Various motor using transportation system in land-sea-air, high speed mobile terminal with 5G specification, and renewable energy storage equipment have required innovative metal rechargeable batteries compared with lithium ones. In particular, magnesium has huge potentialities as an anode material from the standpoint of its theoretical volumetric capacity superior to that of lithium. Secondly, magnesium has been one of the most abundant elements in the Earth’s crust. Moreover, the potential safety by short-circuiting evading with non-dendritic deposition of magnesium. In general, magnesium-based ribbon as an anode has been manufactured by cold rolling which requires multistage process including heat treatment. We have studied rapid liquid quenching process in order to develop low-cost manufacturing technique. On the other hand, we have focused Mg–6 mass%Al–3 mass%Ca alloy due to this unique microstructure which consist of primary crystals and intermetallic compounds along grain boundary. In addition, calcium has affected to prevent of molten magnesium burning in air atmosphere. The structural properties and surface morphology are investigated by XRD and Digital Microscope, respectively. Microstructure has been observed by FE-SEM and FE-TEM. Moreover, these electrochemical properties have been examined by constant current charge - discharge tests using 3 electrodes type cell. Mg–3 mass%Al–1 mass%Zn alloy cold rolled thin plate has been investigated as comparison. The ribbons that exhibited electrochemical properties had a fine microstructure. It is suggested that the grain refinement and dispersion of the second phase are important to improve the charge-discharge properties of Mg–Al–Ca based anode materials.

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Melt spun Ni₇₀Ga₃₀, Ni₇₀Sn₃₀ and Ni₇₀In₃₀ show different oxidation behaviour following heat treatment at 900°C in air. The Ni₇₀Ga₃₀ ribbon develops a continuous layer of Ga₂O₃ oxide, which passivates the surface and prevents further oxidation of the Ni₃Ga bulk phase. On the contrary, the Ni₇₀Sn₃₀ and Ni₇₀In₃₀ ribbons undergo considerable segregation and decomposition and aside from the Ni and NiO and the primary Ni₃Sn and Ni₃In also comprise SnO₂ and In₂O₃ phases. Results are conformed from XRD, TEM and XPS analysis. The oxidation behaviour especially in the case of the Ni₇₀Sn₃₀ ribbon is promising with view for development of fine Ni particles on the Ni₃Sn support.

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Radiofrequency (RF) reactive magnetron sputtering was used to deposit thin SiCN and CrSiCN films on high-speed steel or silicon substrates. Nanoindentation, scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM-EDS), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) analyses were used to investigate the changes in the mechanical properties and microstructure of the CrSiCN films after annealing. The CrSiCN (37.6%Cr) film deposited on the Si substrate showed little change (−12%) in the indentation hardness and microstructure after annealing in air at 800°C for 1 h. Comparatively, the hardness of the same films deposited on high-speed steel substrates was greatly degraded (−36% to −50%). The microstructure of the films also changed remarkably after annealing in air or even under vacuum using the same temperature and time conditions. TEM/XPS analyses suggested that the mechanism of degradation of the CrSiCN films involved decomposition of the SiCN phase, induced by CrN and diffusion of Fe from the substrate. The diffusion of Fe formed Fe–Si in the films, while CrN generated Cr–C, which induced grain growth of the CrN phase and degraded the indentation hardness of the films. Thermodynamic calculations were performed to demonstrate the possibility of these reactions. The formation of crater wear faults in the CrSiCN hard coatings used for machining tools was also discussed.

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We have performed an ab initio study of disordered ferrimagnetic Ni_1.9375Mn_1.5625Sn_0.5 martensite. Employing the supercell approach combined with the special quasi-random structure concept for modeling of disordered states we have determined thermodynamic, magnetic, structural, elastic and vibrational properties of the studied material. Its atomic and magnetic configuration is found to exhibit a pressure-induced increase of the total magnetic moment, i.e. the total magnetic moment increases with decreasing volume. This peculiar trend is revealed despite of the fact that the magnitudes of local magnetic moments of atoms decrease (or stay constant) with decreasing volume. The origin of the identified phenomena may be related to (i) the ferrimagnetic nature of the magnetic state when the parallel and antiparallel magnetic moments nearly compensate each other and (ii) chemical disorder that leads to different local atomic environments and, consequently, also to different local magnetic moments and their different response to hydrostatic pressures (the antiparallel moments are more sensitive). The studied state is mechanically and dynamically stable (no imaginary-frequency phonons) but, regarding its thermodynamic stability, it is an excited state.

