The transition of wear mode during the running-in process of silicon nitride sliding in water

When silicon nitride slides against itself in water, an extremely low friction coefficient can be obtained by having a suitable running-in condition. This paper focuses of the dynamic running-in process of silicon nitride sliding in water under the conditions of load at 1-3 N, sliding velocity at 30-120 mm s(-1) and temperature at 20-80 degrees C with a pin-on-disc apparatus. The results show that the following. (1) Wear mechanisms change from mechanically dominated wear to tribochemically dominated wear as the sliding distance increases during the running-in process. This is mainly because of the reduction of contact pressure and smoothing of the friction surface. (2) Wear particles change from transgranular fracture-induced wear particles, intergranular fracture-induced wear particles and film delamination-induced wear particles, to net-like agglomerates of wear particles as sliding distance increases during the running-in process. (3) Net-like agglomerates of wear particles came mainly from powdering, oxidation and hydration of large transgranular and intergranular-induced wear particles. (4) Water lubrication of silicon nitride with a pin-on-disc configuration is partially hydrodynamic lubrication due to the ultra-smooth surface and partially boundary lubrication due to the colloidal silica layer. (C) 1997 Elsevier Science S.A.