Effect of aluminum addition on the transformation of NiTi alloy

The transformation behavior of ternary NiTi(Al) alloy was investigated with a differential scanning calorimeter in order to clarify the effect of aluminum substitution in NiTi, showing the shape memory due to the thermoelastic martensitic transformation between a high temperature phase and a low temperature phase. An intermediate phase appears due to aluminum substitution and its temperature region is broadening with increasing number of thermal cycles. By replacing titanium by aluminum, a unique behavior is observed in the transformation from the intermediate phase to the low temperature phase. The transformation behavior of NiTi(Al) depends significantly on the concentration of the substituted aluminum. The temperature region of the intermediate phase is controlled by the substituted aluminum. The shape memory effect also occurred in the transformation between the high temperature and the intermediate phases. Therefore, the substitution of aluminum is useful for various applications of the transformation to the intermediate phase.