Effect of cathodic current density on the microstructure and performance of W-ZrO2 composites coating prepared in Na2WO4-WO3-ZrO2 molten salt

Abstract

The dense and smooth W-ZrO2 coating was prepared by electrodeposition on a copper substrate in Na2WO4-WO3-ZrO2 melt at 1173 K. The coatings composition are α-W and monoclinic ZrO2, and the content of ZrO2 increased with the increase of current density. The effect of cathode current density on the morphology, microstructure and performance of the coating was investigated in this paper. The microstructure of the coating was a field-oriented texture type, including an equiaxed grain nucleation layer and a columnar grain growth layer. The roughness has the minimum value of 4.783 μm at 30 mA/cm2, and the maximum value of 8.586 μm at 60 mA/cm2. Then, the surface roughness dropped to 6.479 μm at 80 mA/cm2. The surface micro-hardness increased with the current density increasing, and reached the maximum value of 482 HV at 60 mA/cm2. W-ZrO2 coated copper has excellent electrical conductivity and high temperature oxidation resistance at 30 mA/cm2, 40 mA/cm2, and 80 mA/cm2. The electrical conductivity of coatings prepared at 50 mA/cm2 and 60 mA/cm2 is slightly poorer due to their rough surface and strong preferred orientation. Overall, the texture of the composite material is the most influential factor for electrical conductivity. In summary, as the current density increases, the composition, morphology and microstructure of the coatings changes regularly, which further leads to a predictable change in performance.