The effect of nitrogen on the oxidation behavior of 25Nb25Ti50Al

• Published in: Scripta metallurgica et materialia 1992-03, Vol.26 (5), p.767-770
• Main Authors: Brady, M.P, Hanrahan, R.J, Randall, S.P.Elder, Verink, E.D
• Format: Article
• Language: English
• Subjects: Applied sciences; Corrosion; Corrosion mechanisms; Exact sciences and technology; Metals. Metallurgy
• ISSN: 0956-716X
• DOI: 10.1016/0956-716X(92)90435-H

The oxidation kinetics of a 25Nb--25Ti--50Al (at.%) alloy was studied in air, pure oxygen, and an air--O survey environment to determine if the presence of nitrogen effects the oxidation of the alloy. Oxidation kinetics was monitored by thermogravimetry at 1300 deg C for 24 h and the scales formed were characterized intact by X-ray diffraction. Paralinear oxidation kinetics was observed in air, and near parabolic oxidation kinetics was observed in pure O. The 24 h weight gain was moderately greater in air than in pure O. Exposure to the changing air--O survey environment produced a 24 h weight gain > 100% that observed in air or O. The oxidation kinetics from 6-24 h was near parabolic. During the first 6 h of exposure, a complicated mix of parabolic and linear rate laws was followed (two approximate parabolic regions connected by an inflection point characteristic of break away oxidation and a linear region). TiO sub 2 was the predominant reaction product produced in all three test environments. The scales formed in air and pure O also contained large quantities of AlNbO sub 4 and Al sub 2 O sub 3 . However, the scales formed in the air--O environment contained only trace quantities of AlNbO sub 4 and Al sub 2 O sub 3 . The results suggested that the presence of the nitrogen during the oxidation of this alloy significantly affected both the rate and the mechanism of oxidation.