Kazuo Kasahara1, Kenki Hashimoto1, Haruo Doi1 and Tokuzou Tsujimoto1
1National Research Institute for Metals, Meguro-ku, Tokyo 153, Japan
The oxidation behavior of the intermetallic compound TiAl with additions of Cr, Y, Mn and Si as the third elements has been investigated in a temperature range between 1123 and 1223 K under the atmospheric environment. The oxidation products have been examined by X-ray diffraction, scanning electron microscopy, and electron probe microanalysis.
The mass gain by oxidation increased with small additions of Cr or Y and decreased with their additions above 1 at%. The oxidation rates of those alloys were always larger than those without the third elements. Thus, it was concluded that the addition of Cr or Y does not improve the oxidation resistance. The oxidation resistance of the alloy containing Mn was not good. The addition of Si decreased the mass gain with increasing Si content up to 0.5 mass%. However, no further increase in oxidation resistance was observed by adding more than 0.5 mass%Si.
The surface oxides were composed predominatly of three layers, i.e., TiO2, Al2O3 and TiO2+Al2O3 from the outer side. Only in the alloys containing Mn and Si, other oxides, i.e., MnTiO3 and SiO2, were detected. A continuous film of SiO2 was formed at the alloy/oxide interface in the alloys containing more than 0.5 mass%Si. It was concluded that the formation of the continuous SiO2 film assisted the protective ability of the Al2O3 layer against oxidation by decreasing the diffusion rates of the alloy elements and oxygen ions.
The weight of the oxide spalled on cooling decreased considerably in the alloys containing Y as compared with those of the other alloys. This result indicates that the addition of Y improves the adherence of the surface oxide.
intermetallic compound, titanium-aluminum-chromium alloy, titanium-aluminum-silicon alloy, titanium-aluminum-manganese alloy, titanium-aluminum-yttrium alloy, high temperature oxidation, oxide layers, oxide analysis
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