WEDGE-LIKE MICROSTRUCTURE IN MARTENSITES

The wedge-like microstructure commonly seen in martensites, especially in shape-memory alloys, is an important mechanism for thermoelastic austenite-martensite transformation. This microstructure is analyzed using a suitable energy minimization principle. The Hadamard jump condition is used to characterize coherent interfaces. The crystallographic theory of martensite follows as a consequence of this. It is shown that only very special materials whose lattice parameters satisfy certain highly restrictive conditions can form the wedge-like microstructure. The lattice parameters of common shape-memory alloys satisfy these relations and their morphology shows good agreement with the predictions. This suggests that the microstructure and consequently the macroscopic behavior of martensites may depend very delicately on the lattice parameters.