Theoretical Prediction of Transition Metal Alloying Effects on the Lightweight TiAl Intermetallic

Abstract

The structural, mechanical properties and Debye temperature of doped intermetallic Ti7Al8X (X = Sc, Ti, V, Cr, Y, Zr, Nb, Mo, Hf, Ta, W) have been investigated by employing the pseudo-potential plane-wave approach based on density functional theory, within the generalized gradient approximation (GGA) function. The calculated lattice constants of TiAl are found to be within 1 pct error, compared with the experimental values. The stability of calculated structures of Ti7Al8X at 0 GPa is measured by studying mechanical stability conditions and formation energy. All the single crystals are proved to be elastically anisotropic. The Young’s modulus as a function of crystal orientations has been systematically investigated. Mechanical properties of polycrystals are computed from values of shear modulus (G), bulk modulus (B), Young’s modulus (E), Poisson’s ratio (υ), and microhardness parameter (H) for Ti7Al8X. It is indicated that addition of alloying elements reduces the brittleness and microhardness of TiAl intermetallic. Debye temperature of TiAl calculated using elastic data of the present work is found to be influenced by the addition of alloying elements, which is further confirmed by the phonon dispersions of Ti8Al8, Ti7Al8Zr, and Ti7Al8Hf.