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Abstract: The deleterious low-temperature tetragonal phases in prototypical Pt-based superalloys have variously been reported as taking the tI16-U3Si (DOc), tI16-Ir3Si (DOc′) and tP16-Pt3Ga structure-types in contrast to the high-temperature cubic cP4-Cu3Au (L12) phase. We have investigated the relative stability of these four structure-types at absolute zero by using density functional theory. We find that the ground state of stoichiometric Pt3Al is tP16-Pt3Ga and that the other three lattices are mechanically unstable at absolute zero. Experiments are needed to measure the internal displacement parameters of these three competing tetragonal phases. [Copyright &y& Elsevier]

• Development of titanium-palladium based systems as potential high-temperature shape memory alloys. • Parameterization was effective to develop the potential parameters for titanium, palladium and ruthenium. • The relative stability of the alloy system was deduced from derived sets of potential parameters. • Lattice expansions predicted the transformation temperature of ternary alloys at high temperature. • Addition of Ru reduces the transformation temperature minimally. Titanium-palladium based systems are in high demand currently, particularly for the development of high-temperature shape memory alloys with a unique application in the aerospace industry. In particular, the Ti 50 Pd 50-X Ru X is found to be one of the promising alloys. This is due to their shape memory effect and superelasticity. Previous studies revealed that these alloys are mechanically stable above 25 at. % Ru with a positive C ′ at 0 K. So, an understanding of its transformation temperature behavior is required, which is currently not clear. The self-consistent-charge density functional tight-binding (SCC-DFTB) approach was used to develop parameters for Ti 50 Pd 50-X Ru X employing the parameterization technique. The structural, electronic and elastic properties were determined to check their relative stability on derived potentials using DFTB + code. As part of the validation for the developed set, the results were reproducible to within 5 % agreement as compared with other theoretical findings. Furthermore, the SCC sets of parameters were also used to determine the lattice expansions and check the transformation temperature of ternary Ti 50 Pd 50-X Ru X. It was observed that the addition of Ru reduces the transformation temperature. The findings imply that the SCC-DFTB approach was able to predict the stability and transformation behavior of Ti 50 Pd 50-X Ru X alloys. [ABSTRACT FROM AUTHOR]

Abstract: We investigated the phase stability from B2 to L10/B19/B19′ in equiatomic PtTi alloy using the density functional theory within the generalized gradient approximation. Their structural, energetic, electronic and the mechanical properties were determined to show the stability trend of the shape memory binary alloy. The lattice parameters are well reproduced and agree to within 2% with the available experimental data. We found that the calculated heats of formation and density of states predicted B19 and B19′ PtTi to be the most stable structures compared to B2 and L10. On the other hand, their mechanical stability predictions show consistency with regard to the elastic constants and phonon dispersion curves. The elastic instability (negative C ij) and soft modes were observed in the B2, B19 and B19′ structures and not found in the L10 structure. [Copyright &y& Elsevier]

Abstract: The first principles pseudopotential calculations based on the Perdew–Burke–Ernzerhof (PBE) form of generalized gradient approximation (GGA) within density functional theory (DFT) have been utilized to investigate the structural and elastic properties of cubic-based Mg–Li alloys. The heats of formation and elastic moduli were used in predicting structural stability profile, and their results are consistent with each other. In terms of phase stability, an interesting correlation between the calculated tetragonal shear modulus (C′) and formation energy of corresponding bcc and fcc ordered compounds relative to hcp Mg and Li lattices is drawn. The predicted stability trend due to structural energy difference was further confirmed by electronic structure calculations based on Jones-type analysis. [Copyright &y& Elsevier]