EFFECT OF ZINC ACETATE CONCENTRATION IN A CA(H₂PO₂)₂–ZN(CH₃COO)₂ ELECTROLYTE ON THE STRUCTURE AND PROPERTIES OF PEO COATINGS ON ADDITIVELY MANUFACTURED TI-6AL-4V ALLOY

Abstract

This study investigated the effect of the concentration of zinc acetate (Zn(CH₃COO)₂) in a calcium hypophosphite (Ca(H₂PO₂)₂) electrolyte on the formation and properties of coatings produced by plasma electrolytic oxidation on Ti-6Al-4V alloy manufactured by selective laser melting. The plasma electrolytic oxidation process was carried out under constant conditions, while the Zn(CH₃COO)₂ concentration was varied within the range of 0.1-0.4 mol/L. The coating morphology, elemental composition, phase structure, thickness were studied using light microscopy and scanning electron microscopy with energy dispersive X-ray spectroscopy, X-ray diffraction. The mechanical properties of the coatings were characterized by microhardness and wear resistance tests. Zinc acetate was found to significantly affect the growth and structure of the oxide layers. With increasing Zn(CH₃COO)₂ concentration, the coating thickness increased from 1.51 ± 0.26 to 5.21 ± 1.27 μm, the zinc content in the surface layer increased, and the morphology changed from an open porous structure to a denser one. According to X-ray diffraction analysis, the titanium substrate made the main contribution to the diffraction patterns, whereas the Ca- and Zn-containing components were in an amorphous, poorly crystalline, or nanodispersed state. The best tribological properties, including the lowest coefficient of friction, were obtained at 0.2 mol/L Zn(CH₃COO)₂. A further increases in Zn(CH₃COO)₂ concentration result in greater coating heterogeneity and reduced microhardness of the substrate-coating composite. The results confirm the possibility of controlled modification of plasma electrolytic oxidation coatings for medical applications.