Non-diamond finishing of silicon nitride for low friction against steel

A reduced friction coefficient in a silicon nitride-against-steel hybrid bearing combination in a tappet shim-cam lobe couple can lead to a fuel economy benefit, as previously reported (CESP 20[4] 25-32, 1999). Here, we describe the process that is used to achieve the non-diamond ceramic finish associated with the low lubricated friction. Low cost follows from the use of aluminum oxide wheels to provide a special surface finish on silicon nitride based ceramics (U.S. Patent No. 6,050,881). Low friction follows from the smooth, phosphorus-containing deposited surface layer that is derived from conventional oil additives. The alumina-enriched silicon nitride surface is similar to that of iron oxides on steel for which the phosphorus-containing additives are designed to interact.