Fretting of titanium nitride and diamond-like carbon coatings at high frequencies and low amplitude

Abstract

Physically vapour-deposited TiN and chemically vapour-deposited diamond-like carbon (DLC) coatings were tested against corundum under conditions of fretting at frequencies of 750 and 1500 Hz and at a displacement amplitude of 1 μm. A ballon-flat configuration without external lubrication was used. The energy dissipated in the contact was calculated from the evaluation of experimental tangential force-displacement hysteresis loops. Fretting damage and material modifications in the contact zone were evaluated with light optical microscopy, scanning electron microscopy, laser profilometry and micro-Raman spectroscopy. Information from on-line mechanical analysis and from off-line material behaviour analysis is used to present an explanation of the damage processes. The degradation of the TiN coating is dominated by the development of an oxidation reaction. Under certain conditions the amorphous structure of the DLC will undergo partial graphitization. A comparison with fretting tests at lower testing frequency and higher displacement amplitude shows that the mechanisms of degradation are very different.