Effect of interface roughness on the tribo-corrosion behavior of diamond like carbon coatings on titanium alloy

Abstract

Substrate surface morphology can significantly affect the functional performance and durability of the subsequently deposited coatings. In the present work, diamondlike carbon films were prepared by radio frequency plasma enhanced chemical vapor deposition on Ti-6Al-4V alloy substrates with different premediated surface roughness parameters (average roughness Ra, Skewness Rsk and Kurtosis Rku), and their mechanical, electrochemical, and tribo-corrosion properties were studied. The surface parameters, the microstructure, and the chemical composition were assessed by optical profilometry, scanning electron microscopy, Raman spectroscopy, and energy dispersive spectroscopy. The mechanical properties were evaluated using depth-sensing indentation and scratch testing, and the films' tribo-corrosion behavior was determined using a reciprocating tribometer in a ball-on-flat configuration with the tribological contact (Al2O3 counterpart) immersed in a 3.5% NaCl sea waterlike solution. The evolution of the corrosion potential as a function of time before, during, and after the wear tests indicated that the tribo-corrosion behavior is strongly affected by the surface roughness parameters. The potential of samples with Ra = 20 nm was unaffected by the rubbing process under the chosen tribological conditions compared to samples with higher Ra values. A similar trend was observed for samples with negative Rsk as opposed to those with Rku values greater than 3. The poor tribo-corrosion behavior of samples with Ra > 20 nm and high Rku (greater than 3) is mainly due to the significant height of asperities that constitute initiation sites for stress and strain failure on the surface. The predominant degradation mechanism was abrasive wear for samples with high surface roughness, tested under dry wear conditions. In the tribo-corrosion process, a synergy between the abrasive wear and corrosion was found to contribute to the overall material loss.