MgO particles dispersed AZ61B composite alloys were fabricated via equal channel angular bulk mechanical alloying (ECABMA) and following sintering and hot extrusion processes. α-Mg grain refinement was drastically occurred with increase in the MgO additive content of the composites due to dynamic recrystallization during hot extrusion. Regarding the micro hardness of the matrix, it increased with increase in MgO contents because of the synergy of the grain refinement and MgO hard particles dispersion strengthening effects. However, such a strengthening behavior was gradually decreased in the elevated temperature at 473 K. When comparing the strengthening effect by the grain refinement and MgO particles dispersion by using Hall-Petch coefficient at ambient and elevated temperatures, it was clarified that the latter effect was more dominant in the MgO/AZ61B composite alloys.

As is well known, defects such as a vacancy, an interstitial ion, substitution species and positional disorder, have much influence on various physical and chemical properties of crystalline oxides. Therefore, it can be regarded as one of the key issues to reveal defect distributions and local environments around defects in crystals. However, general analytical methods for crystal structures such as the Rietveld refinement often give us vague information on defects unfortunately since the defect structures is atomic arrangements without periodicity. In order to clarify defect structures underneath crystal structures, we have focused on pair distribution function (PDF) obtained from neutron and synchrotron X-ray total scatterings. This is because the PDF analysis enables us to discuss a non-periodic atomic arrangement up to nanoscale distance. In this paper, we review briefly how to obtain PDF and analytical methods of PDF. We also introduce our recent results of the PDF analysis especially on ionic-conduction crystals in the latter part.

From the macroscopic point of view, shrinkage during sintering can be treated as a linear creep of a porous body under the thermodynamic driving force, i.e., the sintering stress. The final shape of the product and the internal stress which arise during sintering will be predicted by the simulation, if the sintering stress and the bulk viscosity are given as functions of relative density. These macroscopic properties in heterogeneous materials are defined as the average over the representative volume element (RVE). Using X-ray microtomography, it is possible to follow the 3-D microstructure evolution during sintering. Here, we developed methods to estimate macroscopic properties from 3D visualization of microstructures in the scale of RVE observed by X-ray microtomography.

Magnesium silicide (Mg₂Si) is an n-type promising material for thermoelectric (TE) power generation using waste heat with temperature range of 300 to 600°C. Fabricating the multilayer composite of Mg₂Si and metallic material is a useful method for overcoming the weak point in the mechanical property of the material and for making the anisotropic TE material. The transverse TE force is occurred by giving vertical temperature difference in the tilted anisotropic TE material (transverse TE effect). In this study, the Mg₂Si/Ni multilayer composite was focused on for transforming the isotropic Mg₂Si to the anisotropic TE material. The TE properties of the Mg₂Si/Ni tilted multilayer composite were estimated using a finite element simulation. The influences of structural conditions (thickness ratio of Mg₂Si layer and tilt angle) of the tilted multilayer composite on the TE properties were investigated. The TE properties could be related quantitatively with the structural conditions. The structural conditions existed in which the tilted multilayer composite had the power factor greater than Mg₂Si. The optimum structural conditions giving the maximum TE performance were found out.