To improve estimation of sea salt deposition distributions on structural surfaces such as that of an airborne sea salt and corrosion sensor, we numerically simulated approaching flows with particles around a vertical flat plate. This is a typical object that mimics a sensor with a support plate. We used a computational fluid dynamics (CFD) model based on the unsteady Reynolds averaged Navier–Stokes equation. After validating the results by comparison with existing studies for flows with particles around a cylinder, we examined the changes in particle impaction efficiency on the plate with different approaching flow directions (0, 45 deg) and particle diameters (5×10^-6 − 1.6×10^-4 m). The impaction efficiency increases rapidly with particle diameter, whereas the influence of flow direction is small. Such increases in impaction efficiency are due to contributions from inertial impaction, and thus the variation in Stokes number with wind speed and the plate size can be used to predict the flow and particle conditions required for increases in impaction efficiency. The efficiencies for small particles on the front surface of the plate are higher than those on a cylinder. The impactions of small particles on the plate are locally activated by flow separations around a bluff body, whereas those on a cylinder are caused by intercepts without flow separations.

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Non-combustible magnesium alloy garnered attention in lightweight automobiles. Nonetheless, its practical application necessitates the support of joining and welding techniques. Self-pierce riveting (SPR) has widespread adoption in aluminum alloys. However, there are few reports concerning non-combustible magnesium alloy SPR joints. This study investigated the fatigue property of Mg-4%Al-1%Ca-0.2%Mn (hereinafter referred to as AX41) alloy similar and dissimilar material SPR joints based on failure mechanism analysis. AA6061 (Al-1%Mg-0.05%Si) and SPCC (Steel Plate Cold Commercial) were used for the dissimilar material joints. The influencing factors on strength were discussed based on the result of the fatigue test. According to fatigue test results, except for the joint with SPCC as the upper sheet, the fatigue life of dissimilar material joints was longer than that of similar material joints. According to the observation of the fracture surface, the processing cracks near the rivet foot act as a secondary influencing factor of fatigue strength properties. The processing cracks near the rivet foot may induce rotation of a rivet, which makes the lower sheet easy to bend. To investigate the influence of bending stiffness on fatigue strength, different thicknesses of an upper and a lower sheet were prepared to test. The test results affirmed that bending stiffness is the primary influencing factor of fatigue strength. The bending stiffness ratio of the upper/lower sheets directly affects the failure mode of SPR joints.

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Among Al-Zn-Mg alloys, A7003 alloy is considered to be an excellent alloy from the viewpoint of weldability because it is an alloy with relatively low Zn and low Mg composition.

In this paper, changes in mechanical properties and microstructure during aging treatment are investigated by the addition of Si in the Al-5.6 mass%Zn-0.75 mass%Mg alloy containing Cu, Mn, Zr and Fe.

Cast billets of alloys with different Si contents (Si: 0.05 mass%, 0.15 mass%, and 0.30 mass%) were prepared, and these cast billets were homogenized and extruded. After extrusion, four aging treatments were performed: one step aging at 423 K for 8 hours, and two step aging at 373 K for 3 hours, 6 hours, and 9 hours, followed by 423 K for 8 hours.

The higher the amount of Si, the smaller the thickness of recrystallization layer near the inner surface and near the outer surface, and the smaller the existence rate of recrystallized grains in the cross section.

After one step aging at 423 K for 8 hours, Si: 0.05 mass% showed lower strength than Si: 0.15 mass% and Si: 0.30 mass%. On the other hand, two-step aging resulted in Si: 0.05 mass%, Si: 0.15 mass%, and Si: 0.30 mass% with similar strength. The low strength of Si: 0.05 mass% after one step aging at 423 K for 8 hours is thought to be due to the coarse η phase, which was precipitated in the grain boundaries and grains. In Si: 0.15 mass% and Si: 0.30 mass%, Al(Mn,Fe)Si which formed during homogenizaiton process is present in the grain boundaries and grains after extrusion. It is thought to suppress the generation of the precipitate of the coarse η phase in the aging at 423 K for 8 hours, which is a condition that the coarse η phase is easy to generate.

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This review delineates the mechanisms of pit nucleation and growth, establishes the foundational principles of etching technology, and presents the findings from investigations on the behavior of anodic dissolution and anodic film formation on high-purity aluminum foils for electrolytic capacitors based on electrochemical analyses and surface electron microscopic observations of etched surfaces. To elucidate pit nucleation and growth mechanisms, the effects of crystalline oxide and small amounts of lead on etching behavior were investigated. Pits initiate at cracks surrounding MgAl₂O₄ spinel or γ-Al₂O₃, resulting from the crystallization of the oxide film at metal ridges on the aluminum substrate. Using ultra-high-resolution field-emission scanning electron microscope (FE-SEM) , high-angle backscattered electron (BSE) images revealed the presence of lead as the bright nanoparticles, approximately 10nm in size, at the surface oxidation layer along rolling lines attributable to pick-up inclusions during hot rolling.

