Alloy Design Based on Molecular Orbital Method
A molecular orbital approach to alloy design has recently made great progress. It is based on the electronic structure calculations by the DV-Xα cluster method, and new alloying parameters are obtained for the first time from the calculations. A theory for alloy design relevant to transition-metal based alloys have been developed using alloying parameters. For example, New PHACOMP has been developed in order to predict the formation of harmful and brittle phases (e.g., σ phase) in nickel-based superalloys. A universal relation has also been discovered between electron density minima and atomic (or ionic) radii in various materials from a series of molecular orbital calculations. Furthermore, another electronic approach is explained focusing on the energy expression of the chemical bond between atoms in hydrides and hydrocarbons. All the hydrides and hydrocarbons are located on an atomization energy diagram, despite the significant differences in the nature of the chemical bond among them. One of the applications of this approach is the catalyst design. The catalytic activities of metal oxides (e.g., Nb2O5) are evaluated quantitatively on the dehydrogenation reaction of magnesium hydride (MgH2), MgH2 → Mg + H2.