Effect of Prior Transformation on Transformation Start Stress and Temperature in an Fe-based Shape Memory Alloy

Transformation start conditions in an Fe-Cr-Ni-Mn-Si polycrystalline shape memory alloy are found to be determined by the martensite start stresses in the stress-strain plane and the austenite start temperatures in the temperature-strain plane. The martensite start stress changes nonlinearly with the extent of prior reverse transformation, and the austenite start temperature with the extent of prior martensitic transformation. In both cases the prior transformation is shown to be characterized by means of the two parameters. The alloy performance is similar to that in some Cu- and Fe-based alloys but quite different from the data in TiNi alloys and the thermodynamic prediction, suggesting a generalization of the theory, especially of the form of the driving force