Interatomic bonding and mechanical properties of trialuminides: an ab initio study for Al(3)(Sc,Ti,V) (abstract only).

On the basis of ab initio density-functional calculations we have analyzed the character of the interatomic bonding in the intermetallic compounds Al(3)(Sc,Ti,V) with the D0(22) and L1(2) structures. In all structures we found an enhanced charge density along the Al-transition-metal (TM) bonds, a characteristic feature of covalent bonding. The series Al3Sc-Al3V corresponds to gradual d-band filling which leads to a gradual increase of bond strength and covalent bond formation. For this series, the tensile anisotropy in the elastic limit has been investigated and a trend towards an increased anisotropy of the elastic constants and Young modulus has been observed. Additionally we performed a study of the response of trialuminides to uniaxial tensile deformation along the [110] direction. This direction is known to be the weak direction for face-centered cubic (fcc) materials under tensile strain, and it is generally accepted that their deformation path is characterized by a 'flip strain' instability which restores the fcc structure after full relaxation by interchanging the [110] and [100] directions. The structures of trialuminides have a close structural relationship with fcc metals. We found that L1(2)-type trialuminides respond to tension along the [110] direction differently to fcc metals, and the 'flip strain' mechanism is not active here. Their deformation path is strongly affected by TM-TM interaction acting along the [001] direction. In contrast, the D0(22)-type trialuminides react in the same way as the fcc metals and regenerate with the same 'flip strain' mechanism.