Effect of ECAE-processing on the thermo-mechanical behavior of Ti34 wt.%Nb0.14 wt.%O shape memory alloy

The effect of ECAE (equal channel angular extrusion)-processing on the thermo-mechanical behavior of Ti34 wt.%Nb0.14 wt.%O shape memory alloy was studied by measuring the tensile stress–strain curve at various temperatures and using DSC, X-ray diffraction, and TEM. An ultrafine (0.4 μm) grain structure was developed by severe plastic deformation and by the formation of alpha-particles on grain boundaries, which was facilitated by oxygen. Severe grain refinement led to a large decrease of Ms from 216 °C to 106 °C. Furthermore, the elimination of oxygen by α-particles led to an abrupt decrease of the stress for reorienting the martensite variants and to an increase in the transformation strain. Subsequent ω-aging treatment further stabilized the β-phase at room temperature, resulting in a superelastic property.