Transformation stress of shape memory alloy CuZnAl: Non-Schmid behavior

We establish an atomistically-informed model for predicting the non-Schmid behavior of critical stresses for bcc to orthorhombic (L2₁ to 18R) martensitic transformation in CuZnAl alloys. The interplay between the stacking fault displacements and the applied stress tensor components are shown to be responsible for the variation of the CRSS levels as much as a factor of almost 2.5 (25 MPa–60 MPa) depending on the crystal orientation. The predicted transformation stresses exhibit excellent agreement with the experimental results in this study and the measurements reported in the literature. The possible role of deviations from crystallographic ordering was also investigated illustrating the increase in transformation stress levels upon introduction of local disorder.