Abstract
According to the basic information of sequences of characteristic atoms in the FCC Ti–Al system, the compositional variations of the atomic states, atomic potential energies, atomic volumes, lattice constants and cohesive energies of the ordered FCC Ti 3Al-type alloys have been calculated. Without considering the influence of the second nearest neighbouring atoms, the D0 22- and L1 2-Ti 3Al compounds have the same atomic state, same atomic volume, same lattice constant and same cohesive energy. Their average atomic state is 0.75[Ar](3d n) 0.229(3d c) 2.5669(4s c) 0.5448(4s f) 0.6593 +0.25[Ne](3s c) 1.772(3p c) 1.008(3s f) 0.22. Considering the influence of second neighbouring atoms, the calculated atomic potential energies, formation energies and lattice constants of the D0 22- and L1 2-Ti 3Al compounds are, respectively, ε a = - 4.8158 eV / atom , Δ H=−0.3378 eV/atom, a=0.39131 nm, c=0.44108 nm, c/a=1.1272; and ε a =−4.7952 eV/atom, Δ H=−0.3172 eV/atom, a=0.41091 nm. The D0 22-Ti 3Al compound is slightly more stable than the L1 2- Ti 3Al compound. The correctness of these results has been proved indirectly by the calculated results of the D0 22- and L1 2-TiAl 3 as well as HfGa 2- and ZrGa 2-type TiAl 2 compounds with the same basic information and the same method. Between 0 and 40 at.%Al, the HCP lattice is more stable than the FCC lattice, for which the atomic state factor may play determining action. The brittleness order of these compounds is L1 2-Ti 3Al<D0 22-Ti 3Al<L1 0-TiAl<D0 22-TiAl 3.
Published Version
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