A theoretical study of Ni segregation through NiTi (110)/TiO2-x interface

JUAN J.; BECHTHOLD P.; BRIZUELA, G.; JUAN A.; GONZÁLEZ E.; JASEN P.

Conferencia; EVC-15; 2018

The Nitinol (acronyms for NiTi Naval Ordnance Laboratory) is quasi equiatomic alloy of Ni-Tiknown for its properties of shape memory, superplasticity, strength and biocompatibility. It is themost widely used form memory alloy in the production of biomedical devices. However, thepresence of Ni in metallic or oxidized form on its surface or the release of it from the core of thealloy is a serious problem because of its allergenic properties and toxicity to human tissue. The mostusual procedure is the modification of the surface by a coating that resists corrosion and isbiocompatible. 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 DFTstudy of Ni segregation for different oxide coverage. Our results show that Ni diffusion is stronglydependent of the presence of Ti and o vacancies and the nature of an intermediary oxidation layer.We also analyzed the changes in the electronic structure and bonding at the interface.