In this paper, Al_xCoFe_1.9Ni_2.1 (x = 0.5, 0.8, 1.0, 1.5) high entropy alloys are prepared by vacuum arc melting furnace. The effect of aluminum content on the microstructure and mechanical properties of Al_xCoFe_1.9Ni_2.1 high entropy alloys was studied. The microstructure of high entropy alloy was characterized by SEM, X-ray diffraction and EDS. The results show that with the increase of aluminum content, the microstructure varies from FCC to FCC+BCC structure and finally to single BCC structures. And when the aluminum content is 0.5, the microstructure exhibits slender dendritic structure, then turns to mixture of eutectic structure and FCC phase at x = 0.8 and x = 1.0. when x reaches 1.5, the microstructure changes into dendritic structure. With the increase of aluminum content, the yield strength increased from 172.3 MPa to 949.6 MPa, and the hardness increased from 127 HV to 479 HV, which significantly improved the strength and hardness of the alloy.

We developed a hot stamping method for panel parts with a step-shaped wall. The die-set for the developed method divides the punch at a step-shaped wall into an outer punch and an inner punch. The outer punch is placed first. In addition, an opening is added to the blank of the developed method. The developed method makes it possible to change the main forming type from draw forming to cylindrical stretch flange forming in the middle of a forming stroke. The stretch flange forming can prevent a fall in temperature at a hole edge, because the hole edge does not come into contact with the die-set during forming and because the high ductility of high-temperature materials can be used, making it advantageous for hot stamping. If the preceding amount of the outer punch is large with the developed method, the effect of suppressing wrinkles is large but the sheet thickness reduction that can cause cracking rises. If the preceding amount of the outer punch is small, the rate of sheet thickness reduction ratio is greatly restrained, but the wrinkles become larger. By setting an appropriate preceding amount of the outer punch with the developed method, forming without cracks or wrinkles is possible.

This Paper was Originally Published in Japanese in J. JSTP 61 (2020) 75–80. Figure 1 is slightly modified. Table 2 is slightly modified. The caption of Fig. 9 is slightly modified.

One significant issue associated with in situ stress measurements is that the uncertainty of the results cannot be determined. In this study, we propose a novel analytical procedure for the anelastic strain recovery (ASR) method, an in situ stress measurement method, enabling us to conduct uncertainty quantification based on Bayesian statistical modeling (BSM). The new procedure consists of the following steps: i) measuring the ASR of a rock core with strain gauges, ii) applying a probability model based on BSM to the measured ASR data and simulating the probability densities of the elements of an in situ stress tensor and other parameters; and iii) regarding the probability densities as the results of in situ stress measurements with uncertainty. This paper presents the results obtained by applying the proposed procedure to simulated ASR data. The results show that the uncertainties of some parameters are reduced by giving the elastic moduli. Notably, the rates of uncertainty decrease vary for each parameter. To reveal the cause of these differences, we introduce the new evaluation tool, Sobol’ indices, which comprise a global sensitivity analytic tool, to facilitate a quantitative discussion.

This Paper was Originally Published in Japanese in J. Soc. Mater. Sci., Jpn. 70 (2021) 573–580.

Thermal barrier coatings (TBCs) applied to turbine blades in jet engines or gas turbines are at risk of high-velocity impingement from different foreign objects, which can cause severe damage from delamination of the TBC. In this study, a high-velocity impingement test system is developed under high-temperature conditions to understand the delamination mechanism of TBCs under actual operation conditions. In this system, a spherical impactor with a diameter of 1–8 mm can be impinged onto a TBC specimen at different temperatures up to 900°C. High-velocity impingement tests were conducted on atmospheric plasma-sprayed TBC specimens with 8 mass% yttria-stabilized zirconia topcoat (TC) under room temperature (RT) and 900°C conditions. The results indicate that a hemispherical indentation was formed at 900°C, which indicates plastic deformation of the TC, unlike the brittle deformation observed at RT. In addition, vertical and interfacial cracks formed under both RT and 900°C conditions. Cross-sectional observation revealed that the formation process of the interfacial crack at 900°C was different from that at RT. In particular, the interfacial crack tended to become significantly longer at more than 170 m/s at 900°C.

