Constitutive modelling of viscoplasticity in a nickel-based superalloy at high temperature

Inelastic deformation behaviour of an advanced nickel-base superalloy has been investigated at 650 °C under multiple step cyclic and dwell loading conditions and for different strain rates. A viscoplastic constitutive model with strain range dependent cyclic hardening has been proposed. The model is based on the unified Chaboche model modified to account for non-linear kinematic hardening and plastic strain memory. For uniaxial loading, the initial estimates of material parameters were derived from simple strain controlled tests whilst a optimization procedure has been used to obtain the final material parameters. In this paper description of the proposed model, interpretation of the parameters and the optimisation procedure are presented. The predictions of the model are compared with the results for dwell loading tests with different strain rates, cyclic loading tests with selected strain ranges and creep tests under three stress levels. The results predictions show notable improvement compared to the predictions from previous work with respect to stress amplitude. The correlation coefficients and sensitivities of the optimised material parameters were also examined, in justification for the new model.