Reaction diffusion in Ti/Al and Ti–5 mol%O/Al diffusion couples has been investigated by electron-probe microanalysis. Only one intermetallic compound TiAl₃ was observed as an intermediate layer in the temperature range from 773 to 903 K in both the diffusion couples. Si, which is an impurity element in aluminum, was concentrated in TiAl₃. The growth of the intermediate layer turned out to be diffusion limited; the activation energy was estimated to be 237±15 kJ·mol⁻¹ and the temperature dependence of square of the rate constant, k², for layer growth can be described with the following equation in the temperature range from 773 to 903 K in the Ti/Al diffusion couples. k_TiAl_3^2=3.5exp[-(237±15) kJ·mol^-1/RT]m^2s^-1In the case of the oxygen doped diffusion couples, the layer growth of TiAl₃ was significantly suppressed and the activation energy was 263±7 kJ·mol⁻¹ for temperatures from 773 to 873 K . The suppression is explained by aluminum oxide formed between aluminum and TiAl₃. The Kirkendall marker shifted toward the aluminum side, which suggests that diffusion of Al is faster than that of Ti in the intermediate layer.

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Bending and uniaxial tensile tests for Al-base amorphous ribbons were performed at room temperature for a number of compositions. Al-nanocrystal precipitation was observed within vein protrusions on fracture surfaces and along crack propagation paths, as well as within shear bands resulting from bending. A composition dependence of crystallization upon bending was also observed. Effects of local adiabatic heating was observed on fracture surface.

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To study the relationship between hydrogen pressure and holding time for hydrogenation at 680 K, hydriding combustion synthesis of Mg₂NiH₄ were conducted at different heat patterns and hydrogen pressures. The obtained results were summarized in the form of an operating map, which visualized clearly the possible operating conditions for industrializing the process. Pure Mg₂NiH₄ can be synthesized at a high pressure of hydrogen and a short holding time at 680 K . At a lower pressure of hydrogen such as 0.5 MPa, 7.2 ks of a holding time at 680 K is enough to obtain 100% pure Mg₂NiH₄ as a product. The pressure composition isotherm of Mg₂NiH₄, obtained at 623 K, showed a hydrogen capacity very near the theoretical value of 3.6%, together with a reasonable plateau. The specific surface areas of several samples suggested that the product is a porous material.

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Behaviors of carbon nanotubes (CNTs) in H₂ atmosphere or CH₄+H₂ mixtures, transforming mechanism of CNTs to diamond embryo were investigated. Experimental results show that CNTs could be etched by H₂ and transformed to carbon nanoparticles under conditions of hot-filament chemical vapor deposition. The mechanism can be concluded that CNTs were broken down by H₂, transformed to carbon nanoparticles or shorter CNTs; on surface of carbon nanoparticles or end caps of CNTs diamond crystals were nucleated and grown up.

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Thin coherent as well as thicker semi-coherent plate-like precipitates of the same type, i.e. TiCu, were generated by different heat treatments of melt-spun Ti₅₀Ni₂₅Cu₂₅ ribbons. Their influence on the martensitic transformation behavior was investigated by means of differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). It was found that thin coherent plate-like precipitates lower the temperatures of both martensitic and its reverse transformation and broaden the peak form of the DSC signal. On the other hand, thicker semi-coherent plates act to raise both transformation temperatures. The role of coherency stresses, arrangements of misfit dislocations, and compositional aspects are discussed.

