Dresden 2011 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 39: Computational Materials Modelling V

MM 39.1: Vortrag

Donnerstag, 17. März 2011, 16:15–16:30, IFW A

First-principles phase stability calculations of Al₃(Ti_1−xNb_x) pseudobinary alloys — •Yuhong Liu^1,2, Peter Puschnig¹, Ernst Gamsjäger², and Claudia Ambrosch-draxl¹ — ¹Atomistic Modelling and Design of Materials, University of Leoben, Austria — ²Institute of Mechanics, University of Leoben, Austria

In the TiAlNb-system(mole fraction of Al amounts to 0.75), the intermetallic ε-phase can exist in the L1₂, D0₂₂, or D0₂₃ structure. Experimental results indicate that the addition of Nb shows a site preference for the Ti sublattice. Therefore, we calculate the thermodynamic properties of Al₃(Ti_1−xNb_x) by assuming a pseudo-binary alloy system. We utilize the ATAT package to perform the sublattice cluster-expansion approach. Total energies of various ordered super-cell structures are obtained within density-functional theory using the projector augmented wave (PAW) method as implemented in the VASP code. Effective cluster interactions derived from the structure-inversion method are then used in an Ising-type Hamiltonian, which is solved by Monte-Carlo simulations. Our results show that the addition of Nb stabilizes the cubic L1₂ structure relative to the D0₂₂ and D0₂₃ ones. We find the effect of short-range-order on the calculated formation energies to be small compared to random mixing on the Ti-Nb sublattice. At high temperature, thermodynamic quantities such as the enthalpy and free energy are extracted from the Monte-Carlo simulations and compared to results from the CALPHAD method.