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In this paper, we present results of numerical analysis of phase-shifted fiber Bragg gratings aimed at slowing down the group velocity of light propagating through these structures. Using coupled-mode theory and transfer matrix method we model the impact of several parameters such as length of the grating, refractive index modulation depth and phase shift in the periodicity of Brag gratings to calculate transmission spectral properties and to maximize the final group delay. By introducing irregularity into a periodic structure of refractive index, Fabry-Perot like cavity formed in the grating results in a favorable narrow dip in resonance spectra characteristics. Correspondingly, we observe a significant spike in group delay at the same wavelength. Simulations results obtained by numerical approach show a strong need for parameter optimization in process of tailoring gratings behavior. Considerable attention must be put on width of spectral region suitable for large group delay realization and suitable interrogation schemes need to be implemented when adopting studied structures for sensors applications.

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This study aims to compare the behaviour of two Ni-rich non-equimolar AlCoCrFeNi high entropy alloys, i.e. Al₂₀Co₅Cr₂₀Fe₂₀Ni₃₅ and Al₁₀Co₁₅Cr₂₀Fe₂₀Ni₃₅ (at%) in isothermal high-temperature oxidizing conditions. In both cases, mass gain after 100-hr oxidation at 1173 K in synthetic air atmosphere does not exceed 1 mg/cm², indicating good resistance against the corrosive environment. Investigations on the morphology, chemical and phase composition of the alloys after the oxidation process indicate that a mixture of Al₂O₃ and Cr₂O₃ is responsible for the protective properties of the scale formed on Al₂₀Co₅Cr₂₀Fe₂₀Ni₃₅, whereas an additional chromium–iron–nickel–cobalt spinel structure was determined on the Al₁₀Co₁₅Cr₂₀Fe₂₀Ni₃₅ sample after prolonged exposure to the above-mentioned conditions. The oxidation kinetics are slightly better in the case of Al₂₀Co₅Cr₂₀Fe₂₀Ni₃₅ and lower amounts of the remaining constituent elements were detected in the protective scale compared to Al₁₀Co₁₅Cr₂₀Fe₂₀Ni₃₅. Furthermore, the Al₂₀Co₅Cr₂₀Fe₂₀Ni₃₅ substrate was able to maintain its initial morphology throughout the entire alloy after the corrosion process. From all of the above, it can be concluded that Al₂₀Co₅Cr₂₀Fe₂₀Ni₃₅ seems to demonstrate better oxidation properties at a high temperature than Al₁₀Co₁₅Cr₂₀Fe₂₀Ni₃₅.

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In this paper, the changing of microstructures on the surface layer of high manganese steel (HMnS) Mn15Cr2V under the impacted load was investigated. By theoretical calculations based on stacking fault energy (SFE), it was found that at 300 K, the SFE value of this steel was 34.7247 mJ/m² and at 220 K, the SFE value was 34.72173 mJ/m². Thus, with this result, the SFE’s value is much larger than the value of the martensitic transformation, which was about 18 mJ/m². It can be shown that there will be no martensite changes even if the sample is heat-treated with the sub-zero process. The results of the microstructure analysis show that the microstructures were austenite with carbide particles (VC and Cr₇C₃) that had a small grain size (about 40 nm) and were dispersed in the microstructures. The study’s findings revealed that when the number of impact loads is 3,000 times, the surface layer exhibited twinning, slip, and austenite nanoparticles. When the number of impact loads increases by 10,000 times, the microstructure of the surface steel appears in the amorphous phase. The results of theoretical calculations based on the changing of stacking fault energy (SFE) and experimental results show that there is no appearance of martensite form on the surface layer in research conditions.

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To suppress the over-oxidation of solvents, reaction conditions were optimized, and ligands were added to the system to facilitate the oxidation of sulfur compounds with molecular oxygen. The addition of suitable nitrogen ligands led to effective suppression, and 2,2′-bipyridine showed the best performance among the analyzed samples. After the use of the ligand, the yields of by-products from solvent oxidation were reduced by a factor of 15 compared to those from the reaction without any ligands.

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In this paper, the reasons for the formation of “white stripe” in the heat affected zone beside low alloy steel of FB2-30Cr1Mo1V dissimilar steel welded joint are analyzed: the microstructure of “white stripe” is tempered sorbite and the grain is fine. The main cause of “white stripe” is composition segregation which hinder grain growth during welding thermal cycle, resulting fine and corrosion-resistant microstructure generated. The peak temperature of welding thermal cycle is main influence factor. Thermal simulation technology was used to reproduce the “white stripe”, which appeared at the peak temperature between 900°C and 1050°C.

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In situ electron irradiation using high-resolution transmission electron microscopy (HRTEM) was performed to visualize the Frank loop evolution in aluminum–copper (Al–Cu) alloy with an atomic-scale spatial resolution of 0.12 nm. The in situ HRTEM observation along the [110] direction of the FCC-Al lattice, Frank partial dislocation bounding an intrinsic stacking fault exhibited an asymmetrical climb along the 〈112〉 direction opposed to those in the reference pure Al under an electron irradiation, with a corresponding displacement-per-atom rate of 0.055–0.120 dpa/s in a high vacuum (1.2 × 10⁻⁵ Pa). We performed theoretical calculations to simulate the asymmetrical climb of the dislocation with Burgers vector b of 1/3〈111〉. The Cu–Cu bonding in Guinier–Preston zones was described as a possible pinning site of the dislocation climb by molecular dynamics simulation.

