The electrical resistivity ρ, magnetic susceptibility χ, electronic specific heat coefficient γ_e, the Néel temperature T_N and the electronic structure and the magnetocrystalline anisotropy energy (MAE) have been investigated for L1₀-type MnPt alloy system. This alloy system exhibits the characteristic behaviors of pseudo-gap type antiferromagnets, presenting with the highest T_N, the smallest values of ρ, χ and γ_e in the vicinity of the equiatomic composition. The values of ρ, χ and γ_e increase with deviating from the equiatomic composition.
From the linear muffin-tin orbital (LMTO) band calculations, the L1₀-type MnPt alloy system has a pseudo-gap in the electronic structure and the density of states (DOS) at the Fermi energy (E_F) is lowest at the equiatomic composition in accord with the experimental results. Furthermore, the results of the LMTO band calculations including the spin–orbit interaction make it clear that the direction of the magnetic moment of Mn in the equiatomic composition is parallel to the c-axis, consistent with the reported spin structure determined by neutron diffractions. The magnetocrystalline anisotropy constant K is about 1.39×10⁶ J m⁻³ which is larger in magnitude than that of L1₀-type MnNi equiatomic alloy, though the signs are different.

The exchange bias in a ferromagnetic (FM) and antiferromagnetic (AFM) bilayer with a γ-phase disordered structure has been investigated within a framework of Heisenberg model. The magnetic atoms in the AFM layer realize the triple Q structure due to geometrical spin frustrations. This non-collinear spin structure can bring about an exchange bias in the FM/AFM bilayer system. Under the influence of the exchange bias, the uncompensated spin element appears in the AFM layer, accompanied by a shifted loop in magnetization curves, in accord with the measured loop by X-ray magnetic circular dichroism spectroscopy for an AFM layer.

We have investigated the structural and magnetic properties for Co₂(Cr_1−xFe_x)Al (x=0.4, 0.6 and 1.0) full-Heusler alloy films deposited on MgO(001), MgO(011) and sapphire (a-plane) substrates by magnetron sputtering. Substrate temperatures were varied from ambient temperature to 773 K. The XRD patterns reveal that the Co₂(Cr_1−xFe_x)Al films grow epitaxially with the (001), (112), and (011) orientations on MgO(001), MgO(110) and sapphire (a-plane) substrates, respectively. The Co₂(Cr_1−xFe_x)Al films deposited at room temperature (RT) crystallize into the A2 structure, whereas the films deposited at 673 K showed the B2 structure. Especially, for the Co₂FeAl (x=1) films deposited on an MgO(001) substrate at 773 K, the crystal structure is determined to be the L2₁ structure with a flat surface. The saturation magnetization of Co₂FeAl films with the B2 and L2₁ structures exhibits almost the 5 μ_B/f.u., whereas those of Co₂(Cr_1−xFe_x)Al (x=0.4, 0.6) show a reduction from the theoretical values. This reduction of the saturation magnetization might be due to the anti-ferromagnetic coupling between Cr–Cr atoms.

The B2⁄L2₁ order–disorder transition and ferromagnetic/paramagnetic transition temperatures in Co₂(Cr_1−xFe_x)(Ga_1−yAl_y) alloys were determined by differential scanning calorimetry and transmission electron microscopy. It was found that spinodal decomposition cannot be suppressed by quenching in the Al-rich portion of Co₂Cr(Ga_1−yAl_y) alloys, leading to lowering of Curie temperature T_c. The transition temperature T_t^B2⁄L2₁ from the B2 to L2₁-type phase decrease with increasing y for both the Co₂Cr(Ga_1−yAl_y) and Co₂Fe(Ga_1−yAl_y) alloy systems. The T_c in the Ga-rich portion of the L2₁-type Co₂Cr(Ga_1−yAl_y) alloy system is almost constant at about 480 K, whereas that in the B2-type Co₂Fe(Ga_1−yAl_y) alloy system slightly increases from about 1100 K to about 1170 K. By extrapolation from the Ga-rich side of Co₂Cr(Ga_1−yAl_y) alloys, T_t^B2⁄L2₁ and T_c of the metastable Co₂CrAl alloy were determined as 800 and 470 K, respectively. An optimal concentration area for obtaining excellent half-metallic properties and high stability of the L2₁-type phase in the Co₂(Cr_1−xFe_x)(Ga_1−yAl_y) alloys is proposed.

