Deposition, characterization, and performance of tribological coatings on spherical rolling elements

• Deposited and evaluated the tribological performance of CrxN, WC/a-C:H, TiC/a-C and Ti–MoS2 coatings onto balls.
• The coatings were tested under sliding and rolling contact tribometers in boundary layer lubrication.
• Ti–MoS2 coated balls provided a significant improvement over uncoated balls in rolling contact fatigue experiments.
• Ti–MoS2 coating appears to function as a lubricant additive source and creates a protective transfer film on the counterface

Increasing demands on the performance of intricate parts like bearings in biomedical and aerospace systems have created the necessity for tribological coatings that can enable systems to achieve enhanced performance in challenging environments. In this work, we have developed a process to deposit wear-resistant (CrxN, WC/a-C:H, TiC/a-C) and solid lubricant (Ti–MoS2) coatings onto spherical rolling elements. The tribological performance of coated specimens has been evaluated under boundary layer lubrication in rolling and sliding contact tribometers.Although all of the coatings are wear-resistant under sliding contact, only Ti–MoS2 coated balls provide a significant improvement over uncoated balls in rolling contact fatigue experiments. Specifically, in rolling contact fatigue experiments performed using M50 steel rods, Ti–MoS2 coated balls improved L50 life by more than two times over uncoated balls. Ti–MoS2 appears to be a promising candidate for rolling bearing applications in both lubricated and unlubricated conditions.