The effect of cobalt element addition on the characteristics of equiatomic NiTi shape memory alloy

Abstract

Abstract The influence of cobalt addition on the transformation temperatures, microstructure, and micro-hardness of equiatomic NiTi shape memory alloy was studied. The alloys composition was (50 % at. Ni, 50% at. Ti) and (43.45 % at. Ni, 54.728 % at. Ti and Co 1.815 % at.). Vacuum induction melting method is used to produce the shape memory alloys. The investigation of the characteristics of the samples was carried out using, scanning electron microscope conducted with energy dispersive X- ray spectrometer, differential scanning calorimeter, x-ray diffraction measurement and vickers micro-hardness testing. The results show the microstructure of two alloys contain Ti2Ni precipitate phase, the martensite phase layers increase with cobalt addition. The micro-hardness increased, the austenite starts temperature and austenite finish temperature decreases, and thermal hysteresis becomes narrower, after adding a small amount of cobalt.