We investigate the half-metallic properties and the stability of the ferromagnetic state in the alloys (Fe_xRu_1−x)₂CrSi (0≤x≤1) with orderly and disorderly atomic arrangement based on the Heusler structure. It is predicted from the electronic structures that the ordered alloys are half-metals in the range of 1⁄3<x<3⁄4 and ferromagnets with high spin polarization in the range of 3⁄4≤x≤1. However, in the ferromagnetic state, the atomic arrangement with the Fe–Cr disorder tends to be energetically more favorable than the orderly arrangement, and the Fe–Cr disorder decreases the spin polarization of the ordered alloys. This is attributed to the fact that occupation of Cr sites by Fe destroys the gap near the Fermi energy in the minority spin state. But, because the Fe–Cr disorder shows a tendency to keep the spin polarization high as x increases, it is deduced that (Fe_xRu_1−x)₂CrSi are materials with high spin polarization if x is high.

Materials with high spin polarization at the Fermi energy (E_F) are searched by the systematic band calculation for Heusler alloys X₂YZ. It is shown that materials with high density-of-state (DOS) for the majority-spin state at the E_F tend to maintain high spin polarization against chemical disorder. Such materials are predicted, using the characteristics of DOS of Heusler alloys. As a candidates, X₂(Cr_xMn_1−x)Z will be proposed, where X is combination between transition elements including at least one of Fe, Ru and Os, and Z is combination among IIIb, IVb and Vb elements.

Thin disordered layer can be formed by sputter-deposition of alumina on fully ordered L1₀ FePt nanoparticle assembly, due to plasma damage. The thickness of the disordered layer can be tuned by the sputtering power and deposition time of the alumina target. This partial disordering causes substantial decrease in the coercivity, which may be effective to adjust very high switching field of L1₀ FePt to practical magnetic recording systems.

We have studied the additive effects of AlN and MgO on L1₀-FePt nanoparticles by co-sputtering FePt and AlN (or MgO) on MgO(100) substrates at 973 K. Good epitaxial growth of FePt was confirmed both for AlN and MgO. With the increase of the additive content, the long range order (LRO) of L1₀ phase appeared to increase for AlN, whereas it was suppressed for MgO. Morphological observation by addition of AlN, well-isolated FePt particles became to connect each other, and finally formed a maze-like structure. On the other hand, the morphology of FePt particles was hardly affected by addition of MgO.

(001)-oriented FePt films with large perpendicular magnetic anisotropy have been obtained on a soft magnetic underlayer (SUL). A nanocrystalline Fe–Si–B–Nb–Cu alloy film has been chosen as SUL, showing the coercivity H_c of less than 80 A/m after annealing at 400°C. It has been found that the crystal orientation and magnetic properties of FePt films are improved by the introduction of a MgO interlayer between FePt and Fe–Si–B–Nb–Cu. The strong (001) texture and the large coercivity of 565 kA/m have been obtained in the tri-layer structure of Fe–Si–B–Nb–Cu (200 nm)/MgO (5 nm)/FePt (10 nm).

Nanogranular thin films, in which FePt nannoparticles are dispersed in an amorphous 20 nm thick Al₂O₃ layer, were irradiated with 2.4 MeV Cu²⁺ ions up to 5×10¹⁹ ions/m² at room temperature. Electron tomography with a tilt series of bright-field transmission electron microscope images was employed to identify 3-dimensional structural changes due to irradiation. Electron tomography images have clearly revealed that the irradiation with 2.4 MeV Cu²⁺ ions causes anisotropic deformation of FePt nanoparticles with elongation along the direction of ions trajectory and slight shrinkage in the perpendicular directions. Ion-irradiation results in disordering in FePt, but post-irradiation annealing at 923 K for 1 h (3.6 ks) leads to re-ordering without significant coarsening and shape change of FePt particles. It has been demonstrated that electron tomography is a quite useful technique for characterization of shape and dispersion of metallic nanoparticles embedded in an amorphous oxide film.

