Composition and growth rate effects in directionally solidified TiAl alloys

Effects of alloy compositions and growth rates on the microstructure and the deformation behavior of fully lamellar TiAl alloys were systematically investigated by directional solidification (DS) techniques. Some beta stabilizing elements, such as Mo, Nb and Cr, have been added in order to increase the beta phase field in the binary system. It was found that the lamellar orientation was aligned nearly 0-45 degrees to the growth direction in Ti-46Al-2Nb and Ti-46Al-2Cr(at.%) DS ingots grown at the growth rate of 90 mm h(-1). Therefore, it could be concluded that there is a good possibility to control the lamellar orientation by adding some beta stabilizing elements, such as Mo, Nb and Cr, in the TiAl system. In the Ti-47.5Al-2.5Mo DS alloy, the lamellar boundary was nearly perpendicular to the growth direction at growth rates of 180 and 360 mm h(-1), however, it was nearly parallel to the growth direction at the growth rate of 90 mm h(-1). These results indicate that the lamellar boundary orientation of DS ingot has been affected by the growth rate as well as the alloy composition. (C) 1997 Elsevier Science S.A.