Deformation behavior of a new Ni-Co base superalloy GH4251 during hot compression

Abstract

Abstract The deformation behavior of a new Ni-Co base superalloy GH4251 under hot compression tests within the deformation strain window of 0.36 to 1.2 was investigated in the temperature range of 1050 ∼ 1170 °C and strain rate range of 0.001 ∼ 1 s−1. Based on the analysis of true stress-strain curves, constitutive equations were established to describe the rheological behavior during hot compression. Microstructure evolution was investigated by transmission electron microscope (TEM), scanning electron microscope (SEM) and optical metallography (OM). The results show that flow behavior of GH4251 alloy is combinedly determined by the effect of work hardening and dynamic recrystallization (DRX). The deformation activation energies at strain of 0.36 to 1.2 are calculated to be 311 ∼ 536 kJ mol−1 in the super-solvus temperature region, and 796 ∼ 1064 kJ mol−1 in the sub-solvus temperature region. The recrystallization nucleation mechanism of GH4251 alloy is strain induced grain boundary migration (SIBGM). The occurrence and expansion of recrystallization are strongly promoted by high deformation temperatures and high strain rates, while the DRX grain size increases with elevated deformation temperature. When the deformation temperature is below 1090°C, the recrystallized grain can be extremely small (<17μm), which is rather independent on strain and strain rate. However, above 1110 °C the grain size at strain rate of 0.001s−1 is significantly larger than that of higher strain rates. The difference can be ascribed to the presence of γ′ phase, with which the development of dynamic recrystallization is postponed, while the growth of recrystallized grains is inhibited as well.