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 temper ature. The results concerning single crystals (composition Cu-16.9 wt.% Zn- 7.7 wt.% Al, nominal M-s of 273 K) and polycrystals (Cu-15.8 wt.% Zn-8.3 wt .% Al, nominal M-s of 230 K, mean grain size of 1 mm) are reported for two training protocols (sequence of one thermomechanical cycle of education fol lowed by one stress free thermal cycle to check the TWME or twenty consecut ive thermomechanical cycles followed by one or two checking thermal cycles) . The capacity of the trained specimen for producing work under an antagoni st compressive stress is also studied and the behaviour of the deformation of the specimen under such a condition at different temperatures is analyse d in terms of a competition between the contributions of the different vari ants: trained variants with an intrinsic deformation in the direction of th e tensile stress of the training process, trained variants with an intrinsi c deformation which is not well orientated with respect to this direction ( in the polycrystal) and new variants with an intrinsic deformation in the d irection of the compressive stress which can replace the educated variants. (C) 1999 Elsevier Science S.A. All rights reserved.