Thermomechanical cycling in Cu–Al–Ni-based melt-spun shape-memory ribbons

Abstract

Temperature-induced transformations under constant tensile loads (thermomechanical cycling) have been performed on a set of Cu–Al–Ni-based shape-memory ribbons prepared by melt spinning. The rapidly solidified ribbons being already characterized in what concerns martensite and parent phase ageing and their effects on the thermal (stress free) martensitic transformation, the purpose of this study was to complete the characterization of the ribbons, particularly in their shape-memory effect. The results presented for a Cu—13.0 Al—4.0 Ni—0.3 Ti—0.05 B (wt.%) ribbon show larger recoverable strains in the strain–temperature cycles (thus larger shape-memory effect) for ribbons aged at 200 °C than for the as-spun samples. The dependence of the transformation temperatures T on the applied load, quantified through the slope d T/d σ, increases for aged alloys. Both results can be related to the recovery of internal stresses produced by the rapid solidification and some recovery of short-range disorder, both mechanisms favouring higher values of the effective transformation strain. This behaviour is in agreement with the evolution of transformation temperatures in stress free transformation and related microstructural changes produced by ageing the ribbons in parent phase.