Disappearance of long-range atomic order in 10-nm-sized L1₀-FePd (Fe–58 at%Pd) nanoparticles has been studied by electron diffraction using a specimen heating stage attached to a transmission electron microscope. Ordered structure is kept at lowest up to 949 K, while the intensity of superlattice reflection abruptly drops at 982 K. The transformation temperature decreases by about 80 K compared to that of the bulk alloy of Fe–58 at%Pd. Nanobeam electron diffraction from a particle shows a particle size dependence of the transformation temperature and the intensity of 110 superlattice reflection largely decreases below about 15 nm in diameter at 983 K. However, a weak intensity remains in the 110 superlattice reflection even at 983 K, which is attributed to short-range order in the nanoparticles.

We present the displacements of the guest sodium atoms in double caged Na₂@Si₅₀H₄₄ cluster. The cluster consists of a piece of clathrate II consisting of two adjacent Si₂₈ cages filled with guest sodium atoms, being hydrogenated in order to terminate the dangling bonds. Although in a single Si₂₈H₂₈ cage the endohedral sodium atom locates at the center, the sodium atoms in each of the double cage cluster displace about 0.06 nm away from each center of the cages to form a dimer between the endohedral sodium atoms. The displacements are attributed to the formation of covalent bond between the endohedral sodium atoms and the ionic bonding between the sodium atoms and the cage silicon atoms.

An investigation was made on the strain-controlled low cycle fatigue (LCF) of a cast Ni-base superalloy M963 over a wide total strain range of 0.15–0.6% at a temperature range from 700 to 950°C in air. Correlations between dislocation structure and the testing temperature and applied strain amplitude were enabled through transmission electron microscopy (TEM) observation. At a low temperature region (700 and 800°C), dislocation shearing γ′ precipitates by dislocation pairs and stacking faults at medium and high strain amplitudes, and a well-defined dislocation network at low total strain amplitudes were evident. At a high temperature region (900 and 950°C), dislocations by-passing γ′ precipitates was the main deformation mode.

The relationship between hardness and volume fraction of retained austenite (V_γ) was investigated in heat-treated 16 mass% and 26 mass%Cr hypoeutectic cast irons with and without addition of a third alloying element of Ni, Cu, Mo and V. In as-hardened state, hardness changed remarkably depending on the V_γ. Overall, Ni and Cu decreased hardness but Mo increased it. Hardness increased in 16 mass%Cr cast iron but decreased in 26 mass%Cr cast iron by V addition. The V_γ increased with Ni, Cu and Mo addition but diminished with V addition in 16 mass%Cr cast iron. In 26 mass%Cr cast iron, Ni and Mo increased the V_γ but Cu and V reduced it. Higher austenitization caused more V_γ. Curves of tempered hardness showed an evident secondary hardening due to precipitation of special carbides and transformation of destabilized austenite into martensite. High tempered hardness was obtained in the specimens with high V_γ in as-hardened state. Maximum tempered hardness (H_Tmax) was obtained when V_γ was less than 20% and it increased with an increase in Mo content. The H_Tmax slightly increased with V content in 16 mass%Cr cast iron and decreased in 26 mass%Cr cast iron. Ni and Cu did not show significant effects on H_Tmax. The highest value of H_Tmax was obtained in both series of cast irons containing Mo.

The relationship between the crack nucleation and stress-induced martensitic transformation in the retained massive austenites (RM-γ’s) of austempered ductile irons (ADIs) was examined in detail by carrying out tensile tests and scanning electron microscope (SEM) observations for an ADI material. The SEM observations revealed that cracks were not nucleated in the peripheral regions of graphite nodules but were nucleated in the RM-γ’s. Surface relief due to stress-induced martensitic transformation was observed near the cracks in the RM-γ’s, and it was also observed in the RM-γ’s in which cracks were not visible. For this reason, the cracks were concluded to be nucleated mainly in the RM-γ’s subjected to stress-induced martensitic transformation.

