Improved High-Temperature Oxidation Properties for Mn-Containing Beta-Gamma TiAl with W Addition

TiAl-based alloys containing relatively high Mn (e.g., Ti–42Al–5Mn (in at.%)) possess excellent hot workability and cost-effective advantages, but may also have poor oxidation resistance at high temperature. Hence, additional attention needs to be paid on the oxidation resistance of these alloys. In this study, a Mn-containing γ-TiAl-based alloy with the composition of Ti–42Al–5Mn has been chosen, and the oxidation behavior of this alloy with different W additions under thermal cycling conditions at 800 °C was investigated. The morphology and the composition distribution of the oxide scale were analyzed by means of scanning electron microscopy equipped with energy-dispersive spectroscopy, X-ray diffractometry and X-ray photoelectron spectroscopy. Auger electron spectroscopy depth profiling was used to investigate the effect of W on the initial stage of oxidation. It shows that the addition of 1 (at.%) W can significantly reduce the oxidation mass gain, and the oxidation reaction rate constant is decreased by an order of magnitude. The adherence of oxide scale is greatly enhanced with no spallation observed in Ti–42Al–5Mn–(0.8, 1)W after 100-h cyclic oxidation. Tungsten promotes the selective oxidation of Al and formation of a denser oxide scale which prevents the inward diffusion of oxygen; in this way, high-temperature oxidation resistance of the alloy is improved.