Work hardening in metastable high entropy alloys: a modified five-parameter model

Excellent work hardening in transformation-induced plasticity (TRIP)-enabled metastable high entropy alloys (HEAs) owe to persistent austenite (γ) to martensite (ε) phase transformation; non-basal slip activity and deformation twinning in the transformed martensitic phase are additional deformation mechanisms that contribute to work hardening in selected TRIP HEAs. Mechanical response of TRIP HEAs under uniaxial tension is characterized by an intermediate stage distinguished by a gradual increase in work hardening rate preceded and succeeded by stages of rapid drop in the work hardening rate. A five-parameter empirical model that replicates the nature of the work hardening rate curve in TRIP HEAs has been developed. The ease of parametric identification of the model from the global stress-strain response simplifies implementation of the model over physically based models. As the propensity of stress induced transformation in TRIP HEAs is related to the stacking fault energy (SFE) of the parent austenite phase, an attempt is made to correlate the model parameters with SFE. Based on the trends indicated in the correlation of model parameters with SFE as well as the initial microstructure, a method is proposed to predict the tensile stress-strain response of TRIP HEAs.