Effect of high temperature annealing on microstructure and properties of Ti-50.84at%Ni alloy ring

The effect of high temperature annealing treatment at 850℃ on microstructure,transformation and shape recovery rate of Ti-50.84at%Ni shape memory alloy ring was studied by DSC,XRD and optics-microscope.The results show that microstructure of the forged and annealed Ti-50.84at%Ni alloys is rich in Ni-Ti-parent-phases(B2),but the deep-cooled alloy is rich inNi-Ti-martensite(B19′),and all of them have a small quantity of Ni4Ti3.After annealing at 850℃,the Ni4Ti3 precipitates become finer and less,which brings high anti-transformation stress and increases Ni content in the matrix.This leads that martensite transformation temperature(Ms)of the alloy is decreased and martensite transformation is separated from R transformation.The high temperature annealing eliminates the high-density dislocation defect in Ti-50.84at%Ni alloy,which is propitious for martensite reverse-transformation,so it improves the shape recovery rate and restoring force of Ti-50.84at%Ni alloy ring.