Oxidation behavior of silicon-based ceramics such as SiC and Si₃N₄ at high temperatures is important for their practical applications to structural or electronic materials. In the present paper two kinds of oxidation (passive and active) and active-to-passive transition of silicon-based ceramics were discussed thermodynamically, and the rate constants of passive/active oxidation and active-to-passive transition oxygen potentials for SiC and Si₃N₄ were reviewed. Passive and active oxidation behavior depended on the microstructure of oxide films and SiO gas pressure on silicon-based ceramics, respectively. Wagner model, volatility diagram and solgasmix-based calculation were used to estimate the active-to-passive transition.

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It had been reported that the effects of cyclic temperature change on the radiation induced microstructural evolution in Fe–Cr–Ni alloys were very strong and complicated. In order to understand these results, accumulations of defects under varying temperature irradiations were numerically calculated based on the rate theory for defect clustering. The results indicate the microstructural evolution under varying temperature irradiation as follows. Vacancy-predominant condition appears after changing the temperature from low to high due to the decomposition of small vacancy clusters, which had formed during the low temperature irradiation, by reacting with interstitials produced by the irradiation at the high temperature. Interstitial clusters, therefore, shrink, while vacancy clusters grow by absorbing the excess vacancies. In the case of temperature change from high to low, on the other hand, the interstitial-predominant condition is held throughout the whole irradiation period, and hence interstitial clusters grow, while vacancy clusters shrink. In the cyclic temperature irradiation, the large interstitial and vacancy clusters are difficult to be formed because these clusters grew and shrank repeatly during the temperatures changed periodically.

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The lattice invariant shear of the martensitic transformations in the Ti_36.5Ni_48.5Hf₁₅ alloy was determined as a (001)B19′ compound twin by in-situ TEM technique. The morphological features of the (001)B19′ twin lamellas were revealed in detail. The shapes of the martensite variants were either the form of triangular, quadrilateral or lath plates. The mosaic-like morphology of the martensite variants corresponds to the cross section of the triangular, quadrilateral prisms, or the lath plates. The vertical section of the lath plates appears with a spear-like feature. The self-accommodation of the triangle, lateral prisms and the lath plates is usually composed of four martensite variants. There are 18 four-variants combinations of the mosaic-like martensite variants.

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Age hardening and precipitation processes in an Al-0.23 mass%Sc alloy were studied by the hardness test, electrical resistivity measurement and TEM observation. The stable and coherent Al₃Sc phase of the L1₂ ordered structure precipitates directly from a supersaturated solid solution without forming any metastable phases. A plot of the cube of the particle radius against aging time follows a straight line, suggesting that the coarsening obeys the LSW theory of the diffusion controlled ripening process. The apparent activation energy for the precipitation of the Al₃Sc phase determined by electrical resistivity change is 80 kJ/mol.

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The isothermal section at 973 K and the liquidus surfaces of the phase diagram of the pseudo-ternary BaO–Fe₂O₃–B₂O₃ system were determined in a composition range of less than 50 mol% B₂O₃ by thermal analyses and X-ray diffraction. The liquidus surface which is in equilibrium with Fe₃O₄ spreads over a wide composition range and that in equilibrium with BaO·6Fe₂O₃ extends long and narrow to BaO·B₂O₃. The pseudo-ternary BaO–Fe₂O₃–B₂O₃ compound does not exist in the composition range investigated. The ternary eutectic reaction is L→BaO·6Fe₂O₃+BaO·B₂O₃+3BaO·B₂O₃, occurring at 1033 K at the composition 48 mol%BaO-19 mol%Fe₂O₃-33 mol%B₂O₃.

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Reaction diffusion and the Kirkendall effect in Ti–Si binary system have been studied by using sandwich-type bulk diffusion couples consisting of 99.99% Ti, 99.9999% Ti plates and a ⟨111⟩ oriented Si wafer. The results have been compared with our previous one obtained by using 99.99% Ti/Si and 99.5% Ti/Si couples. The faster growth of TiSi₂ formed in these Ti/Si diffusion couples, the higher the purity of titanium. To identify the element which slows down the growth rate of TiSi₂, the effects of oxygen, nitrogen, carbon and iron were studied by adding oxygen and nitrogen into 99.9999% Ti or by depositing carbon and iron on the Ti surface. It has been clarified that iron atoms slow down the growth of TiSi₂.
Silicon atoms diffuse 50 to 100 times faster than titanium atoms in TiSi₂. Iron affects the diffusivity of Si more effectively than that of Ti.
On the basis of these results the role of iron in the Ti/Si bulk reaction diffusion couple has been discussed by taking into account a possibility of diffusion barrier effect or grain boundary diffusion.

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Phase stability and mechanical properties of B2 type IrAl intermetallic alloys are investigated. Three types of IrAl alloys are obtained by arc-melting, followed by homogenization at 2023 K for 14.4 ks in vacuum, and are slowly cooled for removing thermal vacancies. Phase stability is studied using optical microscopy, X-ray diffractometry and differential thermal analysis up to 1973 K. Mechanical properties are investigated by micro-Vickers hardness measurements at room temperature and compression tests up to 1873 K. All alloys after heat treatment have eutectic structures composed of B2-IrAl and fcc Ir solid solution: B2 IrAl is the primary phase and Ir solid solutions exist at grain boundaries. Lattice parameters of both phases are calculated to be 298.8 pm for B2 IrAl and 384 pm for fcc Ir solid solutions. Micro-Vickers hardness is measured to be H_V 1050 in average, H_V 1100 for B2 phases and H_V 1000 through 700 for eutectic structures. Although all alloys show brittleness at room temperature, compressive ductility appears over 1273 K. 0.2% flow stress decreases rapidly with increasing test temperatures: 90 MPa at 1473 K and 30 MPa at 1873 K. It is concluded: (1) IrAl/Ir eutectic structures are induced through solidification, and the eutectic structures remain through the homogenization treatment, and (2) the strength and specific strength of IrAl alloys are higher than those of other intermetallics such as NiAl, Ni₃Al and TiAl.

