Authors: G. Saha, A. Mateen, T. Khan
Affilation: University of Calgary, Canada
Pages: 592 - 595
Keywords: Cermet, near-nanocrystalline coating, WC-17Co, HVOF, tribology
Tungsten carbide based cermet composite coatings possess the unique surface protection properties enabling their increasing use in the oil sands industry to combat severe sliding and high stress abrasion wear and other types of slurry abrasion and erosion. Their successful application, mainly in the spray coating forms, has extended oil sands component and machinery service lives, improved reliability and reduced maintenance costs. Thermal spraying such as the use of high velocity oxy-fuel (HVOF) technique has increased the wear life of coatings based on WC-Co system when compared with high velocity air plasma (HVAP) technique. The ability to deposit HVOF coatings with a nanocrystalline structure provides an even higher wear resistance and fracture toughness over that achieved using conventional microcrystalline coatings of the same composition. In this research, conventional microcrystalline and engineered near-nanocrystalline WC grains were used to obtain two powder feedstocks of WC-17Co composition. Coatings were deposited by HVOF thermal spraying under identical process conditions. The chemical analysis of the powders by XRD and EDS showed that the novel near-nanocrystalline powder had an engineered particle formation with ‘duplex’ cobalt layer surrounding WC core, comparing a typical spray-dried microcrystalline WC-17Co particle. Characterization of the coatings by XRD and SEM suggest that in case of near-nanocrystalline WC-17Co coating an extensive decarburization of WC during the spraying of the powder may have been prevented due to the use of the duplex Co coated WC-17Co powder, a novelty in this research. Tribological properties of the coatings were tested by atomic force microscopy, Vickers microhardness, two-body pin-on-plate (ASTM G133-05) sliding and dry-sand rubber wheel (ASTM G65-04) abrasive wear tests, while the fracture toughness of the coatings were assessed using the indentation technique under the load of 10 kg. In all, the near-nanocrystalline WC-17Co coating had shown significantly better performance than the conventional microcrystalline WC-17Co coating.
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