In-depth study of the influence of electrolyte composition on coatings prepared by plasma electrolytic oxidation of TA6V alloy

Abstract

Coatings were prepared on TA6V alloy by plasma electrolytic oxidation (PEO) using a standard electrical signal. Influence of electrolyte composition on coating characteristics was then extensively studied using four electrolytes of increasing complexity, containing KOH, Na2SiO3 and NaAlO2. The combination of SEM, GDOES, XRD characterizations on the one hand and of thermodynamic calculations on the other hand, deeply clarified coating compositions, showing in particular that they include both amorphous and crystalline phases. Amorphous phase resulted directly from the presence of silicate in solution, and was made of complex Si-based oxides difficult to clearly identify. Depending on electrolyte composition, crystalline phases in coatings included simple oxide (i.e.anatase and rutile TiO2) and/or mixed oxide (Al2TiO5), resulting from both substrate oxidation and deposition from electrolyte. Therefore, this study successfully offered an innovative approach, combining both experimental characterizations and thermodynamic calculations, to study and tune chemical characteristics of PEO coatings on TA6V.