We used two deep learning methods, convolutional neural networks (CNN) and deep neural networks (DNN), to classify three common metal crystal structures (FCC, BCC, and HCP). The training, validation, and test datasets were created by Atomsk and Python scripts, and the data structure was transformed to meet the input requirements of CNN and DNN. To fully train and test CNN and DNN, we constructed four crystal structure datasets using random parameters. The results show that the accuracy of CNN and DNN algorithms on the test set is 100%, indicating that deep learning methods are effective for metal crystal structure classification. Compared with DNN, CNN has fewer parameters, faster training, and faster classification. It lays the foundation for further studying alloy structure detection and phase transition.

We attempted to calculate the hydrogen trapping energies at the incoherent interfaces of MgZn₂ precipitates and Mg₂Si crystallites in aluminum alloys from first-principles calculations. Since the unit cell containing the incoherent interface does not satisfy the periodic boundary condition, resulting in a discontinuity of crystal blocks, the hydrogen trapping energy was calculated in a region far from the discontinuity (vacuum) region. We found considerable trapping energies for hydrogen atoms at the incoherent interfaces consisting of assumed atomistic arrangement. We also conducted preliminary calculations of the reduction in the cohesive energy by hydrogen trapping on the incoherent interfaces of Mg₂Si in the aluminum matrix.

In this work, we investigated the influence of Co on the structure and magnetic properties of Ni_50−xCo_xMn₂₉Ga₂₁ (x = 0, 2, 4, 6, and 8) shape memory alloy ribbons fabricated by using the melt-spinning method. The addition of Co increases the formation of the austenitic crystalline phase in the alloy ribbons. The crystalline grains in rod-shapes with diameter of ∼2 µm and length of ∼10 µm are mostly oriented perpendicular to the ribbon surface. The martensitic-austenitic transformation was performed on both the thermomagnetization and differential scanning calorimetry methods. With the increase of Co concentration, the martensitic-austenitic structural phase transformation temperature (T_M-A) of the alloy gradually decreases while the Curie temperature of the austenite phase (T_C^A) of the alloy increases from 355 K (for x = 0) to 432 K (for x = 8). Besides, the martensitic-austenitic phase transformation is also significantly affected by the external magnetic field. The structural phase transformation temperature of the alloy tends to shift towards lower temperatures as the external magnetic field increases.

In this study, microstructure and phase transformation behavior in Fe₂₀Co₂₀Ni₂₀Cr₂₀B_20−xSi_x alloys prepared by the mechanical alloying (MA) method were investigated by X-ray diffraction (XRD) measurements, scanning electron microscopy, transmission electron microscopy, and differential scanning calorimetry (DSC). The Fe₂₀Co₂₀Ni₂₀Cr₂₀B_20−xSi_x alloys prepared by the melt-spinning method were composed of FCC and compounds, and the FCC and BCC phases predicted by the valance electron concentration parameter were not formed. However, alloy powders prepared by the MA method were revealed to be composed of the FCC and BCC phases. Small amounts of unreacted pure B and Si particles were observed in alloy powders with high and low B content, respectively. XRD and DSC measurements revealed that the BCC phase in MA powder disappeared, and compounds were formed by heating up to 700°C. Especially the compound formation temperature was higher than that of the same alloy prepared by the melt-spinning method, suggesting that the thermal stability of the alloy powders prepared by the MA method was higher than that of the alloy ribbons prepared by the melt-spinning method.

