Investigation on the Mechanism of the Stress-induced Martensitic Phase Transformation of Superelastic Shape Memory Alloys

Heinrich Kern 1Paul Gümple 2Stefan Gläser 3

1. Institute of Materials Technology, Technical University of Ilmenau, Gebäude "Werkstoffe 1", Ilmenau 98693, Germany
2. Fachbereich Maschinenbau (MA), Fachhochschule Konstanz, Brauneggerstrasse 55, Konstanz 78405, Germany
3. ETO MAGNETIC KG, Hardtring 8, Stockach 78333, Germany

Abstract

Superelastic shape memory alloys (SMA) are able to change the phase when charged with an external mechanical tension. On this occasion a material, that shows e.g. an austenitic phase at room temperature will be changed into stress-induced martensitic phase. On the stress-strain-diagram this change of the lattice structure can be seen in a relatively wide ranged pseudo-plastic deformation at nearly constant force.

During the elongation process in the pseudo-elastic field a discontinuous change of the electrical resistance occurs. This change of electrical resistance takes place in a much more distinctive way as it has to be expected depending of the reduction of the cross sectional area of the specimen and its length. The reason of this change in resistance can be derived from the different specific resistances of the two lattices. Some conclusions concerning the mechanical processes during phase transformation can be derived from the resistance dependency on elongation velocity and elongation behaviour.

Experimental results and a differentiation of the resistance influenced processes during the elongation of a superelastic wire will be presented. In addition, some anomalies such as the dependency on velocity of the processes will be shown and discussed.
Furthermore the presented theories will serve as a basis of discussion

 

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Presentation: oral at E-MRS Fall Meeting 2005, Symposium C, by Heinrich Kern
See On-line Journal of E-MRS Fall Meeting 2005

Submitted: 2005-05-27 09:36
Revised:   2009-06-07 00:44