Pseudoelasticity of Cu–Al–Be single crystals: Unexpected mechanical behavior

Abstract

The pseudoelastic behavior of Cu–Al–Be single crystals shape memory alloys was analyzed in the temperature range from 303 K to 393 K. Tensile tests performed at slow crosshead speed show a dependence of the hysteresis associated to the stress induced -18R transformation with temperature. The critical stresses of the -18R transition have been determined giving a negative curvature parabolic dependence on temperature. The effect is more noticeable for the retransformation stress and a consequent increment in the stress hysteresis with temperature is observed. The deformation associated to the stress induced -18R transition has also been found to depend on temperature. These singular features associated with the pseudoelastic behavior of Cu–Al–Be single crystals have been rationalized in terms of a structural distortion of the 18R martensite that has been found to occur in the considered temperature range. The strain associated to the structural distortion was determined as well as the dependence of its critical stress on temperature. The resulting entropy change was thus calculated, resulting fifty times smaller than the entropy change between the bcc parent phase and 18R. The possible mechanisms responsible of this structural distortion of the 18R structure are discussed.