Pulsed electrodeposition of layered brass structures
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I.
INTRODUCTION
PULSEplating
has made it possible to produce coatings and foils consisting of alternate layers of different phases. Generally, square-wave pulses are used in plating so that the deposition current is on and off for preselected time intervals. Cohen, Koch, and Sard u] electrodeposited alternate silver and palladium-rich layers of the same phase. They did so by cyclically varying the current density without pulsing it. Tench and White t2] electrodeposited multilayer Ni-Cu composites by varying the electrode potential and the agitation in a cyclical fashion. Pulse plating has been employed on several occasions p'4'5] to change the composition of electroplated alloys. It is able to do so because the composition of the layer which is being plated is determined by that of the solution adjacent to surface of the deposit. The composition of the solution adjacent to the surface depends primarily on the relative diffusion rates of the involved ionic species from the bulk of the electrolyte. As diffusion from the bulk of the plating solution can take place during the time interval when the current is off while no ions are plated, it is possible to vary the composition of the depositing alloy layer by changing the pulse-plating parameters which are the peak current density, the pulse frequency, and the duty cycle. The duty cycle is the ratio of the time interval when the current is on to the sum of the times when the current is on and off. As the peak current densities used in pulse plating are generally higher than when direct current is employed, the magnitudes of the potentials are also greater. This extra energy can result in a greater nucleation rate and a smaller grain size. The main objective of the investigation reported here was to demonstrate the feasibility of producing a structure similar to that of a lamellar-eutectic alloy. Such a structure was to be produced by varying the composition of the deposit sufficiendy by pulse plating to deposit in the same plating solution alternate layers of a terminal solid solution and an intermediate phase. It is readily possible to plate layers of different compositions in two electrolytes. It has been pointed out, ~2] however, that for practical applications it would probably be necessary to produce the whole deposit in the same plating solution. Copper-zinc alloys were chosen for this investigation because brass plating is widely used and therefore has been R. WEIL, Professor of Materials and Metallurgical Engineering, and J.W. CHANG, Graduate Student, are with Stevens Institute of Technology, Hoboken, NJ 07030. C.C. NEE is Metallurgical Chemist, Shipley Company, Newton, MA 01701. Manuscript submitted September 11, 1987. METALLURGICAL TRANSACTIONS A
extensively investigated. Also it is possible to plate brasses over the whole range of compositions. [6] Several of the intermediate phases including beta brass can be deposited in the stable form. The beta phase can exist in either the ordered or disordered state. This fact offered the possibility of depositing
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