Abstract: This study examined the behaviors of activation volume and strain rate sensitivity in the transformation-induced plasticity (TRIP) Al₅Cr₂₀Fe₃₅Co₃₅Ni₅ high-entropy alloy (HEA) to understand their dependence on the plastic strain, strain rate, and grain size through strain rate jump tests. The observed trends in activation volume and strain rate sensitivity as functions of strain, grain size, and strain rate in the TRIP HEA closely resemble those observed in non-TRIP HEAs studied in previous work. This suggests that the fundamental dislocation processes governing activation volume remain largely unaffected by the phase transformation associated with the TRIP effect. However, the TRIP HEA shows a smaller activation volume than the non-TRIP HEA, especially at finer grain sizes. While the strain rate sensitivity is comparable to that of non-TRIP HEAs when calculated using total stress, it appears markedly higher when evaluated using effective stress. A quantitative model was developed to predict activation volume and strain rate sensitivity in TRIP HEAs, incorporating the effects of twinning, phase transformation, and dislocation activity within a unified dislocation strengthening framework. The proposed model successfully captures the complex experimental trends in activation volume and strain rate sensitivity over a range of strain, strain rate, and grain size conditions in the TRIP HEAs, and can be readly extended to non-TRIP HEAs.

Key words: High entropy alloys, Activation volume, Grain size, Strain rate sensitivity, Transformation induced plasticity