A recently developed beta titanium alloy, Ti–29–13, for biomedical applications has been subjected to microstructure examination and tensile test. Band structure is observed both in the as-received and cold-rolled specimens. By EDX in SEM, the band structure is confirmed to originate from the segregation of beta stabilizer. Thermomechanical processings consisting of repeated solution treatment, water quenching and cold-rolling are performed to reduce the segregation. The considerable reduction of the band structure is found in the processed specimen. The elongation at high temperature of the processed specimen is larger than that of the cold-rolled specimen although no difference in the strain rate sensitivity is confirmed between them.

The effect of stress concentration on the upper yield stress was investigated for an annealed mild steel wire by performing uniaxial tension tests. In order to avoid such a situation that initial yielding occurs at the specimen-clamping ends due to stress concentration, a non-uniform annealing method (the annealing temperature was the highest at the center of the specimen) was employed. For a non-uniformly annealed specimen the upper yield stress was almost twofold of the lower yield stress. In contrast, for a uniformly annealed specimen, the difference between the upper and lower yield stresses was not so considerably high, because the site of clamping-induced plastic pre-strain played a role of starting point of yielding. To examine the effect of stress concentration on the upper-yield point phenomena, FE simulation of the uniaxial tension tests was conducted using a viscoplastic constitutive model proposed by one of the authors (F. Yoshida, Int. J. Plasticity 16 (2000) 359). The results of numerical simulation were in good agreement with the experimental observations. From the results of the experiments and the numerical simulation, it is concluded that, although a material element itself possesses considerably high upper-yield stress, the observed one in ordinal uniaxial tension experiment is generally not so high because of the stress concentration.

Si–Ti–C–O (Tyrano) fibers, with their advantages of light weight and high strength, are increasingly being applied as structural materials in the fields of aerospace and mover engineering. A twisting has been a serious problem on standard tensile test to evaluate the elasticity, fracture stress and strain of the fibers. Thus, stress–strain curves have been obtained by using developed a novel twisting relaxation tensile tester with the constant strain rate. The twisting relaxation apparently enhances the fracture stress and clearly increases the fracture strain of Si–Ti–C–O (Tyrano) fibers at every fracture probability. Although the twisting relaxation decreases the gradient of stress–strain curve, the elongation induced by relaxation mainly enlarges the fracture stress. Our results and discussion show that the twisting relaxation enhances the reliability against fracture for Si–Ti–C–O (Tyrano) fibers.

A 5 KW CO₂ laser has been used to modify the surface microstructure of Al–Mg–Si aluminum alloy with pure Ni and Ni–Cr–B–Si powders. The experimental results indicate that a porosity-free zone can be generated after laser surface alloying (LSA). The Al₃Ni particles were only observed in the LSA Ni sample. In the LSA Ni–Cr–B–Si sample, there are three regions indicated as surface region in the melt zone (region A), bottom region in the melt zone (region B), and amorphous phase in bottom region (region C) from the top to the bottom. In the region A, the Al₃Ni particles are present and the Al₃Ni₂ particles distributed in the region B. The partial Al–Ni–Cr amorphous structures are dispersed in the region C. And, the AlNi and Al₈Cr₅ structures were observed in the interface of region B and C. The hardness of the LSA Ni–Cr–B–Si sample is sharply increased than Al-matrix and Ni specimen, specifically the amorphous structure in region C is about 18 times higher than the Al-matrix.

Changes in hardness of several representative ceramics and semiconductors associated with ion irradiation were systematically studied using a combination of nanoindentation and finite element analysis. We established a new method for obtaining the precise hardness of the embedded damaged layer of ion-irradiated samples. The method was applied to silicon carbide, α-quartz, silica glass and silicon, which enabled us to semi-quantitatively discuss changes in their mechanical properties with irradiation-induced structural changes on the basis of experimentally obtained material parameters. Finally, we propose a new atomistic mechanism for plastic deformation of covalent amorphous materials. The present results will provide a standard framework for discussing mechanical property changes in ceramics with energetic particle irradiation.

