Comparison of PEO-coatings of zirconium alloy in calcium acetate-based electrolytes

The present work is aimed at development of oxide coatings on zirconium alloy by plasma electrolytic oxidation (PEO) in sodium phosphate and calcium acetate based electrolyte systems, with addition of sodium metasilicate or sodium hydroxide. PEO-coatings were characterized in terms of the surface morphology, phase and chemical composition, wettability, corrosion resistance, apatite formation ability, coefficient of friction and abrasion resistance. Uniform porous coatings consisting mainly of tetragonal zirconia and providing a significant increase in the corrosion resistance were obtained. The coatings formed in the base electrolyte without additives exhibit discontinuous overgrowth with hydroxyapatites in the SBF test, the most hydrophilic properties and the best abrasion resistance. The coatings formed in the electrolyte with the sodium metasilicate exhibit the highest corrosion resistance and contact angle; however, they have the smallest wear resistance. The coatings formed in the electrolyte with the sodium hydroxide show the highest apatite forming ability, stable value of the friction coefficient, but lower corrosion resistance.