The interfacial phenomena of multi-walled carbon nanotubes (MWCNTs) embedded in an Al matrix during high-velocity oxygen fuel (HVOF) spraying were investigated. The high thermal energy supplied from the high temperature gas flow of HVOF spraying activated the interfacial reactions of MWCNTs with oxygen and Al, such as MWCNT oxidation and aluminum carbide formation. Interfacial reactions deteriorated the contribution of the MWCNTs to the coating properties by destroying the intrinsic structure of the MWCNTs. In this study, the interfacial reaction mechanisms of the MWCNTs are discussed based on microstructural and thermodynamic analysis. (C) 2012 Elsevier BM. All rights reserved.