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Martensitic transformation and shape memory effect in NiTiCu strip covered by nanocrystalline platinum layer

Tomasz Goryczka 1,  Jozef Lelatko 1,  David Vokoun 2,  Patrick Ochin 3

1. University of Silesia, Institute of Materials Science, 12, Bankowa Str., Katowice 40-007, Poland
2. Czech Academy of Sciences, Institute of Physics, Na Slovance 2, Prague 182-21, Czech Republic
3. Institut de Chimie et des Materiaux Paris Est, 15 rue Georges Urbain, Vitry-sur-Seine 94407, France

Abstract

NiTi-based shape memory alloys (SMA) have been known from their practical application, especially, in medicine and biomedical engineering. However, risk of its influence on a human body is still reported. In order to prevent diffusion of nickel ions, various surface modification have been proposed. Coatings with nitrides, oxides or carbides seem to be an attractive way to create a barrier, which sufficiently reduces corrosion resistance. However, too thick and/or stiff layer can limit occurrence of the martensitic transformation. In consequence shape memory effect may be spoilt.

Proposed paper is focused on characterization of structure and thermal behaviour of the martensitic transformation in Ni25Ti50Cu25 shape memory strip covered by thin nanocrystalline platinum layer. The strip was produced applying twin roll casting technique and covered by platinum layer using magnetron sputtering. Structure of the layer was studied by means of X-ray and electron diffraction. Transformation temperatures were determined from measurements carried out using differential scanning calorymetry (DSC). The layer reveals nanocrystalline structure with average grain diameter of 43 nm. Almost 25% of total grains are oriented along <111> direction. It was stated that the nanocrystalline platinum layer does not limit martensitic transformation in the covered strip, which reveals one step reversible martensitic transformation from the parent B2 phase to the orthorhombic martensite B19.
 

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Presentation: Poster at E-MRS Fall Meeting 2007, Symposium E, by Tomasz Goryczka
See On-line Journal of E-MRS Fall Meeting 2007

Submitted: 2007-05-10 11:47
Revised:   2009-06-07 00:44