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A novel process named Centrifugal Duplex Casting has been proposed: It is a manufacturing process of an aluminum cast pipe with an in-situ composite layer which contains fine intermetallic crystals. In this process, two kinds of molten metal, i.e. molten aluminum (the first melt) and molten Al–Cr alloy with higher liquidus temperature (the second melt), are cast in sequence at a given interval into the rotating mold of a centrifugal caster. The second melt collides with the meniscus of the first melt, and is dispersed as a great number of fine fluid clumps. These fluid clumps are rapidly quenched, migrate toward the outer periphery, and accumulate to form the composite layer. The particle size of the intermetallic crystals in this composite layer is much smaller than that of the Al–Cr alloy centrifugally cast by a conventional process. The solidification structure of the cast pipe produced by Centrifugal Duplex Casting is controlled by cooling capacity of the first melt. For instance, when the first melt has superheat at the moment of the second-melt casting, coarse intermetallic crystals grow inside of the refined composite layer. On the other hand, when the first melt has partially been solidified, the growth of the intermetallic crystals is suppressed. Therefore, the time interval between the two casting operations is an important parameter in this process.

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With the use of the diffusion bonding system of Ni/B/Ni, the liquid layer at the Ni/B interface was studied. In the previous report we suggested that the intermediate layer of pure B which has a high diffusivity in Ni and a high melting temperature can reduce the bonding time of the TLP (Transient Liquid Phase) process. In the present study the Ni/B/Ni specimen was bonded at temperatures of 1433–1473 K in vacuum. As a result, a liquid metal in the bonding zone was formed by mixing the diffused atoms of the intermediate layer of solid state with the base metal. For this procedure incubation time of 25 s was required. The initial width and the maximum width of the liquid layer were 3.5 and 9 times, respectively, wider than the thickness of the intermediate layer. With a similar bonding procedure, pure carbon (C) can be used also as an intermediate layer.

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The effect of the hot-extrusion process on 6061 matrix composites reinforced with alumina short fibers was investigated through the study of microstructures, tensile strength and ductility of the composites before and after the hotextrusion process. Superplastic behavior of 19 vol% Al₂O_3f/6061 composites extruded at 783 K at a ratio of 49 was investigated at 803 K. The results show that the grains of the composites became fine equiaxial grains and most of all the alumina fibers turned out to be directional along extrusion direction after hot-extrusion process. The 6061 matrix composite reinforced with 19% volume fraction of alumina short fiber exhibits superplasticity at a strain rate of 7.2×10⁻⁴ s⁻¹ at 803 K. The tensile strengths of the composites are all lower than that of the unreinforced 6061 alloy at hot-extruded state when the test temperature is lower than 533 K. However, when the volume fraction of alumina fiber exceeds a certain value (12%), the strength of the extruded composite turns to increase with increasing the volume fraction of alumina fiber. Contrarily, the tensile strength of the cast composite turns to decrease with increasing the volume fraction of alumina fiber when the volume fraction of alumina fiber exceeds a certain value (12%) at the lower test temperature than 533 K. Through the extrusion process, the plasticity of the 6061 matrix composites reinforced with alumina short fibers can be improved greatly, especially at ambient temperature.

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Manganese oxide electrodes with some additives enhance oxygen evolution efficiency in seawater electrolysis. Electrodes were prepared by a thermal decomposition method. IrO₂-coated titanium (IrO₂/Ti electrode) was used as the substrate on which manganese oxide (MnO_X/IrO₂/Ti) and oxide mixtures of manganese and iridium, ruthenium, platinum, iron, cobalt, nickel, tin, lanthanum, cerium or molybdenum ((Mn–M)O_X/IrO₂/Ti electrode, M: additives) were coated. The oxygen evolution efficiency of the MnO_X/IrO₂/Ti electrode was 68–70%. The addition of small amounts of nickel, cobalt, iron or tin enhanced the oxygen evolution efficiency. However the addition of excess amounts of these elements and additions of noble metals, cerium or lanthanum were detrimental for the oxygen evolution.
Among the additives examined, molybdenum was the most effective additional element to increase the oxygen evolution efficiency. The addition of a small amount of molybdenum leads to a remarkable increase in the oxygen evolution efficiency up to 91%. The formation of a single phase Mn₂O₃ with molybdenum ions seems to be responsible for the high efficiency for oxygen evolution.

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Transformation characteristic of Ce-TZP ceramic in shape memory cycles was studied by MTS machine in the load and stroke control modes. The shape memory effect did not degrade up to 8 cycles in load control and the residual plastic strain reached 3.8% in stroke control. The yield stress decreased and the reverse transformation temperature of stressinduced martensite increased with the number of the cycles. The dependence of yield stress and transformation temperature on the shape memory cycles is attributed to the damages associated with the transformation.

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