Anodic Dissolution of Surface Layers as a Means of Increasing the Microhardness of Alloy Coatings of Iron Group Metals with Tungsten Prepared by Induced Codeposition

This work demonstrates that the macroscopic size effect, which consists in the influence of electrodeposition surface area on the composition and properties (microhardness and corrosion resistance) of alloy coatings prepared by induced codeposition of iron group metals with tungsten, is a particular case of this type of effects and this requires maintaining the volume current density (VCD) constant during electrodeposition. The effect is associated with the formation of surface oxy-hydroxide and hydrogenated layers. For electrodeposition of Fe–W and Co–W alloys from a citrate bath, it is established that a change in VCD at a definite value for current density of electrodeposition results in changes in the electrode potential, current efficiency, and alloy composition. Anodic dissolution of the modified surface layer allows increasing the microhardness but does not cancel the dependence of coating composition and properties on the electrode surface area.