An experimental and theoretical study of bonding mechanisms in ternary γ-TiAl + X (X = Cr, Mn, Nb) alloys

摘要

The local atomic order and the electronic structure of γ-(Ti_(46)Al_(54))_(97)X_3 (X = Cr, Mn, Nb) alloys have been investigated by Electron Energy Loss (EELS) and X-ray absorption (XAS) spectroscopies. The substitution sites of solute atoms have been determined experimentally by Atom Location by CHanneling Enhanced MIcroanalysis (ALCHEMI), Extended X-ray Absorption Fine Structure (EXAFS) and X-ray Absorption Near Edge Structure (XANES) in the framework of a multiple scattering (MS) formalism. Furthermore, EXAFS provides a way to probe the local relaxation around the atom of interest. A strong elastic relaxation is found to occur around Mn solute atoms, while Nb solute atoms generate almost no elastic strain. From a calculation in the band structure (BS) formalism, the influence of the ternary solute atom on charge density distribution has been studied and has shown that the addition elements mainly improve the intensity of the d-d bonds within the (001) planes. All these results are consistent with the previously observed mechanical properties and dislocation microstructures.