Effect of forging on the oxidation behavior of β-solidifying high Nb-containing TiAl alloy

This study focuses on the oxidation behavior of TiAl alloys containing only γ and β/B2 phases, and investigates the oxidation behavior of the as-cast and as-forged alloys at different temperatures. The oxidation degree is very low at 700 °C for the as-cast and as-forged alloys, and the weight gain are 0.075 mg/cm 2 and 0.066 mg/cm 2 , respectively. The scratches on the surface are clearly visible. When oxidized at 800 °C, the weight gain of as-cast and as-forged alloys are 0.473 mg/cm 2 and 0.413 mg/cm 2 , respectively. The β phase depresses with the formation of TiO 2 particles on its surface, and many holes are formed at the γ phase. When oxidized at 900 °C, the weight gain of as-cast and as-forged alloys are 1.866 mg/cm 2 and 1.846 mg/cm 2 , respectively. There is a mixed product of the Al 2 O 3 and TiO 2 on the surface, and the TiO 2 grows in the outer layer of Al 2 O 3 , but the Al 2 O 3 layer is not completely covered by TiO 2 . The structure of the oxide film is TiO 2 layer/Al 2 O 3 layer/TiO 2 +Al 2 O 3 layer/Nb + Mn + Cr riched layer. During the oxidation process, the β phase in the sub-surface layer decomposes. Oxygen diffuses into the alloy and promotes the phase transformation of β/B2→α 2 . The morphology and distribution of the β/B2 phase in the as-forged alloy limits the diffusion of oxygen into the alloy, and the more uniform grain distribution makes the distribution of oxide particles more uniform, enhancing the oxidation resistance.