Recovery stress characteristics of TiNi and TiNiCu shape memory alloys

The recovery stress characteristics of TiNi binary and TiNiCu ternary shape memory alloys were studied. Both the maximum recovery stresses of TiNi and TiNiCu alloys increase with increasing prestrain level. The recovery stress rate (dσ/dT) of the TiNi alloy increases with increasing prestrain level, but that of the TiNiCu alloy decreases with increasing prestrain level. By comparing the results of differential scanning calorimetry, analysis based on the modified Clausius-Clapeyron equation shows that the recovery stress characteristics have a close relation to the thermoelastic martensitic transformation characteristics. For TiNi binary alloys, the transformation temperature interval decreases with increasing prestrain level, resulting in the increase of the recovery stress rate. For TiNiCu ternary alloy, the transformation temperature interval increases with increasing prestrain level, resulting in the decrease of the recovery stress rate.