Graphene Sheets Decorated With Metal Particles And Copper-Decorated Graphene Doped W-Cu Composites

WCu contact materials,extensively used as the key components of high-voltage circuit breakers,can efficiently transport electrical currents and break the fault current in time when overloaded to ensure the safety of the power grid.When the power is suddenly switched on/off,significant electric arcs can be easily generated and accumulated on the contact surface,causing the copper phase to melt and even evaporate due to the elevated temperatures,thus resulting in the early failure of the material.Extensive studies have been undertaken to investigate the electrical properties and arc characteristics of the WCu contact materials.The method of grain refinement and micro-alloying can provide the contact material with higher strength and improved dispersion of arc characteristics,thus effectively inhibiting the premature ablation failure of the contacts.Although great progress has been made in recent years in the refinement of grain sizes and micro-alloying to improve the strength of materials and uniform dispersion of the arc energy,but the electrical properties of contact materials were decreased inevitably due to the increase of grain boundaries.It is very unfavorable for high-voltage circuit breakers that the voltage level and the breaking current increase constantly.So,graphene with the super-high strength and fascinating electrical properties as a doping phase was added to WCu alloys,for overcoming WCu alloy performance the contradictory relationship,serious interface reaction and poor wettability between graphene and matrix.In this paper,metal-decorated graphene was synthesized using an improved electroless plating method.Then,Cu@graphene/WCu composites were prepared by spark plasma sintering(SPS)and infiltration sintering technique.The microstructure,mechanical properties and electrical properties of metal-decorated graphene and W-Cu alloy were characterized by The SEM,XRD,TEM,AFM,Raman,infrared,Hardness meters and digital metal conductivity meters,etc.The results showed that graphene oxide(GO)was firstly synthesized using the Hummer's method with graphite as a raw material,and then ultrasonically dispersed into dispersing agent solution to obtain a homogeneous GO suspension,which was added into the electroless plating solution containing copper sulfate or nickel sulfate and a reducing agent for reduction.Metaldecorated graphene was synthesized using an improved electroless plating method that was a one-step co-reduction method under alkaline condition.Crystalline copper particles were obtained on the surface of graphene,whereas amorphous nickel particles were obtained.Distribution of these metal particles on the graphene was homogeneous and highly dispersed,which can improve their sinterability.Thus the strong chemical bonds were formed between the metal particles and graphene.The copper-decorated graphene doped tungsten-copper composite powder was sintered at a temperature of 1150°C for 10 minutes and a pressure of 30 MPa,and was sintered into a tungsten-copper bulk by Spark Plasma Sintering.Tungsten-copper alloy consisted mainly of tungsten,copper and graphene.Graphene was distributed in the form of a sheet on the network of binder phase copper.A small amount of doped copper-decorated graphene can partly avoid the reaction of tungsten and graphene to generate tungsten carbide,and on the other hand,the electrical properties and mechanical properties of the tungsten copper alloy were synergistically improved.When the doping amount of copper-decorated graphene was 0.45wt%,the electrical conductivity and hardness of the tungsten-copper alloy were 43.1%IACS,238 HV,respectively.Compared with the pure tungsten-copper composites,increased by 79.65%,15% respectively.The tungsten-copper composite powder containing copper-decorated graphene was sintered at a temperature of 1300°C and a holding time of 90 minutes by an infiltration sintering technique to form a tungsten-copper bulk,which mainly consisted of tungsten,copper and graphene.When the doping amount of copper-decorated graphene was 0.45 wt%,the electrical conductivity and hardness of the tungsten-copper alloy were 46.6% IACS,238 HV,respectively.Compared with the pure tungsten-copper composites,increased by 30.2%,5%,respectively.The formation mechanisms of metal-decorated graphene and SPS sintered copperdecorated graphene enhanced tungsten-copper composites were proposed.Formation mechanism of metal-decorated graphene has been attributed to that the metal ions were adsorbed and bonded around the oxygen-containing functional group onto the edges and surfaces of graphene oxide,then graphene oxide and the metal ions were simultaneously reduced by the reducing agents,and thus strong chemical bonds were formed between the metal particles and graphene.The formation mechanism of Cu@Gr/WCu was that under the action of a DC pulse current flowing from the indenter,a large amount of Joule heat accumulated on the surfaces of the tungsten particles and the copper-decorated graphene,and the accumulated heat was quickly transferred to the other particles and then the entire sample was covered.After sintering,copper-decorated graphene enhanced tungsten-copper alloy with a continuous network structure was obtained,in which the phase tungsten and the doped phase graphene were uniformly distributed around the continuous network-like distribution of the binder phase copper.