Investigation of influence of preparation and heat treatment on deformation behaviour of the alloy NiTi after ECAE

The work objective was focused on investigation of deformation behaviour of NiTi-based shape memory alloys with respect to technology of their preparation. Deformation behaviour was assessed by unconventional forming methods, particularly by equal channel angular extrusion (ECAE)-but in combination with preceding rotary forging (swaging). Classical light microscopy, as well as X-ray diffraction, was used for evaluation of structural framework of castings and of material after forming. It was established that the alloy Ni50.6-Ti (at.%) after ECAE and re-crystallisation annealing shows bi-modal distribution of mosaic blocks, i.e. mosaic blocks larger than 10 μm and blocks smaller than 10 μm. For determination of re-crystallisation temperature in deformed materials 7 modes of heat treatment were applied. It was proven that the temperature of 600 deg. C was the starting temperature that initiated re-crystallisation.