MARTENSITIC TRANSFORMATION IN beta -BRASS AND THE SHAPE MEMORY EFFECT.

Abstract

The discussion is divided into two sections: A) An analysis of the stability of the different structures which include i) the spontaneous martensite that forms on cooling at the temperature M//s(0), ii) the martensite which is induced by an externally applied stress delta at a temperature M//s( delta ) greater than M//s(0) and iii) the structures that form when the martensite is deformed plastically. B) A study of the kinetics of the nucleation and growth of the martensite and the discussion of an atomistic model of the martensitic transformation and of SME. For the experiments single crystals of binary beta -brass were used, ranging in composition from 39. 2 to 40. 6 at% Zn and having an M//s(0) between 70 K and 150 K. The spontaneous and stress induced martensite was investigated by means of optical and transmission electron microscopy, electrical resistivity and acoustic emission.