A Study Of Preparation Of Copper Coated Tungsten Composite Powders By Electrodeposition

Copper-coated tungsten (W@Cu) powders composites have been widely used forthermal and electrical applications, as ultrahigh-voltage electric contact materials,heavy duty electrical contacts, arc resistant electrodes, military material, high densityalloys, microelectronics devices, and heat sink materials for high density integratedcircuits. Compared to the electroless plating, electroplating possess many advantages,such as high deposition rate, recycling electrolyte, low cost of production, lessenvironmental pollution, etc.In this paper, W powders with particle size of3-16m were chosen as substrate,the copper were deposited on the surface of micron W powders by intermittentelectrodeposition. The influence of process parameters and the nucleationmechanisms of copper electrodeposition under the high curre nt density wereinvestigated. The effects of W@Cu powders on the microscopic structure andproperty (Sush as density, hardness, conductive heat conduction performance, andthermal expansion coefficient) of W-Cu composites has been investigated. Themicroscopic structure, surface morphology, and coating elements content ofcomposite powders were analyzed by scanning electron microscopy, energydispersive spectroscopy, and X-ray diffraction. The major findings are as follows:1. The optimum technical parameters were established for preparing W@Cucomposite powders. The composite powders with uniform, dense, and consistent Cucoating were obtained under the conditions of60g dm3CuSO4,40cm3dm–3H2SO4,0.1g dm3sodium dodecyl sulfonate (DOSO3Na)，tungsten powders content8-12g·dm3in the electrolyte, current density12-16A·dm2, stirring frequency20-30h1.The W@Cu powders with a copper coating thickness of~2.5m and with coppercontent of~54wt.%were produced. The efficiency of W@Cu powders productionwas greatly improved.2. Copper nucleated on the active sites of W particles surface as dot deposits atfirst and grew gradually. Finally, Cu cells grew up and merged into a coating. XRDand EDX examinations found that the coating was crystalline state and no impurityexisted.3. Stirring frequency was the key parameter for a successful preparation ofW@Cu composite powders without agglomeration. Proper agitation could effectively prevent the composite powders from agglomeration and promote the tumbling of theW particles in the bath so that each W particle was individually coated with Cu.4. Large current density produced high over-potential and copper nucleiaccording to instantaneous mechanism. And the more negative the depositionpotentials, the closer to instantaneous nucleation mechanism the chronoamperograms.Large current density increased the fraction of nucleation, which is beneficial to thepreparation of copper coated tungsten powders with dense, uniform distribution.5. The role of organic additives in the electrolyte was investigated. Theappropriate amount of polyethylene glycol can effectively increase cathodepolarization, increase the electrochemical reaction resistance, increase the polarizationoverpotential and decrease the nuclei size of Cu. Highly dispersed W@Cu powderswith uniform and dense copper coating were fabricated.6. W@Cu powders can effectively improve the microstructure homogeneity anddecrease the porosity of W-Cu composite materials. A continuous three dimensionalweb structure of Cu phase and the dispersive distribution of W particles were clearlyobserved. Composites made from Cu-coated tungsten powders exhibited higherdensity, hardness, and electrical conductivity than those of composites made fromadmixed elemental powders. However, coeffcient of thermal expansionand electricalresistivity of Cu-coated composites showed lower values. The properties of W-Cucomposite materials was significantly improved.