We modified a previously developed compact compression-test stage for synchrotron radiation micro-Laue diffraction mapping to investigate the deformation of the long-period stacking-ordered phase of a magnesium polycrystal. This modification made it possible to obtain grain-boundary images from two orthogonal directions, realizing to obtain depth information about the position of kink formation. Also, to compare bulk and surface images, a long-focus optical microscope, which can take photographs of the surface morphology of the sample, was introduced into the apparatus.

The influence of the volume fraction of the long-period stacking ordered (LPSO) phase on the strengthening mechanisms acting in Mg/LPSO two-phase extruded alloys is discussed by focusing on compression tests of Mg₉₄Zn₂Y₄ and Mg₉₂Zn₃Y₅ alloys. An increase in the LPSO phase volume fraction increases the yield stress of these alloys, but the magnitude of the increase is not monotonic with the volume fraction. For deformation parallel to the extrusion direction, the rate of increase in the yield stress shows two large gaps between the Mg_99.2Zn_0.2Y_0.6/Mg₉₇Zn₁Y₂ and Mg₉₂Zn₃Y₅/Mg₈₉Zn₄Y₇ alloys. This is derived from the change in strengthening mechanisms. The upper gap between Mg₉₂Zn₃Y₅/Mg₈₉Zn₄Y₇ is derived from the change in the strengthening mechanism between short-fiber reinforcement and the simple rule of mixtures. The lower gap between Mg_99.2Zn_0.2Y_0.6/Mg₉₇Zn₁Y₂ corresponds to the existence of a short-fiber strengthening mechanism or not. As the volume fraction of the LPSO phase decreases, the magnitude of kink-band strengthening to the yield stress decreases; however, it is still effective even in alloys with a low volume fraction of the LPSO phase.

Mg–9 at%Y–6 at%Zn and Mg–2 at%Y–1 at%Zn alloys were processed by equal-channel-angular extrusion (ECAE) to investigate their microstructure evolution and local hardness. The area fraction of the kink bands in the Mg–9 at%Y–6 at%Zn alloys increased with increasing the number of ECAE passes, resulting in higher hardness. In contrast, the number of kink boundaries in the local region near the indentation was almost constant. The relationship between the microstructure factors of the kink bands and the local hardness is discussed in comparison with the forged alloy. In the Mg–2 at%Y–1 at%Zn alloys, the microstructural evolution of the α-Mg matrix phase and long-period stacking ordered (LPSO) phase by 1-pass ECAE and the increase in local hardness were discussed.

In this study, kink band formation behavior of an Al/Al₂Cu eutectic alloy with a mille-feuille structure consisting of a hard Al₂Cu phase and a soft Al phase was investigated under compression at room temperature. In-situ surface observations during compression tests revealed multiple micro kink-bands occurring simultaneously within a single lamellar colony. To analyze the formation behavior of micro kink-bands, the spatial distribution of the lamellar structure over a wide area of the specimen was quantitatively evaluated by performing image analysis using the Radon transform. The results showed that the micro kink-bands generated synchronously in one direction and rotated at a uniform angle. Such uniform and fine kink-bands are expected to contribute to the improvement of strength. To unravel the linkage between microstructure, kink band formation, and accompanying kink strengthening, an attempt was made to construct a model that predicts the spacing between micro kink-bands and critical stress for kinking from the features of the lamellar structure. The validity of the model to predict the spacing between kink bands was demonstrated by the experimental results.

