Magnetorheological finishing of SAE 52100 bearing races for improved tribological and fatigue properties

Rolling element bearings are critical components in aerospace, automotive, renewable energy, and precision manufacturing systems, where performance and reliability are strongly governed by the surface quality of raceways. Even minor irregularities such as grinding marks or waviness compromise elastohydrodynamic lubrication, increase friction, accelerate wear, and initiate rolling contact fatigue cracks. Conventional finishing methods like grinding, honing, lapping, and superfinishing improve surfaces to some extent but remain limited to sub-micrometer finishes and often introduce tensile residual stresses or embedded abrasives. In this study, hardened SAE 52100 steel bearing races were subjected to magnetorheological (MR) nano-finishing to evaluate its capability for producing ultra-smooth surfaces and enhancing functional performance. Experimental results demonstrated a dramatic reduction in surface roughness from ~0.20 µm Ra in ground races to below 0.015 µm, representing a > 92% improvement. MR finishing also increased microhardness by 6–8% and induced compressive strengthening the near-surface layer. Tribological tests confirmed a 35% reduction in friction coefficient and 40% lower wear scar volume compared to conventional finishes, while fatigue testing revealed a 33% improvement in rolling contact life. Vibration amplitudes decreased by 28% and noise by 7 dB, underscoring the benefits for NVH-sensitive applications. The findings establish MR nano-finishing as a transformative, repeatable, and environmentally compatible process for next-generation precision bearing races.