Effects of Cathodic Hydrogen Evolution on Electrodeposited Au-Cu-Cd Alloys

Abstract

Hydrogen can be incorporated into electrodeposited Au alloys either during electrodeposition or by cathodic charging. Incorporated hydrogen in these alloys generally impairs their mechanical properties. In this work, we present results of a study of electrochemical, structural, surface composition, and morphological effects of cathodic charging of Au-Cu-Cd alloys electrodeposited from a cyanoalkaline bath. Different kinds of linear sweep voltammetric behaviors are observed for alloys with different compositions and for repeated scans, which is related to a loss of electrocatalytic activity for high Cu content alloys and prolonged cathodic charging. The surface composition of alloys is altered by cathodic charging, resulting in a decrease in Au content. The surface morphology, as observed by scanning electron and atomic force microscopies, is modified by cathodic charging: large crystallites are attacked and globular features appear on flat deposits. The crystallographic structure of the alloys is affected by prolonged hydrogen evolution; the original preferred orientation is disrupted and a Cu-rich phase appears.Electrodeposited Au-Cu-Cd has been in consistent use for decorative purposes ͑practically all of the electroforming of 14 to 18 carat Au hollow jewelry͒. The electronics industry is also interested in this material ͑high-performance electric contacts, sliding contacts, slip rings, connectors͒. The requirements for both electronic and decorative fields strongly stress the mechanical properties of the Au alloy layers ͑wear resistance, ductility, toughness͒. It has been proved in previous work 1,2 that hydrogen embrittlement is a major cause of mechanical failure of electroplated Au-based alloys. In this work, we report on compositional, structural, and morphological alterations brought about by hydrogen evolution on electrodeposited Au-Cu-Cd alloys of various compositions.Accurate but phenomenological studies of Au-Cu-Cd electrodeposited alloys were proposed in the 1970s and early 1980s. 3-5 More recent work is either focused on very specific problems such as pulse plating 6 or is markedly application-oriented. No description is found in the literature concerning hydrogen evolution effects on these alloys, apart from indirect data on cathodic efficiency. 3,4,6 Structural and morphological data are reported for ϳ18 carat deposits. 4,5 All authors agree on the fact that at least one Au-based disordered solid solution is observed. Steinmann et al. 5 report one such phase with strong ͑111͒ preferred orientation, while Dettke et al. 4 report somewhat doubtful evidence of a polyphasic structure with reflections form four superlattice structures. Materials and MethodsBaths and electrochemical experiments.-The investigated alloys were electrodeposited with the following bath and operating conditions: Au ͑as KAu͑CN͒ 2 ) 5 g L Ϫ1 , Cu ͑as KCu͑CN͒ 3 ) 50 g L Ϫ1 , CdCO 3 1.5 g L Ϫ1 , KCN 20 g L Ϫ1 , KHCO 3 7 g L Ϫ1 , and K 2 CO 3 5 g L Ϫ1 , pH 10.5, temp 70°C. Hydrogen evolution experiments were carried out in a 0.125 ...

Nanocrystalline growth and grain-size effects in Au–Cu electrodeposits

“…A short pulse (t p <5 msec) regime shows a faster decrease in d g with increasing j than does the long pulse (10< t p <30 msec) regime. Also, we have found in electrodepositing Au-Cu from cyanoalkaline-based solutions, as reported elsewhere [10][11], that a decrease in the current density and cell potential favor deposition of the more noble metal species. This result is observed in a ( .…”

“…Alkaline solutions from cyanide salts will be used for the electrodeposition of the AuCu foils. [10][11] Hardness values up to 3.9 GPa are reported for deposits prepared this way. [10] …”

The thermal stability of nanocrystalline Au–Cu alloys

“…Grain size, as determined from equations (1)(2), is proportional to the anneal time (t) raised to the power n, i.e. d g α t n .…”

“…Nanocrystalline foils of Au-Cu alloys [1][2] can be produced by electrodeposition processes. The process of pulsed electrodeposition provides a path to control the as-deposited grain size, e.g.…”

Modeling Nanocrystalline Grain Growth during the Pulsed Electrodeposition of Gold-Copper

“…A recent experimental study (1) for the electrodeposition of nanocrystalline AuCu alloy coatings is briefly reviewed and compared with previous results (2)(3)(4). These results provide the test basis for assessing refinement of a new growth model (1).…”