Wear Behavior of Silicon Nitride under the Lubrication of Micro-Sample Lubricant

The wear behavior of Si3N4 ball on three Si3N4 discs system was investigated withthe lubrication of microliter lubricant,and the results were compared with that of the conven-tional fully flooded lubrication of Si3N4 ball on three Si3N4 discs system. Micro-sample wear testof Si3N4 ball on three Si3N4 discs system was carried out with a 30 min run-in at 396 N underthe lubrication of mineral oil only,and followed by the second segment of the test which wasrun with the lubrication of two microliters of mineral oil,or mineral oil containing oleic acid,stearic acid as well as zine dialkyldithiophosphate(ZDDP)at a load of 396 N. Lubricant failurein this sequence is defined as a sharp increase in friction coefficient,and the wear life(failuretime)was correlated to the wear scar diameter in the conventional wear test.Lubricant aftermicro-sample wear test was determined by a gel permeation chromatography(GPC)analysis,and the result was compared with the GPC analysis of the unused lubricant.Conventional weartests indicate that mineral oil containing 2%(wt)ZDDP is very effective for lubrication ofSi3N4 ball on three Si3N4 discs system. Micro-sample wear result under the tested conditions ofSi3N4 ball on three Si3N4 discs system can be correlated to the wear results of Si3N4 ball on threeSi3N4 discs system in fully flooded lubrication under a load of 98 N. GPC analyses of the lubricant after micro-sample wear test reveal that some high molecular weight product which is so-luble in tetrahydrofuran(THF)was produced,this result differs from the formation of a de-posit which is insoluble in THF at steel-on-steel system. Micro-sample wear test is valuable inunderstanding the tribochemistry of lubricant under boundary lubrication conditions.