Plasma Sprayed Self-Lubricating Cr2O3-CaF2 Coatings: Friction and Wear Properties

Abstract

Abstract An alternative production route to obtain thermally sprayed self-lubricating ceramic coatings is proposed and microstructural, friction and wear properties of these coatings are discussed. A preliminary powder treatment shows to induce a higher degree of homogeneity compared to conventionally deposited composite coatings, offering some perspectives for a further improvement of the lubricating and wear properties. This approach is illustrated using CaF2 as a solid lubricant dispersed in a Cr2O3 matrix, where the high melting point of the latter (Tm{Cr2O3} = 2460°C) necessitates plasma spraying as deposition technique. The microstructure of the coatings is evaluated by a metallographic study of sections perpendicular and parallel to the substrate surface. Wear and friction behaviour is evaluated using reciprocating wear test Wear tracks are analysed by means of laser profilometry. The results are discussed in relation to test and production parameters. Test temperature as well as solid lubricant concentration predominantly affects the wear and friction properties. Using a surface temperature of 400°C, a friction coefficient of 0.25 and a wear volume of 37 x 103 µm3 after 10,000 cycles are obtained for a coating containing 16 vol.% of CaF2.