In this paper, we review our recent investigations on the magnetic properties and microstructure of highly coercive FePt films prepared on both MgO (001) and MgO (110) substrates with various film thicknesses (t_N). Perpendicularly magnetized FePt (001) film were obtained on MgO (001) substrates, while FePt (101) films with the easy magnetization axis canted from the perpendicular direction to the film plane were obtained on MgO (110) substrates. The film morphology changes from a particulate to a continuous state depending on t_N. A drastic decrease in the coercivity has been observed with the percolation of particles for FePt (001) films, when t_N exceeds a critical thickness, t_c=45 nm. On the other hand, the gradual decrease of H_c with t_N has been observed in FePt (101) films and no remarkable change is seen at the critical thickness where the film morphology changes from a particulate to continuous state.

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Very small amount of B promotes the disorder/order transformation of L1₀ CoPt at low annealing temperature along with excellent c-axis orientation. The c-axis is slightly expanded by B atoms interstitially incorporated into the octahedral sites in the L1₀ CoPt lattice. Magnetic measurements using Hall magnetometry have revealed that the magnetic anisotropy energy (MAE) is enhanced by elongation of the c-axis. This result is in harmony with the first principles calculation which predicts that the c-axis elongation enhances the MAE of L1₀ CoPt due to the d band splitting of Co near the Fermi level in the minority spin state.

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Two-dimensionally dispersed L1₀-FePt nanoparticles as small as 12 nm with orientation was fabricated by electron-beam evaporation and post-annealing at 873 K. After a prolonged annealing at 873 K for 86.4 ks, the increase of coercivity was almost saturated and coercivity reached 434 kAm⁻¹ at 300 K, which is very small compared to recent reports on FePt nanoparticles with sizes larger than 20 nm. Long-range order parameter of the fabricated nanoparticles was determined by electron diffraction at 200 kV taking the multiple scattering into consideration. Obtained order parameter remained 0.55±0.02 for the nanoparticles with an axial ratio c⁄a of 0.961±0.003. The low degree of order is thought to be responsible for the small coercivity. Effect of Debye-Waller factor on the order parameter was discussed.

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Since the factors that influence microstructure formation are extensive (e.g., alloy composition, heat treatment condition, etc.), quite a lot of experimental trial-and-error is often necessary when searching for the best combination of desired microstructure and material properties, even when the basic mechanism of microstructure formation is understood. During the last decade, the phase-field method has emerged across many fields in materials science as a powerful tool to simulate and predict complex microstructure evolution. Since phase-field methodology can model complex microstructure changes quantitatively, it is possible to search for the most desirable microstructure by using this method as a design simulation, i.e., through computer trial-and-error testing. In order to establish this methodology, first of all, quantitative modeling of complex microstructure changes using the phase-field method is required. The objective of this study is to model the FePt nano-granular structure formation and the order-disorder phase transition of FePt nano-particles as a typical example of phase-field modeling. We show that it is possible to model FePt nano-granular structure formation quantitatively using the phase-field method. This modeling method may also be applicable to various types of granular structure formation. The simulation result also suggests that there is a size dependence on the ordering of FePt nano-particles. Using the phase-field method to model the microstructure evolutions proved to be a very effective strategy in predicting and analyzing the complex microstructure formation.

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3d/Au (3d = V, Cr, Mn, Fe, Co, Ni) superlattices with tetragonal L1₀ ordered structure are studied by means of the self-consistent full-potential linearized augmented-plane-wave method under the generalized gradient approximation. It is shown that the ground state magnetic configuration changes from intra-layer antiferromagnetic to ferromagnetic with increasing 3d electron number from VAu to NiAu. Based on a Heisenberg model with exchange parameters extracted from ab initio calculations, Monte Carlo simulations are carried out to study the finite-temperature properties. Curie temperature and Néel temperature are obtained and discussed in connection with the 3d electrons filling.

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Aiming at development of ultra-high density magnetic recording media, nanostructured Fe–Pt perpendicular recording media were tailored. In order to obtain a crystal orientation of Fe–Pt(001) for a double-layered perpendicular medium with a soft-magnetic underlayer, a heteroepitaxial layer configuration was applied. A high pressure sputter-deposition method was effective for lowering the fct-ordering temperature of the L1₀ crystal structure. Microstructures of the media were constructed by two kinds of methods, i.e. inducing crystal defects and forming composite films with oxides. The highest SN ratio was obtained by a wall pinning type medium with the induced crystal defects. Design and possibility of the Fe–Pt(001) media were discussed.

