Amorphous sol–gel SiO₂ film for protection of an orthorhombic phase alloy against high temperature oxidation

Silica coating derived by sol–gel processing was deposited on an orthorhombic phase Ti–22Al–26Nb alloy by dip-coating technique. Isothermal oxidation at 800 and 900 °C and cyclic oxidation at 900 °C in static air of the coated and uncoated specimens were performed to investigate the effect of the silica coating on the oxidation behavior of the Ti–22Al–26Nb alloy by thermogravimetry, SEM and XRD. The average parabolic rate constants of the coated specimens were lower than those of uncoated ones. Additionally, the present film exhibited a beneficial effect on the cyclic oxidation resistance of the alloy in air. TiO₂, Nb₂TiO₇ or AlNbO₄ were the main phases formed on the alloy. The thin film could inhibit the growth of the oxides. The possible mechanism of the thin film on the oxidation behavior of the alloy was discussed.