Effects of Ta Addition on Microstructure and Transformation Behavior of Ni-Ti Alloys

The effect of adding Ta on the changes of microstructure and M-s temperature of a dual-phase shape memory alloy with compositions of (Ni51Ti49)(1-x)Ta-x and Ni50Ti50-yTay, were systematically studied. An optical microscope, SEM, X-ray diffraction and DSC were utilized in this work. The evolution of the microstructure as a function of Ta content was characterized. The variation of the Ni/Ti ratio in the NiTi phase plays an important role in the change of the M-s temperatures due to the addition of Ta. A pseudobinary NiTi-Ta phase diagram was proposed based on these results.