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FePt with ordered L1₀ structure is a promising material for high-density magnetic recording media because the material has high magnetic anisotropy energy. The film is considered to show excellent thermal stability. However, the practical use of FePt media is hindered by several problems that must be solved, i.e. decrease of ordering temperature, realization of films with perpendicular magnetic anisotropy, reduction of media noise, and development of writing methods of bits on high-coercive-force media. Among these problems, the former two problems are being resolved, but the problems associated with reducing media noise and developing writing methods still remain unsolved. It is expected that these problems will be solved by introducing new ideas or methods. Hereafter it will be important to form double-layer perpendicular magnetic recording media and to estimate the read and write characteristics of the media.

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Evaluation of microcracking behavior, among other nondestructive evaluations, is important for understanding the fracture of materials and improving their fracture resistance. This paper deals with the principle of the inverse problem analysis of acoustic emission (AE), the method of analyzing the moment tensor of microcracks developed by the author et al., and examples of the method’s application. The paper goes on to introduce the concept of the smart materials and structural systems that perform nondestructive evaluation on their own and function to repair and restore defects. The paper also overviews the present state of research and development.

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We conducted X-ray and neutron diffraction experiments and magnetic susceptibility measurements for γ-MnFe alloys with a small amount of Cu or Pt, and for γ-MnCu and γ-MnZn alloys. γ-(Mn_1−xFe_x)_0.95Cu_0.05 alloy with x=0.26 around 10 K shows a face-centered orthorhombic structure with a=0.3681, b=0.3655 and c=0.3622 nm, and a non-collinear antiferromagnetic structure with μ_a=0 and μ_b⁄μ_c=0.62. With increasing temperature, orthorhombic-tetragonal with c⁄a>1 structural transition occurs at T_o (=125 K) and the tetragonal structure finally transforms to a cubic structure at T_t (=352 K), which is lower than the Néel temperature T_N (=440 K). The γ-(Mn_1−xFe_x)_0.95Pt_0.05 alloy with x=0.13 at 10 K also shows a similar structure with a=0.3745, b=0.3714 and c=0.3649 nm, which has a non-collinear antiferromagnetic structure with μ_a=0, μ_b=1.03 and μ_c=1.94μ_b/(Mn or Fe) atom. The γ-Mn_1−xCu_x alloy with x≤0.26 and γ-Mn_1−xZn_x alloy with x≤0.28 show a tetragonal structure with c⁄a<1 at low temperature.

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Wide range selected area electron diffraction (SAD) patterns on ⟨110⟩ crystal-zones (CZ) of a single variant of R-phase in Ti–50.4 at%Ni alloy quenched from 1223 K indicated that the ⟨110⟩ CZs can be classified into two types, CZ-A and CZ-B, with respect to the 1⁄3⟨110⟩^∗ reflections. Especially the absence of 1⁄3⟨110⟩^∗ on the CZ-A could not be explained by the models proposed up to now. Based on the experimental results, a map that expressed the SAD patterns of single R-phase variant on the (111) stereographic projection was presented. It was suggested that the true structure of R-phase should fulfill three conditions on characteristics of SAD patterns, that is, the reproduction of the unique (111) pattern, the absence of 1⁄3⟨110⟩^∗ reflection at the specific planes on CZ-A and the retainment of three-fold symmetry with respect to the [111]. Bending the TEM sample composed of several R-phase variants caused the integration of the R-phase variants, and resulted in the formation of the B19′ martensite. However both the single variant and the B19′ martensite returned to the initial state of several R-phase variants after 120 hours at room temperature. It was proposed that the unification of the R-phase variants plays an important role on the R-M transformation.

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Amorphous alloys with compositions Fe₄₀Co₄₀Cu_0.5Al₂Zr₉Si₄B_4.5 and Fe₆₂Co_9.5Gd_3.5Si₁₀B₁₅, were prepared by the melt spinning technique in the form of ribbons. Three stages of crystallization process were found in both the alloys and the crystallization kinetics was studied. Supper cooled region was found in Fe₆₂Co_9.5Gd_3.5Si₁₀B₁₅ alloy indicating the ability of formation of bulk amorphous alloy and 1 mm diameter rod was prepared by Cu-mould casting. Curie temperature and the saturation magnetisation of this alloy were found to be 596 K and 0.98 T respectively. Relatively, higher Curie temperature (736 K) and saturation megnetisation (1.18 T) were observed in the as-spun state of Fe₄₀Co₄₀Cu_0.5Al₂Zr₉Si₄B_4.5 alloy. Present study also indicated that partial crystallization of Fe₄₀Co₄₀Cu_0.5Al₂Zr₉Si₄B_4.5 alloy would further enhance the Curie temperature and saturation magnetisation.

