The atomic-scale structure of amorphous Ti_100−xPd_x (x=34, 37, 45 and 48) alloy films produced by RF sputtering has been studied using the EXAFS technique. EXAFS spectra at both Pd K-edge and Ti K-edge have been examined. The interatomic spacings between the nearest neighbors, r_Pd–Pd, r_Ti–Ti and r_Pd–Ti, have been evaluated and compared with those of crystalline films of Pd, Ti and their solid solutions. The magnitudes of these nearest-pair distances are consistent with those evaluated by X-ray diffraction of the same materials. It has been found that r_Pd–Ti is ∼10% smaller than the arithmetic mean of r_Pd–Pd and r_Ti–Ti. This constriction is attributable to covalent bonds formed between Pd and Ti atoms.

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Diffusion coefficients and solubilities of hydrogen in grain-refined aluminum have been measured by a vacuum hot extraction method. Four samples with different grain sizes are prepared by melting, addition of Ti and B, casting, remelting and unidirectional solidification. Grain-refined samples contain some small particles in the matrix. The hydrogen diffusivity follows an Arrhenius type linearity on an inverse temperature dependence at 573 to 873 K. The diffusivity is not influenced by the small particles in the matrix, and depends only on the grain size. We have confirmed a propriety of the “Grain Boundary Cross Effect” relating to both of a fast diffusion along grain boundaries and of a suppressed diffusion by a hydrogen trapping at nodes or junctions of grain boundaries. A linear relationship between the logarithm of a pre-exponential factor (D₀) and the activation energy (Q), the so-called “Compensation Effect”, is realized for all of our hydrogen diffusivity data in aluminum and its alloys.

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A high temperature energy dispersive X-ray diffraction (EDXD) facility has been newly built using a vertical type goniometer, which make it possible to measure the diffraction profiles of melts from room temperature to 1873 K. The fundamentals of this facility were confirmed by obtaining the interference function of a silica glass sample over Q=200 nm⁻¹ at room temperature using the computer program of PEDX for the generalized radial distribution function analysis of EDXD developed by the present authors (Petkov and Waseda). The feasibility for a high temperature melt was made by applying this EDXD facility to a structural study of liquid bismuth germanate (Bi₄Ge₃O₁₂) at 1373 K.

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The effect of magnetic fields on the athermal martensitic transformation in an Fe-31.4Ni-0.5Mn alloy (mass%), whose M_s temperature is about 195 K, and on the isothermal one in an Fe-24.9Ni-3.9Mn alloy (mass%), whose nose temperature is about 153 K, have been examined in order to clarify the difference between the athermal and isothermal kinetics of martensitic transformations by measuring magnetic field susceptibility and magnetization, and by observing optical microstructure, applying pulsed ultra high magnetic fields up to 31 MA/m. As a result, the following characteristics were found: The austenitic state in the former alloy was ferromagnetic, whereas that in the latter alloy was micromagnetic and/or spin glass. Even in the latter alloy, martensitic transformation was induced instantaneously under pulsed magnetic fields higher than a critical one over a wide temperature range, as in the former alloy. This result suggests that the originally isothermal kinetics of martensitic transformation is changed to the athermal one under high magnetic fields. Optical microscopy showed that respective isothermal martensite plates of the Fe–24.9Ni–3.9Mn alloy under no magnetic field grew gradually during isothermal holding. Moreover, morphology of the magnetic field-induced martensites of both the alloys was almost the same as that of thermally-induced ones, irrespective of the formation temperature. A thermodynamic calculation for the critical magnetic field vs. temperature relation was done for both the alloys by using an equation previously proposed, and the calculated relations were all in good agreement with the experimental ones in the wide temperature range examined.

