Cutting Tool Equipped with a Synthetic Diamond Polycrystal with a Polycrystalline Diamond CVD Coating

This study proposes a thin protective polycrystalline diamond CVD coating for cutting tools equipped with a polycrystalline synthetic diamond material produced via the HP–HT method. The deposition parameters were optimized in a magnetically stabilized glow discharge plasma. The coating was synthesized in a hydrogen–methane mixture at a partial pressure of CH₄ ranging from (2.2–2.7) × 10² Pa. The effect of the temperature of the polycrystalline diamond substrate during deposition on the structure of the synthesized coating was investigated. Results indicate that at temperatures between 1060 and 1150°C, diamond crystals in the coatings exhibit well-defined faceting with rectangular or triangular faces of micrometer-scale dimensions. A further increase in synthesis temperature leads to the formation of less-ordered fine-grained components on the surface of the larger, well-formed diamond crystals. At a deposition temperature of 1110–1150°C, a pilot batch of cutting inserts was fabricated using a polycrystalline synthetic diamond material with a 30-µm-thick polycrystalline diamond CVD coating. The impact of the coating on the performance characteristics of tools equipped with these inserts was evaluated during the machining of AK12M2MGN aluminum alloy and MK90 technical ceramics. Results indicate that the coated tool produced machined surfaces with lower roughness when processing the aluminum alloy, while exhibiting a 1.52–1.75-fold increase in wear resistance when machining technical ceramics. This improvement expands the application range and enhances the efficiency of diamond-polycrystal-equipped tools. The study established a synthesis temperature limit of 1175°C, beyond which the coating develops inferior performance characteristics.