Plastic deformation and dynamic recrystallization of a powder metallurgical nickel-based superalloy

Abstract

The mechanisms of hot plastic deformation and dynamic recrystallization (DRX) in a powder metallurgical superalloy were investigated by compression tests in the deformation temperature range of 1020–1140 °C, and the constant strain rate range of 0.001–1.0s−1. The results showed that the stress–strain curves can indicate the intrinsic relationship between the flow stress and thermo-mechanical behavior, which can be used to reflect the internal micro-structural evolution law. All of curves can be divided into three types of DRX flow curves: single peak, cyclic behavior and steady-state flow stress curve. Based on researching of basic constitutive relation, the peak stress can be expressed as follows:σp=0.00013Z0.177. The mechanisms of DRX depended on the operating deformation mechanisms which changed with temperature and strain rate. The inflection point of work-hardening rate curve indicates the onset of DRX. The inflection points are obvious at a low strain rate and a high temperature, while they are not existence at a high strain rate and a low temperature. The strain-rate sensitivity, and thus the deformation mechanisms, are different in the respective temperature regimes as found for the steady-state flow stress and the peak stress, and reflected by the temperature dependence of the stress exponent. Continuous dynamic recrystallization (CDRX) takes place at low deformation temperature. CDRX can lead to a partial softening in hot deformation. A great number of the dislocations are trapped by subgrain boundaries, leading to an increase in grain boundary misorientation and gradual transformation into high-angle grain boundaries (HABs). Discontinuous dynamic recrystallization (DDRX) takes place at high deformation temperature. A great number of new grains formed on the completely dynamic recrystallization microstructure.