Enhanced tensile strength for electrodeposited nickel-copper multilayer composites
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I,
INTRODUCTION
THE history
and potential advantages of metallic composite structures comprised of alternating layers of different composition were recently summarized by Cohen, Koch, and Sard,~ who investigated electrodeposited Ag-Pd layered structures for electrical contact applications. Although electrodeposition of such structures was described by Blum 2 as early as 1921, apparently very little effort has since been directly expended to realize their potential for providing unique or unusual mechanical, electrical, optical, and/or magnetic properties. It should be mentioned, however, that many of the enhanced properties observed with superimposed alternating current and pulsed plating may be attributable to periodic compositional modifications. In the present paper, 90 pct Ni-10 pct Cu layered composites electrodeposited from a single bath are shown to exhibit greatly enhanced tensile strength for copper layer thicknesses of less than 0.4/xm. Note that plating from a single bath, rather than alternately from separate electrolytes, would most probably be required for practical applications of thin-layered composites. Although the thickness of the Ni layers also varied (deposit thickness was held constant), data are reported as a function of the Cu layer thickness, which was always an order of magnitude smaller and thus is more likely to be associated with the enhanced deposit strength observed.
II.
EXPERIMENTAL
Electrodeposition was performed on a 304 stainless steel rotating cylinder cathode from a nickel sulfamate bath containing added copper. The bath composition was 72 to 80 g/L Ni, 0.64 g/L Cu, 37 to 45 g / L boric acid, and 0.15 g/L SNAP (sulfamate nickel anti-pit). The bath operating temperature was 50 -+ 1 ~ and the pH was 3.80 (measured at 25 ~ The rotating cylindrical cathode, 2.54 cm (1.00 inch) in diameter and 1.27 cm (0.50 inch) wide, was sandwiched between fluorochlorocarbon (Kel-F, 3M Company, St. Paul, MN) end pieces of slightly larger diameter, as described previously. 3 The catholyte (1500 mL) was contained in a Teflon beaker separated from the anolyte (contained in a larger polypropylene beaker) via four evenly DENNIS TENCH, Manager, and JOHN WHITE, Senior Technical Associate, are with Electrochemical Processes Group, Rockwell International Science Center, 1049 Camino Dos Rios, P.O. Box 1085, Thousand Oaks, CA 91360. Manuscript submitted April 12, 1984. METALLURGICALTRANSACTIONS A
spaced sintered glass flits (9.0 cm diameter) impregnated with agar gel. The flits were sealed to the Teflon cell compartment via an adhesive (Turco T-5580-G, Turco Products, Carson, CA). A saturated calomel electrode (SCE) was used as the reference (isolated via a glass flit), and the anode was a sheet of Ni 200 concentric with the cathode compartment. The deposit composition was modulated by varying both the cathode potential (or current) and rotation rate. Since the Cu deposition potential is considerably more positive than that of Ni in the bath used, deposits obtained at relatively positive potentials (0.
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