EFFECT OF ORDERING ENERGY AND STOICHIOMETRY IN SIGMA=5 BOUNDARIES IN B2 COMPOUNDS

The relaxed atomistic grain boundary structures in B2 aluminides were investigated using molecular statics and embedded atom potentials in o rder to explore general trends for a series of B2 compounds. We studie d free surface energies and grain boundary structures in three compoun ds: FeAl, NiAl and CoAl. These alloys represent a series of materials with increasing antiphase boundary energies. The misorientations chose n for detailed study correspond to the Sigma 5(310) and Sigma 5(210) s ymmetrical tilt grain boundaries. The effects of both boundary stoichi ometry and bulk simulation block stoichiometry on grain boundary energ etics were investigated in detail. The structures obtained for the thr ee alloys are very similar. Defect energies were calculated for bounda ries contained in both stoichiometric and off-stoichiometric bulks. Th e surface energies for these B2 aluminides were also calculated so tha t trends concerning the cohesive energy of the boundaries could be stu died. The implications of the increasing ordering energy, stoichiometr y, and multiplicity of possible structures for grain boundary brittlen ess are discussed.