Effect of Ta addition on shape memory behavior of Ti–22Nb alloy

Effect of Ta addition on microstructure and shape memory behavior of a Ti–22 at.%Nb alloy was investigated in order to improve the shape memory and superelastic properties. The mechanical properties and shape memory behavior of Ti–22 at.%Nb–(0–8 at.%)Ta alloys were investigated by tensile tests at various temperatures and thermal cycling tests under various constant stresses. The shape memory effect with the maximum recovery strain of 2.7% was observed at room temperature in the Ti–22Nb alloy. The martensitic transformation temperature of the Ti–22Nb alloy decreased by 30 K per 1 at.% addition of Ta. The superelastic strain increased with increasing Ta content. Almost perfect superelastic behavior was observed until 2% tensile strain in the Ti–22Nb–(6–8)Ta alloys. The apparent yield stress decreased with increasing Ta content reaching a minimum yield stress around 4 at.%, and then the yield stress increased by further addition of Ta. The critical stress for slip increased with increasing Ta content. A higher critical stress for slip and a lower stress for inducing martensitic transformation resulted in a larger shape recovery strain above 3.0% in the Ti–22Nb–(4–6)Ta alloys.