Origin of Memory Effect in Cu-Al-Ni Alloy

Abstract

The origin of the memory effect in Cu–14.2Al–4.3Ni (W/O) alloy has been investigated using the techniques of optical microscopy and electron microscopy. As a result the following have been established. The plastic deformation is caused by the growth or creation, and the contraction or disappearance of twins inside martensites, and the growth or contraction of martensites in the β₁ phase region. Upon heating martensites transform back into the β₁ phase and twins are annihilated, whether or not the martensite and twins have been introduced by deformation. These facts explain the origin of the memory effect. Based on these observations, the requirements for the memory effect have been proposed as follows: i) The martensite transformation is thermoelastic. ii) The lattice invariant strains are not dislocations but twins. The correlation between these requirements and the structural properties, and the reason why twins are annihilated upon the reverse transformation is also discussed.