Hideo Miura
Tohoku University, Japan
Title: Degradation of crystallinity and properties of advanced functional materials caused by anisotropic local diffusion of component atoms under severe operating conditions
Biography
Biography: Hideo Miura
Abstract
Recently, mechanical properties of polycrystalline materials have been found to vary drastically depending on their micro texture. The crystallinity of grain boundaries was found to dominate both their mechanical and electrical properties and the long-term reliability. This is because various defects such as strain, vacancies, impurities, and dislocations easily concentrate around grain boundaries and thus, degrade the quality of atomic configuration in grains and grain boundaries. In this study, a grain boundary is defined by volumetric transition area between two grains, though it has been defined as a line interface between nearby grains. The quality of grain boundaries is independent of crystallographic orientation of nearby grains. The diffusion of component elements is remarkably dominated by the local quality of grain boundaries. The degradation of materials mainly starts to occur around grain boundaries with low crystallinity and atomic diffusion, such as strain-induced anisotropic diffusion and electromigration, is accelerated drastically along the poor-quality grain boundaries. Crystallinity of grain boundaries can be evaluated quantitatively by applying electron back-scatter diffraction (EBSD) method. The order of atomic alignment in the observed area is analyzed by the sharpness of Kikuchi lines obtained from the observed area. Various materials properties vary drastically depending on the order of atomic alignment, in particular, in grain boundaries. Both fluctuation and degradation of various properties of materials such as heat-resistant alloys and thin films are investigated from the viewpoint of the crystallinity of grains and grain boundaries.