This Paper was Originally Published in Japanese in the J. Japan Thermal Spray Society 58(1) (2021) 4–10. The abstract and captions of Figs. 1–8, 10 and 11 were slightly modified from the original paper.

In our previous study, a thin wire of a Cu–0.29 mass%Zr alloy produced by repeated intermediate annealing during rolling and wire-drawing (IA wire) exhibited a 0.2% proof stress, σ_0.2, of 600 MPa, an ultimate tensile strength, σ_u, of 630 MPa, and an electrical conductivity, E, of 91.7%IACS. A thin wire of the alloy produced by ECAP-conform processing and subsequent rolling and wire-drawing (ECAP wire) showed larger values of σ_0.2 = 730 MPa and σ_u = 790 MPa but a smaller value of E = 73.0%IACS than the IA wire. This study investigates the causes of the lower value of E and the higher value of σ_0.2 of the ECAP wire, and the higher value of E of the IA wire. The higher value of σ_0.2 of the ECAP wire is attributed to its smaller grain size and higher dislocation density. The lower value of E of the ECAP wire is primarily attributable to the fact that newly found, ordered face-centered cubic (fcc) precipitates having a cube-on-cube orientation relationship to the Cu matrix in the alloy produced by the ECAP-conform processing were cut by dislocations during rolling and wire drawing, resulting in dissolution in the Cu matrix. The IA wire showed the higher value of E because recrystallization by repeated intermediate annealing changed all the fcc precipitates into incoherent fcc precipitates that were not cut by dislocations. Further, based on the obtained results, an attempt was made to fabricate thin wires of the alloy having good strength, ductility and electrical conductivity. All the fcc precipitates in the alloy were made incoherent with the Cu matrix by utilizing recrystallization after sufficient precipitation. Then the alloy was processed by ECAP and subsequently wire-drawn. The fabricated thin wire exhibited higher values of σ_u = 820 MPa, ε_t = 4.0% and E = 86.9%IACS.

This Paper was Originally Published in Japanese in J. Jpn. Inst. Copper 58 (2019) 7–12. The captions of all figures and tables have been modified slightly.

The oxidation behavior of CuNi, CuFeNi, CrCu_0.3FeNi, and Al_0.4CrCuFeNi₂ Co-free Cu-containing concentrated solid solution alloys was investigated in steam conditions under 500, 600, and 700°C for 25 h. All the alloys have a face-centered cubic structure. The kinetic curves of oxidation were measured, and the microstructure and elemental distribution of oxide scales were analyzed. The oxidation of all the Cu-containing alloys indicated parabolic behavior, and those appeared to have better corrosion resistance than normal 316 SS. The parabolic rate constant increased with increasing temperature. The oxidation resistance of CuNi and CuFeNi were relatively poor due to the formation of unprotective NiO and Fe₃O₄ oxide scales, which were thicker than that of CrCu_0.3FeNi and Al_0.4CrCuFeNi₂ at all testing temperatures. Cross-sectional electron probe microanalysis (EPMA) and X-ray diffraction (XRD) results revealed that, by the addition of Cr and Al, CrCu_0.3FeNi and Al_0.4CrCuFeNi₂ had the enhanced oxidation resistance, which is probably due to the formation of Cr₂O₃ and Al₂O₃ inner oxide layer.

In this study, the effects of the nanoporous structure of anodic films on adhesive strength between aluminum alloys and polyamide resin were systematically investigated. Alumina films with different dimensions (such as pore density, diameter, and depth) were formed on A6063 aluminum alloys by various anodizing conditions to compare the anchoring effect. The adhesive strength at the interface between the adherend (anodized aluminum) and adhesive (thermoplastic elastomer resin) was evaluated by a method for determining the tensile lap-shear strength of rigid-to-rigid bonded assemblies. The higher pore density and larger pores in anodic films were important factors for improving the adhesive strength and increasing the adhesion interface area and the amount of adhesive impregnated into the pores. After anodizing in phosphoric acid at 60 V and subsequent pore widening, the adhesive strength of aluminum was 17.4 MPa, which was ∼3.5 times higher than that of an aluminum substrate without surface treatment.

This Paper was Originally Published in Japanese in J. JILM 71 (2021) 234–240. The abstract and the caption (Table 2 and Figs. 3–5) of this paper are slightly modified.

