Frottement à haute température de revêtements d’oxyde de chrome avec ou sans lubrifiant solide

Friction at high temperature of chromiun oxide with or without solid lubricant

¹ I.S.M.C.M., St Ouen
² Renault, Rueil

Abstract

Sliding friction of chromium oxide (Cr₂O₃) against chromium oxide + solid Lubricants (CaF₂ and BaF₂) has been studied at 425° C under different contact pressures. Cr₂O₃ sliding against itself has always presented the following features : irregularities of the friction curve (slip-stick) ; important variations of the coefficients with contact pressure ; visible damage of the sliding surface. Adding a solid lubricant to Cr₂O₃ coatings has improved their tribological properties : more regular friction curves ; lower and stable friction coefficients ; prevention of the surface damage ; reduction of the wear rates by 40 to 100 times and higher critical contact pressure. Microscopic observation and analysis show that the improvement of tribological properties results from the presence of a solid lubricant film. Consequently, strong adhesion (in some contact areas) between Cr₂O₃ / Cr₂O₃ is prevented. The introduction of a solid lubricant decreases surface energy and improves the shearing behaviour of the ceramic coating.