MICROSTRUCTURE CONTROL AND HIGH-TEMPERATURE PROPERTIES OF TIAL BASE ALLOYS

An equiaxed fine grain structure, a gamma grain structure with the pre cipitated alpha(2) laths, and a fully lamellar structure were obtained by the microstructure control using thermomechanical processing and h eat treatment. The key to obtaining the equiaxed fine grain structure using isothermal forging is to decompose the lamellar structure and th en produce the fine grain microstructure through dynamic recrystalliza tion. TiAl base alloys consisting of fine equiaxed grains, in particul ar, Ti-39Al-9V consisting of the gamma and B2 phases exhibited superpl astic elongation of more than 600% at 1423 K. Creep rupture properties of TiAl binary alloys with various microstructures were studied in pu rified He in the temperature range from 1073 to 1373 K. Above 1173 K t he precipitated alpha(2) phase improved the steady state creep rate an d creep life. At 1023 K, the alpha(2) phase did not improve the creep rate, although the steady state creep rate decreased and the creep lif e increased as the gamma grain size increased. (C) 1998 Elsevier Scien ce Limited. All rights reserved.