Research On Diamond Coating On WC-Co Tools In Microwave Plasma CVD

The paper systemically studied effects of methane concentration,deposition pressure,gas flow rate and substrate temperature on diamond coating on WC-Co tools by MPCVD. The best parameters were established by experiments. Influence of diamond film and coating adhesion was compared with two different pretreatments.The research introduced a domestic microwave plasma chemical vapor deposition (MPCVD) equipment with a quartz glass window and watercooled stainless steel reaction chamber in 2450MHz/5 Kw. The machineries and function of the subsystems,including microwave system,gasroute system,vacuum system detecting system,and safeguard system,were also discussed.One of the important applications of diamond coatings is as cutting tools for nonmetals,nonferrous metals and alloys. However,it exhibits very poor adhesion when MPCVD diamond deposited upon WC-Co directly. So reliable tool performance is difficult to obtain for the problem of coating adhesion. Factor contributing to this problem is that the metal cobalt used as the cementing phase easily causes diffusion and dissolution of carbon,promotes graphite growth and inhibits diamond nucleation and growth in the course of competitive growth between diamond and graphitic carbon.In this work,cemented carbide (WC-Co) was used as a kind of depositional substrate and diamond was deposited upon it in an MPCVD equipment. The common method used by domestic and foreign scientists is removing the cobalt from the surface of the substrate by etching substrate using thin acid solution atroom temperature. But the internal Co will still overflow during MPCVD. In order to resolve this problem,cobalt was dealt with acid and chemical substitute. After chemical pretreatment,the surface of the substrate was roughened with lots of tiny grooves and fine holes. All of them contribute to diamond nucleation and coating adhesion. Meanwhile,ultrasonic scratching pretreatment was also applied by using diamond powder to enhance diamond nucleation. The diamond coating was characterized by Xray diffraction (XRD),scanning electron microscopy (SEM),laser Raman spectra(Raman) and polarization microscopy. The experimental results show that the suitable and simple substrate pretreatment can effectively control the overflow of cobalt and inhibit the catalytic effect of cobalt during MPCVD and greatly enhanced the adhesion strength of MPCVD diamond coating to substrate.