Lubrication-microstructure coupled failure mechanism of optimised-carburised BG801 bearing steel under high-temperature rolling contact fatigue

Aero-engine bearings operate under high-temperature, high-speed and heavy-load service conditions and therefore require excellent rolling contact fatigue (RCF) resistance. In this study, the performance of BG801 bearing steel with an optimised-carburised microstructure, wherein coarse original M₇C₃ carbides were replaced by finely dispersed M₂₃C₆ carbides, was investigated under high-temperature RCF at 150 °C. The damage evolution and failure mechanisms were systematically studied via high-temperature RCF tests combined with multi-scale microstructural characterisation and lubrication analysis. Results showed that the synergistic effect of the optimised surface microstructure and tribofilm formation considerably enhanced the initial high-temperature RCF resistance, yielding an L₁₀ life of 0.933 × 10⁸ cycles. However, during prolonged high-temperature operation, lubrication deterioration promoted the expansion of boundary-lubrication zones and progressive surface damage, while cyclic stress induced excessive refinement and partial amorphisation of surface martensite and M₂₃C₆ carbides, causing mechanical degradation. At high temperatures, microcracks preferentially initiated at the M₂₃C₆–martensite interface and propagated, leading to surface-originated fatigue failure. This work elucidates the lubrication-microstructure coupled failure mechanism governing the high-temperature RCF behaviour of optimised-carburised BG801 bearing steel, revealing a critical transition from room-temperature subsurface-dominated failure to high-temperature surface-originated failure. The findings provide theoretical insights and engineering guidance for the microstructural design of next-generation high-temperature bearing steels.