Non-classical austenite-martensite interfaces observed in single crystals of Cu–Al–Ni

Abstract

Interfaces between austenite and a crossing-twins microstructure consisting of four variants of 2H-martensite are optically observed in a single crystal of Cu–Al–Ni shape memory alloy. It is shown that these non-classical interfaces form during thermally induced transitions from compound twinned 2H-martensite into austenite, which is in agreement with theoretical predictions. Individual twinning systems and martensitic variants involved in the observed microstructure are identified. The corresponding volume fractions are estimated based on the compatibility conditions at the habit plane and the macroscopic geometry of the interface. Miscellaneous topics related to the observed microstructures (formation mechanism and planeness of the interface) are briefly discussed.