Masaki Kumagai

Influence of chlorine on the oxidation behavior of TiAlMn intermetallic compound

Abstract Excellent oxidation resistance of reactive-sintered titanium aluminides was reviewed and the mechanism of forming protective Al 2 O 3 film was studied. TiAlue5f8Mn containing more than 200 mass ppm chlorine from raw titanium powder showed very little mass gain after oxidation from 1173 to 1398 K in air. The chlorine effect was found obviously in composition of α 2 + γ and γ regions in the Tiue5f8Al phase diagram. The chlorine effect was found even in a plasma arcmelted TiAlue5f8Mn alloy with chloride covering or oxidized in air containing a small amount of chlorine gas. Also, other halogen elements as fluorine and bromine had the same effect as chlorine. It was clear, in particular by surface analyses that chlorine existed in TiO 2 near the oxide/metal interface in the early stage of oxidation and decreased oxygen ion vacancies in TiO 2 . Then TiO 2 growth was interrupted and protective Al 2 O 3 scale was formed on the titanium aluminide.

Effect of oxidation treatment on wear resistance for TiAl-Mn intermetallic compound.

Wear resistance of reactive-sintered TiAl-Mn which was coated with oxide film was evaluated by pin-on-disk type wear test. Oxide film was coated by using oxidation reaction in air at 1173K. The two coated TiAl-Mn alloys show much less wear loss than uncoated ones. After wear test, oxide film remains partialy in the coated Ti-47.3Al-1.7Mn. On the contrary, oxide film of the coated Ti-43.2Al-1.6Mn is worn over. The low wear loss in the later is due to hard Ti-rich layer which is formed under oxide film produced during oxidation treatment. Thickness of Ti-rich layer increases with titanium content of TiAl-Mn or oxidizing temperature. It is supposed that Ti-rich layer is hardened by solutioning oxygen. Excellent wear resistance of the oxidized TiAl-Mn is caused by not only oxide film but also Ti-rich layer. This superior wear resistance surface can be obtained easily by oxidation in air of reactive-sintered TiAl-Mn containing chlorine.