Study On Surface Metallization Process Of Sic Particles And Its Effect On The Properties Of Copper-based Composites

Since SiC particles reinforced copper matrix composites improve the strength,friction and wear properties,and high temperature creep resistance properties,it has broad application prospect.In this thesis,it is focused on the processes of SiC reinforced copper matrix composites prepared by powder metallurgic method.Surface metallization of SiC particles,mechanical milling of copper matrix powder and spark plasma sintering?SPS?of composite material were mainly explored.Processes of chemical nickel-plating and copper-plating on SiC particle surfaces and its microstructures,process of mechanical milling to prepare copper matrix powder and powder micro-topography,and powder SPS process were discussed,as well as the influences of SPS process on density,phase structure and hardness of the composite materials.Furthermore,the influences of the SiC surface metallization on mechanical properties of copper matrix composites prepared by SPS were also discussed.The results show that the surface of the SiC particles can be metallized by electroless plating,when the concentration of[Ni²⁺]in the electroless plating solution is 0.25 mol/L,the concentration of[NH₄⁺]is 0.6 mol/L,[Ni²⁺]/[H₂PO₂^-],the concentration ratio is 0.4,the citric acid concentration is 0.1 mol/L,lactic acid is 1 mL/L,thiourea is 1 mg/L the pH is 10,and the temperature is 45°C,the SiC particles have the best effect of electroless Ni plating.The activation sensitization process helps the Ni coating.Using the optimized composition of the electroless plating solution:concentration of formaldehyde 15 mL/L,CuSO₄·5H₂O 20 g/L,sodium citrate monohydrate 44 g/L,thiourea 1 mg/L at reaction pH 12.5 and temperature65°C,the SiC particles has the best metallization effects.Unlike Ni coating,the Ag⁺is used to be activator needed before electroless Cu plating.And SiC 20 g/L.At different ball-to-grain ratios,the microscopic morphology of the copper powder is consistent with the advancement at the different milling time,and the mechanical milling of the copper powder resultd in the decreased of density and grain size sintered by SPS.The SPS sintering laws are summarized as:In a certain sintering temperature range,the higher the sintering temperature of SPS,the higher the diffusion and migration rate of the powder and the higher the density of the sintered samples,but the Vickers hardness is continuous decreasing due to the reduction of the stress caused by milling.The increase of the sintering pressure facilitates the sealing or discharge of the pores of the sintered samples,which is beneficial to the densification of the sample.When the sintering time is prolonged,the density of the sintered samples is increased,but an excessively long sintering time causes over-firing.When the mechanical milling of copper powder SPS process parameters are setted as:sintering temperature:850°C;sintering pressure:60MPa;sintering time:15min,the preparation of sintered sample density is the highest.At the same time,it was found that the addition of different SiC particles?SiC,nickel-plated SiC,and copper-plated SiC?having a volume fraction of 10%to the two copper powders?before and after milling?revealed that the surface-metallized SiC particles were greatly improved with the copper-based materials.The combination of interfaces helps to increase the the composite materials of density,hardness,tensile strength,etc.Different surface metallized SiC particles have different degrees of copper matrix strengthening.For denseness and hardness,copper atoms on the surface of SiC particles are fully diffused during the sintering process,so the copper-plating SiC has better strengthening effect.For the tensile strength of composite materials,nickel atom solution strengthening,nickel plating SiC tensile effect is better.In the experiments,it was also found that the mechanical milling had adverse effects on the density,hardness,and tensile strength of the SPS sintered samples.