Effects of ultrasonic nanocrystal surface modification on the wear and micropitting behavior of bearing steel in boundary lubricated steel-steel contacts

An ultrasonic nanocrystal surface modification (UNSM) technique has been used to treat AISI 52100 steel specimens and thrust ball bearing raceways. Tribological performances of untreated specimens were compared to UNSM-treated specimens in reciprocating sliding and rolling/sliding contact under boundary lubricated conditions. Friction and wear coefficients, micropitting, and changes in surface profiles and surface roughness of the specimens were studied. Results showed that UNSM treated specimens had higher wear and micropitting resistance than the untreated specimens. The improvements in wear and micropitting resistance may be attributed to increased surface hardness, refined grain sizes and compressive residual stress near surface region as a result of UNSM treatment. The UNSM technique has been proven to be a powerful tool to improve the durability and tribological performance of contacting surfaces of mechanical components such as bearings, gears, and seals.