CHARACTERIZATION AND PROPERTIES OF SHAPE MEMORY ALLOYS ELABORATED BY NON CONVENTIONAL TECHNIQUES

摘要

The thermoelastic martensitic transformation which gives remarkable functional properties to Shape Memory Alloys (SMA) is very sensitive to the chemistry of the alloys and to its microstructure. In many cases, especially for alloys with high transformation temperatures, applications are limited by the poor ductility. To overcome the brittleness of SMA, two approaches can be effective : ⅰ) modification of the alloy compositions to improve ductility, ⅱ) development of non conventional production technologies which enable to obtain materials in forms close to requirements. Ribbons have been prepared by Planar Flow Casting, wires by In Rotating Water Melt Spinning and strips by Twin Roll Casting. Microstructures and functional properties will be examined in relation with the microstructures induced by the technique. Recently, a new solution has been considered using the superplasticity of an amorphous precursor in the undercooled liquid region, followed by a controlled crystallisation for the recovery of the martensitic transformation.