Preparation Of Core-shell Structure WC-Ni Composite Powder Characteristics Study

Coarse-grained cemented carbide is widely used in geological tools,stamping dies,rolls and so on.Because of its bad working environment,the material performance is very strict.Cemented carbides are mainly composed of cemented carbides and metal bonding phases.The most common bonding agent is metal Co.The wetting angle of Co to carbide is 0 degree,which has a good bonding effect and is called the best bonding agent.But Co is scarce and expensive,so a substitute for Co is needed as a binder.In this paper,WC-15Ni composite powders were prepared by using abundant Ni as metal binder.Of different sintering temperatures and the holding time on the performance of the cemented carbide.The main work and research results are as follows:Preparation of composite powders with low nickel content by fluidized bed chemical vapor deposition.The results show that a layer of nickel nanoparticles can be deposited on WC powders in a short time by fluidized bed chemical vapor deposition.With the increase of reaction temperature,the particles of nickel deposited grow up.At the same time,due to the softening of nickel metal,there will be a phenomenon of bonding loss of flow,Preparation of high Ni content WC-Ni composite powder by fluidized bed chemical vapor deposition is hindered.However,since the surface of the ceramic powder does not have catalytic activity,the WC powder needs to be roughened,sensitized and activated on the surface,and the catalyst palladium is supported on the surface of the WC particle.Electroless nickel plating using catalytically active metal palladium.However,the catalyst particle palladium only catalyzes in the early stage of electroless nickel plating.Once the deposited metal Ni is covered with palladium,the catalytic effect is Ni particles.Therefore,the traditional electroless plating process has two steps:pre-palladium catalysis and late Ni autocatalysis.Therefore,autocatalytic nano-nickel particles deposited on the surface of WC particles by fluidized bed chemical vapor deposition process can be used to prepare high Ni content composite powder by electroless nickel plating.Not only can the complex pretreatment process of electroless plating be omitted,but also the introduction of palladium impurities in the conventional electroless plating process can be prevented.The optimum conditions for electroless plating were as follows:the plating temperature was 80?,the reaction p H was 10,the concentration of the reducing agent sodium hypophosphite in the solution was 45.0 g/L,and the concentration of the complexing agent sodium citrate in the solution was 50.0 g/L,nickel salt hexahydrate hexahydrate concentration 45.0 g/L.At the same time,under the optimal electroless plating conditions,the effects of the size,content and distribution of Ni particles after FB-CVD deposition on the electroless plating reaction rate and plating morphology were discussed,and the optimal FB-CVD conditions were determined.It is750?,5 min.WC-15Ni composite powders were prepared under the optimal FB-CVD deposition conditions and the best electroless Ni plating conditions.By means of hot pressing sintering,the influence of the temperature of hot pressing sintering and the holding time on the properties of the cemented carbide after sintering was investigated,and compared with the mixed powder,the properties and microstructure of the coated powder after sintering were obtained.Morphology is better than mixed powder.The WC-15Ni cemented carbide with a density of 13.305 g/cm~3,a Vickers hardness of 629.3 N/mm~2 and a flexural strength of 1480 N/mm~2 was obtained at an optimum sintering temperature of1250?.