The effect of diamond-like carbon coatings on the rolling fatigue and wear of M50 steel

The rolling contact fatigue and wear characteristics of uncoated and diamond-like carbon coated VIM-VAR M50 bearing steel were investigated at room temperature and 177°C (350°F) and a Hertzian stress level of 4.8 GPa (700 ksi). The coatings were deposited via ion beam enhanced deposition and were approximately 33 nm thick. Rolling fatigue and wear tests were conducted using a ball-on-rod type tester. Results did not indicate any significant difference in the fatigue life of coated and uncoated specimens at room temperature, at 90% confidence level. However, the coating significantly improved the fatigue life (90% confidence level) at 177°C and wear resistance at both temperatures. Some correlation was noted between wear and fatigue life for the uncoated specimens at both temperatures, but none for the diamond-like carbon coated (the fatigue life was independent of wear) specimens. Scanning electron microscopy did not show any sign of coating delamination.