The Wear of Electrodeposited Gold

Abstract

The wear and friction of pure gold and gold alloy electrodeposits were determined. These platings are widely used in sliding electric contacts and include golds hardened with silver, cadmium, nickel, cobalt, or cobalt and indium. In preliminary work, the microstructures, hardnesses, crystallographic orientations of the surface, and topographies of the golds were examined; these properties vary widely, and relationships among them are discussed. Sliding was with thick deposits to eliminate effects of substrate. The experimental method involved repeat-pass unidirectional sliding at 100g in a rider-flat apparatus with plated flats against wrought gold or gold-plated riders. Wear and friction are described for both as-plated samples, and to eliminate distinguishing surface textures, with flats abraded to a common roughness. Wear was found to be related to hardness, topography, and crystallographic orientation. A new result is that prow formation does not occur above a load-dependent critical roughness. For abraded pure gold, the critical value is 25–50 μin. center line average at 100g. The prow formation wear mechanism dominated sliding in runs of 500 revolutions on a 1-in. diameter track. Exceptional were the very hard golds (about 200 KHN) against soft wrought gold riders (about 50 KHN), in which metal from the rider smeared onto the flat prior to the onset of prow formation. A 1% silver-gold alloy showed unusually high wear, and a 1% cadmium-gold alloy wore relatively, little in the as-plated form. The lowest wear rates were with nickel-or cobalt-hardened golds. Coefficients of friction of electrodeposits change during running-in. This is related to changes produced by wear in the relative contributions of the adhesion, plowing and roughness components. The friction of very rough or very smooth as-plated gold decreases in repeat-pass sliding as a middle level of roughness is attained.