First Principles Study Electronic Structure And Mechanical Properties Of Al-based Intermetallics

Al-based intermetallics have wide application,because of their low density, high mechanic strength, corrosion resistance, simple productionprocess, low costs in comparison with other alloys, particularly the significant advantages of easy-recycling. Recent theoretical investigations have revealed that the primary origin of brittleness in intermetallics should be attributed to their electronic structures or chemical bond nature. However, data are very limited due to the complications of sample preparation and the limitations of experimental testing techniques, and the electronic nature of the mechanical properties of Al-based intermetallics is also not clear. Therefore,it is crucial to investigate the electronic structures in detail in order to understand brittleness completely.In this paper, we use the first–principle calculation based on the density functional theory to investigate the crystal structure, electronic structure and mechanical properties of Al-based intermetallics. Firstly, we report the relationship between the electrical and mechanical properties of the Al-Cu intermetallics. Secondly, we carry out a systematic first-principles study on the electronic structure and mechanical properties of Al-based intermetallics with cubic structure and vacancy point defects. The main contents of our work are:1. We use the first–principles calculation based on the density functional theory to investigate the crystal structure and electronic structure of Al-Cu intermetallic compounds (Al2Cu,Al3Cu2 and AlCu3). We calculate work function, ductility, density of states and charge density. The result shows that density of states and charge density can qualitatively affect the mechanical properties of material. And further explore the relationship between the electronic structure and ductility, that is, the relationship of work function and the brittleness. We find that the ductility decreases with increase of work function of intermetic compounds, except AlCu3. It mainly change charge distribution. When the atoms relax, atoms can move from aluminum to copper as the electronegativity of copper is greater than the electronegativity of aluminum. This can cause changes in charge distribution and form the surface dipole potential which can increase the electronic work function and lead to changes of mechanical properties. On the other hand, the electronic structure and mechanical properties is the charge density distribution of the material uniformity and symmetry; the better symmetry the better plasticity of materials which corresponds to the symmetry of charge distribution.2. Electronic structure and mechanical properties of Al-based alloys with cubic structure and vacancy have been investigated by using the first–principles calculation based on the density functional theory. Equilibrium structural parameters were derived and agreed well with experimental value. AlNi3 is easier to form vacancy point defects than AlCu3; the heat of formation and cohesive energy were calculated and showed that Al7Cu24 and Al7Ni24 had the better alloying ability and structural stability. Elastic constants and mechanical parameters such as bulk modulus, shear modulus, Young's modulus, Poisson's ratio and anisotropy have also been calculated. There are a little difference between the imperfect crystal structures and perfect crystal structures from the calculated results and the experimental data. Investigation of the mechanical properties shows that cubic structures with vacancy point defects obey well the requirement of mechanical stability for cubic crystals. Cubic structure with vacancy point defects has a good alloying ability and structural stability due to an increase in the bonding electron numbers below the Fermi level. The effects of the alloying ability, structural stability and mechanical properties with vacancy point defects could be reasonably described and explained in terms of the electronic structure (the density of states and charge density distribution).