9626344 Vitek This study is a combined, experimental and theoretical project on mechanisms of plastic deformation in titanium aluminide, TiAl. The experimental portion is used as input for the theoretical portion and vice versa. The objectives of the study are to fully characterize and identify the deformation modes in polysynthetically twinned single crystals and in lamellar polycrystals of TiAl-based alloys, to show how deformation is transmitted across the various types of boundaries (including domain and grain boundaries), and to determine the sources of the dislocations and twins. The experimental techniques to be employed are mechanical tests on single crystals and polycrystals, followed by characterization of the deformation modes using optical, atomic force, and transmission electron microscopy. The theoretical program involves atomistic modeling of dislocation core structures, interfacial reactions, and twinning processes, using a variety of interatomic potentials. The potentials to be used are the embedded atom and/or Finnis-Sinclair type, as well as quantum mechanically- based bond order potentials. The development of new interatomic potentials for use in this non-cubic structure will be an important part of the program, as will the development of new experimental techniques for the determination of deformation modes. %%% The results of the study are expected to be of great utility in understanding how, and under what circumstances, low symmetry materials can be toughened. Furthermore, it could show what techniques might be used to toughen intermetallic compounds. ***