Kink formation by rolling and its strengthening effects on the mechanical properties of TiNi–V alloy were investigated. The as-cast TiNi–V alloy had a eutectic lamellar structure consisting of B2-TiNi and bcc-V phases. When the alloy was rolled, kinks were formed in the layered structure. The Vickers hardness of the alloy increased after it was subjected to 30% rolling reduction, and then decreased with increasing annealing temperature. After the rolled alloy was annealed at 973 K, its hardness recovered to the original value; however, the layer structure and kinks remained in the alloy. Thus, both dislocations and kinks were introduced into the alloy by rolling, but only dislocations disappeared upon annealing. Therefore, a layered TiNi–V alloy with only kinks but no dislocations was obtained. A comparison of the yield stresses of as-cast, 30% rolled, and annealed alloy specimens revealed that the magnitude of strengthening by dislocations and kinks was about 170 and 40 MPa, respectively. Therefore, kink formation and kink strengthening effects similar to those observed in Mg-based long-period stacking ordered (LPSO) alloys were observed.

X-ray fluorescence holography was applied to dilute Mg_99.2Zn_0.2Y_0.6 alloy annealed at 520°C for 5 h to obtain atomic images around Zn atom. In spite of the extremely low concentration of the solute-element, clear hologram patterns were obtained. The reconstructed atomic images revealed that the Zn atom in this annealed Mg_99.2Zn_0.2Y_0.6 alloy mainly occupy the hcp Mg site. This finding is consistent with the transmission electron microscope image, where fcc-type stacking faults are hardly observed. These results are in contrast to the previous report that Zn and Y form short-range-ordered solute clusters at the fcc-type stacking fault in Mg–Zn–Y alloy. The effect of heat treatment on the atomic arrangement of solute-elements in this dilute alloy is discussed in relation to the previously reported mechanical properties.

High-strength dilute Mg–Y–Zn alloys with cluster-arranged layer/nanoplate (CAL/CANaP) precipitates were developed via combined processes of low-cooling-rate solidification and extrusion techniques. The effects of CANaP morphology and deformation kink bands installation on the tensile properties of the extruded Mg–Y–Zn alloys were investigated. A slow-cooling solidification process with a cooling rate range of 0.1–0.01 K·s⁻¹ produces a CAL-aggregated region in the α-Mg matrix. The CAL-aggregated region comprises long-period stacking ordered (LPSO) nanoplates with an intergrowth structure and the solo-CAL precipitates. The area fraction of the CAL-aggregated region increased with decreasing cooling rate. The microstructure of the extruded Mg_99.2Y_0.6Zn_0.2 alloys prepared from low cooling rate-solidified ingots consisted of three characteristic regions: (i) dynamically recrystallized (DRXed) fine α-Mg grains, (ii) worked coarse α-Mg grains with a CAL-aggregated region, and (iii) worked blocky LPSO grains. The strength and ductility of the extruded Mg–Y–Zn alloys may be controlled by the volume fractions of the worked and DRXed grains, respectively. It is desirable to control the CANaP thickness and spacing to ∼1 µm and ∼0.8 µm or more, respectively, to promote DRX. Conversely, it is necessary to control the CANaP thickness and spacing to ∼1 µm and ∼0.8 µm or less, respectively, to form the worked grains in which kink bands are introduced.

To elucidate the effect of extrusion ratio in hot-extrusion on the deformation behavior during compression of Mg₉₇Zn₁Y₂ alloy containing about 25-vol% long-period stacking ordered phase (LPSO) in the HCP structured α matrix (αMg), in situ neutron diffraction measurements were performed under compressive loading using four types of samples: as-cast and after hot extrusion at 623 K with extrusion ratios of 5.0, 7.5 and 12.5. The macroscopic yielding was observed to appear by the occurrence of basal slip of αMg in the as-cast sample and at the onset of twinning in the hot extruded samples. The applied stress to initiate slip, twinning, and kinking increased by hot extrusion and then decreased with increasing extrusion ratio. LPSO shared higher stress than αMg and the ratio to the strength increased as the extrusion ratio increased. In the extruded samples, the phase stress levels in LPSO when kinking initiated were almost the same for the hot-extruded samples, around 580 MPa, regardless of the extrusion ratio.

