Research On Properties Of HVOF Sprayed WC-Co Coatings

Thermal spraying WC-Co cermet coatings is widely used in aerospace, automotive, metallurgy, electric power, papermaking and other fields to improve the wear resistance of many types of engineering components or to repair worn parts, because of its high hardness, excellent wear resistance and good toughness. However, during thermal spraying of WC-Co powder, decarburization gives rise to the formation of W2C, even to metallic tungsten, which is undesirable for resistance to fracture toughness and wear resistance of the coarings. Feedstock powder characteristics, such as particle size, size distribution, morphology, initial phase cotent, apparent density and so on, which are usually determined by techniques for the synthesis of feedstock powders, have great influnce on the phase distribution and the wear performance of the coatings.In this paper, the coatings are sprayed by HVOF with three kinds of WC-Co powders produced by different manufacturers. Three kinds of powders are examind by SEM and XRD to evaluae the different characteristics. Three kinds of coatings are sprayed by different oxy-fuel ratio and sprying distance, and study the influence of spraying parameters on the coating. In these coatings prepared under different parameters, the paper selects the best coating to in-depth study. These coatings are analysed by SEM and XRD, their porosities, wear resistance, microhardness and bonding strength were compared. The results are as follows:1.Particle size of A powders is greater than B and C powders in the main distribution range, C powder particle size slightly larger than B powder particle size;2.The bonding of WC grains and Co of C powders is loose, high porosity and large pore space, the density lower than A and B powders;3. Different spraying parameters have no significant effect on the porosity of A and B coatings, increasing spraying distance and temperature can reduce the C coating porosity;4.Porosity of A coating is maximum, and mposition of C coating is maximun;5. C powder coating has the highest hardness, wear resistance and elastic modulus, but the fracture toughness decrease.