Investigation of Residual Stresses and some Elastic Properties of Brush-Plated Gold and Silver Galvanic Coatings

Abstract

Nickel-hardened gold and silver coatings were brush-plated from a commercial SIFCO Dalic Solution (Gold Hard Alloy), Code SPS 5370, and Silver Hard Heavy Build, Code SPS 3080, on unclosed thin-walled copper ring substrates. To determine residual stresses, the conventional curvature method (common among the electrodeposition methods) was applied, where the substrate was coated with certain thickness and then the slit increment (bending deflection) of the substrate was measured as an experimental parameter. Residual stresses on gold coatings were also determined by X-ray diffraction (XRD) based on the sin2 method. The values of residual stresses determined by the curvature method and by the XRD technique were comparable. Relaxation of residual stresses was observed. An equation for approximation of the change of residual stresses was applied assuming that the dependence of residual stresses on relaxation time is linear-fractional. The surface morphology and microstructure of the coatings was studied by means of scanning electron microscopy (SEM). The magnitudes of the modulus of elasticity and of the nanohardness of the coatings were obtained by instrumented indentation.