The effect of surface preparation on the oxidation behavior of gamma TiAl-base intermetallic alloys

Abstract

Titanium aluminides, specifically the intermetallic compound gamma TiAl, are being investigated as potential aerospace and automotive materials due to high specific strength and stiffness. The oxidation behavior of gamma TiAl has been studied extensively. Oxygen exposures tend to produce slow growing alumina rich scales at low temperatures. At higher temperatures (approximately 800 C), the alumina breaks down locally and mixed oxide nodules form. At temperatures at and above 1,000 C, the nodules grow rapidly and merge to form a thick mixed oxide scale. The oxidation behavior in atmospheres containing nitrogen is significantly different. Nitrogen reacts with titanium in the alloy to form titanium nitrides at the scale/alloy interface. It is not possible to form a continuous, protective alumina layer, resulting in rapid oxidation in air. Important initial research also pointed to surface preparation as a potential factor in the oxidation behavior of gamma TiAl alloys. The material used for this study was stoichiometric Ti-50Al (nominal composition in atomic percent), a single phase {gamma} TiAl alloy with large equiaxed grains. In addition, material with a lower aluminum content (Ti-48Al) was also investigated. This alloy is notable because it contains significant amounts of the intermetallic alpha-2 Ti{sub 3}Al dispersed in small lamellarmore » colonies as a second phase.« less