Investigation On Preparation And Properties Of Ni Coated Diamond Composite Powders With Core-shell Structure

Nickel coated diamond powders as a type of composite materials possess dual properties of nickel and diamond,such as excellent magnetic conductivity,wear resistance,self-lubrication and durability under high temperature.They can be used as grinding tools.Traditional electroless deposition owns the disadvantages of poor chemical stability of plating solution,complicated pretreatment processes,high cost of production and heavy environmental pollution.Here,a method of electrodeposition was used to prepare Ni coated diamond powders with compact and uniform Ni coating which has a certain thickness to avoid these disadvantages.Synthetic diamond with micron size(20-40?m)was used as raw material,nickel was deposited on the surface of diamond particles by direct electrodeposition and electroless deposition.In order to improve the effect of deposition,the pretreatment process was optimized via activating diamond powders prior to plating.The parameters of electroless process were studied to choose appropriate conditions.The effect of activators on the coating of diamond was investigated.The surface morphology,phase structure and coating thickness of the composite powders were analyzed by scanning electron microscope(SEM)and X-ray diffraction(XRD),the surface composition of elements were detected by energy dispersed X-ray spectrometer(EDS).The results are achieved as follows:(1)The surface morphology of nickel coated diamond composite powder prepared after activation and electroless plating or electroplating was characterized by SEM.the activation effects were compared by different activation methods on diamond.(2)The optimal preparation processes of Ni/diamond powders,such as concentration of the reductant,temperature and pH vaule,were determined by analysis of plating efficiency,nickel content and surface morphology of the composite plating powders.The optimal the bath is composed of 30 g·dm-3 NaH2PO2·H2O,10 g·dm-3 citric acid,10 mg dm-3 sulfocarbamide,25 g·dm-3 NiSO4·6H2O.pH value was controlled to4-5,plating was conducted at85?.(3)The structures and properties of the composite powders were changed with various activators.The concentrations of activators also had a great impact on the morphologies and phase structures of the coating on the diamond particles.Complete,uniform and fine-coated composite particles can be prepared,when using silver nitrate solution as an activator(0.1g·dm-3).With the concentration of silver nitrate increased,the coatings were more compact,and the intensity of Ni(111)plane peak increases.(4)Phase structure of nickel coatings influenced the tribological properties of diamond grinding wheels.When there was higher peak of nickel crystal in(111)plane orientation,the mechanical and tribological properties of diamond grinding wheels made from Ni coated diamond composite powders were improved.