DEVELOPMENT OF COMPOSITE COATINGS BY THERMAL SPRAYING FOR IMPROVED MECHANICAL AND TRIBOLOGICAL PERFORMANCE

Abstract

The influence of Ce02 modification of flame sprayed nickel-tungsten carbide coatings on to the steel substrate is studied. The as sprayed coatings were characterized by optical microscopy (OM), Scanning electron microscopy (SEM), X-ray diffraction (XRD), map scanning analysis, porosity measurements, surface roughness measurements and normal hardness measurement. All coatings obtained were subjected to abrasive wear against SiC paper, sliding wear against EN 32 steel disc, erosion against Si02 loaded slurry and alumina particles entrained in a gas jet respectively. It was found that the NiWC coatings containing CeO2 are featured with less porosity, lower surface roughness and higher hardness than the pure NiWC coatings. The coatings containing CeO2 have exhibited significant increase in their resistances to abrasion, sliding and erosion compared with those of pure NiWC coatings. However, excessive addition of CeO2 has a deleterious effect on the mechanical and tribological properties of the coatings due to the increased inclusion and porosity levels resulting in lower hardness values. The possible mechanisms related to the improved microstructures, abrasive, sliding and erosion resistances of the coatings containing CeO2 are also discussed.