Effects on the martensitic transformations and the microstructure of CuAlNi single crystals after ageing at 473 K

Isothermal treatments at 473 K were performed in CuAlNi single crystals to study their effects on the main properties of this shape memory material. Both the stress and thermally induced martensitic transformations were monitored after these ageing treatments. An increase of the critical transformation temperature was detected and the type of induced martensite changed from [gamma]' into [beta]' after a long enough ageing time. Pseudoelastic cycling was studied after thermal ageing; mechanical behaviour evolved on cycling and a repetitive behaviour was obtained after a small number of cycles. Changes in microstructure were analysed in the [beta] phase by transmission electron microscopy which allowed observing the morphology and distribution of [gamma] precipitates. The changes obtained in shape memory properties were discussed considering the atomic ordering evolution and characteristics of the precipitates.