【国外标准】 Standard Specification for Electrodeposited Coatings of Palladium-Cobalt Alloy for Engineering Use

This specification covers requirements for electrodeposited palladium-cobalt alloy coatings containing approximately 80% of palladium and 20% of cobalt. It also covers composite coatings consisting of palladium-cobalt with a thin gold overplate for applications involving electrical contacts. Palladium and palladium-cobalt remain competitive finishes for high reliability applications. The specification deals with material classification, ordering information, materials and manufacture, coating requirements, sampling, test methods, special government requirements, and other requirements.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 <3 % (1). 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 (2, 3).1.3 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.