DFT study of Ni segregation on Nitinol/oxide system

JUAN J; BECHTHOLD, P.; BRIZUELA, GRACIELA; E. GONZÁLEZ; JASEN, P.V.

Bariloche

Simposio; XXIII Latin American Symposium on Solid State Physics; 2018

The Nitinol (acronyms for NiTi Naval Ordnance Laboratory) is quasi equiatomic alloy of Ni-Ti known forits properties of shape memory, superplasticity, strength and biocompatibility. It is the most widely used formmemory alloy in the production of biomedical devices. However, the presence of Ni in metallic or oxidized form onits surface or the release of it from the core of the alloy is a serious problem because of its allergenic propertiesand toxicity to human tissue. The most usual procedure is the modification of the surface by a coating that resistscorrosion and is biocompatible. The simplest of the procedures consists of a surface oxidation that manages togrow an oxide film on the NiTi, the Ti being oxidized preferentially. For this reason we performed a DFT studyof Ni segregation for different oxide coverage. Our results show that Ni diffusion is strongly dependent of thepresence of Ti and o vacancies and the nature of an intermediary oxidation layer. We also analyzed the changesin the electronic structure and bonding at the interface