Effects of Thermomechanical Treatment on Phase Transformation of the Ti₅₀Ni₄₉W₁ Shape Memory Alloy

Abstract

The Ti50Ni49W1 alloy has a B2 ↔ 19’ martensitic transformation but slightly lower shape recovery than the Ti50Ni50 alloy. The B19’ martensite structure in the Ti50Ni49W1 has the lattice parameters a = 0.301 nm; b = 0.423 nm; c = 0.472 nm; and β = 97.5°. The hardness increment and transformation temperature depression of Ti50Ni49W1 are greater than those of Ti50Ni50 under the same degree of cold rolling and the same number of thermal cycles; owing to the Ti50Ni49W1; with higher inherent hardness from solidification strengthening of W atoms. Both thermal cycling and cold rolling on Ti50Ni49W1 also promotes R-phase transformation. The effects of thermal cycling and cold rolling on the martensitic transformation temperature (Ms) of the Ti50Ni49W1 alloy follow a linear trend; and the Ms decreased with the hardness.

Keywords

• shape memory alloy
• martensitic transformation
• thermomechanical treatments