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Buckling, impact resistance and energy absorption of dynamic axial compressed aluminum square tube are discussed. Numerical analysis of the deformation of the square tube is made by a finite element method. The result shows that ripples of buckling are produced in the surfaces of the tube wall when the striking mass reaches to a certain value. The wave pattern on the deformed tube wall of 1 mm thick is concave-convex pattern in adjoining surface, while that of 2 mm thick is convex pattern in all surfaces. Absorbed energy of the deformed tube increases in proportion to axial displacement of the tube. Experimental results agree approximately with those of the finite element method analysis.

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It is known that thermal residual stress in particulate ceramics results from the mismatch of thermal expansion coefficients of particulates and matrix and contributes to toughening of ceramic composites. In this study, alumina-zirconia composites with agglomerated structures were prepared using alumina or alumina-zirconia powder to obtain large-sized compressive zones in particulate ceramics without degrading flexural strength. Agglomerated powder was obtained by pre-sintering. Then several samples used different fraction and size of agglomerated powder were prepared by pressureless sintering. Microstructure and crack paths of prepared samples were examined by scanning electron microscopy (SEM); flexural strength and fracture toughness of samples were evaluated by four-point flexural test and controlled surface flow method, respectively. Alumina-rich agglomerated structures and a zirconia-rich matrix were formed in samples that were produced using pre-sintered powder. Addition of zirconia to pre-sintered alumina powder prevented coarsening of alumina grains in agglomerated structures. Grain coarsening and cracking caused the decrease in flexural strength of samples with agglomerated structures. Agglomerated structures enhanced fracture toughness. In particular, a specimen using 21.1 vol% of pre-sintered alumina-rich powder of 32 to 150 μm exhibited increase in fracture toughness by approximately 30% without sacrificing average flexural strength. A SEM observation of crack paths showed that grain bridging did not occur in samples. Thereby, we inferred that the compressive residual stress zone in agglomerated structures played an important role in raising fracture toughness.

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We have developed a new manufacturing process for nickel-free austenitic stainless steel. In combination with machining and a nitrogen absorption treatment, this process makes it possible to form small precise devices. The new manufacturing process can be used to manufacture small devices with a great deal of precision and parts with a maximum thickness or diameter of 4 mm. However, the temperature for the nitrogen absorption, 1473 K, was sufficiently high for grain growth, and coarsening was observed after nitrogen absorption. Therefore, a nitrogen absorption treatment that allows the retention of strength and ductility is performed with a grain refinement process before nitrogen absorption. In this study, we attempted the refinement of grains by thermo-mechanical treatment before nitrogen absorption treatment in order to increase the mechanical properties after nitrogen absorption treatment. The mechanical properties and microstructures of Fe–24Cr–2Mo with fine grains before and after nitrogen absorption treatment were evaluated to understand the effects of grain refinement on nitrogen absorption. The austenitic phase was obtained only from the surface to a 0.5-mm depth in the alloy with nitrogen absorption at 1473 K for 7.2 ks. The balance between strength and elongation in the alloy with nitrogen absorption at 1473 K for over 10.8 ks was the same as that in conventional austenitic stainless steel. The value of ultimate tensile strength in the alloy with nitrogen absorption increased with the grain refinement process attempted in this study. The elongation in the alloy with nitrogen absorption over 18.0 ks decreased because of grain growth. Therefore, grain refinement before nitrogen absorption treatment can increase the mechanical properties of nickel-free austenitic stainless steel.

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Copper–tellurium films were electrochemically deposited from a solution containing CuCl₂, TeO₂ and HCl. This study revealed the relationship between the copper/tellurium ratio in the solution and the metal ratio in the deposited film. The Cu/Te ratio of the deposited film was successfully controlled by conducting electrodeposition under diffusion-limited conditions. The [Cu]/[Te] ratio in the solution was linearly related to that of Cu/Te in the deposited film, since the partial current density originating from the copper and tellurium ions was directly proportional to the concentration of each. The deposited films crystallized to Cu₂Te at the Cu/Te ratio of 2.5. The films were deposited at −0.4 V vs. Ag/AgCl from a solution in which [Cu]/[Te] = 2.5, [CuCl₂] = 1.0×10⁻³ M (= kmol m⁻³), [TeO₂] = 4.0×10⁻⁴ M, and pH = 1.

