Progress report - ESR 7: Larissa Ihara

date: May 09, 2022

category: News

Green PVD surface engineering for tribology

The deposition of coatings with desired properties over the original surface of a component is one widely adopted solution of Green Surface Energy to mitigate resource consumption and pollutant emissions due to friction, wear and lubrication in a tribosystem. The objective of this project is to conduct an evaluation of the tribological performance and environmental impact of pure DLC coatings for steel gears, deposited by different techniques, viz., dcMS, HiPIMS, PECVD, and µW‑PECVD, in order to identify the critical factors of their ‘greenness’ and ultimately shift the paradigm for green coating design. The results to date analyse DLCs deposited by PECVD (“PCDLC”) and HiPIMS (“HiDLC”). The coatings were characterised in terms of: adhesion, thickness, vibrational energy mode, nanohardness and elastic modulus, and surface roughness. The tribological tests utilised a Mini-Traction Machine for friction measurement, with uncoated balls against coated discs in base oil under boundary lubrication regime, then the wear volume on the discs was measured by white light interferometry. Hardness was 20 and 44 GPa for PCDLC and HiDLC, respectively, which translated into a two-fold higher wear rate for the PCDLC. In turn, the coefficient of friction of PCDLC was 0.071, but 0.085 for HiDLC, which reflected the roughness Sq of 24 nm for PCDLC versus 42 nm for HiDLC, caused by formation of carbon droplets due to arcing during deposition. It is noteworthy that PCDLC consumed 39.7 kJ/nm due to heating and substrate bias, whilst HiDLC consumed 18.0 kJ/nm, mostly due to cathode power supply. The next steps will be to deposit the coatings via dcMS and µW‑PECVD, in addition to testing all coatings in fully formulated oil.