In order to measure bonding strength of vanadium carbide(VC)coating and substrate and analyze combination mechanism, VC coating is prepared on the surface of cold worked die steel Cr12MoV with thermal diffusion (TD) process. The surface and interfacial morphologies, interfacial element distribution of elements V and C and the bonding strength are analyzed respectively with observation by scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and scratch test, and the failure mechanism of VC coating is discussed. The experimental results show that the bonding interface of the VC coating-substrate prepared by the TD process is an element grad, bonded with the change of element grad in the transition layer in which the V content decreases gradually from its surface to the substrate while the C content increases gradually. Chemical elements are combined mutually in the bonding interface, which forms a metallurgical combination. The average value of interfacial bonding strength is 45.7 N measured with a scratch test. The coating failure with the scratch test is an interfacial fracturing, and the bonding strength of the VC coating depends mainly on its compressive residual stress.
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