Influence of cemented carbide substrate microstructure on CVD diamond coating characteristics

CVD diamond coatings on WC-Co cemented carbide substrates are widely utilized in cutting tools. However, insufficient coating adhesion remains a critical challenge in industrial applications. This study investigates the impact of slight variations in the WC substrate grain size on the morphology, quality, and adhesion of diamond coatings. The coatings were characterized using SEM, Raman spectroscopy, X-ray diffraction, and Rockwell indentation tests. Results show that coatings on the finer-grained WC substrate (sample #1) are smoother and more uniform with a higher nucleation density, while coatings on the coarser-grained WC substrate (sample #2) are rougher with larger diamond crystals. Coatings on the finer-grained WC substrate exhibited lower residual stress and better adhesion. Raman analysis revealed that coatings on the coarser-grained WC substrate displayed higher crystalline quality but contained more non-diamond phases. The study verifies that the substrate microstructure, even slight variations in WC grain size, significantly affects diamond coating morphology, crystalline quality, phase purity, and adhesion strength. These effects are attributed to the interaction between WC grain size, Co mean free path, and WC contiguity. This research provides valuable insights into optimizing the performance of CVD diamond-coated cemented carbide tools by manipulating substrate microstructure.