Shape recovery mechanism observed in single crystals of Cu–Al–Ni shape memory alloy

Abstract

Micromechanism of the shape recovery process is optically observed in single crystals of the Cu–Al–Ni shape memory alloy. Formation of X and λ-interfaces (interfacial microstructures with two intersecting habit planes) is documented, both in a thermal gradient and during a homogeneous heating. The observed growth mechanisms (i.e. mechanisms of nucleation and growth of the twinned structures) are described and analysed. Weakly non-classical boundaries between austenite and two crossing twinning systems are also documented.

Keywords:

• shape memory alloys
• shape recovery process
• martensitic microstructure
• non-classical boundaries

Acknowledgements

This work was supported by project AV0Z 20760514 of the Institute of Thermomechanics ASCR. Authors would like to acknowledge J. Kopeček, V. Novák and S. Ignácová (Institute of Physics ASCR) for specimen preparation and DSC measurements. The first author would also like express his gratitude to Prof. Sir J. M. Ball (Oxford University) for support, comments and discussions.

Notes

Notes

1. Bhattacharya 10 mentions only two alloys able to form an austenite–to–single variant habit plane. For the overwhelming majority of known SMAs, the habit plane is possible only between austenite and a microstructured martensite.

2. This effect does not involve any reordering or lattice distortion as it is in the case of thermal stabilization induced by ageing in martensite.