The Torrington Company, under contract from the Advanced Research Projects Agency (ARPA), has developed a hybrid bearing with improved properties for difficult applications. M50 and M50 NiL steel rings were nitrided to produce rolling contact raceway surfaces with hardnesses near Rockwell C 70. Rings were assembled with NBD-200 silicon nitride balls. Full-scale bearing tests were run under conditions that included 150°C temperature, surface flaws created by hard particle contamination, partial EHD lubrication, and the sliding action of balls running under thrust loading. The hybrid bearings had longer life than all steel bearings and demonstrated resistance to the surface peeling mode of failure initiation. Higher strength of the rolling contact surfaces, high residual compressive stresses in the nitrided layers, and a more favorable action in ceramic to steel rolling contact are discussed as the reasons for improved performance of the hybrid over all-steel bearings.

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