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Considering the effect of the friction force due to volume diffusion of a solute on the driving force, a new kinetic model has been proposed for diffusion induced recrystallization (DIR) in the A(B) system in which solute B atoms diffuse into a pure A metal or a binary A-B alloy. The energy balance model [M. Kajihara and W. Gust: Scr. Mater. 38 (1998) 1621] has been combined with the columnar geometry and boundary diffusion model [C. Li and M. Hillert: Acta Metall. 29 (1981) 1949] and the extended model [Y. Kawanami et al.: ISIJ Int. 37 (1997) 921] in order to describe mathematically the growth rate of the fine grain region (DIR region) formed by DIR as a function of the reaction time. DIR in the Ni(Cu) system was experimentally observed by Kawanami et al. [Y. Kawanami et al.: Mater. Trans., JIM 39 (1998) 218] at 923 and 1023 K . The new model has been utilized to analyze their observations theoretically. According to the observations, the migration rate v of the moving boundary gradually decreases with increasing reaction time. However, the decrease in the migration rate v is negligible during a small time interval of Δt=1 s at the experimental reaction times. Thus, the value of v was assumed to be constant at each time step with Δt=1 s in order to simplify the analysis. Using the mobility M of the moving boundary as the fitting parameter, the thickness of the DIR region was calculated as a function of the reaction time by a numerical technique. The calculation gives values of M=3.73×10⁻¹⁷ and 1.51×10⁻¹⁵ m⁴/Js at 923 and 1023 K, respectively, and thus M₀=1.03 m⁴/Js and Q_M=290 kJ/mol for M=M₀exp(−Q_M⁄RT). The temperature dependence of the mobility indicates that the grain boundary migration may be governed by the solute drag effect for which the volume diffusion of the solute along the moving direction in the untransformed matrix ahead of the moving boundary has the most important role.

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The effects of temperature and strain rate on elongation of Al–4.5Mg alloy were investigated at 10⁻⁴–10⁻² s⁻¹ and at 573–773 K . The elongation depended on the temperature and strain rate even in the solute-drag creep region; as a result, a large elongation of 352% was attained at 653 K and at 10⁻³ s⁻¹. Necking developed due to a decrease in plastic stability arising from apparent strain softening behavior at 10⁻² s⁻¹ at 653 K or the low strain rate sensitivity at 10⁻³ s⁻¹ at 573 K . Also, significant cavitation was caused due to grain boundary sliding at 10⁻⁴ s⁻¹ at 653 K and at 10⁻³ s⁻¹ at 773 K . The development of necking and cavitation is responsible for the temperature and strain rate dependence of elongation.

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The present study was carried out to improve the corrosion resistance of pure magnesium in Hank’s Balanced Salt Solution (HBSS) through the surface modification. Three kinds of alkaline compounds, such as sodium hydrogen carbonate, sodium carbonate, and lithium hydroxide, were used for treatment. Only magnesium treated with aqueous sodium hydrogen carbonate solution gave a good corrosion resistance in HBSS solution at 25°C up to 75 days, while almost no effect in sodium carbonate and lithium hydroxide. It was likely that hydrogen carbonate ions were essential for the surface improvement of magnesium. X-ray diffraction patterns of modified magnesium showed new peaks of magnesium carbonate and others on the surface. New surface structure of needle-shaped crystals was observed by scanning electron microscopy (SEM). Both elemental mapping, and energy dispersive (EDX) techniques in SEM showed the precipitation of calcium magnesium phosphate (low crystallinity whitlockite:(Ca,Mg)₃(PO₄)₂) on the surface of magnesium specimen. It could be concluded that surface modification with sodium hydrogen carbonate made it possible to apply metal magnesium in biomedical, dental, and other industrial usage.

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Four 6061 aluminum systems were prepared in this study, including the DC cast 6061 alloy processed by TMT and ECAP, the PM modified 6061 alloy added with 1 vol% nano-SiO₂, and the commercial 6061/20%SiC_w composite. All materials possessed fine grain sizes ∼ 0.3–1 \\micron after processing, but only the latter two could maintain fine grain size upon loading at high temperatures and achieved HSRS over 300% at 570–590°C and 1–5×10⁻¹ s⁻¹. The texture was weaker and the grain boundary misorientation distribution was more random in the 6061/1%nano-SiO₂ alloy as compared with the unmodified 6061 alloys. The 1%nanoSiO₂ modified alloy exhibited low stresses ∼ 4 MPa, true strain rate sensitivity ∼ 0.5, smooth GBS and a limited amount of liquid phase at high temperatures and strain rates, similar to those observed in HSRS composites. The current results suggest that the addition of a small amount (1 vol%) of SiO₂ or Al₂O₃ nano-particles into commercial Al alloys can effectively suppress grain growth at high temperatures and enhance HSRS.

