Tribological behavior of Si₃N₄ sliding against Dy-sialon ceramics under lubrication of phosphazene lubricants

Purpose - The purpose of this paper is to investigate the tribological properties of Si₃N₄ sliding against Dy-sialon ceramics lubricated by two novel phosphazenes bridged fluorophenoxycyclotriphosphazene (coded as L-2P) and metal halide-stabilized linear phosphazene derivatives (coded as LMZn-3). The traditional phosphazene tetrakis (3- trifluoromethylphenoxy)-bis(4-fluorophenoxy) - cyclotriphosphazene (X-1P) was also tested as the reference. Design/methodology/approach - The lubricity characteristics of phosphazene derivatives were evaluated on an Optimol SRV oscillating friction and wear tester. The morphology of the worn sialon surface was analyzed with a scanning electron microscope (SEM) and X-ray photoelectron spectroscope (XPS). Findings - The two novel phosphazenes are effective lubricants for Dy-sialon and show superior tribological properties to traditional phosphazene X-1P and glycerol. Among all lubricants, linear phosphazene LMZn-3 exhibits the lowest wear volume loss at 20 C or 100 C. Moreover, LMZn-3 and L-2P show much better antiwear ability than X-1P under higher load than 60N. The decreased friction coefficient and wear volume of Dy-sialon ceramics under lubrication of the phosphazene lubricants are attributed to the tribochemical products mainly consisting of organic oxyfluoride or carbonfluoride species and silicon fluoride. Research limitations/implications - The paper deals with only limited compounds. The paper works on the subject progressively to explore more combinations for better tribological properties. Practical implications - The phosphazene derivatives present better tribological performance used as base oils and additives. Originality/value - There are few data about other phosphazene with different structures, such as bridged cyclotriphosphazene and metal halide-stabilized linear phosphazene, used as lubricants for ceramics materials.