Pseudoelastic Cycling between Austenite, 18R and 6R Phases in CuAlBe Single Crystals

Abstract

CuAlBe shape memory alloys exhibit successive reversible stress induced martensitic transformations from austenite to 18R phase and from 18R to 6R phase. The particularities associated with these transformations result in CuAlBe being an attractive candidate material for damping applications. Recently, a stress-temperature phase transformation diagram has been proposed for this system, which, besides the above mentioned phases, also includes the structural distortion of the 18R previous to its stress induced transformation to 6R. In the present work, pseudoelastic cycling of CuAlBe single crystals has been performed at different test temperatures. Both transitions, i.e., austenite-18R and 18R-6R, have been studied. As hysteresis plays a significant role in shape-memory alloys intended to be used for energy dissipation, special attention has been devoted to its evolution during cycling. In addition, the kinetics of stabilization of martensites has been analyzed under dynamic (pseudoelastic cycling) and quasistatic (constant transformed fraction) conditions. A strong enhancement of martensitic stabilization under dynamic conditions compared with stabilization at quasistatic conditions was observed and the possible mechanisms responsible for the effect are mentioned.