Pitting attacks predominantly occur in the oxidation layer owing to the less noble potential for tunnel dissolution in the initial DC etching phase. Increased titanium content within the aluminum foil accelerated hydrogen evolution in the pit and hydrous oxide formation during the cathodic half-cycle of alternating current etching. The crystallization of anodic oxide films around MgAl₂O₄ spinel crystals, formed in a boric acid solution, was observed using transmission electron microscopy (TEM). Round-shaped γ'-Al₂O₃ formed around the MgAl₂O₄ crystals and expanded across the surface as the formation voltage increased.

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In Al-Zn-Mg alloy, hydrogen (H) leads remarkably to the degradation of mechanical properties. It is indispensable to suppress this phenomenon called hydrogen embrittlement (HE) for developing the high-strength Al-Zn-Mg alloy. Because intergranular fracture (IGF) is mainly observed when HE occurs in the alloy, we need to understand the initiation behavior of IGF in order to suppress HE. Heterogeneous distribution of stress, strain and H concentration usually influence the IGF initiation in polycrystalline material. In the present study, we investigated distribution of stress, strain, and H concentration in actual fractured regions by simulation employing a crystal plasticity finite element method and H diffusion analysis in a 3D image-based model, which was created based on 3D polycrystalline microstructure data obtained from X-ray imaging technique. Combining the simulation and in-situ observation of the tensile test sample by X-ray CT, we examined the distribution of stress, strain, and H concentration in actual crack initiation behavior. Based on this, the condition for intergranular crack initiation were discussed. As a result, it is revealed that stress normal to grain boundary induced by crystal plasticity dominates intergranular crack initiation. In contrast, accumulation of internal H due to the stress has little impact on crack initiation.

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Metal matrix composites (MMCs) were produced using iron (Fe) and niobium carbide (NbC) powders and synthesized with different NbC contents (0, 5, 10, and 20 wt.%) by high energy ball milling. As a result, a Fe_0.99Nb_0.01 solid solution was formed, which influenced the lattice distortion and peak shift. The Fe-NbC composites were subsequently consolidated by rapid sintering at 850°C and sintering pressure of 60 MPa. The hardness of Fe-NbC composites were ranged from 128.9 ± 10.4 to 374.5 ± 14.6 kg/mm², which was related to the hall petch relationship. This enhancement is attributed to the dispersion strengthening effect of the agglomerated powders through high energy ball milling, and the control of grain growth by the spark plasma sintering. Particularly, the oxidation resistance of Fe-NbC composites increased gradually as the NbC contents increased, indicating that the oxidation layer such as Nb₂O₅, Fe₂O₃, and Fe₃O₄ locally formed on the Fe-NbC composites surface. The oxidation layer decreased from 204.34 to 12.99 µm with the rise in NbC content.

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Si is opaque to visible light, but transparent to infrared rays. Therefore, when the infrared laser is focused inside Si, the focal portion becomes ultra-hot, forming a modified volume (Laser induced modified volume: LIMV) inside. After the laser beam is injected into the Si wafer at equal intervals (for example, 5 µm) in the cross direction, and then a force is applied from the outside. Then, cracks are formed from LIMV, and the Si wafer is divided into small pieces of 5 µm square. This is the stealth dicing (SD) technology, which is now widely used in the manufacture of semiconductor devices. In this process, clarifying the nature of LIMV is of great industrial and academic significance. The authors have been engaged in elucidating the mechanism of LIMV development by TEM observation. This phenomenon, which at first seemed extremely puzzling, was finally elucidated. In this overview, we would like to describe the process that led to this elucidation in chronological order. This phenomenon is extremely puzzling, and due to the author’s lack of knowledge, there were errors in the contents of the papers published so far, so we have corrected them in this overview.

 

This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 88 (2024) 69–80. The captions of Tables 4 and 6 and Figs. 1, 3, 7–16, 21, 22, 27, 28, 30 and 33 and Figs. 20, 31 and 32 are slightly modified.

