Shape memory alloys

Abstract

The rich thermomechanical properties of shape memory alloys result from an austenitic-martensitic phase transition of the metallic lattice and from a twinning deformation in the low temperature phase, the martensite.

The thermodynamicist is interested in the phenomena, because — once again like in all phase transitions — they provide a non-trivial example for the competition between energy and entropy, with entropy gaining the upper hand at high temperatures. Recognizing this we are able to produce a model for shape memory behaviour which is capable of simulating all the observed features, at least qualitatively. Actually we describe several models, a thermodynamic one, a kinetic one and a numerical one. The latter employs molecular dynamics; it is particularly instructive and the accompanying CD permits the reader to view the crystalline rearrangement by observing the atoms shifting between their potential wells.

Shape memory alloys have found numerous small technical applications, and applications in the medical field. We start the chapter with a selective review.