CHARACTERISTICS OF HVOF WC-Co COATING USED FOR ROCKET NOZZLE APPLICATION
V. G. Varanasi, T. M. Besmann, W. Xu
MATERIALS FORUM
abstract:The high velocity oxy-fuel (HVOF) sprayed tungsten carbide cobalt (WC-Co) coating have shown some attractive behaviors, which makes them applicable for high temperature application, such as for temperature insulator for rocket nozzle. This work studies the effect of surface preparation, in this case the grit blasting process, on the characteristics of the coating. The microstructure of the coating was examined by using optical microscope and scanning electron microscope (SEM) equipped with energy dispersive x-ray spectroscopy (EDXS). The results show that the higher the grit blasting pressure, the rougher the surface of the substrate. The surface roughness and topography affects the bonding strength of the coating, although quantitative results were not obtained in this study. The WC-Co coatings showed high hardness and low porosity. The composition of WC-Co coating varied in different region, but in average was close to the composition of the starting powder, meaning that there was no material loss during spraying. Microanalysis also indicates diffusion of tungsten to the interface between the coating and the substrate that may explain the high bonding strength possessed by the coating. The mentioned characteristics may partly suggest that the HVOF sprayed WC-Co is appropriate to be coated to rocket nozzle. More tests on erosion resistance are suggested.
keywords:optical microscope; bonding strength; ROCKET NOZZLE; surface preparation; EDXS; grit blasting pressure
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