Journal of Thermal Analysis and Calorimetry, Vol. 66 (2001) 7–16 GUARANTEED BEHAVIOR IN SHAPE MEMORY ALLOYS Short- and long-time effects related to temperature and phase coexistence V. Torra * , A. Isalgue and F. C. Lovey ** CIRG-DFA-ETSECCPB-UPC, Campus Nord B-4, E-08034 Barcelona, Spain Abstract A phenomenological approach, in the parent phase of Cu–Zn–Al shape memory alloy, establishes a predictable model (or mathematical equations) relating the dependence of Ms with the temperature over a long period of time (i.e. seasonal or yearly room temperature). High-resolution resistance and temperature measurements vs. time are used. The long time Ms tracks the external room temperature via two temperature dependent time constants. In steady state, the changes in Ms approach 17 per cent of the ‘room’ temperature change. The detailed analysis shows the puzzling disappearance of the after quench effects. Keywords: aging effects, guaranteed behavior, martensitic transformation, phase coexistence, pre- dictable behavior, resistance, shape memory alloys, temperature Introduction In shape memory alloys (SMA), among which Cu–Zn–Al alloys can be considered as a prototype, the martensitic transformation is considered a first order phase transition. The transformation originates a number of particular properties like the thermo- elasticity or pseudoelasticity, the one-way memory behavior and the two-way mem- ory effect. The martensitic transformation in copper-based alloys is thermoelastic, i.e. the transformation progresses following the undercooling below the equilibrium tem- perature (T 0 ). The applicability of the material for on-off actions needs only a poor re- liability. Reliable industrial applications in long-time intervals (several years) and/or dozens of thousands of cycles are relatively difficult. In Cu–Zn–Al alloy, the parent phase (bcc structure) is a metastable phase at room temperature obtained by quenching from higher temperature [1]. Avoiding other parasitic effects as grain boundaries or arrays of dislocations, the equilibrium temperature T 0 (and the Ms value) is a function of the atomic order. In the present 1418–2874/2001/ $ 5.00 © 2001 Akadémiai Kiadó, Budapest Akadémiai Kiadó, Budapest Kluwer Academic Publishers, Dordrecht * Author for correspondence: E-mail: vtorra@fa.upc.es ** Permanent address: Instituto Balseiro and Centro Atomico, 8400 S.C. de Bariloche, Argentina