Abstract
• A novel CVD-diamond thick film-Si3N4 brazed WC-Co tool was proposed. Sandblasting-nanodiamond seeding pretreatment method was adopted for the diamond thick film deposition on Si3N4 substrates. • Tribological behaviors of the polished diamond film, diamond thin film and PCD were compared. • Cutting performances and wear mechanisms of CVD-diamond thick film-Si3N4 brazed WC-Co, diamond coated and PCD tools were investigated. Chemical vapor deposition (CVD) diamond thick film, due to its higher hardness and better wear resistance, is a potential competitor of the poly-crystalline diamond (PCD) when used as the brazed tool tip. Besides, compared with the thin diamond coated tool, the diamond thick film brazed tool does not have the risk of catastrophic coating delamination. However, due to the fragile characteristic of the free-standing diamond thick film, the conventional polishing is complicated and inefficient. In this study, a novel CVD-diamond thick film-Si 3 N 4 brazed WC-Co (i.e. DB) tool is proposed. The diamond thick film was deposited on the Si 3 N 4 substrate by microwave plasma CVD (MPCVD), using the optimized deposition parameters: microwave power = 3.5 kW, reactant pressure = 20 kPa and methane concentration = 10 %. Adopting the sandblasting and nanodiamond seeding pretreatment methods could improve the film surface smoothness and suppress the voids formation on the film-substrate interlayer, which are beneficial for the post polishing process. In addition, Si 3 N 4 as the supportive substrate could help to prevent the diamond film breaking from polishing. The polished CVD diamond thick film-Si 3 N 4 was laser cut to small tips and then brazed on the WC-Co cutter body. The cutting performance of DB tool was tested in dry turning hypereutectic Al-Si alloy, adopting the PCD and thin diamond coated WC-Co (i.e. DC) tools as comparisons. The cutting results suggest that DB tool outperformed the PCD and DC tools in term of service life and surpassed the DC tool in machining quality. Moreover, the novel tool in this study avoided some typical problems for the conventional diamond tools, such as the coating delamination for thin diamond coated tool and preferred wear of the binder for PCD tool. Noteworthy is that the worn DB tool still presents a rather sharp cutting edge, only some micro-columnar diamond crystals chipped from the flank face.
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