In the field of metals, especially in magnesium alloys, a new concept has been reported that introducing a kink by applying compression or other deformation to a material with an LPSO structure, in which hard and soft layers are alternately stacked, results in higher strength. Because crystalline polymers are alternately layered with a crystalline phase, the hard layer, and an amorphous phase, the soft layer, it is expected that crystalline polymers can be made stronger if kinks can be introduced by applying compression or other deformation. In this study, the effects of a high-pressure press on the tensile properties and morphology of polypropylene (PP) were investigated. We found that a high-pressure press reduced the strain at break but increased the tensile modulus and the stress at break in the stress–strain curves. Thus, we succeeded in developing high-strength PP using a high-pressure press. In addition, it is found that the tensile properties were isotropic with no directional dependence after press. This implies that the tensile strength can be increased isotropically. Observing the morphology parallel to the press direction by small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS), it was found that the crystal lamellae spread isotropically. Conversely, observation of the morphology perpendicular to the press direction by optical microscopy (OM) and transmission electron microscopy (TEM) revealed the formation of a shear band where deformation was concentrated owing to pressure. In the shear band, it was found that lamella fragmentation occurred and a kinked structure was formed. In this region, the molecular chains may be constrained by pressure, and become a tension state, which leads to the improvement of the mechanical properties.

Synchrotron radiation small- and wide-angle scattering measurements have been performed for Mg_98.6–Y₁–Zn_0.4 alloys. In the early stage of phase transformation from supersaturated solid solutions, isotropic scattering suggesting segregation at grain boundaries was observed. It grew with temperature during heating the sample at a constant rate of 0.133 K/s. Above 600 K where introduction of stacking faults is expected, needle-like scattering became visible, which represents platelet shape segregation of cluster layers called cluster arranged layer (CAL). The layer eventually developed to form multiple layers, cluster arranged nano plates (CANaP) at higher temperatures. Microstructure change by hot rolling after the heat treatments has been examined from a viewpoint of kink-deformed microstructures.

This study describes the basic capabilities of an “Explicit” kink model based on Field Theory of Multiscale Plasticity (FTMP), where the incompatibility tensor-incorporated additional degrees of freedom (DOFs), mediated by the Rank-1 connectivity-based projection direction with variable shear measure, directly drives the kink field evolutions in addition to the conventional slip mode. Not only inhomogeneous but realistic kink morphologies but also slightly improved energy releasing characteristics are shown to be reproduced. Furthermore, virtual double compression tests are performed on thus obtained kinked samples, demonstrating the kink strengthening that qualitatively agrees with experiments. Further enrichment of the model via the incompatibility-based DOFs introduced also in the slip model is shown to be able to simulate even more realistic kink morphologies and the attendant rotation angle distributions accurately.

We discuss not only kink formations but also the attendant primary strengthening taken place during the formation processes, by proposing anew an “Implicit” kink model based on Field Theory of Multiscale Plasticity (FTMP) only by utilizing the incompatibility tensor-incorporated Rank-1 degrees of freedom in the hardening law of the slip constitutive equation. Demonstrated is either realistically inhomogeneous kink field morphologies and successfully-raised flow stress level throughout the deformation, with the help of prescribed soft/hard structure accompanied by initial misorientations. A preliminary attempt is also made for identifying the critical roles of the empirically-found “scale-free” nature in the AE characteristics, based on the proposed model combined with the interaction field formalism in FTMP, resulting in further improved kink morphologies as well as slightly increased flow stress level.

In order to clarify the orientation dependent deformation behavior of the MAX phase ceramics, compressive deformation behavior was examined in a textured Ti₃SiC₂ (TSC) at a high temperature of 1200°C. Depending on the relationship between the texture and loading directions, both the deformation behavior and microstructure were strongly influenced, and the resultant basal slip, kink formation and delamination affected the compression behavior of the textured TSC. When the stress was loaded parallel or perpendicular to the basal plane (0TSC and 90TSC), the stress-strain (S-S) curves showed higher peak stresses followed by the reduction in the flow stress. When the stress was loaded 45° to the basal plane (45TSC), the S-S curve showed strain hardening after yielding, but did not show peak stress. Although the strength was higher both in 0TSC and 90TSC than in 45TSC, both 0TSC and 90TSC showed the formation of cracks and delamination, resulting to the large drop in the flow stress. In contrast to 0TSC and 90TSC, although 45TSC did not exhibit the peak stress, it exhibited work hardening due to the kink boundary formation, irrespective of the formation of delamination. It is reasonable to conclude from the deformation behavior and the deformed microstructures that for the TSC, the kink boundary plays an important role for attaining both deformability and strength.