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Recent research has shown that some intermetallic compound particles with high interfacial hydrogen trap energies (e.g., Mg₂Si) are prone to damage at high hydrogen concentrations. In this study, the acceleration of particle damage in an A6061 alloy was observed in-situ via X-ray CT. The damage behavior of the particles that are located in the crack tip stress field, where high stress triaxiality causes a local increase in the hydrogen concentration, was analyzed. The influence of hydrogen on the damage behavior of the dispersed Mg₂Si particles was investigated by preparing a material charged with hydrogen to achieve extremely high hydrogen concentration, and further hydrogen enrichment in a crack tip region was also utilized. Interfacial debonding of Mg₂Si particles was frequently observed in the vicinity of a crack tip immediately prior to tensile fracture. Even though the fracture is typical of ductile fracture, hydrogen accelerates particle damage and reduces the macroscopic ductility of the aluminum alloy. This can be considered as a form of hydrogen embrittlement of aluminum alloys. Even in materials with relatively low hydrogen concentrations (0.85 mass ppm), interfacial debonding occurred in the hydrogen-enriched crack tip regions. A higher hydrogen concentration promoted interfacial debonding over a wider range of particle sizes and particle shapes. It can be inferred that localized hydrogen enrichment, which is expected to occur due to external hydrogen exposure, stress corrosion cracking, corrosion or crack tips, can directly contribute to debonding at the Mg₂Si particle/aluminum matrix interface. According to the analysis, reduction of the diameter and simplification of the shape of Mg₂Si particles are effective method for suppressing such hydrogen-induced debonding.

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The porosity of rocks is one of the most fundamental physical properties and is required to quantitatively evaluate the characteristics of rocks in drilling projects in fault zones. In the drilling project of the Futagawa fault, which ruptured during the 2016 Kumamoto earthquake mainshock, although the porosities of intact rock core samples were measured, there was no continuous porosity profile because core samples could not be obtained in fractured zones. Therefore, we estimated a vertical, continuous porosity profile for a depth interval of approximately 300–660 m, except for 383–399 m in borehole FDB-1 of the project, using sonic log data. First, we tested several different empirical equations proposed in previous studies for both sedimentary and volcanic rocks and proposed a new equation considering the effects of compaction and lithology on sedimentary rocks. Second, we compared the estimated porosities with the core porosities at the depths of the measured core samples. As a result, our new equation provided better estimates for sedimentary rocks, but a previous equation called Li et al.’s equation provided closer estimates for volcanic rocks. The porosities estimated by our new equation for sedimentary rocks were approximately 50% at depths of approximately 300–330 m and approximately 20–40% at approximately 330–350 m and 510–660 m. The porosities estimated by Li et al.’s equation were approximately 15% for volcanic rocks (massive lava) at depths of approximately 380–460 m and approximately 30–40% for volcanic rocks (autobrecciated lava) at approximately 350–380 m and 460–510 m. Obviously, the porosities derived from the sonic logs of volcanic rocks were greater than those measured using intact core samples due to existing fracture porosity and alteration. Therefore, the derived porosity profile might reflect a reasonable in situ state in the borehole of the Futagawa fault drilling project.

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Breaking trade-off relationship between strength and ductility in steels has been a perpetual topic, since researchers have been pursuing more energy and resource-efficient manner to use steels. In this study, rolling, tempering and inter-critical annealing were innovatively combined to obtain high strength- high ductility combination in Fe-4Mn-4Ni-3Al-0.1C steel. The process referred as multi-step inter-critical annealing (MIA) was designed to accomplish the following objectives: (a) a stretched lamellar-shaped grain structure resulting from rolling at non-recrystallization region of austenite, (b) Mn/C-heterogeneous austenite inherited from carbides formed during tempering. Therein, Mn/C-depleted austenite areas originated from ferrite; meanwhile, Mn/C-enriched austenite areas originated from the carbide dissolution, (c) transformation hardening of Mn/C-depleted austenite area during cooling in the inter-critical annealing, (d) stress relaxation of Mn-enriched austenite area retained as retained austenite at room temperature. The specimen achieved excellent mechanical response through the optimized MIA process (tempering at 400 °C for 3 hours, then inter-critical annealing at 765 °C for 40 minutes). The obtained microstructure was composed of alternating lamellae of bainite and a special annealed martensite on microscale, with the latter consisting of secondary martensite and retained austenite films on nanoscale. The yield strength and total elongation of steel were increased from 858 MPa and 12% in direct inter-critical annealing process to 1011 MPa and 32% in MIA respectively. The modified Crussard-Jaoul analyses were used to evaluate the deformation behavior of the steels. Due to lots of bainite formation, a relatively high initial strain hardening exponent (0.72 m^-1) was observed for the DIA steels. While lower initial strain hardening rate (0.32 m^-1) and more stages of work hardening because of increasing stable austenite and secondary martensite in the MIA steels ensured the excellent strength–ductility combinations.

