Superplastic deformation behavior and microstructure evolution of a new extruded nickel‐based powder metallurgy superalloy

Abstract A new type of extruded nickel‐based powder metallurgy (P/M) superalloy was subjected to isothermal compression and tensile experiments to explore its superplasticity. Based on the compression flow curves, the hot working maps of strain rate sensitivity index ( m ) were established at various strain levels. When compressing at 1020–1110 °C, in the strain rate range of 0.001–0.01 s −1 , the m value was always greater than 0.3, indicating that the superalloy exhibited superplasticity in this deformation region. The tensile results showed that the superalloy exhibited excellent superplasticity under the conditions of 1050 °C/0.01 s −1 , 1080 °C/0.01 s −1 and 1110 °C/0.001 s −1 , with elongation after fracture reaching up to 1011%, 1038% and 951%, respectively. At low‐temperature conditions and high‐temperature/low strain rate conditions, both continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) were activated. As the deformation temperature increased, the γ′ phases gradually dissolved into the matrix, and the primary γ′ phase changed from irregular shape to spherical or near‐spherical shape. The interaction of the γ′ phase with the dislocation promoted dynamic recrystallization (DRX) nucleation and thus slowed down the grain growth rate, which was essential for the superplastic deformation of the alloy.