Fifth European Symposium on Martensitic Transformations and Shape Memory Alloys

J. Phys. IV France 11 (2001) Pr8-281-Pr8-286
DOI: 10.1051/jp4:2001848

The effect of time on the evolution of the martensite structure and strain caused by magnetic field in Ni₂MnGa shape memory alloys

N. Glavatska¹, V. Gavriljuk¹, I. Glavatsky¹, Y. Ge², O. Söderberg², A. Jääskelainen², K. Ullakko³ and V.K. Lindroos<sup>2

1</sup>  Institute for Meta1 Physics, Department of Alloyed Steels, 003680 Kiev 142, Ukraine
²  Helsinki University of Technology, Laboratory of Physical Metallurgy and Materials Science, P.O. Box 6200, 02015 Hut, Finland
³  Helsinki University of Technology, Laboratory of Biomedical Engineering, P.O. Box 2200, 02015 Hut, Finland

Abstract
Kinetics of the martensitic transformation, change in the preferential martensite variants, field-induced strain and magnetisation under applied magnetic field are studied in-situ. Two Ni₂MnGa alloys of the non-stoichiometric composition which reveal large strain (0,5-5%) under magnetic field were investigated using the X-ray diffraction θ-2θ analysis, optical metallography and measurements of the field-induced strain. It is shown that evolution of the martensitic structure under applied magnetic field occurs with time at constant values of the field and temperature. The kinetics of the direct and inverse processes is strongly determined by the relation between the crystallographic direction of easy magnetisation and that of the applied magnetic field. The results of the X-Ray diffraction study are consistent with the data of optical microscopy and measurements of the field-induced strain.

© EDP Sciences 2001