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In this paper, the interaction of C with edge dislocations in α-Fe with Burgers vectors of 1/2〈111〉, 〈100〉, and 〈110〉 has been investigated using the classical force-field method in conjunction with the newly-developed Tersoff/ZBL interatomic potential of Fe–C. Here, the potential was constructed from the first-principles database containing force and energy information of various defect complexes with C in body centered cubic (BCC) Fe. The interaction of C and dislocations has been analyzed from the viewpoint of Voronoi volume formed by C and surrounding Fe atoms. It is found that the interaction between dislocations and C is more attractive when the Voronoi volume around C becomes larger. This tendency is similar to the case of grain boundaries reported previously. It is also found that the grain boundaries and dislocations trap C strongly compared to a single vacancy in BCC Fe, and among them more unstable defect structures attract C more strongly. The obtained tendency might offer a useful guideline to analyse the atomistic distribution of C in Fe with extended defects.

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In order to reveal the change in electrical resistivity and strengthening due to plastic deformation and microstructural evolution, investigation of mechanical and electrical properties was performed. From microstructural observations, it was found that the heterogeneous-nano structure having “eye”-shaped twin domains was formed of which volume fraction becomes largest at 90% of rolling reduction. Ultimate tensile strength increases with increasing rolling reduction and reaches about 735 MPa at 90% and 95% reductions. The electrical resistivity measured at 77 K changes from about 39.6 nΩ m to about 61.9 nΩ m, and correspondingly, the conductivity at 293 K changed from about 28.0%IACS down to about 19.9%IACS. When compaering the total changes in electrical resistivity before and after reduction of 80%, the latter was larger. The more obvious changes in mechanical and electrical properties over reduction of 80% are associated with the formation of heterogeneous-nano structure in addition to increasing dislocation density.

 

This Paper was Originally Published in Japanese in J. Jpn. Inst. Copper 60 (2021) 56–61. Section 2.1 and 2.5 are slightly modified.

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The formation mechanism of α′′-martensite (α′′_Mt) induced by tempering at 450–550°C for a short time was investigated using Ti–10Mo–7Al alloy. The solution treated and quenched (STQ) sample was composed of β phase and a small amount of α′′_Mq, and a large amount of α′′_Mt was generated by rapid tempering at 550°C for 3 s using a salt bath. However, α′′_Mt was completely transformed into a single β phase by aging at 200°C for 3 min. Reversibility was observed between the α′′_Mt transformation and the β reverse transformation. In-situ high-temperature X-ray diffraction measurements revealed that α′′_Mq → β reverse transformation occurred at 200°C and that a thermally activated α′′_iso was generated at 450°C due to the slow heating rate. In-situ optical microscopic observation of STQ sample with rapid lamp heating revealed that α′′_Mt was formed during heating process. However, α′′_Mt did not generate under following conditions; that is, a slow heating rate, thin sample plate, and a small temperature difference until tempering by preheating. On the other hand, rapid tempering using thick plate from liquid nitrogen (−196°C) to 250°C was performed to ensure a sufficient temperature difference, but α′′_Mt was not generated at all.

From the cross-sectional observation of the STQ plate, it was found that α′′_Mq was hardly formed on the surface of the sample, but was formed abundantly inside the sample. On the other hand, in the rapidly tempered plate, a large amount of α′′_Mt was distributed in the surface layer than inside sample. These results suggest that the thermal compressive stress induced by rapid heat treatment contributes to the formation of α′′_M.

 

This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 85 (2021) 405–412.

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The heterogeneous-nano (HN) structure consisting of twin domains, shear bands, and lamellar grains developed by heavy cold rolling of FCC metals with low stacking fault energy is known to provide extremely high strength. In the present study, the effects of the rolling pass schedule on the development of HN structure and the mechanical properties in a Cu–38 mass%Zn alloy were investigated. Rolling was conducted on two different pass schedules; one was conventional unidirectional rolling (1-DR) up to 90% reduction in thickness, and the other was the two-directional rolling (2-DR), in which the specimen was unidirectionally rolled to 25% reduction, then rotated 90° around the rolling direction, and subsequently, unidirectionally rolled up to the total reduction of 90%. At a total reduction of 50%, the number of grains with deformation twins in the 2-DR specimen was higher than that in the 1-DR specimen. Further cold rolling up to 90% produced the HN structure in both specimens. The size of twin domains in the 2-DR specimen was finer and their volume fraction was larger than those in the 1-DR specimen. Also, the 2-DR specimen exhibited a better strength-elongation balance than the 1-DR specimen. It can be concluded that the finer size and larger volume fraction of the twin domains effectively improved the strength-elongation balance in the 2-DR specimen.

