SILVER COATED TUNGSTEN CARBIDE POWDERS FOR COMPOSITES IN ELECTRICAL CONTACT APPLICATIONS

摘要

Composite materials based on tungsten carbide and silver (WCAg) are well known and widely used electrical contact materials. Most commonly infiltration methods are used for production as they are superior to mixing-pressing-sintering. Nevertheless, infiltrated WCAg shows certain inhomogeneities and more or less porosity. Moreover, the silver content and particle size of tungsten carbide is limited. Therefore new methods were investigated applying electroless deposition techniques. Aqueous solutions containing different complexing agents for silver, such as ammonium hydroxide, benzoic acid and ammonium acetate have been tested. It was found that the use of aqueous suspensions of tungsten carbide in solutions of ammonium hydroxide and ammonium bicarbonate shows the best coverage. The silver coated tungsten carbide powders were consolidated by uniaxial cold pressing and liquid phase sintering. The sintered WCAg had a distinctly higher homogeneity than infiltrated products.