Coating Properties of Nanostructured WC-Co for Process Variables of HVOF

摘要

High velocity oxy-fuel thermally sprayed coating of the WC-Co cermet material is a well-established process for modifying the surface properties of the structural components exposed to the corrosive and wear attacks. The hard WC phase in the coating resists to the wear while the soft metallic Co increases the adhesive and cohesive bonding properties. The coating properties deposited by the HVOF process are greatly dependent on the feedstock materials and processing parameters. The effects of the feedstock material and process parameters including the in-flight particle parameters and resultant coating microstructures were observed in this study. Both the NW10Co powder containing nano-sized WC particle and the micro-sized WC embedded MW12Co powder were thermally sprayed by the table of orthogonal array of the processing parameters. The in-flight particle parameters such as the particle temperature and velocity were directly measured along the hot gas downstream using the DPV-2000 system. In-flight particle parameters were affected by the properties of the feedstock materials. Especially, the particle temperature of the NW10Co was higher than that of the MW12Co from the barrel exit point to the deposition point, irrespective of the condition of the processing parameters. Porosity in the as-sprayed HVOF coating was measured using an image analyzer. And the Vickers microhardness was measured under applied load of 300 g for 15 seconds. Phase compositions of the as-sprayed HVOF WC-Co coatings were measured and analyzed using the X-ray diffraction. The effects of the feedstock materials and process parameters on the coating properties of the as-sprayed HVOF coatings were discussed in terms of the in-flight particle properties during processing.