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Recent ab initio calculations of ceramic interfaces such as grain boundaries and metal/ceramic interfaces by the authors' group are reviewed, and the future direction of the interface design is discussed. In ab initio calculations of SiC grain boundaries, we have found that the tensile strength and fracture of SiC boundaries depend on the polarity of each interface, namely the interface stoichiometry. In ab initio calculations of metal/ceramic interfaces such as SiC/metal, alumina/Cu and titania/Au interfaces, we have also found that the interface stoichiometry strongly affect the structure and properties, such as adhesive energies, Schottky barrier heights, tensile strength, and interface electronic structure. These results can well explain the recent experimental observations of metal/ceramic interfaces. It can be concluded that the interface stoichiometry is one of the most important keywords for the interface design of ceramic materials.

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Parallel tight-binding molecular dynamics(TBMD) and hybrid TBMD/MD methods are implemented on a computational GRID to analyze the grain-boundary stability in nanostructured ceramics.We summarize our previous results on the high-energy grain boundary of Si and SiC using the above techniques.The hybrid method is also applied to an analysis of the effects of a hydrogen atom and its thermal diffusion on the grain-boundary stability.

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Thermal conductivity of M₂O₃-doped ZrO₂ was calculated by means of perturbed molecular dynamics. It is found that addition of La or Al greatly reduce thermal conductivity by as much as 25% without introducing any structural defects. Details of the reduction was analyzed in this work.

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The grain boundary segregation and structure in yttria-stabilized zirconia have been investigated by lattice statics calculations. It is found that yttrium ions segregate to the region which is confined to within several atomic layers of a grain boundary plane, and that the grain boundary segregation of yttrium ions induces the peculiar grain boundary structure as compared with pure zirconia.

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Coarsening of particles by surface motion was studied by simulation. The particles with higher coordination number coarsened, while particles with lower coordination number shrank.

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A micro-macro method for simulating a sintering process of ceramic powder compacts based on the Monte Carlo and finite element methods is proposed. Macroscopic non-uniform shrinkage during the sintering is calculated by the viscoplastic finite element method. In the microscopic approach using the Monte Carlo method, powder particles and pores among the particles are divided into many cells, and the growth of grains in the particles and the disappearance of pores are simulated by means of the Potts model. The microscopic and macroscopic approaches are combined by exchanging microscopic and macroscopic information in each step. In the Monte Carlo method, the effect of macroscopic plastic deformation on the microstructural change is taken into consideration by including plastic strain-rate calculated by the finite element method in the disappearance frequency of pore cells. The shrinkage behavior in the sintering of circular two-layer compacts is simulated by the proposed micro-macro method.

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Temperature dependence of internal friction on silicon nitride was analysed using parallel Maxwell model. Creep defromation was calculated with the obtained parameters on this model. The result was compared with the experimental data.

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Effect of particle size and shape on erosive wear of single andpolycrystalline alumina was evaluated. Indentation fracture experiments wereconnected to erosive wear properties. The applicability of the present modeldue to erosive wear was discussed.

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Because of the unique combination of high hardness, high heat resistance, and chemical inertness, ceramic materials are serious candidates for the tribological materials used under sever operating conditions. In this study unlubricated wear tests were carried out to investigate the effect of microstructure on wear properties of structural ceramics (silicon nitride, sialon and alumina ceramics) with diverse microstructures. For alumina ceramics wear rate increased with microstructure change from fine equiaxed grain morphology to coarse and/or anisotropic morphology, consistent with previous works reported by many researchers. On the contrary, for silicon based nitrogen ceramics such as sialons and silicon nitrides, wear rate decreased with microstructure change from fine equiaxed grain morphology to fine bimodal, accompanied with an increase of fracture toughness; but it increased when microstructure became coarse bimodal.

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In order to investigate the sliding wear mechanism of alumina, the wear suraface and its vicinity were observed with TEM. In case of the very low wear rate at room temperature, a layer of very fine particles and deformed grains with dislocations were observed at the wear surface. Lubrication effect by the layer may result in the low wear rate.

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Although SiC/SiC composites are mostly fabricated with continuous fiber for toughening, the fabrication process may be complicated. In the case of fabrication with short fiber, although the process for the fabrication of dense SiC ceramics is simpler, it is necessary to highly control the fiber orientation in order to enhance the toughening of SiC ceramics.In this study, the fiber orientation of SiC ceramics fabricated with chopped Si-Al-C fiber was investigated. The chopped fibers tended to arrange perpendicular to the hot-pressing direction. We found the possibility that the control of these fiber orientation contributes to increasing the fracture toughness.

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This paper presents the Al2O3-YAG eutectic structure by using three-dimensional observation and discusses evolution of the entangled structure. In addition, a novel melt shaping is also presented. In the process, solidification from the undercooled melt produced by melting the metastable Al2O3-YAP eutectic structure is used for shaping.

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The intergranular glassy phase was generated during the liquid phase sintering of Si₃N₄ ceramics to enhances the densification. The glass phase reduces thermal conductivity of Si₃N₄ ceramics due to its low thermal conductivity. To improve the thermal conductivity of Si₃N₄ ceramics, elimination of glassy phase by post-sintering heat treatment under difference nitrogen gas pressure at varying temperature was examined in this study. Y₂O₃-Al₂O₃ and Y₂O₃-SiO₂ additive systems were used for the sintering of Si₃N₄ ceramics. The SiO₂ has high vapor pressure which can be eliminated from the ceramics by the vaporization. Samples were fabricated by gas pressure sintering at 1850^oC for 2 h under a nitrogen gas pressure of 1.0 MPa with BN/ Si₃N₄ packing powder. After heat treatment at 1950^oC for 8 h under a nitrogen gas pressure of 1.0 MPa, thermal conductivity of 5wt% Y₂O₃ - 3wt% SiO₂ - added Si₃N₄ increases from 36 W/m.K to 84 W/m.K by the decreasing of glass phase volume. Effects of heat treatment conditions on the intergranular phase structure, chemical composition and thermal conductivity will be discused.

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Addressed are the recent progresses in the indentation contact mechanics applied to characterizing/analyzing the mechanical properties (elastic, plastic, elastoplastic, and viscoelastic properties) of engineering materials in micro/nanoscopic regime.

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