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The prediction accuracy of the deformation behavior of materials by finite element (FE) simulation depends on the parameters in selected material models. Although the parameters are conventionally identified from standard material tests (e.g., uniaxial tensile and multiaxial material tests) to characterize the deformation behavior, the identification process requires a large number of experiments. We develop a novel inverse methodology for estimating the material model parameters by combining digital image correlation (DIC) measurement and FE simulation coupled with an ensemble-based four-dimensional variational method (En4DVar). En4DVar incorporates the experimental data obtained from a material test into the FE simulation that reproduces the test and inversely estimates the parameters such that the simulation results follow the experimental data, allowing for the reduction of experimental effort. We use the proposed method to estimate the parameters of a strain-hardening law and anisotropic yield function from the results of uniaxial tensile test of a round bar of aluminum alloy. DIC measurement is conducted to obtain experimental data of the three-dimensional displacement and strain field over the surface of the specimen, including the post-necking range. The results demonstrate that En4DVar is a promising method for inversely estimating the parameters and characterizing the deformation behavior of a material from the results of a small number of tests.

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Mechanical properties of Li_10.35Ge_1.35P_1.65S₁₂(LGPS) solid electrolytes with different grain sizes were investigated via indentation tests. Hand-milled LGPS (HM LGPS, d₅₀:1.32 µm) and wet-milled LGPS (WM LGPS, d₅₀:0.46 µm) powders were uniaxially pressed to obtain pellet samples. The HM LGPS and WM LGPS pellets had a similar bulk density of 1.63 g cm^–3. At the initial loading/unloading, the WM LPGS pellet showed a large deformation owing to a decrease in cavities compared with the HM LGPS. In the subsequent cycles, both pellets exhibited elastic deformation behavior in the pressure range up to 20 N. The elastic modulus and relative residual depth of HM LGPS and WM LGPS were 21.7 GPa and 0.41 GPa and 0.75 and 0.71, respectively. This result revealed that WM LGPS is more elastically deformable and less plastically deformable than HM LGPS, which could be associated with the grain boundary strengthening interpreted by the Hall-Petch relation. Based on these mechanical properties, the superior cycle stability at the In-Li electrode/WM LGPS electrolyte interface during charging/discharging was discussed. Controlling the mechanical properties of sulfide solid electrolytes by the grain size is important for suppressing physical degradation in all-solid-state batteries.

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Extremely low cycle fatigue tests, up to a total axial strain amplitude of 10%, were conducted on Fe-15Mn-10Cr-8Ni-4Si bidirectional transformation-induced plasticity (B-TRIP) steel. The fatigue life was approximately five times longer than that of SUS316 when the total strain amplitude was 4% or higher. The improved fatigue life of Fe-15Mn-10Cr-8Ni-4Si was attributed to reversible bidirectional γ ↔ ε transformation during fatigue deformation, which might mitigate fatigue damage. In contrast, the fatigue life tended to decrease with increasing strain rate when the strain rate was varied from 0.1 to 2.5%/s with a total strain amplitude of 10%. Fractography revealed that the fracture surface varied significantly with strain rate. At low strain rates, crystallographic fracture surfaces characterized by facets and secondary cracks were observed, whereas these features were not observed at high strain rates. Electron backscatter diffraction measurements of the postmortem microstructure showed that frequent ε-martensite formation occurred at low strain rates, whereas martensitic transformation was suppressed at high strain rates. The change in the specimen surface temperature was evaluated in terms of the Gibbs free energy difference between γ-austenite and ε-martensite (i.e., ΔG^γ→ε), and the effect of strain rate on the extremely low cycle fatigue was discussed from the viewpoint of the deformation mechanism. At a low strain rate, the condition for B-TRIP to work effectively, that is, ΔG^γ→ε is negative but close to zero, was maintained over the entire life span. At a high strain rate, the deformation mechanism changed to one in which γ-austenite was dominant because of the increase in ΔG^γ→ε caused by self-heating; the fatigue damage mitigation mechanism provided by B-TRIP was less likely to occur at high strain rates, which reduced the fatigue life.

 

This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 72 (2023) 858–865. The captions of Table 1 and Figs. 1, 6, and 7 are slightly modified.

