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Technical Paper

The Performance of 52100, M-50, and M-50 NiL Steels in Radial Bearings

The performance and microstructural behavior of several bearing steels tested in radial ball bearings were interpreted in terms of their microstructural alterations, residual stress and resistance to tempering. The bearings were fabricated out of 52100, M-50, and M-50 NiL steels and tested under identical conditions: a radial load of 1111 kg to produce a 3.62 GPa maximum Hertzian contact stress and a speed of 3 000 rpm to produce a calculated lambda ratio of 5.5. The plastically deformed region below the ball track surface of bearings which had run for extended periods was examined metallurgically and measurements were made of the hardness and circumferential residual stress. The 52100 steel bearings exhibited a white-etched microstructure in the softened worked region. The M-50 developed much less plastic flow without work softening, and the M-50 NiL exhibited the least microstructural alteration.
Technical Paper

Tribological Evaluation of Silicon Nitride Against Retainer Materials

Sliding wear tests were conducted with silicon nitride (Si3N4) against five retainer materials using different lubricants. The sliding wear tests were conducted with the Torrington Tribology tester at three normal loads and one sliding speed at an ambient lubricant oil temperature and one hour duration. The retainer materials were polyetheretherketone (PEEK) with glass fill, PEEK with carbon graphite/PTFE (polytetrafluoroethylene) fill, machined aluminum with a WS2 coating, machined steel with a silver plating, and machined bronze. The Si3N4 ceramic specimens (both NBD-100 and NBD-200) did not experience any measurable or observable wear. Friction coefficients varied between 0.03 and 0.16 depending upon the retainer material and the lubricant; the lowest values were obtained with the PEEK materials. Large wear scars were generated on the machined bronze, along with high friction coefficients and slip-stick behavior.