Wear property of silicon nitride in steel-on-Si₃N₄ and Si₃N₄-on-Si₃N₄ systems

A ball-on-three-disc modification of the four-ball wear tester was utilized to evaluate the wear property of Si₃N₄ lubricated with mineral oil, containing additives such as oleic acid, stearic acid and zinc dialkyldithiophosphate (ZDP). For comparison, the wear of a steel ball on Si₃N₄ discs and an Si₃N₄ ball on Si₃N₄ discs was investigated for identical test conditions, and the worn surfaces of the discs were analyzed using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The study indicates that the steel ball-on-Si₃N₄ disc system usually gives less wear of the Si₃N₄ disc compared with the Si₃N₄ ball-on-Si₃N₄ disc system. Among the three tested additives, ZDP shows best antiwear property even at a load of 396 N in the Si₃N₄ ball-on-Si₃N₄ disc system. XPS results reveal that a protective surface film containing the products of degraded ZDP was formed on the rubbed surfaces.