Interfacial adhesion characteristics of nanocrystalline and microcrystalline diamond coatings deposited on tungsten carbide (WC-Co) substrates were studied and analysed using a scratch tester. Coating failure events and critical point loads were identified by acoustic emission, tangential force measurement and image analysis carried out on the scratch track. In this respect, enhanced scratch resistance properties were observed in microcrystalline diamond (MCD) coating in comparison to nanocrystalline diamond (NCD) coating. Significant difference in critical loads for adhesive failure was observed for MCD and NCD coatings. These loads were 42 N and 20 N for MCD and NCD coatings, respectively. The reason for these two distinctly different adhesive characteristics was attributed to the microstructure of the respective coatings. The surface morphologies at critical failure point and wedge spallation regions of the scratch tracks were completely different for NCD and MCD coatings. Critical point regions were analysed by Raman stress mapping to study the scratch induced residual stresses in the strained diamond flakes and deformed coating of the scratch track. In this respect, high tensile stresses were observed in the regions of critical failure. This behaviour is strongly dependent on magnitude of stress and nature of deformation during the scratch test of NCD and MCD coatings. © 2014 Elsevier B.V. All rights reserved.