Elastic constants of Ti₅₀Ni₃₀Cu₂₀ alloy prior to martensitic transformation

Abstract

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 ć and c₄₄ 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.