Atsushi Nogami

Electronic structure analysis of magnetic properties of Fe16N2

SummaryThe magnetic properties of Fe16N2, bcc iron and bct iron were studied using the linear muffin tin orbital method in combination with the atomic sphere approximation (LMTO-ASA). The following results were obtained: The magnetovolume effect is the most important for the large magnetic moment of Fe16N2. The magnetic moment of iron increases with the distance from the nitrogen. The nitrogen atom plays a role in expanding the lattice. The effect of local lattice relaxation of the iron atoms that are first- and second-nearest neighbors to a nitrogen atom was examined.

A Study on First Principle Calculation of Alloy Phase Diagram by Monte Carlo Simulation

A method of first principle calculation of alloy phase diagram was developed by the combination of first principle energy band calculation, cluster expansion method (CEM) and Monte Carlo (MC) simulation, where the effective multi-body potential energy for the flip test in MC simulation was obtained by the decomposition of the total energy by CEM. This method was applied to Cu-Au binary system. The calculated phase diagram agreed with that of CVM by introducing the dependence of the lattice constant on the concentration of the whole system. Furthermore an attempt of introducing the effect of local lattice relaxation was performed by the consideration of the local concentration. The order-disorder transition temperature became closer to the experimental value by adjustment of the local lattice constant depending on the concentration in the local region consisted of up to the second nearest neighbors of the atom tested for flipping.

AN ATTEMPT OF FIRST PRINCIPLE CALCULATION OF ALLOY PHASE DIAGRAM

A method of the first principle calculation of alloy phase diagram was developed by the use of Monte Carlo simulation, where the energy change associated with a flipping was calculated by the summation of changes in multibody interaction energy due to the flipping. The multibody interaction energy had been obtained in advance by the decomposition of the total energy calculated by a band calculation program LMTO. The decomposition was made by cluster expansion method. Au-Cu binary phase diagram was simulated by the use of the presently proposed method. Current problems were discussed in application of the present method to Ti-Al binary system.

A Corrosion Database System for Exposure Tests

A computerized corrosion database system for exposure tests has been designed and developed. This system was developed to help researchers carry out each experimental procedure in exposure tests. The system includes a function to manage not only the experimental data but also the timetable of exposure tests and the environmental factors of exposure sites. An easily used graphical user interface (GUI) and graph plot software are provided for users to help analyze exposure test results from various viewpoints. The data accumulated in this system are measurements of past exposure tests and exposure tests in progress. The analyses of past exposure tests using the present database system resulted in several ideas on atmospheric corrosion different from the conventional ideas on atmospheric corrosion. If the data of exposure tests in progress are compared with past data, the relationships between atmospheric corrosion and environmental factors will be more clarified.