 

This Paper was Originally Published in Japanese in J. Japan Institute of Copper 60 (2021) 11–15. The abstract and caption of Fig. 6 have been slightly modified.

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To process ingots of Fe–Ga alloy single crystals into wafers, Fe–17% Ga alloy crystals were cut using multi-wire sawing or electric discharging and rolling. Further, their properties of magnetization and magnetostriction were analyzed using electron backscatter diffraction (EBSD) and X-ray diffraction (XRD). It was observed that the magnetization and magnetostriction curves changed with increasing rolling reduction. Although magnetization was negligibly affected by deformation, the shape of the magnetostriction curve of the as-grown crystal could be modified by a slight reduction in rolling or a slight plastic deformation. EBSD results show that rolling introduced dislocations to form heterogeneous dislocation cell walls and decreased the surface roughness of the wafers. The pole figures obtained by XRD indicate that the samples were single crystals; however, the crystal orientation was different from the ideal orientation after rolling. Residual stress measurements using the cos α method revealed that compressive and tensile stresses remained in the polycrystalline surface layers of the samples cut by multi-wire sawing and electric discharging, respectively. Moreover, the stresses were affected by the tensile strains or magnetic fields when the residual stresses were relatively small in the sample. Although the magnetization and magnetostriction of a single crystal are affected by rolling, they are not significantly reduced by small rolling reductions.

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Effects of pre-aging of Corson alloys with high concentrations of Ni and Si (Cu–4.2 mass%Ni–0.93 mass%Si) followed by heavy cold rolling and full-aging on strengthening were systematically investigated. Especially, development of heterogeneous-nano (HN) microstructure was focused. And the relationship of mechanical/electrical properties was precisely examined. The pre-aged alloys exhibited a considerable strengthening after 90% cold rolling. This was attributed to the increase in the volume fraction of deformation twin domains in the HN microstructure after cold rolling as well as the precipitation strengthening. The sample prepared by a thermo-mechanical process via pre-aging at 723 K, subsequent cold rolling and full-aging at 673 K for 600 s exhibited the best strength/conductivity balance with an ultimate tensile strength (UTS) of 1096 MPa and electrical conductivity (E) of 29% IACS. When examined the effects of solid-solution (SS) temperature on the microstructure and properties, SS at 1223 K derived finer grain size than at 1323 K and the achieved best balance of UTS and E with 1061 MPa and 33% IACS. Therefore, grain refinement prior to pre-aging had no significant effect on strengthening but contributed to modification of electrical conductivity.

 

This Paper was Originally Published in Japanese in J. Japan Inst. Copper 60 (2021) 45–49.

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In the present study, we investigated the effects of Cu or Ni additions on the precipitation of intermetallic phases in the heat-resistant aluminum alloy with a ternary composition of Al–5Mg–3.5Zn (mol%). The quaternary alloys with 1 mol%Cu or 1 mol%Ni content were solution-treated at 480°C and subsequently aged at 300°C for different periods. Both Cu and Ni additions have a slight effect on the age-hardening of these alloys at 300°C. The added Cu element partitioned into not only the T-Al₆Mg₁₁Zn₁₁ phase but η-Zn₂Mg phase precipitated in the α-Al matrix. The observed Cu enrichment in the precipitates of the T phase indicated high stability of the T phase in the Al–Mg–Zn–Cu quaternary system, which was different from the results of thermodynamic calculations using the existing database. The added Ni element enhanced the formation of fine Al₃Ni phase located at grain boundaries and slightly influenced the precipitation of T phase in the grain interior. These results provided new insights to design novel heat-resistant Al alloys using the Al–Mg–Zn–Cu–Ni system.

 

This Paper was Originally Published in Japanese in J. JILM 71 (2021) 275–282.

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This study investigates the acoustic properties of a metal near its phase-change temperature using laser ultrasonics. A Pb-free solder sample was prepared, and its temperature was increased stepwise from 40°C to 210°C with concurrent measurement of laser ultrasonic waves on the solder surface. Noticeable change in the waveforms was observed at 203°C and 209°C. These sudden changes occurred with a 1°C change in temperature. The change at 203°C was attributed to an acoustic mode transformation from Rayleigh-like to Lamb-like as we also found that part of the solid solder became thin as a result of partial melting from the bottom and rim. Only the sound through the air was detected at temperature of 209°C and higher, where this sound was due to ablations. This phenomenon was responsible for local melting at the laser irradiation point, generating the ultrasonic waves.

