Tohoku University, Japan
Title: Evaluation of Atomic Scale Damages of Advanced Materials Based on the Order of Atom Arrangement
Biography: Hideo Miura
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 talk, 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. The initial micro texture of various heat-resistant alloys has been found to degrade under operating conditions of advanced high efficient thermal power plants based on this strain-induced accelerated diffusion of component elements. The quality of thin-film interconnections in advanced semiconductor devices has been decreased under operation by electro-and stress-induced migration of component elements. Therefore, it is very important to evaluate the crystallinity of advanced materials quantitatively for assuring safe and reliable operation of various products. 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.
Recent Publications :
- Murakoshi T, Shinozaki T, Suzuki K, and Miura H (2016) Initial Degradation Process of Heat-resistant Materials Based on the Change of Crystallinity of Grains and Grain Boundaries, Procedia Structural Integrity 2, 1383-1390.
- Murakoshi T, Ochi M, Suzuki K, and Miura H (2015) Elucidation of the High Cycle Fatigue Damage Mechanism of Modified 9Cr-1Mo Steel at Elevated Temperature, Proc. of ASME IMECE2015, No.53341, 1-6.
- Suzuki K, Murakoshi T, and Miura H (2015) Crsytallinity Degradation Caused by Alloying Elements Diffusion During Creep of Ni-base Superalloy, Proc. of ASME IMECE2015, No.53341, 1−6 .
- Ohnishi M, Suzuki K, and Miura H (2015) Effects of uniaxial compressive strain on the electronictransport properties of zigzag carbon nanotubes”, Nano Research, DOI10.1007/s12274-016-10220-0.
- Murata N, Suzuki K, and Miura H, (2012) Quantitative Evaluation of the Crystallinity of Grain Boundaries in Polycrystalline Materials, Proc. of ASME IMECE 2012, No. 87426, 1-6.