Deformation mechanisms of near-stoichiometric single phase TiAl single crystals: A combined experimental and atomistic modeling study

Abstract

The purpose of this paper is to present the results of a combined experimental and theoretical investigation of the reason why the room temperature deformation of PST (polysynthetically twinned) crystals of TiAl occurs primarily by twinning while deformation of single phase TiAl occurs by dislocation slip. It is not clear at present whether this difference in deformation behavior is due to differences in microstructure or differences in composition. Since the stress needed to produce twinning in PST crystals is substantially less than the stress required to produce dislocation slip in the single phase material, it would appear that the twinning stress is dramatically increased by increasing the aluminum content. This suggest is indeed supported by the results of atomistic studies of dislocation dissociations and core structures in the L1{sub 0} TiAl presented in this paper. However, since it is impossible to grow single crystals of single phase material having less than 54 at% Al, this finding cannot be easily checked experimentally For this purpose the authors have developed a novel sample preparation technique, Employing solid state diffusion to reduce the Al content, which allows them to produce layers of 51 at% Al single phase TiAl sandwiched between Ti{sub 3}Al andmore » TiAl with a surplus of Al. These samples were then tested in compression and it was, indeed, found that the single phase TiAl with low aluminum content deforms by twinning, in the same way as the PST crystals with a similar aluminum content.« less