| A fully lamellar y-TiAl based alloy Ti-44Al-8Nb-1B was investigated for its oxidation behavior in this study. This alloy subjected to exposure at 700℃in air for 0-1000h. Exposed specimens were prepared with different surface conditions including grinding and grinding+ electro-polishing. The oxidation layers of the alloy formed at the high temperature were analyzed by XRD, SEM (equipped with EDS). The effects of the oxidation on tensile properties and the related mechanism were revealed for the whole oxidation process (200h. 500h and 1000h). In the meantime, the oxidation kinetics curves were established using thermo gravimetric analysis equipment.It was found that the oxide scales were composed of TiO2 and Al2O3 and is only 1-2μm thick when exposed to the 700℃air for 1000h. The oxidation layer is heterogeneous in term of phase structure and the distribution. There is a Al-enrichment layer in the oxide scales and it enhances the oxidation resistance for the alloy. Besides, as the oxidation proceeds, Nb is enriched under the oxidation scale, preventing the further diffusion of oxygen atoms. As a result, oxidation resistance of the high Nb-containing alloy is improved. The room temperature ductility of the alloy was deteriorated significantly, while the strengths remained essentially unchanged. Compared with grinding-only samples, the grinding and electro-polishing samples can improve the oxidation resistance slightly but no improvement in tensile properties can be achieved. Also found was that the borides on the surface and grain boundaries tend to oxidize faster than theα2+γlamellae matrix probably because of the depletion of Al in the borides and faster diffusion along the grain boundaries.
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