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J. Phys. IV France
Volume 07, Numéro C5, November 1997
IVth European Symposium on Martensitic Transformations
Page(s) C5-155 - C5-159
IVth European Symposium on Martensitic Transformations

J. Phys. IV France 07 (1997) C5-155-C5-159

DOI: 10.1051/jp4:1997524

Two-Stage Martensitic Transformation in NiTi Alloys Caused by Stress Fields

H. Morawiec, J. Ilczuk, D. Stróz, T. Goryczka and D. Chrobak

University of Silesia, Institute of Physics and Chemistry of Metals, Bankowa 12, 40-007 Katowice, Poland

It has been proved that the two-stage martensitic transformation in the NiTi alloys preceded by the R-phase transition my be induced by : low temperature annealing of the deformed alloy, thermal cycling and precipitation caused by ageing. The TEM observations of samples with two stage transformation have shown that the dislocations are distributed inhomogeneously and form a small-angle subgrain boundaries. The Granato-Lucke analysis of the internal friction peaks related to the two-stage transformation confirmed the difference in dislocation density released in both stages. Thus the two stage martensitic transformation is caused by the inhomogenity in the stress field which results from the dislocation configuration during the previous mentioned processes.

© EDP Sciences 1997