Oxidation resistance of TiAl significantly improved by combination of preoxidation and Hf addition

The cyclic-oxidation resistance of a TiAl coupon in a flow of purified oxygen at 1300 K has been significantly improved by preoxidation at 1200 K for 100 ks in a pack of a mixture of 70 mass% chromia and 30 mass% metallic chromium powders under an Ar atmosphere. The excellent oxidation resistance obtained is attributable to the formation of alumina scales by the preoxidation, where oxygen partial pressure was thought to be maintained very low. The addition of 0.24 mass% Hf to TiAl improved the oxidation resistance by forming scales rich in alumina. A combination of the preoxidation and the Hf addition further improved the oxidation resistance. After 10 cycles (200 h) of oxidation at 1300 K the scale thickness was still less than 1 μm.