| There are two key problems that hamper the batch production and widespread applications of the diamond coated WOCo hardmetals products. One is low adhesion between the substrates and diamond films, the other is difficult to control the quality of diamond films. To solve the problems, it is necessary to find out and master the correlativity and change regularity of the influence factors on diamond nucleation, growth and properties on WOCo hardmetals, which are correlative with not only the diamond deposition process but also pretreatment process. The research contents and methods of the paper are as followings:1)The substrate surfaces were chemically pretreated with the one-step, and especially two-step etching methods, using Murakami reagent and acid solutions. Diamond films were deposited on the WOCo substrates by a hot-filament chemical vapor deposition reactor.2)The substrates surface properties and properties of the diamond coatings were characterized by means of XRD(X-ray diffraction), SEM (scanning electron microscope), EDXS (energy dispersive X-ray spectroscopy), Raman spectroscopy and so on.3)Theories were systematically and comprehensively investigated, including the main influence factors on diamond deposition process and pretreatment process, influence of WOCo substrate properties on diamond film nucleation, and the characteristics and change regularities of morphology, texture and properties of diamond films on WOCo hardmetals.4)The temperature field model of HF CVD diamond coated WOCo hardmetals was established and calculated, and the influence factors on the temperature field model were discussed.5)Orientation growth process and mechanism of microcrystalline diamond films on WOCo substrates were studied in detail.6) The substrate surface pretreatment processes were performed, including magnetron sputtering Molybdenumintermediate layer deposited on WC-Co alloy, plasma nitriding on WC-Co alloy. The pretreatment surface properties and diamond films properties were characterized, and the influence factors on their properties were discussed.Based on the research results, the following main conclusions can be drawn.l)The two-step chemical etching method was effective to removing Co contents on the substrate and prevent .the Co negative effects, the properties of diamond films on the WC-Co alloys could be improved, matched with the suitable HF CVD process.2)The two main influence factors on the transformation of morphology and texture, and properties of diamond films on WC-Co alloys are the Co contents and temperature distribution field. Which one is more important depends on the changes of the concrete conditions. The diamond film grain sizes become smaller with the decrease of the deposition temperature. Within the temperature field of 800-1000C, the diamond film grain sizes became 5 times smaller when the deposition temperature was decreased by 100C. The chemical quality of diamond coatings is very low when the deposition temperature drop to lower than temperature of 700C.3) It is different from the ball cap nucleus in shape, the diamond nucleus shape should be considered when calculating the nucleation rate of diamond films. The nucleation rate of diamond films on the WC-Co alloys is expressed asdN/dt=A*pNAns{exp(Ed -Es - G* /kT) - exp(-Es / kT)}/When the dislocation density increased by the surface pretreatment, the nucleation rate of diamond films on the WC-Co alloys is governed by the following equationBesides the dislocation density, when the defects, such as vacancies and boundaries, density increased by the surface pretreatments, two factors as exp(-Q /kT) and exp(-Eb /kT) should be added into the above equation, where Q-vacancy surface diffusion activation energy , Eb-boundary surfacediffusion activation energy.4)Under the lower deposition temperature (about 800C) and higher pressure, microcrystalline diamond films with {001} Orientation growth and 1-3 Mm sizes on WC-Co substrates were obtained. Its growth mechanism shows the substrate surface texture of W...
|
PDF Full Text Request