Study On The Deposition And Binding Properties Of Boron-doped Diamond Coatings On The Surface Of Cemented Carbide

CVD diamond cemented carbide tools are widely used in extreme conditions such as aerospace,CNC turning and geological mining due to exceptional advantages of ultra-high hardness,wear resistance and tenacity.However,the insufficient bonding force between CVD diamond coating and cemented carbide substrate seriously restricted its wide application.The bonding force between the coating and the substrate was mainly related to the nucleation density of diamond on the substrate and the corresponding deposition process parameters.Therefore,this work aims to improve the bonding force between the diamond coating and the cemented carbide substrate by improving the diamond nucleation density and optimizing the gradient boron doping process parameters.(1)The nanodiamond seeds(NDs)and the boron/carbon atomic ratio(B/C)in the nucleation stage were first adjusted to control the nucleation density of diamond.The effects of a single variable and the coupled process parameters on the coating quality and bonding properties were systematically studied.The results demonstrated that the nucleation density of diamond coating is the largest when the concentration of NDs seeding solution is 0.1% and the surface of NDs is hydrogen-terminated.Meanwhile,as the B/C ratio in the nucleation stage increased,the nucleation density of diamond increased.The combined optimized parameters further improved the bonding performance between the coating and the substrate,reaching the highest standard(HF1)in the German VDI3198 standard at a load of 600 N.And the crystallization properties of the diamond are enhanced.(2)Furthermore,the effects of diamond deposition process parameters on coating quality,bonding properties and friction and wear properties were studied by controlling the boron doping process(including total boron doping levels,concentration gradient and the transient B/C cutoff ratio).The results demonstrated that as the total boron content increased,the diamond grains became finer and the component ratio of(100)crystal planes increased,and meanwhile increased the content of boron and cobalt compounds in the coating.When the concentration gradient of boron doping increased,the half-peak width and residual stress of diamond decreased.In addition,when the transient B/C cut-off ratio increased,the diffraction peak of diamond shifted toward low wavenumbers and the number of boron atoms in diamond grains increased accordingly.Under the 1470 N load,the optimized coating adhesion force can still reach the HF1 in the VDI 3198 standard,and the high-speed reciprocating friction and wear test for 3 h under the 100 N load,the coating does not fall off,that is,the coating shows excellent binding performance under dynamic friction and wear conditions.