B19 orthorhombic martensitic Transformations in Aged TiNiCu Shape Memory Alloys

This paper gives details about the B19-rhombohedral martensitic transformations in TiNi44.5Cu5.5 Shape Memory Alloys (SMA) aged at 150°C. The martensitic phase transformation sequences observed in this present study by using differential scanning calorimeter (DSC) as follows: As-solutionized and aged for 4 hrs samples exhibits B19↔B2; Aged for 24 h, 48h and 72 h sample exhibits B19↔B19’↔B2 and prolonged aged sample for 96 hrs exhibits B19’↔B2 transformations. The strong diffraction peak can be identified as the (020)B19 in TiNiCu aged at 150°C for 24 hrs. It is clear from X-ray diffraction phase analysis formation of equilibrium Ni3Ti (S.G. P63/mmc (194), Hexagonal crystal structure) precipitates reaches maximum counts with (020) plane in aged for 48 h sample as compared to the aged for 24 h sample. The high DSC values (J/g) of the exothermic peak was recorded in aged for 48 hrs samples was concluded formations of the B19’ martensites