Microstructure and Properties of Shape Memory Alloys

Abstract

This paper deals with NiTi and CuAlNi shape memory alloys and especially with the two-way memory effect which was successfully introduced in wire specimens by a specific thermo-mechanical heat treatment called training. In order to enable a systematic variation of the microstructure with respect to dislocation density, second phase particles and grain size, the investigations were carried out on three different alloy systems. 4000 thermal cycles were performed on the trained shape memory elements, continuously observing the changes in the deformation behavior. The influence of work hardening, grain size and high internal stress-fields on the development and the stability of the intrinsic two-way shape memory effect is discussed, supported by microstructural investigations. It is shown that the stability of the two-way shape memory effect can be optimized by establishing an appropriate microstructure. Furthermore this work deals with the production of thin ribbons of shape memory alloys by melt-spinning and optimization with respect to microstructure and functional properties.