A STRUCTURAL STUDY OF OXIDATION IN AN AL2O3 FIBER-REINFORCED TITANIUMALUMINIDE COMPOSITE

A composite of titanium aluminide, reinforced with ZrO2 toughened Al2O 3 fibers, has been produced by pressure casting. The stability of the microstructure during vacuum and air annealing was investigated by sca nning and transmission electron microscopy (TEM). Processing resulted in partial dissolution of ZrO2 of the fiber into the molten metal whic h solidified into a two phase lamellar alpha(2) + gamma matrix. Vacuum annealing caused dissolution of Al2O3 fiber into the matrix, transfor mation of the matrix into gamma and precipitation of ZrO2 and Al2Zr wi thin gamma. During air annealing diffusion of O through the fiber resu lted in the formation of Al2O3 coated ZrO2 nodules extending from the fiber surface into the matrix in some regions and in the other regions the growth of Al2O3 into the gamma of the lamellar matrix. An A15 pha se with the metal composition, Ti3Al2, was found between the external oxide scale and the metal matrix.