Rolling contact fatigue under water-infiltrated lubrication

This paper describes bearing life under water-infiltrated lubrication, which is often much shorter than the calculated bearing life. Bearings that failed in the field under water-infiltrated lubrication were analyzed to identify the mechanism. However, this was difficult due to insufficient information of the failure process. New fatigue life test methods were then developed to reproduce short life under water-infiltrated lubrication, to precisely observe the flaking process, and to study what material parameters affect the bearing life. It was found that failure under water-infiltrated lubrication initiates from nonmetallic inclusions on the rolling contact surface and propagates initially following grain boundary and then cutting through the grain, which eventually results in flaking. Higher cleanliness, which means less failure initiations, and nickel (Ni), which strengthens grain boundaries, improves bearing life under water-infiltrated lubrication. Hydrogen-induced failure is also experimentally studied to further understand water-induced failure. Hydrogen-induced failure is different from water-induced failure in the mechanism.