ASTM B984 Standard Specification for Electrodeposited Coatings of Palladium-Cobalt Alloy for Engineering Use
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ASTM International
Standard Specification for Electrodeposited Coatings of Palladium-Cobalt Alloy for Engineering Use
N B984
Annotation
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.
Properties-Palladium is the lightest and least noble of the platinum group metals (1)2. IIt 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 surface provides a hard surface finish (ASTM E18) thus decreasing wear and increasing durability. Palladium-cobalt coated surface also has very low coefficient of friction 0.43 compared to hard gold 0.60 thus providing lower mating and unmating forces for electrical contacts (1) 2. Palladium-cobalt has smaller grain size (ASTM E112), 50 - 150 Angstroms, compared to Hard Gold 200 - 250 Angstroms (1)2. 5 - 15 nanometer, compared to hard gold 20 - 25 nanometer (1)2. Palladium-cobalt has low porosity (ASTM B799) 0.2 porosity index compared to hard gold 3.7 porosity index (1)2. Palladium-cobalt coated surface has higher ductility (ASTM B489) 3-7 than that of hard gold <3 (1)2. The palladium-cobalt coated surface is also thermally more stable 395°C than hard gold 150°C, and silver 170°C. The following Table 1 compares the hardness range of electrodeposited palladium-cobalt with other electrodeposited noble metals and alloys (3,4).2
