THE OXIDATION RESISTANCE OF A SPUTTERED, MICROCRYSTALLINE TIAL-INTERMETALLIC-COMPOUND FILM

The oxidation behavior of a cast TiAl intermetallic compound and its sputtered microcrystalline film was investigated at 700-900 degrees C in static air. At 700 degrees C, both the cast alloy and its sputtered microcrystalline film exhibited excellent oxidation resistance. No scale spallation was observed. However, at 800-900 degrees C, the oxidation kinetics for the cast TiAl alloy followed approximately a linear rate law, which indicates that it has poor oxidation resistance over this temperature range. The poor oxidation resistance of TiAl was due to the formation of an Al2O3 + TiO2 scale which spalled extensively during cooling. Nevertheless, the sputtered, TiAl-microcrystalline film exhibited very good oxidation resistance. The oxidation kinetics followed approximately the parabolic rate law at all temperatures. Although the composition of the scales was the same as that of scales formed on the cast alloy, the scales formed on the sputtered microcrystalline-TiAl film are adherent strongly to the substrate. No scale spallation was found at 700-800 degrees C, while a small amount of spallation was observed only at 900 degrees C. This indicates that microcrystallization can improve the oxidation resistance of the TiAl alloy.