In order to obtain the solubility and activity of oxygen in Pb–Bi melts, the research for oxygen analysis and oxygen partial pressure measurement in a lead–bismuth eutectic alloy (LBE) was performed. The analytical condition of oxygen in low melting metals by an inert gas fusion-infrared absorption method was established using Pb or Bi equilibrated with its corresponding oxide at 973 K as a standard sample for the oxygen analysis. After establishing the analytical condition, oxygen analysis in liquid LBE in equilibrium with solid PbO at various temperatures was done. The temperature dependence of oxygen solubility in liquid LBE was expressed by the following equation, log(C_O/mass ppm)=-4.74×10^3/T+7.06(±0.03) (878≤T/K≤1073) Oxygen partial pressure in LBE–(PbO and/or PbO+Bi₂O₃) equilibrium was measured using an oxygen sensor of a zirconia solid electrolyte (ZrO₂−Y₂O₃), and obtained as a function of temperature as 2 & log( p_O2/P^°)=10.96-2.259×10^4/T &  & (720≤T/K≤1098)
& log( p_O2/P^°)=2.49-1.330×10^4/T &  & (1098≤T/K≤1252) From the results, the oxygen potential in LBE at the oxygen unsaturated region was estimated as, RTln( p_O2/P^°)/(J/mol)=-58.59T-2.510×10^5+38.29Tlog(C_O/mass ppm) The activity coefficient of oxygen in liquid LBE obtained using Blander’s oxygen dissolution model was compared with these experimental data and those of other investigators.

Platinum-group metals (PGM) are important precious metals in many industrial fields. However, their natural resource deposits are strictly limited. Accordingly, their recycling process from wastes and/or secondary resources must be considered. In this study, the leaching of PGM from automotive catalyst residue was performed based on the formation of their chloro-complexes in various concentration of acidic solution. The recovery of platinum, palladium and rhodium from the samples after hydrogen reduction pretreatments was examined in the leaching process by using a mild solution mixture of NaClO–HCl and H₂O₂ at 65°C for 3 h. Effect of other solution mixtures on the extraction of the precious metals was also compared with NaClO–HCl–H₂O₂, such as HCl–H₂O₂ and NaClO–HCl. The optimum condition to dissolve platinum, palladium and rhodium was achieved by the mixture of 3 vol% NaClO, 5 kmol·m⁻³ HCl and addition of 1 vol% H₂O₂. The recovery of platinum, palladium and rhodium after 3 h leaching reaches 88%, 99%, 77%, respectively.

The equilibria of yttrium(III) and europium(III) (RE) extraction with PC-88A dissolved in Shellsol D70 from nitric acid solutions were studied under nonideal conditions in order to develop a chemically-based model enabling the engineering prediction of the equilibrium distribution ratios. The distribution of the extractant between the nitrate solution and the diluent was also examined. As a result, it was found that (i) the majority of PC-88A is dimerized in the organic phase, (ii) the cation exchange extraction is predominant in the low-acidity region, and (iii) solvation extraction becomes appreciable in the high-acidity region. By using a model that considers these two extraction equilibria together with the complexation of the RE with NO₃⁻, the nonideality of the PC-88A dimer, and the competing extraction of HNO₃, the extraction equilibrium constants and the coefficient for the effective concentration of the extractant were determined by the nonlinear least-squares method. The proposed model can reproduce the experimental data with good accuracy for single-metal systems over wide feed concentration ranges of RE up to 0.1 kmol·m⁻³, nitric acid (0.05 to 3 kmol·m⁻³), and the extractant (0.25 to 1 kmol·m⁻³). Its applicability to the prediction of the extraction from a binary metal system was also confirmed.

Nanometer-scale magnetite particles were prepared in a dispersing system with a dispersant at a very low concentration. The mean sizes of the particles prepared under optimum conditions were determined using transmission electron microscopy (TEM) to be approximately 3.8 nm. X-ray diffraction and electron diffraction pattern showed that the particles’ phase was consistent with magnetite. The magnetic characteristics were studied using a vibration sample magnetometer (VSM). The dried samples exhibited approximately superparamagnetic behavior.

