The Influence Of Plasma Boronitriding Pretreatment On The Diamond Coating On Cemented Carbide

To improve the life and performance of tungsten carbide cutting tools, applying diamond coating on their surface is an effective approach, while the most difficult obstacle lies in the existence of cobalt in the cemented carbide substrate which would catalyze the growth of graphite between coating and substrate, so as to weaken their adhesion, and finally impede their pratical appliance in industry. To overcome this problem, two plasma pre-treatment methods(plasma boronitriding pre-treatment,plasma boronizing pre-treatment)and a typical traditional pretreatment method(MC pre-treatment)have been used to attenuate the adverse effect of cobalt in the thesis. Through these processing, nano-crystalline diamond films possessing smooth, uniform surface were deposited on cmented carbide by MPCVD(microwave plama chemical vapor deposition) with methane,hydrogen and argon as gas sources in bell jar-type system. The research results in the thesis incicate:(1) The compact and uniform passivating layer without Co phase, while mainly contained CoWB was obtained on the surface of cemented carbide using plasma boronitriding pre-treatment. By such a processing, high boron-doped amount to 77.24% could be reached at 700℃.The smooth and uniform nano-crystalline diamond coated on as-pretreated substrate have the smallest indentation radius and the longest life compared with other pretreated methods in this thesis.(2) Passivated layer composed of primary Co WB and CoW2B2, which effectively solidified Co was formed on cemented carbide by boronizing pre-treatment, as well as the boron-doped amount to 36.45% through EDX analysis. The indentation radius of nano-crystalline diamond film coated on as-treated substrate was slightly bigger than previous preteatment.(3) Nano-crystalline diamond film coated on MC reagent method pre-treating substrate has the biggest indentation radius comparing with two plasma passivating pre-treatment,which had the worst value.(4) Graphite amount between coating and substrate gradually rised for plasma boronitriding pre-treatment, plasma boronizing pre-treatment, MC reagent pre-treatment, which indicated that plasma boronitriding pre-treatment has the best effect for solidifying Co and restraining the growth of graphite.Three pre-treatment methods including MC-pretreatment and plasma boronizing pretreatment and plasma boronitriding pretreatment were researched from passivating layer in appearance and phase quantity and amount of boron and boronizing temperature,characterization of diamond coating in appearance and crystalline size, diamond film indentation test,cutting test,the result shows plasma boronitriding pretreatment was an effective approach to improve film-substrate bonding strength.