Deposition of Smooth Diamond Films with High Adhesive Strength on WC-Co Inserts and Their Cutting Performance in Turning GFRP

Abstract

Deposition processes of conventional diamond films and smooth fine-grained diamond films on cemented tungsten carbide inserts (SCMT120408-HR, 6wt. %Co) in the hot filament chemical vapor deposition (HFCVD) apparatus were investigated. A novel combined pretreatment of Murakami’s reagent, acid etching and microwave plasma decarburization in Ar-H2 gas was carried out. The adhesive strength of the films to the substrates, diamond-coated tool wear and surface roughness of the workpiece were further studied by turning glass fiber reinforced plastics (GFRP) cylindrical bars. Scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), and Raman spectroscopy were employed to characterize the substrates and diamond films subjected to different pretreatments and deposition processes. Optical microscope and surface scanning profilometer were utilized to monitor the evolution of tool wear and surface roughness of the workpiece respectively during the cutting test. The experimental results showed that the novel combined pretreatment was more effective in enhancing the adhesive strength of diamond films to the substrate. Fine WC interlayer generated during the initial stage of the diamond film deposition played an important role in improving the adhesion. Diamond coated tools subjected to such pretreatment demonstrated up to 6 times longer tool life than uncoated ones. Varied parameter deposition process produced smooth fine-grained diamond films, which led to remarkably lower surface roughness of the workpiece in turning GFRP