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This study investigated whether it is really reasonable to insist that being “rich in frequency” represents an advantage of pulsed eddy current testing when compared with conventional eddy current testing. More specifically, this study compared the capabilities of pulsed eddy current testing and conventional eddy current testing in evaluating the thickness of non-ferromagnetic plates with thicknesses of 1–20 mm. To avoid any instrumentation effect, the investigations were performed based on signals obtained by finite element simulations, and the correlations between the thickness and a scalar feature value extracted from measured signals were discussed. This study considered two typical excitation waveforms, a Gaussian pulse and a step function simulating the sudden termination of the excitation currents, and four simple and conventional scaler feature values: peak amplitude, time to peak, time to attenuate the signal into a certain level, and logarithmic slope of the signal attenuation. Narrowing the Gaussian pulse led to difficulty in terms of the thickness evaluation, although it should make the pulse richer in frequency. Subsequent analyses compared the capabilities of the pulsed and conventional eddy current testing to evaluate plate thickness under the assumption that they have the same signal-to-noise ratio. The results revealed that the error in the thickness evaluation using the pulsed eddy current testing was somewhat larger than the error using the conventional eddy current testing with three frequencies. Whereas the target of this study was limited to the thickness evaluation of non-ferromagnetic plates, the results of this study point out that what is important is using frequencies in a proper range as well known in the conventional eddy current testing. They also indicate that it is not reasonable to postulate that “richness in frequency” always leads to a better nondestructive evaluation when using the pulsed eddy current testing.

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The time dependence of the corrosion behavior of tantalum (Ta), which is used in nuclear fuel reprocessing equipment, in sodium hydroxide (NaOH) solutions was investigated by immersion tests, and the mechanism of the time dependence was examined via surface observations and electrochemical measurements. The immersion tests were conducted at room temperature with NaOH concentrations ranging from 1 to 7 mol·L⁻¹ for immersion periods of 24 to 168 h. The corrosion rate increased with the NaOH concentration but peaked with the immersion period and then decreased. The time to peak of the corrosion rate was shorter with higher NaOH concentration. The X-ray diffraction (XRD) patterns and Raman spectra of the surfaces of the specimens immersed in the 7 mol·L⁻¹ NaOH solution for more than 48 h showed Na₈Ta₆O₁₉ formation. The polarization resistance showed a constant value or an increase after a decrease immediately after immersion. It was suggested that the change in corrosion rate is affected by the formation of film during immersion, since the time dependence of polarization resistance and the sum of film resistance and charge transfer resistance have same tendencies. The film was considered to be mainly Na₈Ta₆O₁₉ formed by the dissolution of Ta.

 

This Paper was Originally Published in Japanese in Zairyo-to-Kankyo 70 (2021) 192–198.

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An improved combination of strength and ductility is generally a trade-off relationship, and it remains a major research topic in the field of structural materials. A bimodal grained microstructure, consisting of a coarse-grained region “core” and a surrounding fine-grained region “shell”, exhibits a good balance between strength and ductility. Therefore, the exact reason for the strengthening mechanism needs to be investigated. In the present study, we conducted nanomechanical characterization to evaluate the individual strengthening factors, including matrix strength (σ₀), and grain boundary effect (k), in the Hall–Petch model for each region of the core and shell to clarify the strengthening mechanism in the bimodal grained microstructure. The nanoindentation technique was applied locally in the “grain interior” to evaluate σ₀, and “on grain boundary” and “near grain boundary” to assess the grain boundary effect associated with the k value. The grain interior nanohardness was found to be higher in the core region than that in the shell, which is explained by the higher pre-existing dislocation density in the core region. The nanomechanical characterization of the “on grain boundary” and the “near grain boundary” regions show a higher barrier effect due to the grain boundary in the shell than that in the core, which is presumably dominated by the higher internal strain at the shell grain boundary. Furthermore, a Hall–Petch plot was constructed using nanohardness, Vickers hardness, and grain size to estimate the k value. The plot showed a higher k value in the shell, which is consistent with the higher strengthening effect of the shell grain boundary that is evaluated independently in the local region. Therefore, the macroscopic strength of the shell region is significantly affected by both grain boundary effect as well as fine grain size.

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To evaluate the effect of oxidants, which are formed by radiolysis of water under gamma-ray irradiation, on the corrosion of a carbon steel in a humid environment, ozone was introduced as a model oxidant into humidity-controlled air at 50°C in a thermo-hygrostat chamber. Corrosion monitoring of carbon steel was performed by using an Atmospheric Corrosion Monitor-type (ACM) sensor consisting of a carbon steel anode and an Ag cathode, and a Resistmetric Corrosion Monitor (RCM) sensor consisting of carbon steel sheets. The corrosion rates obtained from the outputs of the sensors were increased with the increase in relative humidity and were obviously increased with the increase in the introduced ozone concentration at each relative humidity, indicating that ozone accelerates the corrosion of the carbon steel. The effect of ozone on the corrosion acceleration is attributed to its easy reduction reaction and/or fast dissolution reaction into water compared to that of oxygen.

 

This Paper was Originally Published in Japanese in Zairyo-to-Kankyo 70 (2021) 358–364.

