Energy of Planar Faults as a Function of Composition in Binary and Ternary Tial Alloys

Establishing the chemical dependence of thermally activated processes which govern plasticity in intermetallic alloys requires that the dislocation dissociation reactions be determined as a function of composition. A major parameter governing such reactions is the relative fault stability as a function of composition. Here the results of first principles electronic structure calculations, using the layer Korringa-Kohn-Rostoker method, are reported for planar faults in γ TiAl at various compositions. The influence of dilute substitutional impurities on the fault energies is treated using the coherent potential approximation. The variation of fault energies as a function of binary composition (TixAl1-x where 52≤x≤49) and the addition of transition metals (Cr, Mn and Nb at 2% concentration) are presented. The influence of this chemical dependence on the stability of <101] super-dislocations is discussed, along with expected trends in the flow stress behavior.