Corrosion Properties of Electrolytic Coatings Based on СоW, CoRe, and CoWRe Alloys

Abstract

We established the chemical composition, current efficiency, and corrosion properties of CoW and CoRe binary alloys and CoWRe ternary alloys obtained from electrolytes of two types: citrate and citrate-pyrophosphate. It was discovered that the alloys deposited from citrate electrolyte contain much more refractory metals [51.0 at.% Re and 46.2 (W + Re)] for the same current density of deposition (10 mA\u2009⋅\u2009cm–2) than the alloys deposited from citrate pyrophosphate electrolytes [13.5 at.% Re and 23.9 at.% (W + Re)]. The main advantage of application of citrate-pyrophosphate electrolytes is their high current efficiency (of up to 85.7%). The results of corrosion investigations carried out in a 3.5% NaCl solution show that the corrosion resistance of CoWRe alloys is higher than the corrosion resistance of CoRe alloys. Actually, they are equal to 3.2 and 2.8 k\u2009Ω\u2009⋅\u2009cm2 for citrate electrolytes and 5.4 and 3.6 k\u2009Ω\u2009⋅\u2009cm2 for citrate-pyrophosphate electrolytes, respectively. The corrosion resistances of the coatings depend on their phase compositions, in particular, on the formation of a solid solution of rhenium in cobalt for the CoRe alloy and appearance of a nanocrystalline coating for the CoWRe alloy.