The performance of Ni/SrO-doped CeO₂ (SrDC) anode-supported cells, combined with the Sm₂O₃-doped CeO₂ (SDC) electrolyte layer, has been investigated for the direct supply of a dry CH₄. The SrO content in the Ce_1−xSr_xO_2−x solid solution affects the porous structure of the starting anode support comprising of the sintered NiO and Ce_1−xSr_xO_2−x grains and denseness of the SDC layer by co-sintering. The cell using the 5 mol% SrO-doped CeO₂ shows the highest cell performance without time-dependent degradation even at 750°C. This cell (the 5SrDC cell) also provides better cell performance with decreasing operating temperature than the conventional Ni/YSZ anode-supported cell (the YSZ cell); the maximum power density of the 5SrDC cell is higher than that of the YSZ cell by 73% at 650°C. This enhancement effect is discussed in light of the mixed ionic-electronic conduction of the CeO₂-based solid electrolytes.

Organic-inorganic dual-coated photocatalytic TiO₂ nanoparticles (NPs) were obtained by two-step surface modification of i) an inner SiO₂-coating and ii) outer alkylation through a silane coupling reaction, exhibiting tunable photocatalytic activity. Evaluation of the photocatalytic activity under ultraviolet ray irradiation revealed that the dual coating on the surface of the TiO₂ NPs changed the reaction rate-determining step of the photocatalytic decomposition of methylene blue (MB) from an adsorption-limited manner to a diffusion-limited manner. Unmodified TiO₂ NPs decomposed MB as soon as MB was adsorbed on the surface, while the decomposition reaction proceeded in the concentration-independent diffusion-controlled manner in the surface-modified NPs. The double shells might confine both outward excited electron diffusion and inward substance diffusion, preventing the generation of active oxygen on the surface of TiO₂ NPs.

The purpose of this study is to investigate a nondestructive method for predicting the fatigue limit of spheroidal graphite cast iron using high resolution X-ray CT. Axial load fatigue test specimens were cut out from a large spheroidal graphite cast iron equivalent to FCD 350, and graphite and defects in the material were detected using high resolution X-ray CT for all specimens. Fatigue limit was estimated from the graphite and defect sizes using the fatigue limit estimation formula based on the four-parameter method.

Axial load fatigue test was performed in accordance with JIS (Japanese Industrial Standards). Repetition frequency was 17 Hz, stress ratio was R = −1, and number of cycles during the test was 1.0 × 10⁷. The specimen used was JIS type 1 of 8.00 mm in diameter. Fracture origins were observed in all fatigue fracture surfaces using a scanning electron microscope (SEM) in order to compare the results between the defects observed by X-ray CT and the fracture origins observed in the fatigue test.

The fatigue limit estimated by the defect with the largest volume detected by X-ray CT was 5% lower than the experimental fatigue limit of 125 MPa, which is considered safe estimation. However, in the fatigue test, the fracture origin was not necessarily the defect with the largest volume. Therefore, the fatigue limit was estimated by the average defect size when the cumulative distribution function of ten defects with the largest volume of each test piece was F = 50%. The result was 11% larger than the experimental fatigue limit, which is considered a dangerous estimation. These results indicate that estimation of fatigue limit using a nondestructive method is feasible.

This Paper was Originally Published in Japanese in J. JFS 91 (2019) 264–269.

Dimensional scattering is a severe problem in press forming of ultrahigh-strength steels (UHSS), because of material strength scattering in mass production. In this study, camber back, which occurs in longitudinally curved parts, was examined, and a new forming method whereby dimensional scattering of camber back can be suppressed by the Bauschinger effect was developed. The new method consists of two processes. In the 1st process, a blank is formed with a small radius of curvature compared with that in the 2nd-process. In the 2nd process, that part is formed to a larger radius of curvature than in the 1st process, and the Bauschinger effect is utilized to decrease the amount of camber back. The new method was applied to hat-shaped models of 590, 980, and 1180 MPa-grade steels in which the radius of curvature in the longitudinal direction was 1600 mm. The experimental results showed that the difference in the amount of camber back between the 590 MPa and 1180 MPa steels formed by the developed method decreased by 95% compared with parts formed by the conventional method.

