Constitutive Equations for the Thermomechanical Response of René 80: Part 2—Effects of Temperature History

Abstract

The unified constitutive equations for René 80 developed by Bhattachar and Stouffer (1992) are used to predict the thermomechanical fatigue (TMF) response of a Nickel base superalloy René 80 between 649°C and 1093°C. Predictions using these equations suggest that temperature history effects are significant during TMF, and that the TMF response of René 80 cannot be predicted completely using only isothermal parameters. It is postulated without metallurgical observations that the two deformation mechanisms in René 80, planar slip at low temperatures and dislocation climb at high temperatures, produce characteristic microstructures which interact under nonisothermal conditions to produce extra hardening that is not present during isothermal deformation. A state variable approach has been used to model this interaction. The nonisothermal model with temperature history effects could successfully predict the initial and saturated TMF response, and block isothermal response of René 80 from several tests between 649°C and 1093°C.