The behaviour and kinematic model for γ′ evolution and grain growth during solution treatment of a powdered metallurgical Ni-based superalloy

The evolution of the microstructure and the kinematic model during solution treatment of a powdered metallurgical Ni-based material were investigated in this work. The results showed that the solvus temperature of the γ′ phase was as high as 1170 °C–1200 °C. An improved JMAK model was used to describe the γ′ dissolution behaviour over a continuous temperature range. In the model, the constants were regarded as the equations for temperature, and the correlation coefficient R was 0.9994. The grain growth behaviour below 1200 °C was different from that above 1200 °C; therefore, the raw material was well understood with a segmented model, and R was 0.9771. During the cooling stage, as the cooling rate was increased, the size of γ′ decreased quickly at the beginning and then entered a stable phase; finally, it exhibited secondary reduction. As the γ′ size decreased, the hardness of the alloy first increased and then changed slowly. A cubic polynomial was established to calculate the size of γ′ at different cooling rates, and R was 0.97367. A new hardness prediction model was used to predict the hardness with different values of γ′ for the alloy, and R was 0.9710.