Development, Production and Tribological Characterization of Ceramic Coated Bearings for Media Lubricated Pumps

Pumps in which the sliding bearings and mechanical seals are lubricated only by the pumped media are widely used in chemical and plant engineering. Currently, bearing components of these pumps are mainly made of or coated with cobalt-containing tungsten carbide. However, tungsten and cobalt suffer from tribo-corrosive attack when operated in aqueous media. Hence, alternative solutions are being sought to replace tungsten carbide with other ceramic materials or coatings which simultaneously optimize the tribological behavior of bearing components. In this work, mixed ceramic coatings were applied using high-velocity suspension flame spraying (HVSFS). Three material systems have been tested and evaluated: (1) TiO2/TiC; (2) Al2O3/ZrO2 and (3) Cr3C2/Cr2O3. A precision grinding process is also developed and matched on the coating to achieve the required tight dimensional and form tolerances. Tribological component testing of coated shaft sleeves have been performed and compared to state of the art HVOF sprayed WC-Co coatings in aqueous media. A SiC bushing segment (SSiC material) was used as a counterpart in the tribo-system. Results show that performance of the ceramic coatings is at least as good as the reference system. Therefor ceramic coatings may represent a technically implementable possibility to replace tungsten carbide cobalt-based systems.