Transformation conditions in an Fe-based shape memory alloy under tensile–torsional loads: martensite start surface and austenite start/finish planes

Transformation conditions are determined experimentally in Fe-9%Cr-5%Ni-14%Mn-6%Si polycrystalline shape memory alloy in the axial stress–shear stress–temperature space. The martensite start condition is represented by an oval corn, exhibiting a strong anisotropy, whereas the austenite start/finish conditions are given by the parallel planes, the normal vector of which depends on the direction of pre-stressing. The von Mises type condition does not fit to the data. The normality condition is almost acceptable. The thermodynamic consideration explains well the results under the condition that only one martensite variant is formed during proportional loading.