Effect of rough surface patterning on the tribology of W–S–C–Cr self-lubricant coatings

• W–S–C–Cr coating exhibited low friction on very rough patterned surfaces.
• The coverage of the surface by patterns influences coating ability to retain low friction.
• Grooves acted as solid-lubricant reservoirs.

In this work, self-lubricant W–S–C films were alloyed with Cr by co-sputtering chromium and composite WS2–C targets. Besides the usual physical, chemical and mechanical characterization, including the evaluation of the chemical composition, the structure, the morphology, the hardness and the cohesion/adhesion, special attention was paid to the friction and wear analyses of the film deposited on intentionally roughened surfaces. The substrates were steel polished disks with different types of patterns produced by micromachining. To analyze the sliding process, in-situ techniques were applied, such as optical microscopy and Raman spectroscopy monitoring of the wear track. The surfaces in the contact were then analyzed by scanning electron microscopy (SEM) and 3D profilometry.The results showed that W–S–C–Cr coating exhibited remarkable ability to reduce the detrimental effect of deep grooves with irregular shape. For specific patterns on the substrate the friction and wear was even slightly lower compared to a polished sample. The grooves were filled with self-lubricant material and acted as reservoirs supporting formation of a low-friction tribolayer.