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Tangled dislocation structures inside the dislocation channels of rapid-cooled and tensile deformed aluminum single crystals were investigated by using BF-STEM. Inside the dislocation channels, arrays of the prismatic dislocation loops belonging to the primary slip system, i.e., (1 1 1)[1 0 1], were mainly formed. Dislocations of the primary coplanar slip systems such as (1 1 1)[0 1 1] and (1 1 1)[1 1 0] were activated due to the internal stresses caused by the primary dislocations pile-up inside the cleared channels. The activated primary coplanar dislocations leave the dislocation loops elongated along the edge dislocation directions behind them. Inter-dislocation-loop interactions take place especially at the arrays of the prismatic dislocation loops of the primary slip systems and produce “butterfly shape” dislocation loops. Since the “butterfly shape” dislocation loops have “sessile” junctions, they should act as “obstacles” against the following multiplications and glides of the dislocations. As the interactions proceed, the arrays are stabilized and grow as “tangles”.

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In this study, to clarify the weld area shape that achieves excellent fatigue properties in laser welded joints, an ϕ-shaped weld, which is a combination of a circular weld and a linear weld, was selected for evaluation. Joints with a linear weld having three different linear weld angles with respect to the load axis were fabricated and fatigue tests were conducted. The results showed that the effect of the linear weld angle was remarkable in a relatively high loading amplitude range, and the fatigue life increased as the angle increased. In addition, three-dimensional observation of fatigue cracks was carried out to investigate the fracture mechanism and the factors causing the difference in fatigue strength. It was clarified that the crack propagation life is increased because the crack propagates in the thickness direction not only at circular weld area but also at the linear weld area, when the linear weld angle respecting to loading direction are 45°, 90°. Furthermore, three-dimensional FEM analysis was carried out to recognize the stresses field around the linear weld area. It was clarified that the stresses around the weld area were distributed as the linear weld angle increased, which delayed crack initiation, leading to excellent fatigue properties. Therefore, the fatigue life in the high test-force amplitude region can be improved by providing a weld area shape that distributes the stress and allows the crack to propagate in the thickness direction.

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In the present study, the effects of copper and zinc addition on the microstructure and indentation creep behaviors of SnSb8Cu4 Babbitt alloy were systematically investigated. An indentation creep testing device with a flat tip indenter was used to characterize the creep behaviors of the Babbitt alloys at ∼100°C with different loads. By increasing the copper content from 4 wt% to 8 wt%, coarser and shorter Cu₆Sn₅ dendrites with larger volume fraction were observed. The corresponding Brinell hardness increased from 21.9 to 28.1 at room temperature. However, the improvement in creep resistance was not obvious. After adding 0.72 wt% zinc, large number of small-sized SnSb particles precipitated along the grain boundaries of tin matrix. The total volume fraction of intermetallics, i.e., Cu₆Sn₅ and SnSb particles, increased from 15.1% to 20.9%. Although, the increment of Brinell hardness was not remarkable at room temperature, dramatic improvement in creep resistance was observed. The addition of zinc caused the decrement of the solid solubility of Sb in tin matrix, while more network-like SnSb particles precipitating in tin matrix were found, giving rise to the pinning effect against grain boundary sliding during creep deformation. However, increment of copper content showed no obvious effect on the solid solubility of Sb in tin matrix. Meanwhile, an exponential relationship between indentation creep rate and indentation stress at the steady creep stage was found. Based on the measured data, the indentation stress exponent of SnSb8Cu4, SnSb8Cu8 and SnSb8Cu4Zn was deduced to be 2.949, 2.865 and 2.743, respectively.

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Crystallographic assessment of the hydrogen embrittlement behavior of Al–Zn–Mg alloy was performed by means of a technique combining fracture trajectory analysis and synchrotron X-ray diffraction contrast tomography. The 3D microstructure reconstructed using diffraction contrast tomography contained 119 grains. Fracture surfaces revealing intergranular fracture, ductile fracture, and quasi-cleavage fracture were observed in the alloy. While the intergranular crack initiated at a grain boundary with high grain boundary energy and a high angle between the grain boundary plane and loading direction, the crack propagation itself was not observed to be sensitive to these two parameters. The quasi-cleavage fracture surfaces were not characterized by any specific crystal orientation because of variation in the free surface segregation energy of hydrogen uniforms without depending on surface orientation.

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The effect of thermal aging on the behavior of vacancy-hydrogen (H) cluster generation and the mechanical properties of tantalum (Ta) were investigated by positron annihilation lifetime spectroscopy (PALS) and tensile tests. Based on the PALS results, vacancy clusters that included 8–15 vacancies were generated after aging at and above 200°C, and vacancy-H clusters were generated in 3 and 6 h-charged specimens after aging at 300°C. The loss of ductility in Ta and crack generation were observed by conducting tensile tests in 6 h H-charged specimens after aging at 200°C for 2000 h and in 3 and 6 h H-charged specimens aged at 300°C for 2000 h. The reduction of ductility due to thermal aging of Ta was also observed under these thermal aging conditions. These results suggested that vacancy-H cluster and vacancy cluster generated by dissolved H during thermal aging. And it was considered that the ductility loss was caused by acceleration of crack propagation by vacancy cluster connection and the local aggregation of hydrogen induced by vacancy-H generation.

