Open Access
Article Number 02030
Number of page(s) 7
Section Principles, Simulations, Materials: Background
Published online 01 September 2009
ESOMAT 2009, 02030 (2009)
DOI: 10.1051/esomat/200902030

In-situ TEM cooling/heating experiments on deformed NiTi shape memory single crystals

T. Simon1, A. Kröger1, Ch. Somsen1, A. Dlouhy2 and G. Eggeler1

1  Ruhr-University Bochum, Institute for Materials, 44780 Bochum, Germany
2  Institue of Physics of Materials, ASCR, Ziskova 22, 61662 Brno, Czech Republic

Published online: 1 September 2009

In the present study we report about the influence of dislocations on martensitic transformations in NiTi single crystals. Microstructural investigations are performed on Ni50.4Ti49.6 (at.%) single crystals using in-situ cooling and heating transmission electron microscopy (TEM). Solution heat-treated Ni50.4Ti49.6 single crystals were oriented by electron backscatter diffraction (EBSD) and compressed in [111] B2-direction to different strain levels. DSC measurements on undeformed and deformed material states reveal a two step transformation from B2 to R-phase and then from R-phase to B19´ confirmed by TEM. The analysis of the dislocation structure of a 3.3% compressed single crystal shows that mainly screw dislocations with [001] type burgers vectors are present. During cooling, the martensitic R-phase grows homogeneously. On further cooling in some regions a burst like growth of B19'-neddles can be observed in addition to B19'-regions that nucleate and grow promoted by the stress-fields of dislocations. Dislocation analysis after back transformation suggests that dislocations form as a result of the martensitic transformation.

© Owned by the authors, published by EDP Sciences 2009