Nanostructured Cermet Coatings with Enhanced Properties Produced by HVOF Thermal Spray

Abstract

There is an increasing interest in the last years for materials with nanometric grain size because of the enhanced properties that could be achieved when reducing to the nanometric scale. Three coatings using conventional, nanostructured and bimodal (mixture of conventional and nano) WC-Co powders were obtained through High Velocity Oxygen-Fuel (HVOF) technique. The powders were sprayed under different spraying conditions in order to improve trybological properties for nanostructured powders. The relationship between spraying conditions and decomposition has been studied using in-flight measurements and XRD techniques. The nanostructured coating showed more decomposition than the other ones during spraying process, but this decomposition was reduced through the new conditions. Nanostructured coating showed more hardness using producer conditions, but the bimodal coating showed better abrasive and friction wear resistance. Nanostructured and bimodal coatings also provided an enhanced corrosion protection to the substrate when compared with the conventional one. An important improvement in the abrasive wear resistance for the nanostructured coating was obtained with the new conditions, due to the reduction in the decomposition.