EARLY-STAGE OF HIGH-TEMPERATURE OXIDATION OF TIAL AND FEAL AT LOW-OXYGEN PARTIAL PRESSURES

The oxidation behavior of Ti-50 mol%Al and Fe-40 mol%Al at high temper atures and at low oxygen partial pressures was investigated mainly by means of X-ray photoelectron spectroscopy and scanning electron micros copy. The layer structure consisting of the outer TiO2 layer and the i nner TiO and Al2O3 mixed layer was formed on the surface in the early stage oi oxidation of TiAl in air, The existence of TiO was manifested in the oxide products of TiAl. At low oxygen partial pressures, the s tacking of such layers was no longer present, but instead there was th e mixture of Ti-oxides and Al2O3 on the surface, without forming any p rotective Al2O3 layer against oxidation. The grain size of the oxides formed on TiAl increased with increasing temperature and with decreasi ng oxygen partial pressure. The layer structure consisting of the oute r Fe2O3 layer and the inner Fe3O4 and Al2O3 layer was formed in the ea rly stage of oxidation of FeAl in air. In this case, the inner Al2O3 l ayer acted to be a protection layer against the oxidation. On the othe r hand, only Al2O3 was observed on the surface of FeAl oxidized at low partial oxygen pressures and high temperatures except 1473 K. At 1473 K, a little Fe3O4 was also observed on the Al2O3 layer. Tile oxide mo rphology in FeAl did not change with the oxidation conditions so large ly as that in TiAl.