Recent advances in understanding the origin of martensite aging phenomena in shape memory alloys

The martensite aging phenomena (martensite stabilization and rubber-like behavior) found in many shape memory alloys have puzzled material scientists for over 60 years without a definite answer. In this article we critically reviewed previous models to understand the aging phenomena, which include pseudotwin-type model, LRO model, SRO model, twinning dislocation model, and domain (twin) boundary pinning model. We showed that these models failed to meet generality criterion, although being able to explain the phenomena to some extent. Then we focused on a very recent general model (Ren and Otsuka, Nature, 389, 579–582, 1997) which makes use of only two common features of martensitic transformation and aging, i.e., diffusionless symmetry change during martensitic transformation and diffusion during aging. This model appears to be able to explain all of the available experimental observations on the aging phenomena. In view of recent development in this field, we have reason to believe that we are approaching the final solution to the aging problem.