J. Phys. IV France
Volume 115, June 2004
Page(s) 287 - 295

J. Phys. IV France
115 (2004) 287
DOI: 10.1051/jp4:2004115034

Effect of strain on NiTi surface-optical reflectivity

A. Danilov1, T. Tuukkanen1, J. Tuukkanen2 and T. Jämsä1

1  Department of Medical Technology, 90014 Oulu, Finland
2  Department of Anatomy and Cell Biology, University of Oulu, PO Box 5000, 90014 Oulu, Finland

The mechanical interaction of living cells upon a NiTi surface was simulated with external loads. The surface structural response was studied. Optical reflectivity, which is a sensitive indicator of structural changes at the surface, was used. The behaviour of reflectivity under tension and compression within the range of strains up to 5% was analysed. The probability of reversible martensitic transformations (MT) in the surface oxide layer was demonstrated. The peculiarities of these MT in comparison with those in the bulk of the alloy were considered. Irreversible structural changes occurred in surface oxide under external stresses, despite complete strain recovery after unloading. A correlation emerged between the strains caused by external stresses and the residual augmentation of reflectivity. The probable mechanisms of irreversible structural changes initiated at the NiTi surface by external load action are discussed.

© EDP Sciences 2004