Triboactive CrAlN+MoWS coatings deposited by pulsed arc PVD

Abstract

Cathodic arc physical vapor deposition (arc PVD) is widely used due to its high deposition rate and degree of ionization. However, reducing droplet emission and surface roughness without compromising the deposition rate remains challenging. CrAlN+XS coatings (X = Mo, W) have shown potential for friction and wear reduction under dry-running conditions by forming solid lubricants MoS2 and WS2. Nevertheless, the evaporation of electrically low conductive materials like MoS2 or WS2 in arc PVD presents difficulties. This study investigates the use of pulsed arc PVD as a promising technology to address these challenges. CrAlN+XS coatings were developed using pulsed arc PVD, with a focus on analyzing their properties, including the incorporation of triboactive elements (S, Mo, W). Additionally, variations in coating architecture, substrate material, and process temperature were explored for CrAlN+MoS coatings. Subsequently, tribological investigations were conducted under dry-running conditions using a pin-on-disk tribometer. The results revealed that pulsed arc PVD effectively decreased droplet emission and thus surface roughness of the coatings. Moreover, the triboactive coatings exhibited significantly lower wear and friction compared to uncoated steel references. Raman spectroscopy was employed to examine the tribofilms on coated parts. This work represents the first-time deposition of CrAlN+XS coatings (X = Mo, W) using pulsed arc PVD. Notably, the CrAlN+MoS coating displayed the highest sulfur content of xS = 9 at.-%, as verified by electron probe microanalysis. The tribofilm analysis provided evidence that CrAlN+MoS coatings deposited by pulsed arc PVD can form solid lubricant MoS2 under tribological load, resulting in a reduced coefficient of friction. In conclusion, pulsed arc PVD shows promise for applications that require the evaporation of electrically low conductive target materials during coating deposition, while achieving a low surface roughness. The findings contribute valuable insights into the performance of CrAlN+XS coatings and their potential for enhancing tribological applications.