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 h igh velocity oxy-fuel spray conditions on the adhesive strength of high vel ocity oxy fuel (HVOF) sprayed composite coatings were studied using three a ggregated WC cermet powders, Cr3C2-25NiCr, Al2O3-Ni powders, and W-Ni powde r. 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 fo und that an adhesive strength higher than the strength of the test adhesive s 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 sig nificantly influenced by the spray parameters. Finally, Al2O3-Ni coating ha d a very limited adhesive strength. The results suggested that the formatio n of a solid-liquid two-phase particle in the HVOF process is a necessary c ondition 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 a chieve high adhesive strength for HVOF WC cermet and W-Ni coatings. The adh esive strength of HVOF cermet coatings will be increased with an increase i n the density of the solid material component in the two-phase particle. (C ) 2001 Elsevier Science B.V. All rights reserved.