Kink boundaries formed in Mg-based long period stacking order (LPSO) alloys play a key role in strengthening of these materials. As the kink structure grows, many high-angle kink boundaries are eventually formed which has inclination angle close to 34 degrees. We show that this peculiar structure is a result of irreversible structural transformation and is energetically stable. We also calculate segregation energies of alloying elements Y and Zn to this boundary. Finally, the critical resolved shear stress for the migration of kink boundary is estimated for a pure-Mg kink and that with saturated with segregation. We show that segregated kink boundary requires very high shear stress about 700 MPa for migration.

We analyzed the kinematic (geometric) aspects of kink bands with multiple basal shear using rank-1 connection to investigate the type of disclination and annihilation of disclinations in kink microstructures. We found that wedge disclinations occur in connecting kink bands for realistic magnitude of shear that can occur, regardless of the shear direction. The normal vector of the junction plane between kink bands and Frank vector of the resulting wedge-disclination varied continuously with respect to the changes in the magnitude and direction of the basal shear. Annihilation of disclinations is possible even between the kinks which are formed by multiple basal shears. Kinematical model of the three-dimensional wavy kinks are proposed using the obtained results.

Cu/A5052 dissimilar metal laminates (DMLs) were fabricated by an accumulative roll bonding process. The Cu/A5052 DML consisted of hard and soft layers, in other words, high and low shear modulus layers, which is called a mille-feuille structure (MFS). The Cu/A5052 DML with the MFS showed kink deformation during monotonic compression. Kink formation was analyzed by in-situ optical microscopy and digital image correlation. The development behavior and morphology of the ortho-type kink depended on the annealing conditions prior to the compression tests. Based on the observations and measurements, criteria for kink formation in the DML with the MFS were proposed.

Magnesium antimonide (Mg₃Sb₂) is a promising thermoelectric compound utilized for thermoelectric power generation. We have found out that the Mg₃Sb₂ compound can be made from Mg and Sb powder mixture via the combustion synthesizing reaction. In this study, we manufactured the compounds from the compacted bodies with different Mg fractions between 60.0 and 75.0 at% in an argon gas flow at 650°C for 1 hour via the combustion synthesis process. Morphology, porosity, phases and thermoelectric properties (electrical resistivity and Seebeck coefficient at room temperature to 500°C) were investigated for the manufactured samples. All samples manufactured with different Mg fractions mainly consisted of Mg₃Sb₂ and became foamed bodies with a porosity between 50 and 70%. The thermoelectric properties changed with the Mg fraction. The maximum power factor of 42.1 µW/mK² at 488°C was obtained in the foamed body with the Mg fraction of 64 at%. The dimensionless figure of merit (ZT) of the sample was also estimated using the thermal conductivity, which was calculated considering its large porosity. The maximum dimensionless figure of merit (ZT_max) would be 0.13 at 488°C.

This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 68 (2021) 399–404.

