Transformation Conditions and Subloops In an Fe-Based Shape Memory Alloy Under Thermomechanical Loading

Abstract: The rnartensitelaustenite start and finish conditions, the transformation lines in the stress-temperature plane, are determined in an Fe-Cr-Ni-Mn-Si polycrystalline shape memory alloy under the mechanical and/or thermal loads. The transformation lines are show to be almost linear with nearly the same slope. The martensitic transformation zone and the reverse transformation zone are apart to each other, and the latter is very wide; T A ~ - TA,- 180 K. Both the martensite start stress and the austenite start temperature are strongly dependent on the extent of prior transformations, the amount of preload and residual strain. The alloy performance is, therefore, fully contrary to the prediction of the thermodynamic theory and to the experimental result by Paskal and Monasevich in TiNi alloy. The effect of hold stress and temperature is measured to compare the transformation start condition with the yield condition in plasticity. 1