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In the present paper, ac electric transport behavior of La_0.64Ba_0.36Mn_1−xFe_xO_3−δ with x=0 (the ferromagnetic phase) and x=0.05 (the paramagnetic phase) are comparatively investigated at a temperature of 300 K . The reactance X is positive for the x=0 but negative for the x=0.05. For x=0, the impedance Z increases at first, undergoes a peak and a valley, and finally increases again with increasing ac frequency. On the contrary, for x=0.05, the impedance decreases monotonically with increasing ac frequency. Meanwhile, the giant magnetoimpedance effect has been found in both ferromagnetic x=0 and paramagnetic x=0.05 at 300 K . Results also show that with increasing frequency the change ratio of the magnetoimpedance (Z(0)–Z(5172 A·m⁻¹))⁄Z(0) increases for the sample x=0 but decreases for the sample x=0.05.

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The performance of a high hydrogen capacity alloy, V–16%Ti–12%Ni–1.4%Nb–0.96%Co–2.8%Ta, is sensitively influenced by dissolved aluminum and oxygen, both of which can be removed from vanadium by a refining process, but the process currently used is too expensive. It is necessary to develop a process to remove these impurities at a reasonable cost. We propose a new method for production of the alloy. A V–15%Ni–1.8%Nb precursor with a low enough level of aluminum was produced by alumino-thermic reduction from a mixture of V₂O₅, Nb₂O₅ and nickel. Subsequently, a V–16%Ti–12%Ni–1.4%Nb–0.96%Co–2.8%Ta alloy was obtained by alloying the precursor and the other constituents of titanium, cobalt and tantalum, and by adding mischmetal as a reducing agent to remove oxygen to a low enough level. It was demonstrated that, by the method described here, the vanadium-based alloy could be produced at a reasonable cost.

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New Cu-based bulk glassy alloys with high glass-forming ability and good mechanical properties were formed in Cu–Zr–Ti–Be system. The glass transition temperature (T_g), supercooled liquid region defined by the difference between crystallization temperature (T_x) and T_g, ΔT_x(= T_x−T_g) and reduced glass transition temperature (T_g⁄T_l) are 728 K, 50 K and 0.64, respectively, for the (Cu_0.6Zr_0.3Ti_0.1)_92.5Be_7.5 and 720 K, 42 K and 0.64, respectively, for the Cu₅₄Zr₂₇Ti₉Be₁₀ alloy. The use of the 7.5%Be and 10%Be alloys has enabled us to form glassy alloy rods with diameters up to 5 mm. The bulk glassy 10%Be alloy exhibits high tensile fracture strength of 2450 MPa and Vickers hardness of 710, in combination with Young’s modulus of 146 GPa, compressive fracture strength of 2500 MPa and compressive elongation of 3.5%. The tensile strength level is the highest among all bulk metallic glasses and hence the new Cu-based bulk glassy alloys have significant importance in basic science and engineering aspects.

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High-strength Cu-based bulk glassy alloys were synthesized in Cu–Zr–Ti and Cu–Hf–Ti ternary and Cu–Zr–Hf–Ti quaternary systems by copper mold casting. The critical diameter was 4 mm for the Cu₆₀Zr₃₀Ti₁₀ and Cu₆₀Hf₂₅Ti₁₅ ternary alloys and the Cu₆₀Zr₂₀Hf₁₀Ti₁₀ and Cu₆₀Zr₁₀Hf₁₅Ti₁₅ quaternary alloys. As the substitution amount of Zr or Hf by Ti in Cu₆₀Zr₄₀ and Cu₆₀Hf₄₀ alloys increases, the glass transition temperature (T_g), crystallization temperature (T_x) and temperature interval of supercooled liquid region ΔT_x(=T_x−T_g) decrease, while the liquidus temperature (T_l) has a minimum of 1127 K around 20%Ti, resulting in a maximum T_g⁄T_l of 0.63 in the vicinity of 20%Ti. The high glass-forming ability was obtained at the compositions with high T_g⁄T_l. The bulk glassy alloys exhibit high fracture strength of 2040–2190 MPa and plastic elongations of 0.3 to 1.9%. The finding of the Cu-based bulk glassy alloys with high T_g⁄T_l above 0.60, high fracture strength above 2000 MPa and distinct plastic elongation is encouraging for the subsequent development as a new type of bulk glassy alloys which can be used for structural materials.

