Elastic constants of Ti50Ni30Cu20 alloy prior to martensitic transformation

Elastic constants of Ti50Ni30Cu20 alloy prior to the martensitic transformation B2 --> B19 was measured for the first time by using the rectangular parallelepiped resonance method. The softening in both shear modulus c' and c(44) was found with approaching transformation temperature. As a result of soft c(44), the anisotropy factor shows a low value of 2.8 in the vicinity of the transformation temperature. c(11), c(12), and bulk modulus were found to show little temperature dependence in the vicinity of the transformation temperature. Compared with the binary Ti50Ni50 alloy, Ti50Ni30Cu20 alloy exhibits a 40% higher and increasing anisotropy with approaching transformation temperature. Based on the experimental results, we explained why Ti50Ni30Cu20 transforms into B19 martensite, while Ti50Ni50 transforms into a strange monoclinic B19' martensite.