TEM investigations concerning the effect of nitrogen on the oxidation of TiAl

New results are presented regarding the influence of nitrogen on the oxidation behavior of gamma-TiAl, Isothermal oxidation experiments were carried out in air at 900 degrees C for various times. The samples were investigated by cross sectional transmission electron microscopy (TEM). Exposure in air resulted in a fast growing mixed oxide scale consisting of aluminum and titanium oxides. The presence of nitrogen leads to the formation of titanium nitrides at the metal/scale interface and influences the initial behavior. After 5 min oxidation, a layer enriched in nitrogen was observed beneath the oxide scale. After a 1 h exposure, a two phase region consisting of Al2O3 and TiN had formed at the metal/scale interface. A similar microstructure could be observed also after long time oxidation up to 500h. The formation of an Al-depleted zone beneath the oxide scale was observed after 1 h oxidation. This layer developed from a single phase region to a two phase region during longer exposure times.