Ni segregation through NiTi B2/TiO 2-x interface. A DFT study.

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

Santa Fe

Conferencia; VI San Luis Conference; 2018

The Nitinol (acronyms for NiTi Naval Ordnance Laboratory) is a quasi equiatomic alloy of Ni-Ti known for its propertiesof shape memory, superplasticity, strength and biological compatibility. It is the most widely used memory form alloy inthe production of biomedical devices. However, the presence of Ni in its metallic or oxidized form is toxic to the humantissue because of its allergenic properties. The most usual procedure is the modification of the surface by a coating thatresists corrosion and is biocompatible. The simplest of the procedures consists of a surface oxidation that manages to growan oxide film on the NiTi, the Ti being oxidized preferentially. For this reason, we performed a DFT study of Ni segregationfor different oxide coverages. We built interfaces from NiTi B2 (100) and (110) matched with TiO 2 (100) and (110) planes.Our results show that Ni diffusion is strongly dependent of the presence of Ti and O vacancies and the nature of anintermediary oxide layer. We also analyzed the changes in the electronic structure and bonding at the interface.