Constitutive Equations for the Thermomechanical Response of René 80: Part 1—Development From Isothermal Data

Abstract

This work describes the development of a unified nonisothermal constitutive model to predict the thermomechanical fatigue (TMF) response of a Nickel base superalloy, René 80. Nonisothermal deformation mechanisms are modeled using state variables. The flow equation of the Ramaswamy-Stouffer model was rewritten in the form of an Arrhenius equation with explicit temperature dependence. The isothermal predictions were correlated with the test data at four test temperatures between 538°C and 982°C. Material parameters were verified using nonisothermal tensile calculations. This verification showed that modeling the transition between planar slip and dislocation climb accurately is crucial for obtaining reliable TMF predictions. The revised constitutive model could successfully predict René 80 response from several TMF tests between 760°C and 982°C.