Study on the Influence of Microstructure on the Rolling Contact Fatigue Performance of Silicon Nitride Ceramics Balls

This study prepares three types of Si₃N₄ ceramic bearing balls with distinct microstructures by regulating the content of Al₂O₃-Y₂O₃ sintering aids, and systematically investigates the influence mechanisms of microstructure, grain boundary phase distribution and grain aspect ratio on the rolling contact fatigue (RCF) failure behavior. The experimental results show that a low content of sintering aids leads to insufficient liquid phase formation, hindered densification and porous defects inside the material, with spalling as the dominant RCF failure mode and the Weibull modulus being only 1.877. With the increase in sintering aid content, the liquid phase promotes densification and the growth of elongated β-Si₃N₄ grains; when the average grain aspect ratio reaches 4.47, the grain toughening mechanism significantly improves the RCF life, with the characteristic life attaining 1.035 × 10⁷ cycles. However, an excessive content of sintering aids induces the steric hindrance effect, which inhibits grain growth and increases the content of soft grain boundary phases, thus leading to the transition of the failure mode to wear and a subsequent decrease in service life. This study demonstrates that an appropriate liquid phase content is crucial for balancing the densification degree, grain morphology and RCF performance of Si₃N₄ ceramic bearing balls.