Microstructure and microtexture evolution characteristics of a powder metallurgy Ni-based superalloy during static recrystallization

Static recrystallization (SRX) characteristics of a powder metallurgy superalloy were investigated by isothermal compression at 1080–1170 °C under strain rates of 0.01–0.1 s⁻¹, strains of 0.1, 0.22, or 0.5, and holding time of 0–300 s. The impacts of temperature, strain rate, holding time, and strain on the SRXed grain size, volume fraction, and microtexture were explored by electron backscatter diffraction technique. It was found that temperature played a key role in these processes. As SRX progressed, the <110> fiber parallel to the axis compression direction gradually weakened and was replaced by the <001> fiber because <001> was the preferred recrystallization orientation and grain growth direction for the Ni-based superalloy. Moreover, high temperatures and low strain rates promoted the formation of the <001> fiber. Three nucleation mechanisms during SRX process were found: grain boundary bulging, primary twin assistance, and subgrain coalescence. Grain boundary bulging occurred under all process conditions; however, at low temperatures and high strain rates, the latter two mechanisms could provide additional nucleation modes. In addition, SRX size and volume fraction models were established.