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

H. Morawiec; J. Ilczuk; D. Stróz; T. Goryczka; D. Chrobak

doi:doi:10.1051/jp4:1997524

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Numéro		J. Phys. IV France Volume 07, Numéro C5, November 1997 IV^th European Symposium on Martensitic Transformations


Page(s)		C5-155 - C5-159
DOI		https://doi.org/10.1051/jp4:1997524

IV^th 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

Abstract
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.