Thermomechanical cycling and two-way memory effect induced in Cu–Zn–Al

The two-way shape memory effect (TWME) has been induced by thermomechanical cycling in Cu–Zn–Al alloys using a dedicated hydraulic mechanical testing soft machine with complete computer control of force, elongation and temperature. The results concerning single crystals (composition Cu–16.9 wt.% Zn–7.7 wt.% Al, nominal Ms of 273 K) and polycrystals (Cu–15.8 wt.% Zn–8.3 wt.% Al, nominal Ms of 230 K, mean grain size of 1 mm) are reported for two training protocols (sequence of one thermomechanical cycle of education followed by one stress free thermal cycle to check the TWME or twenty consecutive thermomechanical cycles followed by one or two checking thermal cycles). The capacity of the trained specimen for producing work under an antagonist compressive stress is also studied and the behaviour of the deformation of the specimen under such a condition at different temperatures is analysed in terms of a competition between the contributions of the different variants: trained variants with an intrinsic deformation in the direction of the tensile stress of the training process, trained variants with an intrinsic deformation which is not well orientated with respect to this direction (in the polycrystal) and new variants with an intrinsic deformation in the direction of the compressive stress which can replace the educated variants.