The improvement of high-temperature oxidation of Ti–50Al by anodic coating in the phosphoric acid Original Research Article

The high temperature cyclic oxidation resistance of Ti–50Al can be improved by anodic coating in phosphoric acid aqueous solution (4 wt% H3PO4) at 18°C. Sparking occurs sporadically on the surface as the voltage is over 300 V and the instantaneous current density after 45 min of anodization increases with increasing voltage. The anodic films are amorphous and contain substantial amount of phosphorus. Cyclic oxidation test indicates that the anodization can remarkably reduce the oxidation in air at 800°C and the improvement increases with increasing anodizing voltage up to 400 V, at which the parabolic oxidation rate constant can be reduced to about 1/600 of that for as-homogenized Ti–50Al. Raman spectra show that the anodic film can slow down the formation of rutile and α-Al2O3 during oxidation. The doping effect of phosphorus ions in titanium oxide accounts for the improvement of high temperature oxidation of Ti–50Al.