Characterizations of anodic oxide films formed on Ti6Al4V in the silicate electrolyte with sodium polyacrylate as an additive

Anodic oxidation coatings were prepared on Ti6Al4V alloy in Na2SiO3-based electrolyte with sodium polyacrylate (PAAS) as an additive, to develop a route of making thicker films under 200 V. The addition of PAAS as an anion species in the anodic electrolyte increased the conductivity of the solutions, leading to the reduction in breakdown voltage and thus the more vigorous discharging process on the metal surface during anodization. With the addition of PAAS, more and bigger porous and thicker ceramic coatings were obtained as shown by scanning electron microscopy (SEM) and Image-pro Plus software; the addition of PAAS promoted the growth of robust rutile TiO2 and/or Al2TiO5 in the anodic coatings; however, the excessive addition of PAAS resulted in the incorporation of more amorphous silicates in the thicker outer anodic films as shown from the EDS measurement, X-ray diffraction and Raman spectra. Therefore, the microhardness and adhesion of the anodic samples with PAAS at an appropriate concentration of 0.7 g/L improved by about 2 times and 4 times, respectively; their friction coefficient and wearing rate were also reduced to quite lower values compared to those for the anodic sample without PAAS addition.