The high-temperature oxidation behavior of vanadium-aluminum alloys

The oxidation behavior in air of pure vanadium, V-30Al, V-30Al-10Cr, and V-30Al-10Ti (weight percent) was investigated over the temperature range of 700–1000° C. The oxidation of pure vanadium was characterized by linear kinetics due to the formation of liquid V₂O₅ which dripped from the sample. The oxidation behavior of the alloys was characterized by linear and parabolic kinetics which combined to give an overall time dependence of 0.6–0.8. An empirical relationship of the form: W/A=Bt + Ct^1/2 + D was found to fit the data well, with the linear contribution suspected to be from V₂O₅ formation for V-30Al and V-30Al-10Cr, and a semi-liquid mixture of V₂O₅ and Al₂O₃ for V-30Al-10Ti. The parabolic term is presumed related to the formation of a solid mixture of V₂O₅ and Al₂O₃ for V-30Al and V-30Al-10Cr, and TiO₂ for V-30Al-10TiThe addition of aluminum was found to reduce the oxidation rate of vanadium, but not to the extent predicted by the theory of competing oxide phases proposed by Wang, Gleeson, and Douglass. This was attributed to the formation of a liquid-oxide phase in the initial stages of exposure from which the alloys could not recover. Ternary additions of chromium and titanium were found to decrease the oxidation rate further, with chromium being the most effective. The oxide scales of the alloys were found to be highly porous at 900° C and 1000° C, due to the high vapor pressure of V₂O₅ above 800° C.