Stress dependence of non-chemical free energy contributions in Cu–Al–Ni shape memory alloy

A Cu–24.0 at.% Al–2.2 at.% Ni–0.5 at.% B shape memory alloy was investigated experimentally under uniaxial tensile stress (σ) up to 10 MPa. Transformation temperatures and transformation strains as a function of σ were evaluated from the simultaneously measured temperature–elongation and temperature–resistance curves. Using appropriate analysis [Philos. Mag. B 82 (2002) 105; Scripta Mater. 43 (2000) 691; J. Phys. IV 11 (2001) Pr8], it is possible to determine the stress dependence of the volume derivatives of the elastic and dissipative free energies at the start and finish points of the forward and reverse transformations from the measured transformation temperatures and strains. From our experimental data, the above volume derivatives were calculated as a function of stress. The dissipative contributions both of the forward and reverse transformations increase with increasing stress. In case of elastic contributions, the difference between the forward and reverse transformation values as well as their decreasing tendency with increasing stress was clearly proved.