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A basic study on dry separation process for rare earth element by vacuum distillation combined with selective reduction of iodides has been carried out. A possibility for vacuum distillation of di and triiodide mixture is demonstrated. The process is based on large differences in the redox potential of the rare earth iodides and in the vapor pressure of rare earth di and triiodides. Experimental proof of the vacuum distillation is provided for binary iodide systems, neodymium-samarium and samarium-dysprosium. The apparent separation factors, calculated from the compositions of diiodide-enriched and triiodide-enriched deposits, are β_Sm/Nd>890 and β_Sm/Dy=2300, respectively. These values are large enough to produce commercial pure metals used in the rare earth magnets. Thermodynamic consideration of the process is made on the basis of data reported in the literature and some thermodynamic assumptions.

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Glassy Fe₅₈Co₁₄Hf₈B₂₀ and Fe₆₀Co₂₀Hf₆Nb₂B₁₂ alloys in a thick sheet form were prepared by a meltclamp forging method. Their thickness was 0.78 mm and 0.49 mm, respectively. The glassy sheets have nearly the same values of glass transition temperature (T_g), onset temperature of crystallization (T_x) and Curie temperature (T_c) as those for the melt-spun ribbon samples. The T_g, T_x and T_c were 826 K, 895 K, and 598 K respectively for the Fe₅₈Co₁₄Hf₈B₂₀ alloy, and 799 K, 841 K and 638 K respectively for the Fe₆₀Co₂₀Hf₆Nb₂B₁₂ alloy. The same thermal properties between the forged and the melt-spun samples are presumably due to the formation of a similar glassy structure. The success of manufacturing Fe-based glassy thick sheets by the forging method is encouraging for future progress as a new engineering material.

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A phase relationship of the BaO–Bi₂O₃–TiO₂ system at 1273 K was studied using a solid state reaction. A new compound of BaBi₆Ti₂₀O₅₀ was found in this ternary system. In the BaTiO₃–Bi₄Ti₃O₁₂ pseudo-binary system, the solid solution of Bi₄Ti₃O₁₂ into BaTiO₃ was observed up to 4 mol%  Bi₄Ti₃O₁₂. The lattice parameters of tetragonal BaTiO₃ varied depending on Bi₄Ti₃O₁₂ content in the solid solution range. The structure of BaTiO₃ became cubic with the addition of more than 4 mol%  Bi₄Ti₃O₁₂. The temperature dependence of permittivity obeyed the Curie-Weiss-like behavior in the solid solution range. The highest permittivity of BaTiO₃ decreased and the peak of permittivity became broader with increasing Bi₄Ti₃O₁₂ content.

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An invariant reaction of “Liquid(L)→Solid(S)+Gas(G)” was considered as a eutectic reaction in previous literatures. However, since one of the resultant phases is not a solid phase, the invariant reaction of L→S+G should be distinguished from the eutectic reaction. The nomenclature of the L→S+G reaction is suggested to be a gas-evolution crystallization reaction.

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The structure of a one-dimensional Al–Co–Ni quasicrystal in an Al₇₁Co₁₉Ni₁₀ alloy annealed at 1100°C for 11 h has been studied by atomic-scale observations of high-angle annular detector scanning transmission electron microscopy and high-resolution transmission electron microscopy. Its structure can be characterized as a two-dimensional aperiodic arrangement of columnar clusters of atoms with a decagonal section of 2.0 nm in diameter and with pentagonal symmetry. In the arrangement of the atomic clusters, pairs of two lattice planes with high density of the atomic clusters are periodically arrayed with an interval of about 3 nm along the one direction. The atomic clusters with two orientations of pentagonal symmetry are randomly arranged with no special ordering manner.

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