Effect of deposition method on the RCF performance of Cr x N thin film ball coatings

Abstract

Abstract Cr x N thin films are of interest due to their wear and corrosion-resistant attributes. However, the tribological and functional performance of these coatings greatly depends upon their material properties and deposition processes. In this study, the tribological and functional performance of Cr x N coatings on AISI 52100 spherical rolling elements were evaluated. Two types of deposition processes were used to apply the coatings: a closed-field unbalanced magnetron sputtering system (CFUMS) and an ion beam assisted e-beam deposition (IBAD) system. Whereas the mechanical and compositional properties of the coatings obtained from the two deposition processes were found to be similar, the topographical and microstructural properties of the coatings differed. The tribological performance of the coated specimens was evaluated under boundary layer lubrication in a rolling (three ball-on-rod) contact tribometer, and the functional performance of these coatings on spherical rolling elements was examined in thrust ball bearings. The L 5 0 fatigue life of M50 rods paired with IBAD-coated balls was four times greater than that obtained with the 52100 balls. Significantly, the L 5 0 fatigue life of the M50 rods paired with the IBAD-coated balls was comparable to the fatigue life of M50 rods when paired with high-quality ceramic (Si 3 N 4 ) balls. Finally, bearings with IBAD-coated balls were observed to operate with lower torque than those with CFUMS-coated balls.