Influence of cycling on the reversible martensitic transformation and shape memory phenomena in TiNi alloys

Abstract

TiNi alloys are important shape memory materials because of their excellent memory phenomena accompanied with superior mechanical and corrosion properties. Thermal and mechanical treatments can suppress slip deformation resulting in increase in flow stress and modify the transformation temperatures, recovery stresses and recovery strains. The key characteristic for numerous technical and medical applications is the degradation of fundamental memory parameters (change in transformation temperatures, loss of shape memory effect, loss of reversion stress) and unacceptable changes of element geometry as a consequence of cyclic thermal and/or mechanical loading. The present paper is devoted to the investigation of degradation mechanisms of the work hardened and annealed TiNi shape memory wires, during cyclic thermal changes under a constant load.