Effect of load on tribological properties of silicon nitride/steel under rolling-sliding contact condition

The tribological behaviors of Si3N4/GCr15 tribo-pair under dry rolling-sliding friction condition at different loads were investigated by using a modified rolling-sliding contact device. The pure sliding friction under the same condition was executed as a comparison test. The results showed the friction coefficient and the wear rate at rolling-sliding contact condition were below that at pure sliding contact condition. For the rolling-sliding contact condition, when the loads were 10 N and 20 N, the wear mechanisms of Si3N4/GCr15 tribo-pair were adhesive wear and abrasive wear. Hence, the friction coefficients were higher (0.58 and 0.4 respectively). With the load continuously increased from 30 N to 100 N, the dominant wear mechanisms were the combination of adhesive wear, delamination wear and contact fatigue, and the friction coefficient decreased with an increase in the load. In addition, it also can be seen that the rotational number of the ball showed an increasing trend with the increase of the load with the aid of high-speed camera. At the loads of 30 N and 50 N, a discontinuous tribofilm was formed on the worn surface and the friction coefficients were 032 and 0.23 respectively. At the loads of 70 N and 100 N, the friction coefficients were as low as 0.14 and 0.08, the wear rates of both ball and disk were the order of magnitude of 10−7 mm3N−1m−1, and the worn surfaces were quite smooth with a handful of spalling zone, which can be attributed to the tribo-chemical reaction products. For the pure sliding contact condition, the wear mechanisms of Si3N4/GCr15 tribo-pair were mainly dominated by mechanical wear at the loads of 10 N, 20 N and 30 N, and when the load was 50 N the dominating wear mechanism was tribo-oxidation reaction.