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The temperature dependence of fatigue crack growth in stage IIb was investigated in Ti–0.49 mass%O with an alpha single phase. It was found that the fatigue crack growth rate in stage IIb was temperature independent at temperatures above 300 K. EBSD maps beside the fatigue crack showed that prismatic slips with 〈a〉 dislocations were dominantly activated during the fatigue crack growth. The reason why the prismatic slips were dominantly activated is discussed with numerical crystal plasticity analysis. It was shown that the local strain rate at the notch tip was higher than the macroscopic strain rate, which leads to the suppression of non-prismatic slips at the fatigue crack tip.

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In zinc hydrometallurgical processes, copper was removed as copper precipitate powder by a cementation process, and, in the present study, leaching medium using Cu²⁺ and O₂ in sulfuric acid solution was proposed to enhance the leaching rate of Cu from the cementation Cu precipitate powder. The leaching efficiency of Cu increased with increasing agitation speed, temperature, and initial Cu²⁺ concentration and decreasing pulp density. When the effect of gas type on the leaching was examined, the leaching efficiency was faster in the order of O₂, air, and N₂. The leaching efficiency of Cu increased to 100% in 1 mol/L sulfuric acid solution at 70°C and 600 rpm with 2% pulp density, 10000 mg/L Cu²⁺ and 1000 mL/min O₂. In the kinetic study, the leaching behavior of Cu followed the reaction-controlled model, and the activation energy was determined to be 19.2 kJ/mol. Therefore, these results suggest that the addition of Cu²⁺ and O₂ could enhance the leaching rate of Cu from the cementation Cu precipitate.

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It is well known that the types of automotive corrosion can be divided into perforation corrosion and cosmetic corrosion. Although the mechanism of perforation corrosion has been studied extensively, the mechanism of cosmetic corrosion has not yet been clarified. The authors investigated the cosmetic corrosion behavior of cold-rolled steel sheets without galvanizing with an in-situ observation device. After coating the samples by cathodic electrodeposition (ED), the sample surface was scribed with a cutter. Corrosion resistance was evaluated under cyclic corrosion test. It was found that the progress of under-film corrosion consisted of 3 steps. The 1st step occurs in the initial stage of the dry process in the 1st cycle. In this step, red rust gradually changed to black rust. The 2nd step occurs in the latter stage of the dry process, and under-film corrosion progressed from the scribed part. The 3rd step occurs in the wet process, and in this step, the tip of the under-film corrosion displayed swelling behavior. In the 2nd cycle, the 2nd step and 3rd step of the 1st cycle were repeated. Under-film corrosion progressed at almost the same rate as in the 1st cycle.

 

This Paper was Originally Published in Japanese in Zairyo-to-Kankyo 69 (2020) 212–220.

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A new press-forming technique using in-plane shear deformation was developed for suppressing fractures and wrinkles of curved shapes in the height direction, for automobile body parts such as the front-side member rear. The developed technique is a two-step processes, draw-forming to induce in-plane shear strain and bending into a curved shape. From experiments on a simplified curve part, in-plane shear deformation which is effective for suppressing fractures and wrinkles occurred in the first process when the press stroke changed along the longitudinal direction of the part. When the induced in-plane shear deformation was increased, a part with a higher curved angle in the height direction could be formed in the second process. Then, we conducted press trials of a front-side member rear model using a 1180 MPa-grade ultrahigh-strength steel sheet to evaluate the effectiveness of the developed technique. The results suggested that a complex curved part could be formed without fractures or wrinkles when in-plane shear deformation was induced in the first process.

 

This Paper was Originally Published in Japanese in J. JSTP 61 (2020) 63–68. The caption of Fig. 20 was slightly modified.

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The casting defects inside the aluminum alloy castings in the expendable pattern casting (EPC) process were evaluated by measuring the density of castings. The effect of melt velocity on the density of plate aluminum alloy castings was investigated experimentally. There was the tendency for the casting density to decrease with increasing melt velocity. This result seemed to be due to the increased entrainment of pattern decomposed liquid resin into the molten metal. In the case of bottom pouring, the casting density with reduced pressure is larger than that with non-reduced pressure. The result seems to be due to the increase in the discharge of the liquid resin at the coat surface through the coat layer. However, when the pouring temperature was high, in the high melt velocity region, there was the tendency for the casting density to be lower than that with non-reduced pressure. This phenomenon seemed to be caused by the forward flow of molten metal. In the case of top pouring, the casting density was higher than that in bottom pouring, and the effect of the reduced pressure was not significant. From the result of observing the castings by an X-ray computed tomography (CT) imaging, it was predicted that the density decrease of the castings might be due to voids by the residual resin defects.

 

This Paper was Originally Published in J. JFS 93 (2021) 728–734. Some spelling errors were modified (Figs. 8–13, 15, 16).