Mo₃₅Ni₁₅Rh₁₅Ru₃₅, Fe₁₄Mo₃₅Ni₁₅Rh₁₅Ru₂₁, Mo₂₅Ni₂₅Rh₂₅Ru₂₅, and Fe₂₀Mo₂₀Ni₂₀Rh₂₀Ru₂₀ (at%) alloys were designed by referring to hexagonal close-packed (hcp) Nb–Mo–Ru–Rh–Pd high-entropy alloys (HEAs) reported by Liu et al., with the help of Pearson’s Crystal Data. X-ray diffraction profiles of the Fe₂₀Mo₂₀Ni₂₀Rh₂₀Ru₂₀ and Fe₁₄Mo₃₅Ni₁₅Rh₁₅Ru₂₁ alloys prepared via the conventional arc-melting and subsequent annealing at 1700 K for 1 h show an hcp structure. Further scanning electron microscopy observations combined with elemental mapping via energy-dispersive X-ray spectroscopy confirmed the single hcp structure. The Fe₂₀Mo₂₀Ni₂₀Rh₂₀Ru₂₀ HEA annealed at 1700 K for 1 h exhibited a mixing entropy (S_mix) normalized by the gas constant (R) of 1.846, 14% higher than the configuration entropy (S_config) normalized by R (S_config/R = ln 5). This study reveals two new ultrahigh-mixing-entropy alloys (UHMixEAs) that satisfy S_mix > S_config, the Fe₂₀Mo₂₀Ni₂₀Rh₂₀Ru₂₀ and Fe₁₄Mo₃₅Ni₁₅Rh₁₅Ru₂₁ alloys. The evaluation of S_mix/S_config for the present UHMixEAs and referential Co-containing HEAs from early studies revealed that S_mix/S_config of the former are constant whereas those of the latter increase at the magnetic transition (Curie) temperature or below.

The paper presents the results of investigating the influence of Cu concentration on structure, mechanical properties and corrosion resistance of Ti₅₀Ni_50−xCu_x (x = 0, 5, 10, 15 and 20) alloy ribbons. The ribbons with a thickness of about 25 µm were prepared by using melt-spinning method with a tangential velocity of copper wheel of 40 m.s⁻¹. All the ribbons reveal a single crystalline phase of (Ni,Cu)Ti with the martensitic-B19 structure at room temperature when Cu substitutes for Ni. The structural transformations temperature, tensile strain and elastic modulus increase with increasing Cu concentration whereas the hardness and dislocation density trendly decrease. The corrosion potential E_corr in 3.5% NaCl aqueous solution increases from −0.67 V (for x = 0) to −0.46 V (for x = 20) indicating the better resistance against electrochemical corrosion by Cu addition.

Free-cutting brass contains 3% lead to obtain excellent machinability, but because lead is harmful to the human body, lead regulations are being tightened in Europe, starting with the 2010 and 2014 lead control laws for drinking water-related equipment in the United States, and including RoHS regulations, ELV regulations, and the 4MS Positive List. Being affected by these increasingly strict lead regulations in Europe and the United States, demand for brass with significantly reduced lead content is on the rise.

In order to meet the needs of the times, the authors have developed the world’s first lead-free, free-cutting α + β brass “62.5Cu–1Si–Zn alloy” with a lead content of less than 0.1%.

As a result of investigating the machinability of this alloy by comparing it with CW510L, it was demonstrated that the quality of machined products made of the 62.5Cu–1Si–Zn alloy is good due to reduced cutting resistance realized by shear type chips that can be generated by the action of Si solid-solubilized in the β-phase, the presence of fine P compounds, and the effect of fine α-crystal grains.

This Paper was Originally Published in Japanese in J. Japan Institute of Copper 61 (2022) 213–217.

