Characterization of hot deformation behavior of GH925 superalloy using constitutive equation, processing map and microstructure observation

Abstract

The hot deformation behavior of the GH925 superalloy has been investigated by hot deformation compression tests carried out in the deformation temperature range of 950–1250 °C with strain rates of 0.01–10 s−1 to a total strain of 0.7. The flow curves of the alloy over the investigated temperatures and strains rates are typical of dynamic recrystallization, which is the principal softening mechanism in the hot working of GH925. The constitutive equation of the alloy is established, which describes the peak stress as a function of the deformation temperature and strain rate. The processing maps for the alloy are constructed at the strains of 0.2 and 0.6 based on the dynamic material model. There is a stable domain with the peak efficiency about 0.41 at the deformation temperature of 1075–1150 °C and the strain rate of 0.01–0.1 s−1. The degree of recrystallization and the grain size increases with increasing deformation temperature and decreasing strain rate. The main instability domain locates within the high strain rate domain, in which instability is primarily manifested as flow localization. Optimum hot working parameters for GH925 are in the temperature range of 1075–1150 °C and strain rate range of 0.01–0.1 s−1.