Solid oxide fuel cells, SOFCs, have attracted worldwide attention from wide applicability in a large-sized power plant, a distributed power supply, and an efficient cogeneration apparatus with extremely high efficiency of power generation. Doped-lanthanum gallate (La(Sr)Ga(Mg)O₃), which has been recently proposed as a new solid electrolyte, replaces Yttria Stabilized Zirconia (YSZ), lowers the operating temperature of SOFC and then improves the mechanical reliability of the cells. In this study, the doped-lanthanum gallate was produced by combustion synthesis and its sintering behavior, the electrical conductivity, and life cycle assessment of this process from energy requirement and a carbon dioxide emission were analyzed by comparing with the conventional solid-state method. In the experiments of the combustion synthesis, lanthanum oxide, strontium carbonate, gallium oxide, metallic magnesium, and sodium perchlorate were well mixed with different substitution ratios of gallium by magnesium; 80, 60, 40, and 30 mole%, by using a ball mill and were ignited at one end of the mixture at nitrogen atmosphere to complete the combustion wave propagation of the exothermic reaction to the other end without any additional energy. As a result, all of the products, except the 80 mole% magnesium-containing lot, showed definite peaks of intermediates containing lanthanum gallate in X-Ray Diffraction (XRD) patterns. Most significantly, the product containing 30 mole% magnesium, which was completely sintered at 100 K lower temperature (1673 K) compared to the solid state method (1773 K), showed the highest electrical conductivity, 0.08 Scm⁻¹ at 1073 K without the dependency of oxygen partial pressure, being almost the same as the world record. The results demonstrated that the combustion synthesis of SOFC electrolyte had the possibility of an innovative production process with several benefits, such as shortening of processing time, minimizing energy requirement and carbon dioxide emission, and deriving the excellent property of SOFCs.

Three separate charges of cobalt 9.2 kg in weight, 3.0 kg nickel and 1.6 kg titanium have been melted in ultrahigh vacuum (UHV) using cold-crucible induction melting (CCIM) furnace, in which UHV of better than 1×10⁻⁷ Pa is attainable. The effects of CCIM in UHV on the purification of these metals due to the removal of gaseous impurities, and the characteristics of CCIM in UHV have been investigated by the analysis of the melting conditions such as the total pressure and the mass spectra of gases during CCIM, and analytical results of these ingots. CCIM in the present UHV degree and quality is found to be very effective for the purification due to the removal of gaseous impurities in cobalt and nickel, in particular, for the decrease in oxygen, and very important for melting of ultrahigh-purity titanium without any contamination by gaseous impurities, in particular, oxygen.

The compo-casting of ceramics by cast iron is expected to be one of the useful casting process that can expand the application fields of cast iron. The largest problem in compo-casting method is cracking caused by thermal shock. Although this cracking can be prevented by reducing the thermal stress by preheating ceramics, the necessary preheating temperature is high and its precise control is difficult at practical foundries. In this study, we tried to estimate numerically the critical preheating temperature of ceramics using the thermal stress analysis during transient thermal conduction and the Newman’s diagram. We also found that the preheating of ceramics to reduce thermal stress can be replaced with placing an appropriate cast iron covers around the ceramics. We describe new compo-casting method that needs no preheating of ceramics and proved the usefulness experimentally.

Various powder mixtures from the starting powders of Ti/Si/C, Ti/SiC/C, Ti/Si/TiC, Ti/SiC/TiC and Ti/TiSi₂/TiC were used for the synthesis of ternary compound titanium silicon carbide (Ti₃SiC₂) by using a pulse discharge sintering (PDS) process. The Ti/Si/TiC powder was found to be the best among the five powder mixtures for Ti₃SiC₂ synthesis. Phase purity of Ti₃SiC₂ can be improved to ≈99 mass% at the sintering temperature of 1300°C for 15 min. The relative density of all the synthesized samples is higher than 98–99% at the sintering temperature above 1275°C. The nearly single phase Ti₃SiC₂ was found to show plastic deformation at room temperature and good machinability. Both electrical and thermal conductivity were found to be greater than two times of the values of a control pure Ti sample fabricated by the same sintering process. The thermopower of the synthesized Ti₃SiC₂ was measured to be nearly zero in the testing temperature range, much lower than some common low thermopower substances such as gold or carbon. Their mechanical properties at ambient and elevated temperatures were also examined. The ternary compound Ti₃SiC₂ is referred to as a “metallic ceramic” according to its physical and mechanical behavior representing both metals and ceramics.

