Preparation And Applied Basic Research Of CVD Diamond Coated Cemented Carbide Cutting Tools With High Cobalt Content

Chemical Vapor Deposition(CVD) diamond coated cutting tool has excellent cuttingperformance, it is the most ideal tool for the processing of nonferrous metals and alloy, composite,nonmetallic materials and other difficult-to-machine materials efficiently and accurately.Diamond coated cemented carbide cutting tool is the main direction of research and developmentat present. Depositing CVD diamond coating on the cemented carbide with high cobalt contentcan improve its toughness and strength, therefore, it is very important to research on thepreparation technology and properties of CVD diamond coated cemented carbide cutting tool withhigh cobalt content.In this thesis, according to indexable turning tool and drill, the effect of two methods oncoating quality, adhesion performance and cutting performance has been studied-interlayer andboron doping. The main work and results are as follows:1. The preparation technology of diamond coating tools based on the Niobium interlayerobtained by Double-Glow Plasma alloying has been studied. The results show that thickness of theinterlayer is moderate(~5μm) and the uniformity and invasiveness is better when the eching timeis2min and the holding time is2h. The interlayer can fill the loosened layer and also restrain thediffusion of Co as a result of high substrate temperature. Diamond coating has been deposited byHFCVD. The results show that two-step method combined with interlayer is better, thispretreatment can restrain the diffusion of Co more effectively, enhance the diamond nucleationand promote the formation of better shape crystals, there is a great improvement on the coatingquality and adhesion performance. The niobium interlayer turns into carbide and compounds dueto the high temperature during the deposition, which improves the adhesion performanceSignificantly. The coated turning tool is smooth and sharp.2. The preparation technology of boron doped diamond (BDD) coating has been studied andthe coated drill has been prepared. In order to study the effects of boron doping on the frictionproperties and adhesion performance of diamond coating easily, the BDD coating has beendeposited on flat carbide blade firstly. The results show that diamond nucleation density increasesand quality of the coating is improved as the boron doping concentration is moderate. Meanwhile,the boride compounds were produced, which suppressed outward diffusion of cobalt. The resultsof the friction and wear test against Si3N4ball show that the high temperature friction properties ofthe boron doped diamond is best when the boron doping concentration was3000ppm and thetemperature is300℃. BDD coating has been deposited on the drill by using the optimized parameters, The SEM results show that there are no cracks and collapses in the coating.3. Cutting test with the prepared coated turning tool and drill against the silumin, PCB andother difficult-to-machine materials has been studied. The results show that the flank wear of thecoated tool is smaller; anti-adhesion performance of the coated drill is good and the wear amountis small, the machined surface has a high precision, the coating does not come off during the test,which shows good adhesion and cutting performance of the coated drill.