First principles study of influence of alloying elements on TiAl: Lattice distortion
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First principles study of influence of alloying elements on TiAl: Lattice distortion Y. Song,a) R. Yang, and D. Li Titanium Alloy Laboratory, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110015, People’s Republic of China
W.T. Wu State Key Laboratory for Corrosion and Protection, Institute of Corrosion and Protection of Metals, Chinese Academy of Sciences, 62 Wencui Road, Shenyang 110015, People’s Republic of China
Z.X. Guo Department of Materials, Queen Mary and Westfield College, University of London, Mile End Road, London E1 4NS, United Kingdom (Received 13 September 1998; accepted 20 January 1999)
The influence of ternary additions Cr, Fe, Mn, Ni, Zr, Nb, Mo, Hf, Ta, Si, Ga, Ge, In, and Sb, as well as the anti-site defects of both Ti and Al, on lattice parameters of TiAl were studied by the first principles electronic structure calculations with a discrete variational cluster method. The results of the calculation show that the effect of ternary additions on the distortion of TiAl lattice varies with the substitution behavior of the individual alloying element involved. The addition of alloying elements in TiAl causes a change in the electronic structure and the density of states of the system and results in variation of the bond strength between the atoms. The total and partial density of states (DOS) of binary TiAl and of ternary TiAl–M, M ⳱ Cr, Zr, and Sb, etc., were comparatively examined. The relationship between the DOS and the bond strength is discussed. The present work suggests that the origin of the lattice distortion of the ternary TiAl–M systems lies in the variation of the electronic structure.
I. INTRODUCTION
Alloys based on the ␥ titanium aluminide, TiAl, are potential high-temperature structure materials for advanced aerospace and automotive applications because their excellent weight-specific and high-temperature properties. However, owing to the room-temperature brittleness, their application has been rather limited. The room-temperature brittleness of TiAl is believed to be due to the lower mobility of dislocations. The dislocations in TiAl usually consist of the superdislocations with the 〈101] and 1⁄2 〈112] Burgers vector, the ordinary dislocation with the 1⁄2 〈110] Burgers vector, and Shockely partial with the 1⁄6 〈112] Burgers vector.1 In binary TiAl, c/a ⳱ 1.02, resulting in |1⁄2 〈101]|
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