DIFFERENT MORPHOLOGIES OF LAMELLAR STRUCTURE IN A GAMMA-PHASE TITANIUM ALUMINIDE

Different morphologies and the formation mechanism of the lamellar structure of a Ti-48at.%Al alloy were investigated. The wavy lamellar structure was obtained when the alloy was annealed at high temperatures in the sigma+gamma region. Equiaxed alpha and gamma grains transformed into short plates, and neighboring short plates with a similar orientation connected with each other to form the wavy lamellar structure. The acicular structure was formed when the alloy was cooled from the alpha region. The results suggested that the orientation relationship of the acicular structure was not the same as that of the primary lamellar structure. This is probably because of the precipitation of the gamma phase on the non-close-packed planes of the alpha phase. The discontinuously coarsened lamellar structure was obtained when the primary lamellar structure was given a stabilizing treatment. Coarse lamellae nucleated on both the gamma and alpha(2) matrices, resulting in packets of lamellae with different orientations.