy with complete heat treatment. The results show that the peak stresses are decreased from 1069 to 1189 MPa at 550 °C to 620–1059 MPa at 750 °C. Through the orientation distribution function, the domain textures for hot deformation were identified as cube texture <100> and Rt-Goss texture {110}<110>. The results of the observations on the substructure and grain boundary components of the deformed alloy confirmed that the onset temperature of recrystallization in PAAM alloy is approximately 750 °C. The recrystallization nucleation mechanism of PAAM IN718 alloys was identified as discontinuous dynamic recrystallization. A deformation constitutive equation for hot deformation was established using the Zener-Hollomon parameter, with an average activation energy of 508.93 kJ/mol. A processing map for the hot working of PAAM alloy was developed, and the reasonable processing domains are located at a temperature 700–750 °C/strain rate 10−2–10−1 s−1 with a power dissipation efficiency range of 0.41–0.47. The high-temperature fracture mechanism of PAAM alloy was discussed, identifying the important inducements for high-temperature fracture failure including carbides, residual Laves phase, and δ phase in the PAAM alloy.