The Relevant Role of Dislocations in the Martensitic Transformations in Cu–Al–Ni Single Crystals

Abstract

The interaction between dislocations and martensitic transformations in Cu–Al–Ni alloys is shortly reviewed. Results from many researchers are critically analyzed towards a clear interpretation of the relevant role played by dislocations on the properties of shape memory alloys in Cu-based alloys. Both thermally and stress-induced transformations are considered and focus is paid on two types of transitions, the β→β′ and the formation of a mixture of martensites: β→β′ + γ′. After cycling in the range where both martensites are formed, the twinned γ′ phase is inhibited and cycling evolves into the formation of only β′. A model which considers the difference in energy of each γ′ twin variant due to the introduced dislocations quantitatively explains the inhibition of γ′ in both thermally and stress-induced cycling. The type of dislocations which are mainly introduced, mixed with Burgers vector belonging to the basal plane of the β′ martensite, enables also to explain the unmodified mechanical behavior during β→β′ cycling. The reported behavior shows interesting advantages of Cu–Al–Ni single crystals if mechanical properties are comparatively considered with those in other Cu-based alloys.