Theoretical Research Of Double Doped ?-TiAl Based Alloys' Structures And Properties

Lightweight high-temperature structural materials have broad applications in the aerospace and aviation field, and it is one of the key projects in current materials research. In TiAl intermetallic compounds, the bonds are simultaneously similar to the metal bond and covalent bond. This property makes such material has not only the high plasticity like metal,but also has high-temperature strength like ceramic. In addition, its density is only half of the Ni-base high-temperature alloys. Alloying with other elements is a commonly used and effective method to improve the performance of TiAl alloy.By using the first-principles method based on density functional theory, the doped ?-TiAl systems are studied in this article, in order to discover a ?-TiAl based alloy with better performance, and try to clarify the meanings and reasons of doping.The cell models are built by the Materials Studio 6.1 software, and using appropriate calculation settings to optimize the geometry of the structure. Based on the optimized ?-TiAl based structures, the microstructure, electronic characteristics, and mechanic properties were calculated, researched and analyzed.The obtained total energies and formation energies show that: in the singly doping cases,Nb tend to substitute Ti; the tendencies of Cr and Mn are not clear, but Cr slightly tend to substitute Ti, Mn slightly tend to substitute Al; in the Nb, Cr compositely doping cases, Nb still tend to substitute Ti, the original tendency of Cr disappears; in the case of Cr, Mn compositely doping, Cr is obviously tend to substitute Ti. By analyzing the axis ratio c/a of doped ?-TiAl based alloy systems, it could be found that: Cr or Mn substituting Al can improve the isotropic degree of ?-TiAl based alloy, and then improve the ductility; Nb, Cr compositely doping system is even better. By analyzing the populations and the overlap populations of the system, some results can be found: doping with Nb, Cr can help to weaken the covalent bonds, and then improve the ductility. Cr substituting Al system and Nb, Cr compositely doping systems are more prominent. Research on the elastic modulus ratio G / B value indicates that: Mn, Nb and Cr doping will improve the ductility of the alloy system, and Nb, Cr composite doping improves the ductility even more apparently.