Effect of Rare Earth Gd on Thermal Deformation Behavior of Ni-Cr-Mo Alloys

As a neutron shielding material for spent fuel storage， Ni-Cr-Mo-Gd alloy has broad application prospects， but it is prone to cracking during thermal working. In order to optimize the hot deformation process parameters of the alloy，this paper focuses on the study of Ni-Cr-Mo alloy， investigating the microstructural changes induced by the addition of Gd. Isothermal hot compression experiments were conducted at deformation temperatures of 1 000 ℃-1 200 ℃ and strain rates of 0.01 s^-1-5 s^-1 to calculate the relevant material constants and the activation energy for thermal deformation. Thermal working map was established to determine thermal deformation window， while the influence of Gd element on the thermal deformation behavior of the alloy was analyzed in conjunction with the microstructure. The results indicate that the addition of 1.2% Gd to the Ni-Cr-Mo alloy reduces the deformation activation energy from 472.15 kJ/mol to 422.9 kJ/mol. This results in higher energy consumption efficiency during thermal deformation and more comprehensive microstructure evolution. The plastic instability zone gradually shifts from high to low temperatures， expanding the safe deformation zone of the alloy at low temperatures of 1 000 ℃-1 060 ℃ and low strain rates of 0.01 s^-1-0.32 s^-1. Optimal thermal deformation zone for alloy is determined to be a true strain of 0.5 at temperatures of 1 113 ℃-1 164 ℃ and strain rates of 0.01 s^-1-0.2 s^-1. Gd precipitates as the intermetallic compound GdNi₅ at grain boundaries or dendrite interfaces. The presence of GdNi₅， as a hard brittle phase， leads to significant strain accumulation during the thermal deformation process， resulting in higher stored energy in the microstructure， thereby promoting recrystallization of the surrounding deformed grains and reducing the residual strain in the microstructure.