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A new model, which is able to explain systematically for both the natures of athermal and isothermal martensitic transformations, has been proposed, referring to the experimental results obtained on the effect of magnetic fields on those martensitic transformations in Fe–Ni–Mn alloys. The model has been derived by making three assumptions, in which a new condition is introduced that martensitic transformation may start when some numbers of particles make a cluster and are simultaneously excited in any place in the austenite. According to the model, the following characteristics were well explained: No C-curve exists for the athermal transformation and a C-curve does for the isothermal one, depending on a difference in their temperature dependence of the Gibbs chemical free energy difference between the austenitic and martensitic states. The minimum size of the cluster for making the martensitic transformation start, which was involved in the model as a parameter, was obtained to be about 1.4 nm in cube at most by best fitting with the TTT diagram of the isothermal martensitic transformation previously examined. Based on the model, the influence of external forces, such as uniaxial stress, magnetic field and hydrostatic pressure, on the isothermal martensitic transformation in an Fe–Ni–Mn alloy is predicted.

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The effects of aging on transformation temperatures, morphology and atom arrangement in Cu–Zn–Al shape memory alloys have been examined by differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and channelling enhanced microanalysis (ALCHEMI), respectively, and they have been investigated for both the parent and the martensite phases by using Cu–11.4Zn–18.7Al and Cu–11.2Zn–17.1Al (at%), respectively. The aging in the parent phase did not change significantly the transformation temperatures and the atom arrangements. On the other hand, the aging in the martensite phase increased reverse transformation temperatures. This increase was attributed to some change in atom arrangement and to some decrease in the density of stacking faults during aging.

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The grain boundary reactions in Ag–Cu alloys with or without 1.5 mass%Sn were investigated by optical microscope, electric resistivity, SEM, and hardness tests. The results are summarized as follows.
Electric resistivity, hardness, and nodule formation were investigated as a function of aging time for 93Ag–7Cu and 91.6Ag–6.9Cu–1.5Sn alloys at temperatures between 250 and 350°C.
With aging time, the electric resistivity of Sn-added alloy decreased rapidly and reached a constant value after passing a minimum.
In the 91.6Ag–6.9Cu–1.5Sn alloy, very fine particles of β-Cu were precipitated in the α′-Ag phase with Cu supersaturation at the initial stage of the aging treatment at each temperature, while nodule formation was significantly retarded. The reverse was observed for the 93Ag–7Cu alloy.

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The apparent hydrogen diffusivity data for pretreated pure iron and steel membranes have been analysed for hydrogen-trapping effects. Modified equations, valid for the appropriate boundary conditions of charging, have been derived to compute the trap density from the apparent diffusivity. In general, the traps are saturable in nature. The dependence of diffusivity of hydrogen in iron and steel on the charging current density or overvoltage indicates trapping of hydrogen at dislocations and grain/interfacial boundaries.

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From single phase to two-phase alloys, creep crack growth behavior of Fe–15Cr–25Ni austenitic steels has been examined for different grain sizes at 973 and 1123 K. The creep crack growth rate increases with increasing grain size. An equation was found to describe the relation between the initiation time t_i or rupture time t_r and grain size d: t_r(i)·d^β=C. The precipitation of grain boundary carbide decreases the effect of grain size on creep crack growth. Different grain size dependences on creep crack growth in other materials were also analysed. A damage model based on constrained cavity growth was shown to provide good predictions on the grain size effect on creep crack growth behavior.

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The partition of Al₂O₃, MgO, and TiO₂ between magnetite and Na₂O·2B₂O₃ melts was studied by the flux growth method as a function of solute concentration at 1073∼1373 K under a controlled oxygen partial pressure. It was found that Al₂O₃, MgO, and TiO₂ in the Fe₃O₄ crystal as well as in the flux obey Henry’s law and the partition coefficients, k_i(=x_i^crystal⁄x_i^flux), of Al₂O₃ and TiO₂ increased with temperature, whereas that of MgO decreased slightly with temperature.

