MicroROM: A Physics-Based Constitutive Model for Ni-Based Superalloys

In this article, a physics-based constitutive model is developed for representing the stress–plastic strain response of Ni-based superalloys by considering the hardening mechanisms that contribute to the macroscopic yield stress and the subsequent strain-hardening response in order to derive the entire tensile stress–strain curve. It is demonstrated that the log stress vs log plastic strain curves of Ni-based superalloys such as 702 Li and ME3 exhibit a bilinear behavior with a lower strain-hardening exponent in the low plastic strain regime and a much higher strain-hardening exponent in the high plastic strain regime. These two hardening regimes can be modeled on the basis of self-hardening of individual slip planes and latent hardening of five operative independent slip systems due to cross-slip from {111} planes to {001} planes, leading to the formation of incomplete and complete Kear-Wilsdorf locks. The proposed physics-based constitutive model, dubbed as MicroROM, exhibits a form that is similar to the Ramberg–Osgood (RO) constitutive model, which is widely used in structural analyses of engineering designs and components. MicroROM is applied to predict the tensile stress–strain curves of 720 Li and ME3 with either a subsolvus or supersolvus microstructure for temperatures ranging from 24 °C to 815 °C. The agreement is good between model predictions and experiment data from the literature. The sensitivity of the predicted stress–strain response to individual microstructural parameters is highlighted and the relation to individual hardening mechanisms is elucidated.