Martensitic Transformation in Nanostructured NiTi Alloy Studied by X-ray Diffraction In-Situ Heating

Abstract

In this work martensitic transformation of Ni-rich NiTi alloy subjected to 17, 20 and 35% cold-rolling in the martensitic state followed by annealing at 450 degrees C for 15 min has been studied by in-situ X-ray Diffraction, Transmission Electron Microscopy and Differential Scanning Calorimetry. It has been found that the material after thermo-mechanical treatment has ultra-fine grained structure with small number of large grains with high dislocation density. Phase composition of that nanostructured alloy consists of B2 austenite, B19' martensite and R rhombohedral phases. B2 and B19' were stable at high as well as at low temperatures. DSC measurements revealed that the studied material shows multistage character of phase transformation. Therefore it was decided to adopt in-situ XRD analysis.