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The monitoring of invasion/permeation hydrogen on entry/exit surfaces of cathodically charged SUS316 columnar crystals was conducted with a scanning Kelvin probe force microscope (SKPFM) under atmospheric pressure. Columnar crystal specimens covered with oxide films on their surfaces under room conditions were prepared for cathodic charging tests and subsequent SKPFM measurements. The invaded hydrogen on the entry surface was detected at the δ-ferrite phases for 7 d after charging, and the segregation of invaded hydrogen at the boundaries between the δ-ferrite and austenite matrix was prolonged for >10 d after charging. The permeated hydrogen on the exit surface was detected at the δ-ferrite phases for 3 d after charging, but was not substantial at some of the δ-ferrite phases regardless of the charging. Segregation of permeated hydrogen at the boundaries between the δ-ferrite and some of the intermetallic precipitates was prolonged for 7 d after charging. The behaviors of invaded/permeated hydrogen based on heterogeneous microstructures are discussed to improve understanding of the hydrogen embrittlement mechanism in weld metals.

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In this study, the electrical properties and stability of silver nanowire transparent conductive electrodes (TCEs) were improved through the platinum electroplating process (AgNWs@Pt TCEs). After electroplating, environmental and thermal stabilities increased considerably, whereas sheet resistance was greatly reduced. Sheet resistance sharply decreased from 181.3 Ω/□ to 16.59 Ω/□. Meanwhile, the thermal stability of the AgNWs@Pt TCEs was enhanced by 20°C compared with that of TCEs based on silver nanowires. The sheet resistance of the AgNWs@Pt TCEs remained nearly constant after exposure to ambient air for five months. The optimal electroplating condition was achieved at an electroplating current of 10 µA for 30 s. Under this condition, the sheet resistance, transmittance, and figure-of-merit (FOM) values of the AgNWs@Pt TCEs were approximately 16.59 Ω/□, 83.89%, and 123 Ω⁻¹, respectively.

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Molecular dynamics (MD) simulation has an intrinsic limitation when calculating thermal conductivity of metals. That is, only phonon (lattice) thermal conductivity can be derived from trajectory of atoms, which is obtained by solving the Newton ’s equations of motion numerically. Therefore, significant contribution of electrons in metals remains unaccounted for. In this study, a Light Gradient Boosting Machine (LightGBM) regression model is employed to predict thermal conductivity of metals using heat flux calculated by MD simulation, electrical conductivity and others as input variables. The LightGBM model successfully predicts the complex non-linear Green-Kubo relation for thermal conductivity calculation even though the underlying physical mechanisms are not entirely clear. The model predicts various temperature dependences of thermal conductivity of metals accurately. Furthermore, the model trained with known compositions of Al-Cu alloys is proved to estimate the thermal conductivity of alloys with unknown compositions. The model also demonstrates a certain level of predictive ability for alloys with different compositions and temperatures. This study demonstrates the potential of a data-driven approach as an efficient method for uncovering complex relationships between incomplete data from MD simulations and true materials properties, especially in cases where the underlying physics is elusive.

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The aluminum alloy shell fabricated by ‘bending + high-frequency welding’ is the core component of the Chinese new energy vehicle battery pack. Still, this process cannot produce the next generation of shell products with unequal wall-thickness. In this study, we take the unequal-wall-thickness square 3003 aluminum alloy battery shell with a wall thickness of less than 0.5 mm and a tolerance range of ±30 µm as the research object. According to the cold work, hardening characteristics of 3xxx series aluminum alloys, hot extruded hollow blanks were prepared, and a new cold drawing process was attempted to be developed on this basis. Based on the analysis of the stress-strain field during cold drawing of defective workpieces, the size of the die inlet’s R angle and the blank’s size were optimized to solve the problems of local fracture and tearing of the blank. The results show that the maximum stress during cold drawing occurs at the fillet where the sizing zone intersects with the wall-thinning zone. This location is subjected to tensile stress, normal pressure from the inner and outer dies, and tangential friction force, causing a material accumulation phenomenon; the material flow velocity along the cold drawing direction is inconsistent, which will cause U-shaped patterns on the surface of finished products; the strain value along the cold drawing direction first increases and then decreases with the rise of R angle, reaching the maximum when the R angle size is 1.5 mm. After optimization, the maximum equivalent stress decreased from 205 MPa to 190 MPa, and the average strain along the cold drawing direction increased from 0.15–0.22 to over 0.3. This study successfully prepared precisely ultra-thin lithium iron phosphate battery shells by optimizing cold drawing process parameters and die structure.

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Announcement Concerning Article Retraction
The following paper has been withdrawn from the database of Mater. Trans., because a description based on a misinterpretation of the experimental results was found by the authors in advance of publication after acceptance.
Mater.Trans. 52(2011) Advance view.
Improvement in Fatigue Strength of Biomedical β-Type Ti-Nb-Ta-Zr Alloy while Maintaining Low Young’s Modulus through Optimizing ω-Phase Precipitation

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