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The purpose of this research is to elucidate an interaction mechanism at an interface between molten iron and the magnesia crucible. Pure iron used in the present study had less content of impurities except for oxygen, the content of which was classified into two groups (15 and 400 mass ppm). Magnesia crucibles were commercial dense products. Iron specimen was molten for 10∼60 min at 1600°C under Ar atmosphere in a tungsten mesh-heater furnace. After cooling, the specimen was treated and observed with optical and scanning electron microscopes. And then the specimen interface was analyzed with an electron probe micro-analyzer, an analytical electron microscope and a surface roughness measuring instrument. It was also identified with an X-ray diffractometer.
The results obtained are as follows:
(1) Depending on the initial oxygen content in the iron specimen, the appearance of the iron specimen-magnesia crucible interface was very different. In the case of a low oxygen content (15 mass ppm) in molten iron, the interface of the magnesia crucible after melting was almost the same as that before melting except for the very slight corrosion at the grain boundary. On the contrary, the magnesia crucible was extraordinarily attacked by molten iron which had a high oxygen content (400 mass ppm).
(2) In the latter case, the solidus temperature of the MgO–FeO phase formed at the interface of the magnesia crucible with molten iron lowers to about 2600°C. Although it is still solid at the experimental temperature, the surface rearrangement among the relevant phases may occur.
(3) Oxygen in molten iron is very interface-active. The dissolved oxygen atoms are concentrated on the interface between molten iron and the crucible, and form FeO monolayer at the iron interface in the case of 400 mass ppm O. On the other hand, no FeO layer is formed in the case of 15 mass ppm O. It is considered that such a monolayer may cause different types of attack on the magnesia crucible by molten iron.

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An investigation was made on the microstructural refinement of Cu-37%Al and Al-17%Si alloys by the vacuum stirring synthesis. In this process, a molten alloy was spattered by a polygonal rotor rotating at a high speed up to 167 s⁻¹ in a heat-controlled vessel. Many primary crystals formed in the spattered droplets were refined with repeating a collision between the rotor surface and the inner wall of the vessel by the stirring action of the rotating rotor. Finally, the slurry of gathered semi-solidified droplets was poured down into a metallic mold. Remarkable refinement of microstructure was achieved by the present stirring synthesis process as compared with the microstructures formed by conventional casting processes. The mean size of primary crystals was about 20 μm in the Cu-37%Al alloy made by the stirring synthesis at a rotation speed of 167 s⁻¹, while the primary crystal size in the alloy cast conventionally without stirring was 300 to 1000 μm. The mean size of primary silicon crystals was about 16 μm in the Al-17%Si alloy made by the stirring synthesis at a rotation speed of 167 s⁻¹, and it was 89 μm in the alloy rheocast at a rotation speed of 70 s⁻¹.

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The present investigation was carried out to see if intricate shaped castings can be made from a eutectic Al–Si (BS LM13) alloy dispersed with 5.5 mass% graphite particles by pressure die casting technique. A bushing spring guide (BSG) component used for electrical applications was selected for the purpose. The study involved the characterization of a few properties e.g. hardness, density and electrical resistivity of the pressure die cast (PDC) composite and their comparison with that of the gravity die cast (GDC) one. The influence of heat treatment on the microstructure of the PDC composite has also been studied.
Visual examinations revealed that the components were perfect in shape and pore free indicating that the technique could be a promising route to synthesize graphitic aluminium alloys into intricate shapes.
Machined sections of the PDC components indicated reasonably uniform distribution of graphite particles in various regions of the former. This was also confirmed by the quantitative analysis of the graphite content recovered from the dissolved specimens. The variation in hardness, density and electrical resistivity of the composite was quite less agreeing well with better uniformity of distribution of graphite particles in the matrix.
The matrix microstructure of the PDC composite was considerably refined over the one processed by GDC technique, although the morphology of the microstructural constituents remained unchanged. The higher rate of solidification in this case was found to be responsible for the improvement in the uniformity of graphite distribution in the matrix and the microstructural refinement. Reduced secondary dendritic arm spacing (DAS) further confirmed a higher rate of solidification as a result of applying the pressure.
Improvement in the graphite/matrix interfacial bonding was found to be one of the interesting features of pressure application. This was attributed to the increased solubility of the dissolved gases in the matrix and squeezing out of the entrapped gases from the latter under the conditions of applied pressure during solidification. The graphite particles were found to have fractured in this case probably due to the possible application of a combination of impact, shear and compressive stresses under the influence of the applied injection pressure.
Heat treatment of the PDC composite was found to have brought about significant and useful modifications in the matrix microstructure at the little loss in properties like hardness, density and electrical resistivity.

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