Martensitic phase transformation in TiNi.

From temperature dependent perturbed angular correlation (PAC) measurements (77-873 K) in equiatomic TiNi intermetallic alloy, martensitic phase transformations have been observed. Three frequency components corresponding to three different phases of TiNi have been found in the temperature range 298-873 K. The results of quadrupole frequency and asymmetry parameters at room temperature are found to be: ω = 14(1) Mrad/s, η = 0 (33%), ω = 40.0(5) Mrad/s, η = 0.66(3) (52%) and ω = 56.7(3)Mrad/s, η = 0.39(2) (15%). The frequency component with η = 0 and which enhances to ~52% at 373 K can be attributed to the cubic austenite phase. The predominant component (~52%) found at room temperature has been attributed to monoclinic martensitic phase of TiNi and the third component with values of ω and η similar to those for the martensitic phase is attributed to the intermediate orthorhombic phase. At 77 K, no intermediate and austenite phases have been found but only the martensite phase is observed at this temperature. From XRD measurements at room temperature also, three phases of TiNi have been observed.