Martensitic transformations in shape-memory Cu-Zn-AI alloys with the -phase particles and the bainite crystals

Abstract
The martensitic transformations in Cu-Zn-A1 alloys undergoing the decomposition of solid solution with the formation of rod-like -phase or of plate-type bainite crystals have been studied by optical microscopy, electron microscopy and electron-probe microanalysis. The fine structure of the phases formed upon the partial decomposition of -phase and upon the subsequent martensitic transformation was studied. The transformation was shown to occur in a crystallographically ordered manner and to obey the Kurdyumov-Sachs orientation relationships. The transformation includes features of both diffusional and martensitic transformations. The -phase formation inclues a crystals lattice reconstruction and the nucleation dislocations in periodically arranged slip planes. At the same time, the shape of the -phase crystals and their coalescence and changes in chemical composition are typical of diffusional transformation. The interactions of martensite crystals with particles of the phase and bainite crystals were studied.