EFFECT OF MICROSTRUCTURE ON OXIDATION OF TIAL INTERMETALLIC COMPOUND

The oxidation of a Ti-50 mol%Al alloy has been investigated at temperatures from 873 to 1073 K in air using cyclic (18 ks x 10 cycles) or continuous (180 ks) oxidation tests for as-cast and homogenized specimens. The microstructure of the as-cast specimen has a lamellar structure consisting of the alpha2 and gamma phases, while the homogenized specimen consists of the gamma single phase. The mass gains of both specimens after cyclic or continuous oxidation at 873 K were very small. At 973 K, the mass gain of the homogenized specimen was small for the cyclic oxidation test, compared with that of the as-cast specimen containing a large amount of the alpha2 Phase. Thus it was concluded that the oxidation resistance of TiAl at 973 K was apparently influenced by the microstructure. At 1073 K, the mass gain of the homogenized specimen apparently increased during cyclic oxidation with fracture of the oxide scale on the specimen surface by thermal stress, because the specimen was covered with a large amount of the oxide scale Of Al2O3 which exhibited poor adhesion to the matrix. The mass gain of the as-cast specimen was smaller than that of the homogenized specimen in cyclic oxidation. This indicates that the adhesion of the oxide scale is affected by the microstructure. However, the mass gain of both specimens after continuous oxidation was small compared with that of the cyclic oxidation. It was considered that the adhesion of the oxide scale is not affected by the thermal stress during the continuous oxidation.