Interatomic bonding , elastic properties , and ideal strength of transition metal aluminides : A case study for Al 3 „ V , Ti ...

On the basis of ab initio density-functional calculations we have analyzed the character of the interatomic bonding in the intermetallic compounds Al3sV,Tid with the D022 and L12 structures. In all structures we found an enhanced charge density along the AlsV,Tid bonds, a characteristic feature of covalent bonding. The bonds in Al3V with the D022 structure are more saturated and stronger than the corresponding bonds in Al3Ti. High symmetry of the transition metal sites in the L12 structure leads to higher metalicity of alloys assuming this structure. The bond strength is quantitatively examined by tensile deformations. The ideal strength of Al3V and Al3Ti under uniaxial tensile deformation was found to be significantly higher than that of both fcc Al and bcc V. We investigated also the changes of the interatomic bonding in Al3V during tensile deformation. We found that the covalent interplanar Al-V bonds disappear before reaching the maximal stress. The weakening of the bonding between the atomic planes during the deformation is accompanied by a strengthening of in-plane bonding and an enhanced covalent character of the intraplanar bonds. Interplanar bonding becomes more metallic under tensile deformation.