Effect of types of ceramic materials in aggregated powder on the adhesive strength of high velocity oxy-fuel sprayed cermet coatings

The effects of the types and compositions of the binder phase in WC cermet powders, types of solid materials in solid-liquid two-phase particle, and high velocity oxy-fuel spray conditions on the adhesive strength of high velocity oxy fuel (HVOF) sprayed composite coatings were studied using three aggregated WC cermet powders, Cr3C2-25NiCr, Al2O3-Ni powders, and W-Ni powder. The examination of the coating microstructure using optical and scanning electron microscopy revealed that all the coatings were deposited through solid-liquid two-phase particles with ceramic particles or W in the powder being in a solid state while the binder in a melted liquid state. It was found that an adhesive strength higher than the strength of the test adhesives of approximately 65 MPa can be reached for all HVOF coatings deposited by WC cermet powders and W-Ni powder. The adhesive strength of HVOF WC cermet coatings was not significantly influenced by the composition of the binder, the powder structure, or the spray parameters. However, for Cr3C2-25NiCr coating the adhesive strength ranged from 35 MPa to over 92 MPa and was significantly influenced by the spray parameters. Finally, Al2O3-Ni coating had a very limited adhesive strength. The results suggested that the formation of a solid-liquid two-phase particle in the HVOF process is a necessary condition to deposit HVOF coatings of high adhesive strength, while the high density of WC and W particles in the powders is a necessary condition to achieve high adhesive strength for HVOF WC cermet and W-Ni coatings. The adhesive strength of HVOF cermet coatings will be increased with an increase in the density of the solid material component in the two-phase particle. (C) 2001 Elsevier Science B.V. All rights reserved.