We have investigated the time-scaling properties of the isothermal crystallization kinetics for amorphous Co₇₅B₂₅, Fe₈₀B₂₀, Fe₄₀Ni₄₀B₂₀, Fe₈₁B₁₇Si₂ and Fe₆₀Ni₂₀B₁₀Si₁₀ alloys by differential scanning calorimetry. All the alloys exhibit a single crystallization stage. The time scale was defined as the time when the crystallization has reached half completion. All the time-scaled crystallization curves of each alloy fall onto a single muster curve of the Johnson-Mehl-Avrami form in each case. The Avrami exponent indicates that the crystallization process of the Fe₆₀Ni₂₀B₁₀Si₁₀ is governed by interface-controlled growth with a constant nucleation rate, whereas those of the other alloys are by interface-controlled growth of a fixed number of nuclei. The Williams-Landel-Ferry equation based on a free-volume consideration gives a universal function of time-scaling parameter as a function of temperature for all the alloys. This suggests that we have to take into account the relaxation occurring in the amorphous phase outside the crystallite in the crystallization process.

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Magnetoresistance effects and film structures have been investigated in [Fe–Mn/Ni–Fe–Co/Co/Cu/Co/Ni–Fe–Co/NiO/Si] sandwiches. The NiO buffer layers increase exchange bias fields applied to the Ni–Fe–Co/Co magnetic bilayers neighboring with the Fe–Mn layers. However, the NiO buffer layers decrease the magnetoresistance ratios of the sandwiches. Therefore, we also inserted Hf buffer layers between the NiO buffer layers and the Si substrates. The Hf buffer layer, 1.0 nm in thickness, increases the magnetoresistance ratios of the sandwiches.

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The temperature dependences of strength of L1₂ type compounds Co₃Ti and Pt₃Al were studied in a wide temperature range, paying attention to the low temperature strength anomaly (i.e., the steep increase in flow stress with lowering temperature in a lower temperature range) based on the phase stability of L1₂ phase against the adjoining GCP phases. The low temperature strength anomaly for Co₃Ti may be related to a lowness of its magnitude of SFE, whereas that of Pt₃Al seems to be related to its phase stability of L1₂ against D0_c structure.

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Microstructures and tensile properties of the amorphous Al₈₈Ni_10−XFe_XNd₂ (X=0, 3, 5 at%) alloys at elevated temperatures and their relations with thermal stability were investigated. It was found that the crystallization of the three alloys proceeded through two stages. One is the formation of an Al phase at the low temperature side and the other is the formation of intermetallic compounds (Al₃Ni, Al₃Fe, Al₁₁Nd₃) at the high temperature side. The Al particles smaller than 15 nm and compounds larger than 50 nm in diameter were formed during uniaxial tension tests and found to be uniformly distributed in the amorphous matrix. The ultimate tensile strengths of the three alloys were above 800 MPa at 580 K, which were 3∼4 times stronger than conventional high-strength Al alloys with heat resistance. This is possibly due to both the dispersion strengthening effect by the defect-free Al particles and the enhanced thermal stability by the depletion of Al atoms in the amorphous matrix resulting from the formation of the Al particles. In contrast, a significant decrease in strength was observed at a temperature above 580 K. This is presumably because the concentration of the solute atoms in the amorphous matrix was greatly decreased below the nominal concentration by the formation of the compounds. Elongation increased significantly from 2∼3% at room temperature to over 10∼20% at the temperatures higher than the crystallization temperatures. The temperature at which a largest elongation in the three alloys was obtained corresponded to the exothermic peak temperature in the DSC curve. This fact indicated that such a large elongation originated from the precipitation of the crystalline phase. On the other hand, in a temperature range in which the Al phase is formed, deformation occurs through a shear deformation mode, whereas in a higher temperature range in which the compounds are formed, it occurs viscoelastically.

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The interaction between liquid aluminum and molten salts was studied by metal loss and electrochemical methods. The polarization curves for Al and Used Beverage Container (UBC) alloy in molten salts show that the corrosion rate of UBC is higher than that of pure Al, and the corrosion rate is higher in the equimolar NaCl–KCl+5%NaF salt melt than in equimolar NaCl–KCl molten salt. It was found that magnesium in aluminum alloys dissolves preferentially into these molten salts. This can be rationalized by the more negative free energy of MgF₂, or the lower electrode potential E_Mg/Mg²⁺ compared to E_Al⁄Al³⁺. The metal loss in molten salts increases with time and addition of fluorides. It was found that the metal loss in molten salt was inversely related to the metal and molten salt interfacial tension. Finally, the Girifalco and Good model was used to calculate the interfacial tension between UBC alloy and molten salts based on an interaction parameter calculated from the interfacial tensions between pure aluminum and molten salts. The predicted values are in reasonable agreement with the measured values of interfacial tension.

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The electrobleaching of WO₃ films formed onto a Pt plate by vacuum deposition has been investigated in the aqueous solution containing 0.1 mol/l H₂SO₄ by Raman spectroscopy. Raman bands due to the WO₃ film did not shift in frequency during the bleaching reaction in the solution but increased in intensity with passing time due to the increase in transmissivity of the chromic WO₃ in the visible region. A fact of particular interest is that at the early stage of bleaching the intensity of Raman scattering from the tungsten oxide increased in proportion to the square root of the elapsed time. This fact strongly suggests that the bleaching rate is conditioned by the diffusion of H⁺ from the oxide phase to the solution phase. Raman bands due to hydration were also observed at the very beginning of the bleaching in the solution, which demonstrates that H₂O as well as H⁺ was injected into the oxide in the coloring process.

