Dependence of the martensitic transformation characteristics on concentration in Cu–Al–Ni shape memory alloys

Up to now there have been very few studies of the evolution of the temperatures and characteristics of the martensitic transformation in Cu–Al–Ni shape memory alloys as a function of the concentration. The comparison of these studies is very difficult because of the different microstructural conditions and thermal treatments of the used alloys. Besides, the influence of the two kinds of martensites, β3′ (18R) and γ3′ (2H), into which the β phase is transformed for a large range of concentrations, has not been taken into account. In this work we have carried out a systematic study of the temperatures and characteristics of the martensitic transformation for a wide range of concentrations of technological interest. In order to improve the reproducibility of results, we have always used β phase single crystals under the same thermal treatment. The results allow us to obtain an empirical relationship between the alloying element concentration and the martensitic transformation temperatures. Furthermore, a concentration–martensite phase map has been established, showing clearly the concentration range where both kinds of martensites, β3′ and γ3′, coexist.