Constituting and Investigation of Ion-Implanted Protective Layer on NiTi Alloy for Mechanical and Tribological Applications

Abstract

NiTi exhibits an excellent wear resistance, which can be further enhanced by ion implantation. However, there are some limitations to the implantation effects: only a thin layer of about 100 nm can be created. In this paper, the effect of nitrogen ion implantation on the NiTi wear response is investigated. The different loads and durations of tests are taken into account to show that the implanted layer has the most beneficial effect only in a certain range of contact pressure. It was found that the wear volume changes in a non-linear manner with respect to the load and sliding length, for both non- and implanted samples. For the latter, two distinct stages can be distinguished in the wear process: an initial stage characterized by a low wear-rate and a low coefficient of friction, and a second stage in which the wear-rate drastically increases. The duration of the first stage is longer for lower loads. This specific behavior is explained by differences in the hardness distribution, energy dissipation due to the normal load, and differences in the microstructure of the wear tracks. Our results show that the lifetime of NiTi can be improved by ion implantation, thus boding well for applications in harsh environments.