MECHANICAL-PROPERTIES AND MICROSTRUCTURAL CHARACTERIZATION OF A SUPERPLASTIC TIAL ALLOY

Superplastic deformation in a gamma-TiAl which had a duplex microstructure, equiaxed primary gamma and lamellar alpha(2) + gamma, was investigated with respect to the effect of temperature, strain rate, and environment. A maximum elongation of 540% was obtained at 1280 degrees C and a strain rate of 8 x 10(-5) s(-1) in argon. The specimens tested in argon yield substantially higher ductility than those tested in vacuum. An argon environment is also more favorable than vacuum in terms of desirable microstructure because of the retardation of aluminum depletion at the testing temperature. Microstructural examination revealed significant grain growth and cavitation in a Ti-rich layer near the surface. The a phase interspersed between the gamma phase accommodated grain boundary sliding and retarded grain growth because of the chemical dissimilarity between the alpha and gamma phases. Possible high temperature deformation mechanisms of this alloy are also discussed.