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This study focuses on the effect of tungsten as a Laves phase forming element on the steam oxidation behavior of the Fe-9Cr alloy. Steam oxidation tests of the Fe-9Cr alloys with different tungsten concentrations were conducted in an Ar-15%H2O gas mixture at 923 K for up to 345.6 ks. The results showed that tungsten addition significantly improved the oxidation resistance of the Fe-9Cr alloy. By forming FeWO4 in the internal oxidation zone (IOZ) during oxidation, the oxygen partial pressure in this zone corresponded to Fe(W)/Fe2W/FeWO4 equilibrium, which is slightly lower than the Fe/FeO equilibrium. Therefore, the matrix of the IOZ was not being oxidized to form the inner scale, resulting in an improvement in oxidation resistance. A finer and higher fraction of the Fe2W phase produced by rapid cooling provided better Cr enrichment and improved the oxidation resistance of the alloys. [ABSTRACT FROM AUTHOR]

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]