Tribologie des céramiques et analyse de surface

Ecole Centrale de Lyon, Laboratoire de Technologie des Surfaces, Ecully.

Abstract

Selected ceramic tribomaterial combinations (SiC/SiC, Si₃N₄/Si₃N₄, h-BN/h-BN) were tested in an AES/XPS analytical tribotester, under ultra-high vacuum, and under partial pressures of gases (O₂, N₂, H₂O, C₃H₈, air), respectively. The main purpose of this work is to clarify the correlations existing between the composition/microstructure of friction-induced interface films and the reduction of friction and wear of ceramics caused by ambient gases. In addition to conventional AES, XPS and SIMS analyses, electron microscopy (both TEM and STEM), Electron Energy Loss Spectroscopy (EELS), and Extended Electron Fine Structures (EXELFS) were used to characterize the tribochemical reactions on the ceramic suifaces. Under UHV ceramic surfaces exhibit high friction (f_k > 0.6) that is associated with friction-induced disorder in the interface material. Adsorbed gases did not “lubricate” these interfaces. Reactive gases (O₂) formed films in the contact region that provide lubrication and lower friction. Such lubrication was observed with selected, carbon containing systems and was associated with the formation of sp²-hybridized carbon in the interface films. The wide range of physical and chemical phenomena observed for sliding ceramic contacts and the implications for their use in severe environments will be discussed.