Role of phosphate, silicate and aluminate in the electrolytes on PEO coating formation and properties of coated Ti6Al4V alloy

Abstract

A comparison of PEO layers on Ti6Al4V alloy formed in phosphate, aluminate and silicate-based electrolytes respectively, has been made to reveal the influence of the electrolyte composition on the formation process. The phosphate-based electrolyte has been identified as the most promising one as it has the best coating formation efficiency and the lowest breakdown voltage. On the bases of the microstructure and elemental/phase analysis of the different PEO coatings, it could be observed that the PEO coating formed in phosphate-based electrolyte is mainly composed of anatase and rutile. An amorphous phase is dominant in the coating produced in silicate-based electrolyte. Moreover, there are mainly γ-Al2O3, Na2Al2xO3x+1 and TiAl2O5 present in the coating formed in the aluminate-based electrolyte. The coating formation process in silicate- and aluminate-based electrolytes is more dependent on the deposition originating from the electrolytes. All of the coatings have shown noticeable corrosion resistance and good performance in the photocatalytic test as the degradation rates of methyl orange higher than 45 %. Thus, multifunctional PEO coatings on Ti6Al4V alloy are obtained.