Influence of substrate roughness on the bonding mechanisms of high velocity oxy-fuel sprayed coatings

This paper presents a systematic study of NiCrBSi and WC-Co high velocity oxy-fuel (HVOF) sprayed coatings that were deposited on substrates of various surface roughnesses to reveal predominant bonding mechanism under a pull-off test. During HVOF spray, NiCrBSi was completely melted while solid-liquid two-phase WC-Co particles were generated due to their different thermo-physical properties. The results showed that the adhesive strength of the coatings increases as the substrate surface roughness increases from Ra 0.059 μm to Ra 9.0 μm. The mechanism of adhesion of HVOF metallic coatings deposited with the fully melted spray particles was mainly mechanical interlocking, while the deposition with the liquid-solid two-phase spray particles can lead to the formation of the physical bonding effect in addition to the mechanical interlocking.