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Ti–Cr–V alloys with a BCC structure have high protium (hydrogen atom) capacities. In considering practical use, protium absorption-desorption cyclic properties become an important problem. In this paper, the cyclic properties in high-low hydrogen pressure regions are investigated in order to clarify the change of the crystal structure and the protium capacities of appeared phases of the β, γ protides in the Ti–Cr–V alloys and Ti–Cr–Mo, Ti–Cr–Al alloys. As a result, it was found that the crystal structure of the β protide phase changed from a BCC structure to a BCT structure by increasing the cycle number in the Ti–Cr–Mo, Ti–Cr–Al alloys similar to the Ti–Cr–V alloys. This result suggests that the lattice will be hard to be contracted gradually along the a-axis direction of the absorbing process with an increasing cycle number. It was also found that β protide phase in the alloys which have bad cyclic properties became stable with an increasing cycle number because the low hydrogen pressure region P-C-isotherm curves shifted to the low pressure side with an increasing cycle number. The major reason of this result is considered to be the accumulation of the lattice defects in the alloys with an increasing cycle number.

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The protection of crack formation by a functionally graded layer at the interface of surface-hardened iron alloys has been investigated using a modified reactive diffusion process which consists of the two-stage diffusion heat-treatment for diffusion species. From the stress analysis on thermal shock test and the microstructure observation, it was known that cracks formed on the thermal shock test were onion cracks arising from a radial stress σ_r and radial cracks due to a circumferential stress σ_θ. In the specimens subjected to the modified reactive diffusion heat-treatment, a functionally graded layer was formed at the interface between the surface carbide layer/iron substrate, which effectively suppressed the generation of cracks by shifting a location of the maximum tensile stress toward the substrate and relaxing a stress concentration at the interface.

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Au-nanoparticle dispersed TiO₂ (Au/TiO₂) films were prepared by laser ablation using Au-powder mixed TiO₂ (rutile) sintered targets. The Au content in the films was controlled in the range from 3 to 37 mol% by changing the target composition. As-deposited TiO₂ matrix of the films was amorphous-like anatase, and changed to a well-crystallized anatase phase after heat treatments at 1173 K. The diameters of Au nanoparticles increased from 1.5 to 4.1 nm with increasing the heat-treatment temperature from 573 to 1173 K. Optical absorption spectra by surface plasmon resonance from Au nanoparticles were observed in the heat-treated films. The red-shift of absorption peak from 590 to 635 nm was observed due to the increase in the diameter of Au nanoparticles and refractive index of TiO₂ matrix with increasing the heat-treatment temperature.

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Nanocrystalline Fe–23 at%Al–6 at%C alloy powder was produced by mechanical alloying of the mixture of iron powder and aluminum powder (Fe–25 at%Al) with methanol, and was consolidated into fully dense compact by spark plasma sintering (SPS) at 1273 K. The compacts have nanocrystalline microstructure composed of mixture of α-phase grains and κ-carbide (Fe₃AlC) grains whose average grain size is about 50 nm. Although relatively large grains were also observed in places, their sizes were not over a few micrometers. The mechanisms of the densification and the structural evolution during the SPS process are discussed.

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Low density and high performance Mg-based laminated composites were fabricated by means of sandwiching the AZ31 Mg foils with the carbon-fiber/polyether ether ketone (PEEK) prepreg through hot pressing. Proper surface treatments of AZ31 sheet using CrO₃ base etchants are necessary in order to achieve good interface bonding characteristics. The resulting Mg base laminated composite, with a low density of 1.7 Mg/m³, exhibits high modulus of 75 GPa and tensile strength of 932 MPa along the longitudinal direction. The experimentally measured tensile modulus and strength data along both the longitudinal and transverse directions are within 90–100% of the theoretical predictions by rule of mixtures, suggesting that the bonding between layers and the load transfer efficiency are satisfactory.

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The photocatalytic degradation of methylene blue aqueous solution sensitized by a pyrochlore-related κ-CeZrO₄ phase was investigated under irradiation with Xe discharge light. The optical absorbance of the solution was first decreased smoothly, and then retention was observed in several hours due to the formation of a new absorption peak. The absorbance spectrum resembled that of thionine. The present study confirms that the photocatalytic reaction sensitized by κ-CeZrO₄ was different from that by TiO₂.

