Tribochemistry of a Ti Alloy Under Fretting in Air: Evidence of Titanium Nitride Formation

Abstract

The present investigation focuses on the tribological transformation occurring on a Ti alloy (Ti17) under fretting in air. Several fretting wear tests were performed on a large scale punch on plane configuration (two types of planes tested: bare Ti6242 and CuNiIn-coated Ti6242) at several temperatures from ambient up to 450°C. In all the cases, two zones were identified on the scars: a lateral oxidized rim and a highly deformed region at centre. Metallurgical observations revealed similarities with Tribologically Transformed Structure (TTS), previously observed on various Ti alloys. In the framework of this article, careful analyses were conducted (EDX, DRX, XPS, HRTEM and EFTEM) in order to identify the nature and chemistry of this transformed layer. Results demonstrated the formation of a new phase, nanocrystalline, identified as TiO x N y . The high content of nitrogen found in the TTS indicated its ability to penetrate inside the contact and react with titanium. At 50 lm under the surface, a FIB preparation enabled the observation in TEM of N-rich lamellae (TiO x N y ) in the Ti (a) matrix. Two models were suggested to explain this tribochemical reaction under fretting.

Modelling adhesive wear extension in fretting interfaces: An advection-dispersion-reaction contact oxygenation approach

“…This conclusion is quite interesting as it suggests that in the inner part of the contact, an additional N 2 partial pressure is observed which can explain and potentially quantify the exotic nitriding process observed at room temperature in the inner part of titanium fretting interfaces (Fig. 24b) [9,10,35]. Nitriding of the inner TTS, after [10] inside the scar On the other hand, by depriving oxygen and in turn increasing the concentration of nitrogen gas, such air distilling process presently modelled using ADR approach can explain the nitriding process observed in many closed fretting interfaces.…”

“…although some nitriding processes could be observed [9,35] as detailed in the following discussion (Section 6).…”

The formation of a cobalt-based glaze layer at high temperature: A layered structure

“…Oxygen O 1s and O 2s peaks are also detected in all the spectra, as well as a small quantity of nitrogen N 1s, around 2% of the global semi-quantification. Even if some authors [25,26] have emphasized the role of nitrogen in the formation of some tribological transformed structures on titanium alloy, here it is not the relevant element regarding the glaze layer formation, which is mainly controlled by an oxidation process. In addition, it is interesting to notice that there is no peak of aluminum showing that there is no transfer from the alumina counterface.…”

Influence of cryogenic lubrication on the tribological properties of Ti6Al4V and Inconel 718 alloys under extreme contact conditions

“…Even if this treatment usually requires high temperatures, 600-1000°C, and a long time, one can wonder if an interaction could arise on a microscopic scale where such temperatures can be locally reached. For example, when investigating fretting of a titanium alloy from 20 to 400°C in air, Mary et al 22 observed the formation of a tribologically transformed structure exhibiting a specially high nitrogen content. They highlighted that nitrogen was able to penetrate the contact and form a nanocrystalline titanium nitride phase even at low temperatures due to the energy dissipated by friction.…”