Triply Periodic Minimal Surface (TPMS) sandwich structure has the characteristics of lightweight, high specific strength, specific stiffness, vibration, and noise reduction. There is relatively little research on its sound absorption performance. TPMS sandwich structure based on selective laser melting (SLM) technology can achieve precise control of structure type, porosity, and so on, and has broad prospects in noise control applications. In this paper, the sandwich structure is designed based on tri-periodic minimal surface implicit function, and the titanium alloy sandwich structure is formed by SLM technology, and the sound absorption performance of titanium alloy TPMS sandwich structure is studied. The effects of volume fraction, panel thickness, and cell layer number on the sound absorption performance of the two TPMS structures were systematically analyzed using the transfer function method. The results show that: The GP10 sandwich structure with the volume fraction of 20%, the thickness of the panel is 1.0 mm, and the number of cell layers is 3C parameter combination has better sound absorption performance and higher sound absorption bandwidth, and the sound absorption coefficient is 0.36. For Ti6Al4V sandwich sound absorption structure, it is not suitable to design too thick panels. When the volume fraction is lesser, the increase of the tortuosity factor τ improves the sound absorption performance of the two structures, and excessive volume fraction leads to a decrease of sound absorption performance. The increase of cell layers can broaden the sound absorption bandwidth of the two structures, and the sound absorption capacity increases and then decreases in the range of 150–6400 Hz. The Gyroid structure mostly exhibits resonance sound absorption mechanism, while the Diamond structure exhibits resonance sound absorption mechanism combined with the viscous loss of sound wave. The work done in this paper can provide a theoretical basis for the study of the sound absorption characteristics of TPMS sandwich structure.

Nickel–Chromium–Molybdenum (Ni–Cr–Mo) alloys are widely used for dental applications. This research was aimed to investigate improvement in the mechanical properties of Ni–Cr–Mo alloy through Boron and Cerium doping. These alloys were doped with boron and boron+cerium alloying elements. The mechanical testing of the samples revealed that minor addition of these alloying elements significantly improved the ultimate tensile strength and yield strength. Moreover, the melting points of the doped samples, determined by differential thermal analysis, decreased appreciably with doping elements. Furthermore, detailed wear testing was carried out to analyze the in-situ behavior of the alloys. Significant improvement in wear rate was noted for the boron and boron+cerium added alloy samples. Also biocompatibility for the three alloys in cytotoxicity test proved the suitability for the use of these alloys in dental prostheses.

The stability of solid-solution phases in FCC and BCC lattices was examined in multi-component alloys based on the CALPHAD technique using the compound energy formalism and regular solution model. From the thermodynamic calculations, it was found in ternary systems that the single solid-solution phase became stable around the equiatomic composition where the configurational entropy was the largest value. The transition temperature from the disordered phase to ordered phase(s) or miscibility gap(s) decreased with the increasing number of elements in the system. The order-disorder transition temperature on the FCC lattice was affected by the end member of the ordered phases existing at the equiatomic composition, whereas it was not significant for the order-disorder transition in the BCC lattice. The single solid-solution phase region at equiatomic compositions was affected by variations in the interaction parameters. In multi-component systems, the variations were averaged with increasing the number of elements in the system. This suggests that high-entropy alloys can afford a variety of elements. This study shows that the disordered state can be formed in multicomponent systems around the equiatomic composition and suggests clearly that due to the high-entropy effect, the solution phases are stabilized.

A real-time imaging electrochemical measurement system was developed for an in-situ observation of brass dezincification corrosion. This system allows for a video recording of brass cross-section under galvanostatic polarization. The progress of erosion associated with the dezincification corrosion in the depth direction on the brass cross-section was successfully observed from the video recording during the measurement. The erosion depth at each measurement time could be estimated from the cross-section images, indicating that the erosion depth was drastically increased at arbitrary time under galvanostatic polarization. It suggested that the erosion rate in the depth direction is strongly related to the dissolution behavior of zinc and copper from brass surface, namely, the preferential dissolution and the simultaneous dissolution. The relation between the dissolution behavior and the electrode potential of brass under galvanostatic polarization was discussed.

This Paper was Originally Published in Japanese in J. Japan Inst. Copper 61 (2022) 168–172.

The carbothermic reduction of NiO was carried out by microwave irradiation at 2.45 GHz under a constant rate of temperature rise. The state of reaction was analyzed by means of non-equilibrium thermodynamics. The rates of the dominant reaction was the Boudouard reaction followed by NiO + CO → Ni + CO₂, differing from that by conventional radiant heating. The uncompensated heat of reactions and the enthalpy change of reactions were almost same amount. The activation energy was 141 kJ/mol for the carbothermic reduction of NiO, 115 kJ/mol for the NiO reduction by CO gas and 166 kJ/mol for the Boudouard reaction. The former two values were smaller than conventional radiant heating.