We found that a Ni-rich alloy with the composition of Ni₅₀Pd₃₀P₂₀ had high glass-forming ability. Bulk glassy alloy rods with diameters up to 7 mm can be easily formed by a water quenching method. Its mechanical properties were measured under compressive load. The bulk glassy alloy exhibits relatively high yield strength of 1780 MPa and good ductility as is evidenced from a large plastic elongation of 7.6% before final fracture. The elastic properties of this bulk glassy alloy were also investigated.

The effect of surface asperity (mainly ridge height H, ridge wavelength W and aspect ratio H⁄W) on the diffusion bonding process was investigated. Ridge wavelength W as well as ridge height H have a significant effect on the properties of the diffusion bonded joint. The percent of bonded area increased with decreases in W and H. When the ridge height H was constant, an increase in aspect ratio H⁄W accelerated atomic diffusion at void surfaces and bonding interfaces, facilitated void shrinking and increased the bonded area. This can improve the strength of diffusion bonded joints. The percent of bonded area can be predicted by numerical analysis for surfaces prepared by lathe machining.

AA2024-T3 Aluminum alloy plates of 3 mm thickness were friction stir butt welded at a constant welding speed of 50 mm/min and rotation speeds of 400, 600, 800, 1000, 1250, and 1500 min⁻¹. Effects of rotation speed on microstructures, hardness distributions, and tensile properties of the joints were investigated. Equiaxed grain size increased with increasing rotation speed till 1000 min⁻¹ of rotation speed. Increase of rotation speed more than 1000 min⁻¹ brought about no significant increase of grain size in the stir zone. Also, increasing rotation speed resulted in finer and more homogenous distributions of second phase particles in the stir zone. Hardness increased both in the stir zone and thermo mechanically affected zone as the rotation speed increased and reached to that of base metal. Kissing bond-free joints were fractured at the heat affected zone on the retreating side and a maximum tensile strength of the joints was 402 MPa which was achieved at 1250 min⁻¹ of rotation speed. The joint efficiency was 88%.

Formation and mechanical properties of Cu–Zr–Al–Sn bulk metallic glasses were investigated. The glass-forming ability of Cu₅₀Zr₅₀ alloy is significantly improved with addition of Al, and the critical diameter for glass formation increases from 2 to 7 mm for Cu_46.25Zr_46.25Al_7.5 alloy. Furthermore, the critical diameter is slightly increased to 8 mm by substituting 1 at% Sn for Zr of Cu_46.25Zr_46.25Al_7.5 alloy. The bulk glassy Cu_46.25Zr_46.25Al_7.5 alloy exhibits a limited plasticity of about 1.2% to failure under compression and the plasticity is effectively enhanced due to the addition of Sn, about 4.1% for bulk glassy Cu_46.25Zr_45.25Al_7.5Sn₁ alloy.

The neural network (NN) method is applied to predict the influence of minor additions C, B and Hf on mechanical properties of cast superalloy K44 with heat treatment parameters considered. Furthermore, the influence of minor additions C, B and Hf on phase stability is estimated using d-electrons theory. The results from these two methods indicate that decreasing C content, increasing B content and doping 0.2–0.3 mass% Hf can balance the desired mechanical properties and phase stability in K44 alloy, which also is confirmed experimentally through the relation between mechanical properties and phase stability of base/modified K44 alloys.

Advanced SiC/SiC composites composed of highly-crystalline and near-stoichiometric SiC fibers, SiC matrix by CVI method, and PyC interphase were irradiated up to 1.0×10²⁵ n/m² (E>0.1 MeV, ∼1 dpa) at 1273 K. Unload/reload cyclic tensile test and hysteresis loop analysis were carried out in order to identify neutron irradiation effects on interfacial properties of advanced SiC/SiC. The composites exhibited good irradiation resistance in ultimate tensile strength (∼10% increase), but there were slight reduction of elastic modulus and proportional limit stress (PLS) (∼10%). Wider hysteresis loops and lower gradient of the curves beyond PLS from the strain–stress curves, and longer pullouts of fiber from the SEM observation were observed, which imply weaker F/M interactions after neutron irradiation. From the hysteresis loop analysis, degradation of interfacial sliding stress and negative increment of misfit stress after neutron irradiation were obtained.

