Investigating the Ability of Coating the SiC by APS and HVOF Processes through the Nickel-Phosphorus Cladding on the Primary Powder

In this research, silicon carbide (SiC) powder with a particle size of 30 to 45 micrometers and an irregular morphology was used for coating in an electroless nickel bath. The effect of particle surface roughening parameters in an acidic solution and electroless process time on uniformity and thickness of Ni-P coating on the SiC particles was investigated. SiC(Ni)-70vol.%Co blended powder was coated on simple carbon steel substrates by high-velocity oxy-fuel (HVOF) and atmospheric plasma spraying (APS) processes. The composite powder was obtained from the mechanical blending of cobalt powder with coated silicon carbide SiC(Ni) powder. The microstructure and morphology of powder particles and corresponding coatings were investigated by scanning electron microscopy (SEM). The results showed that the surface preparation of SiC powder by roughening the particles with HF/NaF solution and electroless time of 5 minutes led to the formation of a continuous and uniform Ni-P coating with a thickness of 1-3 micrometers on the SiC particles. Electroless nickel coating during thermal spraying by HVOF protected SiC particles against decomposition and oxidation and as a carrier led to the placement and distribution of SiC in SiC(Ni)-Co composite coating. In the APS process, due to the very high temperature of the plasma jet and thermal decomposition, SiC particles was insignificantly contributed to the coating microstructure. The micro-hardness of two mentioned coatings was measured as 570±40 and 460±30 HV0.3, respectively, and this difference was due to the effect of the significant distribution of SiC in the HVOF coating.