Abstract
Silver‐palladium alloys were electroplated as high quality coatings from a concentrated chloride bath. Adherent, uniform, and coherent deposits were obtained with thicknesses of up to 20 μm. The alloys were found to be homogenous, single‐phase solid solutions, with palladium content ranging from about 30% to 60%, depending on the operating variables. The microstructure of the plated Ag‐Pd alloys consists of very fine grains (100–300Å). These alloys have a fcc crystal structure, and the lattice parameter varies continuously with composition. The useful plating rate with moderate agitation was found to be about 0.44 μm/min at 10 mA/cm2, which is almost twice that of conventional cobalt‐hardened gold, due to the current efficiency of nearly 100%. Alloys containing about 40% Pd were obtained with these conditions. High speed plating of the Ag‐Pd alloy was achieved in a forced flow cell up to rates of about 9 μm/min. To achieve satisfactory deposits, it was generally necessary to use a thin (0.2–0.4 μm) soft gold underplating. Preliminary tests of electrical contact properties revealed that the Ag‐Pd coatings possessed low contact resistance (about 1 mΩ at 100g load). Other relevant properties include intermediate Knoop microhardness (about 200 kg/mm2 at 25g load) and an excellent resistance to formation of corrosion films in accelerated tests using flowers of sulfur. The present study indicates that the plated Ag‐Pd coatings are superior in contact resistance stability to the bulk wrought alloy R156 (40%Ag‐60%Pd). Finally, these coatings show satisfactory wear response in the selected tests provided a hydrocarbon lubricant is present.