This Paper was Originally Published in Japanese in J. JSTP 60 (2019) 155–160. The abstract is slightly modified.

An amorphous powder of starting compound (Sm_0.8Zr_0.2)_1.05–1.10(Fe_0.9Co_0.1)_11.3Ti_0.7 was directly sintered in a carbon die under a pressure of 50 MPa using the spark plasma sintering (SPS) method. This is the first result showing the possibility of using this compound to prepare bulk magnets that have comparatively high magnetic properties. Typical sintered magnets with a density of 6.2 and 6.5 g cm⁻³, which are about 80% and 84% of the theoretical density, exhibited a coercivity of about 430 and 370 kA m⁻¹ and (BH)_max of 50.6 kJ m⁻³ (= 6.32 MGOe) and 57.2 kJ m⁻³ (= 7.15 MGOe) at room temperature, respectively. The crystal structures of the samples with high magnetic properties prepared by the SPS method were a mixture of the 1-9 and 1-12 phases, which is the same result as reported for powder samples prepared by annealing of the same starting compound.

Galvanic corrosion at the joint of AZX611 magnesium (anode) and A6N01 aluminum (cathode) in 1 mass% NaCl solution with different cathode/anode area ratios was evaluated. The galvanic potential was different depending on the area ratio. The anode galvanic current density increased with increasing the area ratio. Anode and cathode weight loss corrosion rates, and the average of anode current densities, were linearly related to the logarithm of the area ratio with different slopes. Scanning vibration electrode technology (SVET) has exhibited the presence of anode current spots that increased with the area ratio. Surface profile of the galvanic joint was in good agreement with the SVET results. The obtained effect of cathode/anode area ratio was analyzed by the mixed potential theory. Finally, the compatibility of magnesium/aluminum joint was compared with other dissimilar metal joints.

This Paper was Originally Published in Japanese in J. JILM 71 (2021) 82–88.

Anisotropic compression behavior of open-cell porous titanium is evaluated at different temperatures. Porous titanium specimens with truncated octahedron unit cells are designed by 3D-Voronoi division. Cubic specimens with the porosities of 85 and 92% are manufactured from commercially pure titanium powder using an electron beam melting process. Compression tests are carried out at different temperatures of 300, 473 and 673 K for three different compression directions of [001], [011] and [111]. In all specimens, the flow stress of [001] direction is highest and the flow stress of [111] direction is lowest. Anisotropic compressive strength can be explained by comparing the bending moment of cell struts. Activation energy obtained by Arrhenius plot is the same as that of base titanium and is independent of the compression direction.

High-velocity compaction (HVC) using a die was investigated as a compaction technique for the fabrication of high-density isotropic Zn-bonded Sm–Fe–N bulk magnets. The compaction characteristics of Zn-mixed Sm–Fe–N powders obtained by HVC were investigated while varying the Zn content. Moreover, the magnetic properties, flexural strengths (σ), and microstructures of the resulting magnets were studied. The relative density (d_r) steadily increased with the piston velocity during compaction and reached approximately 90% at a piston velocity of 11.2 m·s⁻¹ (equivalent to a compaction pressure of 3.45 GPa), regardless of the Zn content. Because the magnets were fabricated using a die, they also had a high dimensional precision. The resulting magnet, with 5 wt% Zn and d_r of 89.1%, exhibited a maximum energy product ((BH)_Max) of 54.4 kJ·m⁻³, remanence (B_r) of 0.56 T, and coercivity (H_cJ) of 965 kA·m⁻¹. σ exceeded 100 MPa when d_r was above 88%, which satisfies the required mechanical strength for applications such as permanent magnet motors.

A new methodology to calculate and visualize the amount of airborne sea salt with a 100 m mesh resolution in high definition has been proposed in this study. A transport calculation module for airborne sea salt is implemented to the atmospheric component of the multi-scale atmosphere–ocean coupled model. The computational fluid dynamics model (NuWiCC-ST) results that can calculate the generation and transport of sea salt particles are incorporated to the transport calculation. The coupled methodology has been applied to create a corrosion environment map for Choshi City. The reliability of the developed method was confirmed by comparing airborne sea salt data measured using the dry gauze method with the calculated data.