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The system Sb(III)-HCl–H₂O has been studied by equilibrating mixtures of antimony trioxide and hydrochloric acid solution (<6 kmol/m³) at 25^°C for 30 days. X-ray diffraction analysis of the solids showed the existence of Sb₂O₃ (HCl < 0.1 kmol/m³) and Sb₄O₅Cl₂ (HCl>0.1 kmol/m³) as the final solid phases. The solubility for both compounds was also determined as a function of HCl concentration. The hydrolysis of antimony(III)-hydrochloric acid solution (Sb(III) = 140 mg/L, HCl = 0.1 and 1.0 kmol/m³) by neutralizing with NaOH solution was then studied in a pH range of 1.1 to 12.3 at 25^°C. The amorphous Sb₈O₁₀(OH)₂Cl₂ (spherical, particle size: 0.05–0.2 μm), crystalline Sb₈O₁₀(OH)₂Cl₂ (orthorhombic, rectangular plate in 1 μm thick layer) and crystalline Sb₂O₃ (orthorhombic) were found to be a solid phase depending on pH and hydrolysis time. The particle morphology of Sb₂O₃ was affected strongly by pH. The minimum solubility of crystalline Sb₈O₁₀(OH)₂Cl₂ (pH 2–3) and Sb₂O₃ (pH 3–11) was at a level of 10 mg/L in Sb(III).

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Spheroidization behavior of cementite in a low carbon steel processed by the equal channel angular pressing technique was investigated. The effects of annealing temperature and time, and accumulated strain on the morphology of cementite and mechanical properties were studied. The results indicated that the application of the severe plastic deformation can improve the kinetics of spheroidization significantly. In this study, the enhanced spheroidization kinetics was discussed in terms of carbon dissolution from cementites and defects induced in cementites by the severe plastic deformation. In addition, the softening of the steel after the spheroidization treatment was evaluated.

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Mold die sticking has been thought to be caused by the increase in die surface roughness and surface area due to silica filler abrasion. In-situ results of semiconductor manufacturers showed a strong dependency on the make of EMC (epoxy molding compound); indicating chemical interaction was apt to be also functioning as a major mechanism. PSII (plasma source ion implantation) using O₂, N₂, and CF₄ was applied to modify sample surface condition from hydrophilic to hydrophobic and vice versa. By comparing surface energy quantified by contact angle and surface ion coupling state analyzed by Auger with pull-out strength, the governing mechanism for the sticking issue was determined to be a result of complex of mechanical and chemical factors.

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The surface roughness created by grit blast treatment affected diffusion bonding quality. The surface treatment is very important to remove the oxide films in combination with superplastic forming and diffusion bonding. Therefore, by using the superplastic magnesium alloys, the diffusion bonding tests carried out to obtain the relationship between the diffusion bonding quality and surface roughness. From the diffusion bonding results, in order to obtain high quality joining, the void shrinkage processes were not only diffusional controlled process but also plasticity controlled process. The optimal surface roughness was estimated equal to grain size.

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Single crystalline BaTi₂O₅ was prepared by a floating zone method. The permittivity of single crystalline BaTi₂O₅ perpendicular to a (010) plane showed the maximum value of 20500 at 748 K obeying the Curie-Weiss law at higher temperatures. The permittivity perpendicular to (100) and (001) planes were 140 and 70, respectively almost independent of temperature. A transition temperature measured by a dilatometer was in agreement with a Curie temperature. The relationship between polarization and electrical field perpendicular to the (010) plane showed ferroelectric hysteresis. No hysteresis was observed in the direction perpendicular to (100) and (001) planes. The electrical conductivity perpendicular to the (010) was larger than those of (100) and (001) planes. The activation energy of electrical conductivity was 147 to 180 kJ mol⁻¹ independent of directions.

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The effect of partial substitution of Ti for Zr on the glass-forming ability was studied in Cu₅₀Zr_45−xTi_xAl₅ (x=0, 2.5, 5, 10) alloys by using thermal analysis and X-ray diffractometry. The glass transition temperature, T_g, of Cu₅₀Zr_45−xTi_xAl₅ alloys decreased from 707 K at x=0 to 700 K at x=2.5, and keeps almost constant with further increase of x. On the other hand, the crystallization temperature, T_x, decreased gradually from 767 K at x=0 to 741 K at x=10. The partial substitution of Zr by Ti in Cu₅₀Zr₄₅Al₅ alloy promotes the glass formation. The maximum diameter for glass formation by injection casting increased from 3 mm for Cu₅₀Zr₄₅Al₅ alloy to 4 mm for Cu₅₀Zr_42.5Ti_2.5Al₅ alloy.

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