The role of KMnO₄–NaF conversion treatment in the galvanic corrosion resistance of AA5083 aluminum alloy coupled to AISI 1045 carbon steel in synthetic seawater (diluted 100 times) was investigated. The 10 min-treated AA5083 was observed to reduce the period of high current density during the early stage of coupling and decrease the number of localized corrosion damages on the AA5083. The 10 min conversion treatment significantly reduced the electrode potential of bulk Al₆(Fe, Mn), and it was concluded that the Al₆(Fe, Mn) particles on the conversion-treated AA5083 no longer acted as a local cathode at the electrode potential when the AA5083 was in contact with AISI 1045 carbon steel. The decrease in cathodic activity of Al₆(Fe, Mn) was attributed to the removal of Fe from the surface film of Al₆(Fe, Mn), addition of Mn by the conversion treatment, and thickening of the film.

The development of titanium (Ti) powder production process is important because Ti powder metallurgy (PM) is a promising method that can result in large cost savings by reducing material loss and the number of steps in the conventional manufacturing process of Ti metal and its alloys. This study investigated the process of producing Ti hydride powder directly from titanium tetrachloride (TiCl₄) using magnesium (Mg) metal and hydrogen gas (H₂). The experiments were conducted at 1073–1173 K when the TiCl₄ feeding rate was in the range of 19.16–57.42 g·min⁻¹ with the use of cooling gas as Ar or H₂ gas. A mixture of Ti and Ti hydride (TiH_1.5) was obtained in an iron (Fe) crucible by the dehydrogenation of Ti hydride as the TiCl₄ reduction proceeded. The concentration of oxygen (O) decreased with a decrease in the specific surface area and/or an increase in the proportion of TiH_1.5 in the powder. As a result, the concentration of O of the mixture of Ti and TiH_1.5 decreased to 0.116 mass% under a certain condition.

Al₂O₃ composites dispersed with 1, 5, 10, and 15 vol% nickel particles were prepared using a pulsed electric current sintering technique. High-temperature oxidation was conducted at temperatures ranging from 1200°C to 1350°C for 6–24 h in air. After oxidation, the sample surface mainly consisted of NiAl₂O₄ oxide. The growth of the oxidized zone in all sample groups followed a parabolic pattern. The influence of the Ni content on the high-temperature oxidation behavior of Ni/Al₂O₃ is discussed. A kinetic model was proposed to explain the growth of the oxidized zone. The diffusion coefficient of oxygen ions through the grain boundaries of the Al₂O₃ matrix can be obtained using the proposed model, which is in agreement with those in the literature.

In recent years, with the active use of Mn-containing high-tensile strength steels as an automotive body material, it has become increasingly difficult to recycle Mn-containing high tensile strength steel scrap as raw material to produce cast iron, due to the fact that Mn is known as an element promoting the chilling tendency of cast iron melt. Therefore, in this study, the effect of Mn on the fatigue limit of flake graphite cast iron was investigated for the purpose of increasing the strength of cast iron and recycling high tensile strength steel. Flake graphite cast irons with different Mn contents (0.5 mass% and 2.0 mass%, the carbon equivalent corresponding to FC200, FC300 and FC400 of JIS specification (G 5501)) were prepared for plane bending fatigue test.

For melting, pig iron and electrolytic iron were used as iron sources, Fe–Si, Fe–Mn, and Fe–S were used as component adjusting materials, and Ca–Si was used as an inoculant. The melting temperature was 1803 K, the inoculation temperature was 1753 K, and the mold was poured at 1723 K.

