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This study investigated the effects of oxygen addition on the microstructure, phase transformations, and oxidation resistance of TiAl alloys at 1023 K. The addition of oxygen stabilized the α (α 2) phase at the expense of the γ phase and reduced the oxidation mass gains of the TiAl alloys by more than 20%. Oxide scales composed of external scattered Ti-rich oxide particles/Al-rich/Ti-rich mixed Ti/Al oxides, and internal affected zones with Al-rich precipitates were observed in all oxidized samples. The results showed that the microstructure and phase transformations of the alloys were altered by adding 1 at% oxygen. The addition of O accelerated the α → α 2 chemical ordering reaction and partly suppressed the α → γ massive phase transformation. The oxidation resistance of the TiAl alloys in air at 1023 K was not significantly affected by the addition of oxygen. • Oxygen induces α→α 2 ordering reaction at the expense of the α→γ massive phase transformation. • α→α 2 ordering phase transformation occurs within 1373–1473 K. • Oxygen addition expands the α(α 2) + γ two-phase region in TiAl alloys. • The dissolved oxygen level in the TiAl alloy increased by α→α 2 phase transformation. • Oxygen addition reduces the oxidation mass gain of TiAl. [ABSTRACT FROM AUTHOR]

Effect of grain refinement from 370 to 34 μm on oxidation of transition Fe–13Cr–5Ni alloy at 973 K in Ar–21 vol%O 2 was investigated. The measured weight gains were fitted taking into account a mixed kinetic model with an initial linear and subsequent parabolic growth behaviour. Different scale microstructural evolution was discussed. Contribution of grain refinement to the oxidation is predominantly due to its effect on the inward oxidation process. Decreasing grain size promoted intergranular oxidation, accelerated formation of the Cr-containing inner scale, contributed to the faster transition to the steady state oxidation and correspondingly slightly improved the oxidation resistance. [ABSTRACT FROM AUTHOR]