Effect of iron addition on the structure and tribological performance of CrAlN coatings

Hard coatings mitigate friction and wear of engineering components, while tribochemical interactions between lubricant and coating strongly influence performance. Masking ferrous surfaces with a coating reduces the effectiveness of additives optimized for steel. This study investigates iron as a triboactive element in CrAlN coatings, as iron and its oxides can catalyze lubricant hydrocarbon decomposition and promote low‐friction tribofilms. CrAlFeN coatings with up to x Fe = 7 at.‐% were deposited on steel substrates by magnetron sputtering. Their composition, surface morphology, and compound adhesion were characterized relative to an unmodified CrAlN reference. Tribological behavior was evaluated under boundary‐to‐mixed lubrication conditions in a polyalphaolefin oil with sulfur‐phosphorus additives using Si 3 N 4 counter bodies, ensuring that iron enters the contact exclusively via the coating. No detrimental changes in topography, morphology, or adhesion are observed upon iron addition. CrAlFeN coatings show reduced friction versus CrAlN, whereas all systems exhibit no measurable wear. Raman spectroscopy associates the friction reduction with the formation of a diamond‐like carbon resembling tribofilm, promoted by the catalytic effect of iron.