This Paper was Originally Published in Japanese in ZAIRYO-TO-KANKYO 69 (2020) 169–174.

The necessity of arsenic (As) removal from metallurgical wastewaters is increasing. Despite its wide recognition as a natural oxidant, the utility of Mn oxide for scorodite production is mostly unknown. In acidic solutions containing both As(III) and Fe²⁺, simultaneous oxidation of the two progressed by MnO₂ and the resultant As(V) and Fe³⁺ triggered the formation of crystalline scorodite (FeAsO₄·2H₂O). At 0.5% or 0.25% MnO₂, 98% or 91% As was immobilized by day 8. The resultant scorodite was sufficiently stable according to the TCLP test, compared to the regulatory level in US and Chile (5 mg/L): 0.11 ± 0.01 mg/L at 0.5% MnO₂, 0.78 ± 0.05 mg/L at 0.25% MnO₂. For the oxidation of As(III) and Fe²⁺, 54% (at 0.5% MnO₂) or 14% (at 0.25% MnO₂) of initially added MnO₂ remained undissolved and the rest dissolved in the post As(III) treatment solution. For the Mn recycling purpose, the combination of Mn²⁺-oxidizing bacteria and biogenic birnessite (as homogeneous seed crystal) was used to recover up to 99% of dissolved Mn²⁺ as biogenic birnessite ((Na, Ca)0.5(Mn^IV, Mn^III)₂O₄·1.5H₂O), which can be utilized for the oxidation treatment of more dilute As(III) solutions at neutral pH. Although further optimization is necessary, the overall finding in this study indicated that Mn oxide could be utilized as a recyclable oxidant source for different As(III) treatment systems.

The performance of vibration power generation using the inverse magnetostrictive effect increases with increasing its device size. In this study, grain-oriented electrical steel that can be largely produced was investigated as a core material, using a U-shaped unimorph device at a laboratory scale. The device using a grain-oriented electrical steel core (16 mm long with a 1.4 mm² cross-section) with the rolling direction (RD) along the stress direction exhibited the effective open-circuit voltage of 0.89 V under an optimum bias magnetic field, when the free-end of the device was vibrated with a maximum amplitude of 2.0 mm at a mechanical resonance frequency of 108 Hz. In addition, an average output power of 300 µW was obtained by adjusting the load resistance. The above-mentioned properties of the RD unimorph core device were superior to those of the transverse direction (TD) unimorph core device, because the magnetic flux density change in the RD core was approximately 0.65 T, which was larger than that in the TD core. Therefore, grain-oriented electrical steel with the RD direction is a useful core material for developing large-sized devices with high performance.

A novel Cu-powder contained solderable epoxy-solder composite (Cu-SESC) was introduced, and its interconnection mechanism was proposed as a means to improve the interconnection properties of the SESC joints. To identify the possibility and strengthening effect for the SESC joints by added Cu powder, two types of wetting tests using planar and line type metallization formed test boards, and a microhardness evaluation were performed. The Cu-SESC showed appropriate wetting and spreading properties. The Cu powders in the wetted low melting-point alloy (LMA) exhibited a uniform dispersion state, and a Cu–Sn intermetallic compound created on the surface of the Cu powders. The SESC that had Cu powders showed a superior microhardness value to that of the SESC without Cu powders because of the strengthening effect from the added Cu powder. Additionally, the selective conduction joint establishment properties obtained through the flowage, integration, and selective wetting behaviors of the fused LMA were not interrupted by the incorporated Cu powders.

This study aimed to investigate the effects of alloying elements on the fatigue properties of magnesium in simulated body fluids. The fatigue life of the Mg–Zn alloy in air was longer than that of Mg–Ca. This result is in accordance with the tensile yield stress. Crack propagation occurred along the grain boundaries in Mg–Ca and among the grains in Mg–Zn because zinc addition significantly effects grain boundary strengthening. In contrast, the fatigue life in simulated body fluid was longer for the Mg–Ca alloy than for the Mg–Zn alloy at a lower stress amplitude. These results suggest that the use of both calcium and zinc as additives contributes to the further improvement of the fatigue life of magnesium in simulated body fluids as the immersion time is prolonged.