Restoration of rolling-contact-fatigued surfaces via nanoskin technology.

Rolling contact fatigue (RCF) is known as the dominant factor determining the service life of bearing materials. In this work, the fatigue life of the typical bearing alloy was significantly improved by introducing a nanoskin layer on the surfaces of the test specimens. The nanoskin layer structure was obtained by means of the ultrasonic nanocrystal surface modification (UNSM) technology. The microstructure of the nanoskin was analyzed via scanning electron microscope (SEM), electron back-scatter diffraction (EBSD), and transmission electron microscope (TEM). SUJ2 and SUJ3 bearings at different states of fatigue were subjected to UNSM treatment. For SUJ2 a rotary-bending fatigue (RBF) life average for three untreated specimens was chosen as 100% life, and then several untreated specimens were fatigued to 25%, 50% and 75% of life with subsequent UNSM treatment. This way used bearing conditions were simulated. The rotary-bending fatigue (RBF) tests of fatigue+UNSM SUJ2 specimens have shown 377-430% improvement of fatigue life, comparing to untreated specimens. For SUJ3 a RCF life untreated specimen was chosen as 100% life, and then several specimens were fatigued to approximately 100% of surface damage with subsequent UNSM treatment. Thus damaged surface conditions were simulated. The RCF tests of fatigue+UNSM SUJ3 specimens have shown 218% improvement of fatigue life, comparing to untreated specimens. This indicates the possibility of the restoration of the RCF life of bearing alloys by means of nanoskin treatment via UNSM technology.