Relaxation of Residual Stresses in Brush-Plated Gold and Silver Coatings on Copper and on Brass Substrates

Abstract

Abstract. The investigated brush-plated gold and silver coatings are used for refining the surface properties of electric apparatuses. Tensile residual stresses generated in the plated coatings were determined by the curvature method and by instrumented indentation testing of a thin-walled open ring substrate, as described in our earlier papers. These stresses relax over time and their dependence on relaxation time was approximated by a linear-fractional function. The Young´s modulus and nanohardness of the coatings were determined. The surface morphology and structure in cross section of the coated substrates were presented. IntroductionHard gold and silver coatings have met application in engineering use (e.g. on generators slip rings, sliding contacts and small machine parts) due to their high hardness and wear resistance as well as their effective protection. They are typically plated on copper (mostly), brass and bronze. Silver is often used as low-price replacement for gold.Brush-plating is a simple processing method for selective plating of desired materials onto metallic materials without dipping the machine part (work piece) into a tank of the electrolyte. As the plating process takes place at room temperature, no heater is required. Usually, alloying metals or nanoparticle composites are added to pure gold and silver. Nickel-hardened gold and silver coatings were brush-plated from an industrial SIFCO Dalic Solution (Gold Hard Alloy) pH 8.4, Code SPS 5370, and Silver Hard Heavy Build pH 11.7, Code SPS 3083, on thin-walled open copper and brass ring substrates of various thickness [1,2,3]. In the present paper residual stresses in the plated coatings were determined by the curvature method and by an instrumented indentation testing technique. Relaxation of residual stresses was observed over a long time and some properties of the coatings, e.g. modulus of elasticity and nanohardness, which affect the service life of electrical components, were determined.

Comparison of Some Mechanical and Physical Methods for Measurement of Residual Stresses in Brush-Plated Nickel Hardened Gold and Silver Coatings

“…where σr is residual stress; H is indentation hardness; Ac is the apparent contact area for a stressed sample and A0 is the apparent contact area for a stress-free sample of a three-sided pyramidal Berkovich indenter used in nanoindentation. Calculation of residual stresses is presented in our previous paper [16].…”

Electrodeposition of Pd–Ag alloy for electrical contacts

“…Contact materials protect electrical components from environmental impacts and ensure a continuous flow of current. Hence, the criteria for these materials are minimal contact resistance, and exceptional solderability [1][2][3]. Considering these factors, gold coating has been considered as the most effective material for electrical contacts [4,5].…”