Rolling Friction, Wear Characteristics and Damage Behaviors of Si₃N₄ Ceramic Bearing Balls

Compared with steel balls, Si₃N₄ ceramic bearing balls possess high revolution speed limit, high bearing capacity, resistance to high temperature and acid-base corrosion, together with certain self-lubricating properties, and are used as rolling bodies in high-speed bearings with absolute advantages and have became the key components of high-speed, high-precision bearings. In this paper, the rolling friction damage characteristics of Si₃N₄ ceramic bearing balls were studied by simulating the real motion of bearing balls in service conditions. The rolling friction wear state and surface damage behaviors of Si₃N₄ ceramic bearing balls against bearing steel raceways under non-lubrication and grease lubrication conditions were investigated, followed by analyzing the rolling friction damage behavior evolution laws and mechanisms of Si₃N₄ ceramic bearing balls. Results showed that the introduction of grease significantly reduced the rolling friction coefficient, particularly alleviated the fatigue damage behavior of Si₃N₄ ceramic bearing balls in rolling friction and wear processes. The rolling friction damage mechanisms of Si₃N₄ ceramic bearing balls were mainly fatigue damage, adhesive wear and accompanied by friction chemical reaction under non-lubrication condition. Mesh structural fatigue cracks in multi-scale were progressively formed during sliding and the cracks also extended to the inside of the Si₃N₄ ceramic bearing ball, resulting in the fatigue flaking among the cracks and cracking of grain boundaries. Meanwhile, amorphous structure appeared at the subsurface layer of the Si₃N₄ ceramic bearing ball under the action of friction. Under the grease lubrication condition, however, the rolling friction damage mechanisms of Si₃N₄ ceramic bearing balls were mainly abrasive wear and micro-brittle fracture. The damage behaviors evolved from scratches to willow-mounted micro-pits, which further increased and deepened, and brittle fracture was presented at the edges of the micro-pits. In this case, cracking of grain boundaries also existed at the subsurface layer of the Si₃N₄ ceramic bearing ball. Because grease alleviated the fatigue damage behavior, there were no amorphous structure and the cracks did not extend to the inside of the Si₃N₄ ceramic bearing ball.