Due to the addition of Mn, the Mn/S ratio increases, resulting in the crystallization of A-Type graphite in high-manganese flake graphite cast iron. With the increase of Mn content, the graphite fraction decreases, the lamellar layer becomes denser and homogeneous, the matrix structure is strengthened, and the tensile strength and fatigue limit of high-manganese flake graphite cast iron are improved. Therefore, it was suggested that high-manganese flake graphite cast iron can be used for thin-walled parts as a cast iron with excellent fatigue strength. In addition, in this thin-walled flake graphite cast iron, Mn acts as a matrix structure strengthening element rather than a chilling promoting element.

This Paper was Originally Published in Japanese in J. JFS 94 (2022) 601–605.

Cu and Ni impurities in Mg alloys are deleterious contaminants that reduce the corrosion resistance of the alloy. Mg₂Cu and Mg₂Ni precipitates can cause significant anodic dissolution of the Mg matrix, owing to their potential difference. Suppression of these phases can prevent the deterioration of corrosion resistance. The neutralization of these impurities through the formation of Mg–Zn intermetallic phases has been studied, because the atomic radii of Cu and Ni are similar to that of Zn. As a result, the MgZn₂ phase may precipitate during the rapid cooling that occurs during the solidification of the Mg–6 mass% Zn alloy, and introduce substitutional impurity atoms in the crystal lattice. Mg(Zn, Cu)₂ and Mg(Zn, Ni)₂ phases can be formed instead of Mg₂Cu and Mg₂Ni, in the presence of both of Zn and these impurities. The microstructures and corrosion properties of the Mg–6 mass% Zn alloy with various Cu or Ni concentrations are investigated in this work. The Cu and Ni impurities are concentrated into MgZn₂ phase in the Mg–6 mass% Zn alloy without Mg₂Cu or Mg₂Ni formation when the concentrations of these impurities are within acceptable limits. Consequently, the corrosion rate of the Mg–6 mass% Zn alloy with 1.4 mass% Cu or 0.25 mass% Ni is almost the same as that of the alloy without Cu and/or Ni contaminations.

Cu fine-particle paste is a promising material to form a low-cost interconnect for flexible electronics devices. It has been reported that Cu particles can be sintered at low temperature (well below the half of the melting point) through two-step heat treatment processes of oxidation and reduction. However, the mechanism of the low temperature sintering is not clear yet. In this study, we investigated the oxidation sintering process of Cu fine particles by thermal gravimetric analysis (TGA) in the temperature range of 200°C∼300°C, X-ray diffraction (XRD), and microstructural observation. It was found from TGA that the oxidation process was initially rate-controlled by surface reaction and then by Cu diffusion at grain boundaries of Cu₂O. Transmission electron microscopy observation revealed the formation of a core (Cu)-shell (Cu₂O) structure during the oxidation process. The adjacent Cu₂O shells were bonded to each other resulting in a cross-linked structure. The subsequent reduction process led to the formation of a porous structure by oxygen removal, but the cross-linked structure was maintained, which would make the low-temperature sintered Cu body as robust as solidified solder and sintered Ag paste.

This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 86 (2022) 224–231.

A solderable polymer composite (SPC) with a low-melting-point solder (LMPS)/high-melting-point solder (HMPS) mixed filler was formulated to solve the bonding property and reliability problems in an SPC system with an LMPS filler. In addition, the possibility of enhancing the mechanical bonding properties of SPC with LMPS/HMPS mixed fillers was investigated. Three types of SPCs (mixing ratios for LMPS and HMPS: 100:0, 50:50, and 0:100) were prepared, and two types of mechanical property investigations (i.e., ball shear and microhardness tests) were performed to measure the mechanical bonding properties of SPCs according to the LMPS/HMPS mixing ratios. The SPC with an LMPS/HMPS mixed filler exhibited enhanced mechanical bonding properties compared with the Sn–58Bi solder paste and SPC with LMPS or HMPS only due to the change in composition and subsequent microstructure transformation of the solder joint after adding HMPS.