Mechanical properties and wear behavior of multi-layer diamond films deposited by hot-filament chemical vapor deposition

Diamond films were deposited on cobalt-cemented tungsten carbide (WC-Co) by Hot-Filament Chemical Vapor Deposition (HFCVD). The mechanical properties and wear behavior of single-layer and multi-layer diamond films were compared, based on the difference of diamond crystal formation and internal structure. Adhesive failure modes and critical loads, post-scratch tests, were identified according to the applied load, acoustic emission and friction force. For single-layer diamond films, the samples produced with lower CH4 concentration evidence columnar crystal diamond structure, which exhibit better adhesive properties. The samples produced with 5% CH4 exhibit the lowest hardness, however, due to their higher crystallinity and nucleation density, they exhibit higher toughness. The multi-layer diamond film with 300 nm alternate thickness per interlayer shows the highest critical delamination load (23.22 N). Concerning the multi-layer diamond films, the hardness and Young's modulus increases from 84.13 to 94.01 GPa and 788.65 to 936.26 GPa, respectively, with the alternate thickness change from 100 nm to 600 nm per layer, which indicates that thicker alternate layers lead to higher hardness and toughness. The wear behavior of the nano-crystalline (NCD) single-layer diamond films is potentially related to the less adequate adhesive abilities to the substrate material.