Microstructure and Transformation Behavior of Ni<sub>50</sub>Ti<sub>50-x</sub>Ta<sub>x</sub> Alloys

The effect of Ta addition on the microstructure, phase transformation temperature and mechanical properties of Ni50Ti50-xTax alloys have been studied in this paper. Beginning with a base composition of Ti50Ni50, Ti was substituted by Ta up to 15at%. A DSC, an optical microscope and SEM were used to characterize the constituent phases in those alloys. The results showed that the ternary Ni50Ti50-xTax (x=2 similar to 15at%) shape memory alloys have lower transformation temperatures than the binary NiTi alloy. The microstructure of Ni50Ti50-xTax alloys changes as a function of Ta content as follows: B-19 phase --> B-2 + beta-Ta phase + Ti-rich dendrites.