Investigation of thermal and stress induced hysteretic curves in CuAl(11.5 wt%)Ni(5.0 wt%) single crystalline shape memory alloy

Thermoelastic martensitic transformation has been studied in CuAl(11.5 wt%)Ni(5.0 wt%) single crystalline shape memory alloy under constant temperature, T, as well as under constant uniaxial stress, σ, measuring the relative deformation, ε, as the function of σ and T, respectively. From the obtained hysteretic curves the stress/temperature dependence of the martensite and austenite start and finish temperatures/stresses were calculated and discussed in terms of chemical and non chemical energy contributions. The difference between the slopes of the start and finish temperatures versus stress functions and the slope of the equilibrium transformation temperature versus stress is interpreted as the consequence of the σ dependence of the elastic energy term. The transformation strain εtr depends both on σ (at constant T) and on T (at constant σ) and both functions have the same saturation value, belonging to the stress induced (single) variant martensite structure. It was obtained that the dissipative terms are practically independent of σ and T, and have higher values for the ɛ∼T than for the ɛ∼σ loops.