γ-TiAl intermetallic alloys can be potentially employed as structural materials for many industries where high temperature and access of atmosphere with variable oxygen partial pressures are often met. Different partial pressures of oxygen may influence oxidation behavior and induce different oxide scale phase constitutes. This study investigated the influences of oxygen partial pressures on the oxidation resistance of a γ-TiAl alloy, Ti-46.7Al-1.9W-0.5Si (at.%), in Ar-O2 environments (5%O2, 20%O2 and 80%O2) at 750, 850 and 950 °C, respectively. The oxidation products were characterized using scanning electron microscopy, energy-dispersive x-ray analysis, x-ray diffraction and transmission electron microscopy. The oxidation kinetic results achieved by a discontinuous gravimetric method revealed that the alloy oxidized following a parabolic rate law. The oxidation resistance of the alloy was enhanced with increasing the oxygen partial pressures at all three experimental temperatures. Multilayered oxide scales of TiO2/Al2O3 were developed during the oxidation process. The enhancement of oxidation resistance was resulted from preferential generation of Al2O3 and the reduction in defects in TiO2 with increasing the oxygen partials pressures.
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The authors gratefully acknowledge the financial support from the European Union (INNOVATIAL Project NMP3-CT-2005-515844) and the access using TEM facilities funded within contract HPRI-CT-1999-00024 of the “Improving Human Potential” program of the European Commission”.
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