Tribochemical Behavior of Si3N4–hBN Ceramic Materials with Water Lubrication

Abstract

The main objective of this article is to study the tribological behavior of Si3N4–hBN composites with different hexagonal boron nitride (hBN) volume fraction under distilled water lubrication. Water-lubricated sliding tests were carried out on a pin-on-disc tester, and Si3N4 was used as friction pair. The results showed that the addition of hBN to Si3N4 resulted in a severe decrease of the friction coefficient, from 0.35 for Si3N4 against Si3N4 to 0.01 for Si3N4-20% hBN against Si3N4 with drip-feed water lubrication; the friction coefficients of Si3N4–hBN/Si3N4 pairs sliding with full immersion water lubrication were as low as 0.01. The morphological and chemical characterization of the worn surfaces were conducted using scanning electron microscopy (SEM), laser scanning microscope, X-ray photoelectron spectroscopy (XPS). The analysis indicated that, with drip-feed water lubrication, hBN in Si3N4–hBN was spalled off during the wearing tests and spalling pits were formed on the wearing surface of Si3N4–hBN composites, then the wear debris were dropped into the pits and reacted with water, and thus a tribochemical film was formed on the wearing surface. The tribochemical film facilitated the wear surfaces of Si3N4–hBN and Si3N4 to smooth with drip-feed water lubrication, while the tribochemical remove facilitated the wear surfaces to smooth with full-immersion water lubrication.