Tribological behaviour of nano-sized beta phase silicon nitride: effects of the contact conditions

Friction and wear behaviour of nano-sized silicon nitride in beta phase (β-Si ) under dry conditions were studied. Flat β-Si samples were prepared by means of the spark plasma sintering method. Sliding tests were performed using a reciprocating ball-on-flat tribometer against silicon carbide (SiC) ball and silicon nitride (Si ) ball under various normal loads. The frequency was set at 1 Hz and the sliding distance at 20 mm. The morphology of the worn surfaces was analysed by scanning electron microscopy. Experimental results showed that for normal load ranging from 11 to 57 N the friction coefficient increases from 0.15 to 0.36 for the β-Si /SiC tribo-pair and from 0.8 to 0.9 for β-Si /Si tribo-pair. Whereas, for both tribo-pairs, the specific wear rate decreases with the increase in normal load to reach an asymptotic minimum for high loads whose value is 0.15 × 10 mm N m for β-Si /SiC and 0.3 × 10 mm N m for β-Si /Si . The experimental results show also that depending on the tribo-pair and normal load, soft and hard wear mechanisms are activated.