Addition of Cu to Ternary Ni47Ti50Fe3 Shape Memory Alloy

Ni₄₇Ti₅₀Fe₃ alloy has been used for hydraulic couplings and fasteners, in part due to the reasonable amount of ductility it has, in comparison to other Ni-Ti based alloys. However, the alloy shows unsatisfactory pseudoelasticity, possibly due to its low yield strength. In the present study, the effect of Cu on the pseudoelasticity of Ni₄₇Ti₅₀Fe₃ alloy was investigated. A series of Cu substituted alloys, Ni_47-x-Ti₅₀-Fe₃-Cu_xS (x=0-4 at. %), were prepared and characterised in terms of their transformation behaviour and mechanical properties. An interesting observation was that the martensitic transformation start temperature (M_S­) increases @ 7^oC/at. % with Cu, which is contrary to the expectation as Cu is expected to substitute Ni sites without affecting M_S. A likely reason for this is that Cu may be substituting both Ni and Ti sites. This work attempts to determine the site preference of Cu in the B2 phase of Ni₄₇Ti₅₀Fe₃ alloy and rationalize its effect on the martensitic transformation and pseudoelastic properties.