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ZnO was synthesized by using layered zinc hydroxide acetate (ZHA), as a precursor. ZHA was aged in zinc acetate (ZnAc), magnesium acetate (MgAc), and barium acetate (BaAc) aqueous solutions under hydrothermal condition. The effect of divalent metal ions, Zn²⁺, Mg²⁺ and Ba²⁺, on the morphology of ZnO was studied. Results show that thin and thick plate-like and rod-like ZnO particles were synthesized for aging in ZnAc, MgAc and BaAc aqueous solution, respectively. In addition, the length to the c-axis direction became smaller in ZnAc and MgAc solution, and longer in BaAc solution, respectively, by increasing the concentration. Zn²⁺ and Mg²⁺ complexes with hydroxide and acetate ion are stable in aqueous solution. They adsorb on the growth plane instead of the growth unit of ZnO, Zn(OH)₄²⁻, and would inhibit the c-axis direction growth. Thus, ZnO particles with shorter length are obtained. On the other hand, since Ba²⁺ complexes are unstable, Ba²⁺ ions would not affect the morphology of ZnO, and therefore ZnO particles with longer length are obtained. It is concluded that morphology of ZnO, especially the c-axis length, is controlled by selecting metal ions with appropriate complex stability constants.

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This study reports on an interfacial design method of Cu–SiC composites by means of nano-diamond/SiC composite particles in melt-infiltration process. In the case of Cu–SiC composites fabricated by melt-infiltration process, reaction layers consisting of spherical carbon particles and Cu–Si solid-solution alloys were observed as SiC particles reacted with melt Cu. Formation of reaction layers is not appropriate to obtain the predesigned characteristics such as physical and mechanical properties of the Cu–SiC composites. To overcome this problem, nano-diamonds, which were chemically inert with Cu, were bonded to the surfaces of SiC particles by amorphous silica as a bond material in order to shield the SiC particles from reacting with melt Cu. It was found that this shielding method enabled us to disperse SiC particles homogeneously in the Cu matrix without reaction layers. This interfacial design based on the composite particles should be expected to be applied to a promising mass production technology of metal-matrix composites (MMCs) due to its short processing time and large amount of production for processing composite particles.

 

This Paper was Originally Published in Japanese in J. Japan Inst. Copper 60 (2021) 271–275.

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In this study, the CoCrNi medium entropy alloy (MEA) coating was firstly fabricated on 5083Al alloy by the resistance seam processing (RESP) method. After processing, the CoCrNi MEA powders were transformed into a simple face-centered cubic (FCC) structural coating with an average thickness of 381 ± 4 µm, and the heat-affected zone was rarely found in the Al alloy matrix. Furthermore, a certain amount of Al element penetrated into gaps of coating and Co, Cr and Ni elements were homogeneously distributed. The average hardness of the coating was 775 ± 68 HV_0.2, which was higher than the similar MEAs prepared by other reported methods. To evaluate its wear properties, the wear behaviors of CoCrNi MEA coating and 5083Al alloy were studied in detail. Although the main wear mechanisms of both materials were adhesive wear, the high hardness and plastic deformation ability of the MEA coating effectively improved its wear performance. Practically, the average wear rate was ∼10 times lower than 5083Al alloy. The RESP method was proved to be an effective method for preparing the high wear-resistance MEA coating on Al alloy.

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Arsenic is a toxic element, and development of effective methods for As removal and stabilization are necessary. Removal and stabilization of pentavalent As as crystalline scorodite (FeAsO₄·2H₂O) is a promising method for As treatment of industrial byproducts. When hematite (Fe(III)₂O₃) powder is added to As(V) solution containing Fe(II) under appropriate conditions, scorodite crystals form from the gel-like precursor. When Fe(II) is not contained in the solution, the formation reaction does not proceed, even if hematite is added. Therefore, it is considered that the Fe(II) in the solution is heavily involved in the formation mechanism. Here, to elucidate the scorodite crystal formation mechanism in the hematite addition method, the origin of the iron in scorodite was investigated through scorodite synthesis experiments with addition of a stable iron isotope (⁵⁴Fe) to the reaction solution. It was estimated that the Fe(III) constituting the scorodite crystals was mainly (more than about 80 atom%) derived from the Fe(II) in the solution. From this result, scorodite formation from the reaction solution with solid hematite can be considered to occur as follows. The gel-like precursor is composed of Fe(II) from the reaction solution together with Fe(III) from hematite. During conversion of the gel-like precursor to scorodite crystals, Fe(II) in the precursor is oxidized by Fe(III), and it then combines with the arsenate ion to form scorodite. With conversion to scorodite crystals, the Fe(II) generated by this electron exchange (originally from hematite) dissolves in the reaction solution. It is speculated that electron exchange between solution-derived Fe(II) and hematite-derived Fe(III) plays an important role in formation of scorodite crystals in this synthetic method.

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