We have proposed a novel bonding process using Ag metallo-organic nanoparticles with the average particle size of 11 nm, which can be the alternative to the current die-attach process using lead-rich high temperature solders. The metallurgical bonding between Ag and Cu can be achieved in Cu-to-Cu joints using the Ag metallo-organic nanoparticles at temperatures lower than 573 K. Bonding parameters of the Cu-to-Cu joints bondability were examined based on the measurement of the shear strength of the joints and the observation of the fracture surfaces and the cross-sectional microstructures. The joints using the Ag metallo-organic nanoparticles had the joint strength from 10 to 50 MPa depending on bonding conditions. From the results, the bonding conditions providing the joint strength equivalent to those using the lead-rich high melting point solders were proposed.

Microstructures and magnetic domain structures of precipitation-hardened Sm(Co_0.720Fe_0.200Cu_0.055Zr_0.025)_7.5 permanent magnets obtained by various heat treatments are investigated by transmission electron microscopy (TEM). It is found that Cu atoms gradually segregate into SmCo₅ phase with the increase in aging time. The domain walls in the solution-treated, 6-h isothermal-aged magnets are straight, while those in the step-aged magnet are zigzag shaped along the cell boundaries of the SmCo₅ phases (1:5 H phases). In the demagnetized state of the step-aged magnet, it is found that the domain wall is located almost on the 1:5 H cell boundary phase containing Cu atoms, where the distribution of lines of magnetic flux strongly deviates from the axis of easy magnetization, particularly near the zigzag domain wall, and the lines of magnetic flux flow symmetrically along the center of the 1:5 H cell boundary phase. In the remanent state of the step-aged magnet, it is confirmed that domain walls are strongly pinned almost to the 1:5 H cell boundary phase containing Cu atoms, eventually resulting in a high coercivity in a Sm(Co_0.720Fe_0.200Cu_0.055Zr_0.025)_7.5 permanent magnet.

The size, aspect ratio and direction angle of the Si particles in the stir zone were investigated for the ADC12 FSW joints to analyze the material flow in the stir zone by quantification of three elements (size, aspect ratio and direction) under various welding conditions. The number of finer Si particles increases with the increasing welding speed, whereas, the change in the number of finer Si particles is not simple when the rotation speed is varied. The stirring action during the FSW is appraised by the size of the Si particles. The aspect ratio of the particles increases with the increasing size of the particles. The welding conditions also influence the direction angle of the Si particles. Under the proper conditions, the flow directions of the Si particles in the top and bottom are horizontally aligned, while they are longitudinally aligned on the retreating side and advancing side. However, under insufficient heat input conditions, the material flow becomes random in the bottom and retreating side regions. Under abnormal stirring conditions, on the other hand, it is random on the advancing side and top regions, even though a defect forms on the advancing side in both cases. This kind of identification of the material flow might be very useful to determine the optimal welding conditions by avoiding any defect formation.

The effect of a grain boundary on deformation has been examined using an aluminum bicrystal specimen composed of crystals having a common tensile axis of [100] by the measurement of orientation change with the electron backscatter diffraction technique. After deformation to a strain of 20%, the crystal rotation axis (CRA) map, which provides the orientation distribution of crystal rotation axes relative to the initial crystal orientations, reveals areas affected by the grain boundary. The thickness of the affected zone was 100 μm in one crystal and 150 μm in the other. In both crystals, the crystal rotation axis relative to the initial crystal orientation differed between the affected zone and the crystal interior. In the crystal interior, two slip systems showed a higher activity than the other slip systems, whereas in the affected zone, three or four slip systems were more active than the other slip systems. The CRA map showed that the width and shape of the affected zones across the grain boundary were not symmetrical with respect to the grain boundary.

Friction stir welding (FSW) was applied to ultra low-carbon interstitial free steels with mean grain sizes ranging from 0.7 μm, prepared by accumulative roll-bonding, to 27 μm. The steel with the intermediate grain size (1.8 μm) is most preferable for obtaining the highest hardness in the stir zone with the smallest grain size.