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

Abstract

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 °C was the starting temperature that initiated re-crystallisation.