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 mu m to Ra 9.0 gm. 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. (c) 2005 Elsevier B.V. All rights reserved.