ASTM B984-12(2020)e1 PDF

1.1 This specification covers requirements for electrodeposited palladium-cobalt alloy coatings containing approximately 80 % of palladium and 20 % of cobalt. Composite coatings consisting of palladium-cobalt with a thin gold overplate for applications involving electrical contacts are also covered. Palladium and palladium-cobalt remain competitive finishes for high reliability applications.

1.2 Properties-Palladium is the lightest and least noble of the platinum group metals (1)2. It has the density of 12 gm per cubic centimeter, specific gravity of 12.0, that is substantially lower than the density of gold, 19.29 gm per cubic centimeter, specific gravity 19.3, and platinum 21.48 gm per cubic centimeter, specific gravity 21.5. The density of cobalt on the other hand is even less than palladium. It is only 8.69 gm per cubic centimeter, specific gravity 8.7. This yields a greater volume or thickness of coating and, consequently, some saving of metal weight and reduced cost. Palladium-cobalt coated surfaces provide a hard surface finish (Test Methods E18), thus decreasing wear and increasing durability. Palladium-cobalt coated surfaces also have a very low coefficient of friction 0.43 compared to hard gold 0.60, thus providing lower mating and unmating forces for electrical contacts (1). Palladium-cobalt has smaller grain size (Test Methods E112), 50 - 150 Angstroms, compared to Hard Gold 200 - 250 Angstroms (1), or 5 - 15 nanometer, compared to hard gold 20 - 25 nanometer (1). Palladium-cobalt has low porosity (Test Method B799) 0.2 porosity index compared to hard gold 3.7 porosity index (1). Palladium-cobalt coated surfaces have high ductility (Practice B489) 3-7 % compared to that of hard gold