First-principles Calculation For Improving Ductility Of Aluminides By Alloying Elements At Room Temperature

The ordered arrangement of atoms is an essential feature of intermetallic compouds (IMCs) which exhibit various kinds of bonding ranging from free-electron-like metallic bonding to directional bonding as in covalent-solid. Therefore IMCs are of many unique characters in magnetism, electricity, optics and high temperature stable. However, the use of IMCs as a structure material has been hindered by the lack of its tensile ductility or toughness at room temperature. Experiments indicate that its tensile ductility can be improved by adding some alloying elements in IMCs. But how to explain impact of the alloying elements is a key problem. In recently years, First-principles calculation within the framework in density -function theory has been used to investigate why these happened with the improvement of computer technology and quantum-mechanics.Generalized gradient approximation (GGA) of the density function theory (DFT) was applied to investigate the structure of improving ductility of NiAl andγ-TiAl by alloying elements at room-temperature. Many properties including band structure, density of states, population analysis, and electron density were calculated by CASTEP-module of Materials Studio software package. It was shown that the slip of dislocation is hindered by a strong bond to p and d hybridization, which leads to the embrittlement of NiAl andγ-TiAl at room temperature. Alloying elements, which are beneficial to improve ductility of NiAl andγ-TiAl, weaken the impact of the bond to p and d hybridization to make the charge distribution uniform. Addition of Fe with lower amount is beneficial to improve ambient ductility of NiAl. With higher amount of Fe, the brittleness of NiAl at room-temperature is increased. The alloying elements, which substitute for Al site and improve ductility ofγ-TiAl, have d-shell unoccupied orbital. And their electronegativities ?i satisfy the inequality 0