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Effects of bonding frequency and surface cleanliness of Al-1 mass%Si film on the bonding strength have been investigated in order to establish a reliable thick Al wire bonding precess. Bonding strength is enhanced considerably by increasing bonding frequency from 60 to 110 kHz, but bonding time and ultrasonic power have little effect on the bonding strength.
Bonding damage occurrence is increased substantially by increasing the bonding time and ultrasonic power. Therefore, high frequency thick Al wire bonding is quite promising for mass production. The mechanism is proposed by measuring SAW velocity change of transistor chips without Al-1 mass%Si film before and after bonding. Carbon on the Al-1 mass%Si film hardly causes the degradation of the bonding strength, but thickness of oxide film influences it.

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Mixing and homogenization, refining and alloying processes in the bulk mechanical alloying by the repeated MA-forging are experimentally investigated to define the standard process condition. Through experimental demonstration of the effect of each process parameter on the above fundamental processes, controllability of the related process parameters to this bulk MA is described towards productive mechanical alloying. The Ag–Cu, Cu–Co and Ag–Co systems are chosen as typical immiscible systems to discuss the intrinsic effect of constituent elements on the solid solubility in the alloying processes.

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The aim of this study is first to find suitable bonding conditions for joining Ni-base single crystal superalloy TMS-26 without the formation of a recrystallized zone at bond-line. Subsequently the study is carried out to investigate the relationship between misorientation angle at bonding interface and joint strength. Joints were made using samples prepared with a {100} crystal plane at the bonding surface. All the samples were joined in a vacuum of 4×10⁻³ Pa using radio frequency heating.
Single crystal TMS-26 can be bonded without the formation of voids and recrystallized zone at the bond-line. The quality of creep rupture of joints deteriorates due to formation of precipitates at the bond-line. There are a few inclusions at the bond-line when the twist angles of 0° up to 3° are used. Creep rupture life of the joints is long. When twist angles greater than 3° are used, many inclusions are formed at the bond-line and joint strengths are very low. The precipitates at the bond-line consist of α tungsten phase and oxides due to surface film.

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The effects of the bonding temperature and voltage on the rate of the enlargement of intimately contacted area in the anodic bonding of the Kovar alloy to borosilicate glass have been studied systematically in order to obtain better understanding of the rate controlling factor of the process. It was suggested that the attainment of intimate contact was controlled by two factors having different activation energies depending on the bonding temperature. At bonding temperatures higher than 669–687 K (depending on the bonding voltage), the estimated activation energy was close to that of the viscous flow of the glass. At lower bonding temperatures, the estimated activation energy was close to that of the conductivity of the glass. A mechanism of the enlargement of intimately contacted area during the anodic bonding is proposed to explain these results.

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The porosity, composition, and temperature dependence of thermal properties in porous Ni/yttria-stabilized zirconia (YSZ) cermets has been investigated at high temperatures by the laser flash diffusivity method. At a temperature range of 1073 to 1273 K, there is no temperature dependence of thermal diffusivity of the cermets. Observable, however, is a slight increase in both of specific heat and thermal conductivity with an increase in temperature. Although the specific heat is governed by the law of mixing in composition, it is independent of the porosity. Pores in the cermet act as heat barriers to prevent heat transfer, in which thermal conductivity is regarded as zero. The relationship between thermal conductivity and porosity can be expressed by the resultant conductivity calculated on the basis of the modified effective medium theory. In this calculation, a porous Ni/YSZ cermet is regarded as a simple cubic resistance network composed of two kinds of unit resistors corresponding to the solid and pore phases. Moreover, the composition dependence of the thermal conductivity of a dense Ni/YSZ cermet could be expressed using the resultant conductivity of the resistance network of unit resisters corresponding to Ni and YSZ. On the basis of these results, the following equation expressing the thermal conductivity of porous Ni/YSZ cermets λ_C/Wm⁻¹ K⁻¹, has been derived as a function of Ni-volume fraction for total solids V_Ni, and porosity P, for 1273 K
(Remark: Graphics omitted.)
where K_A⁄Wm⁻¹K⁻¹=0.16−55.62V_Ni+195.7V_Ni², K_B⁄(Wm⁻¹K⁻¹)²=95.23+1432.3V_Ni+1257V_Ni². The validity is confirmed.

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Electrodeposition of Y on Ni and their alloying by molten salt electrolysis was attempted in an equimolar NaCl–KCl melt containing up to 4 mol% YCl₃ at 1073 K. The electrolysis was carried out using the potentiostatic polarization method at constant potentials of −1.8, −2.0 and −2.2 V vs. Ag/AgCl(0.1) for 1.8 ks. In the potential region below −2.0 V in 49 mol% NaCl-49 mol% KCl-2 mol% YCl₃, a dense, smooth and adhesive monolayer of about 30–120 μm thickness was formed on the Ni specimen. The polarization at less noble potential led to an increase in the thickness of the deposit layer. The layer consisted of intermetallic compounds of Ni₃Y and Ni₅Y. The Ni₃Y formed a matrix of the deposit layer, and the Ni₅Y formed a thin layer along the substrate/deposit interface and particles in the Ni₃Y matrix. The formation of such a layer was thought to result from the fact that reduction of the Y³⁺ ion proceeded effectively at the stated conditions and the reduced Y and Ni diffused into each other to form the intermetallic compounds layer.

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