High temperature oxidation of a Nb-Al-Si coating sputter-deposited on titanium

The oxidation behavior of an amorphous 58Nb-38Al-4Si (at.%) coating sputter -deposited on a titanium substrate has been studied in air at temperatures of 973-1173 K, The oxidation of the coated specimens follows a familiar par abolic rate law for a long time of oxidation at all temperatures examined, in contrast to the paralinear kinetics of uncoated titanium. Even though th e coated specimen has higher oxidation rates than the amorphous Nb-Al-Si al loy itself, the amorphous Nb-Al-Si coating is highly effective in providing protection against the oxidation of titanium, The cross-sectional observat ion and energy-dispersive X-ray spectrometer analysis of the oxidized speci men reveal that titanium diffuses outward in the coating and is also presen t in the inner part of the oxide scale. The oxide scales formed on the coat ed specimens primarily consist of TiO2, AlNbO4 and kappa-Al2O3 The presence of less protective TiO2 within the oxides appears to decrease the oxidatio n resistance of the coating, but is not significantly detrimental. (C) 2000 Elsevier Science Ltd. All rights reserved.