The objective of this study was to optimize the cooling conditions after solution treatment of the JIS AC4CH aluminum casting alloy, and the effects of the temperature range cooled at 0.5°C/s on the microstructure and mechanical properties were investigated. The temperature range of the cooling and cooling rate were simultaneously adjusted by heating using a high-frequency induction heating apparatus and cooling by blowing air. In particular, cooling at 10°C/s (CR10) was used as the basic cooling rate, with a rate of 0.5°C/s (CR0.5) used for a portion of the temperature range. The scanning electron microscopy (SEM) observations of the specimens after cooling revealed that rod-like precipitates formed in the specimens that were cooled at CR0.5 in the range of 400–250°C. In the specimen that was cooled at CR0.5 from 500 to 450°C, granular or rod-shaped precipitates with a small aspect ratio were observed. From the results of a scanning transmission electron microscopy with energy dispersive X-ray spectroscopy (STEM-EDS) investigation, the former were identified as the Mg₂Si intermediate phase, and the latter were composed mainly of Si. An electron probe micro analyzer (EPMA) was used to measure the Mg and Si concentrations in the primary α-Al phase. In the case of the temperature range for CR0.5 cooling above 350°C, the Si concentration decreased significantly as the temperature range of CR0.5 cooling increased. Considering the Si concentration distribution and diffusion distance in the primary α-Al phase, this decrease in the Si concentration could have been caused by the diffusion of Si atoms to the eutectic region. The 0.2% proof stress and tensile strength values after the artificial aging of a specimen that was cooled at CR0.5 from 400 to 350°C, where a coarse Mg₂Si intermediate phase precipitated during cooling, were approximately 10% lower than those of a specimen that was cooled at CR10 over the whole temperature range.

Al–Zn–Mg alloys with different precipitate sizes were investigated to determine the influence of the precipitate size on the flow stress and dislocation density change during tensile deformation. The dislocation density was measured using in-situ X-ray diffraction at the SPring-8 synchrotron radiation facility with a time resolution of about 2 s. In region II with rapid dislocation multiplication, from under-aging to peak aging, the dislocation density increased with increasing aging time. Under over-aging conditions, the amount of dislocation multiplication in region II decreased with increasing aging time. Even in region III, the increase in dislocation density with plastic deformation was the largest for the peak aging conditions. However, the amount of work hardening was small and the contribution of dislocation hardening to the strength of the material was minimal. For over-aging conditions, the increase in dislocation density in region III was smaller than for the other regions, but the amount of work hardening was relatively large. It is considered that the influence of the dislocation density on work hardening is determined by the effectiveness of precipitates as obstacles to dislocation motion.

This Paper was Originally Published in Japanese in J. JILM 71 (2021) 343–348.

One challenge hampering the structural applications of High-entropy alloys (HEAs) is to overcome the strength-ductility trade-off. Inspired by nature, engineering the HEAs with laminated structure composed of alternating soft and hard layers has the potential to strengthen the HEAs while maintaining the ductility. Here, taking the Al_xCrMnFeCoNi HEA as the model material, the laminated HEAs composed by soft and hard layers were successfully prepared by laser additive manufacturing (LAM). The soft and hard laminated layers were achieved through tailoring the Al content. In several combinations of hard and soft, the strength of Al₁₀–Al₁₂ was significantly higher than that of Al₁₂ HEA, indicating that an appropriate soft and hard matching can indeed further strengthen the HEA compared with the homogeneous HEA.

It is well known that the types of automotive corrosion can be divided into perforation and cosmetic corrosion. Although many studies concerning the mechanism of perforation corrosion have been conducted so far, very few have investigated the mechanism of cosmetic corrosion. In our previous work, the authors found that the initial corrosion behavior in cosmetic corrosion consists of three steps by conducting in-situ observation during a cyclic corrosion test. In the present work, in-situ observation of painted samples with a scratch was performed during an exposure test in Okinawa to examine the cosmetic corrosion behavior under an actual environment. It was found that corrosion started at the moment of salt deposition around the scribed part from air containing salts, and the initial corrosion behavior in the exposure test consisted of three steps, which were the same as in the cyclic corrosion test. In the 1st step, black rust of Fe₃O₄ formed at the scribed part, and in the 2nd step, under-film corrosion progressed from the scribed part where the black rust had formed. In the 3rd step, the tip of the under-film corrosion displayed swelling behavior. The behavior of each step was also discussed by combining the in-situ observation results with an analysis of environmental factors such as relative humidity and an EPMA analysis.

This Paper was Originally Published in Japanese in Zairyo-to-Kankyo 70 (2021) 18–27. The captions of Figs. 3, 4, 5, 6, 7, 12 and 13 are slightly modified.

This work investigated the Microstructure and corrosion behavior of wire arc additive manufactured Ti–6Al–xV (x = 0, 2, 4 mass%) alloys with varying vanadium content. It was found that Ti–6Al with pure α phase showed irregular plate-like grains, which was distinct from the grains obtained in α + β alloys. Vanadium additions in the Ti–6Al–xV alloys promoted the formation of martensitic phase. The width of lamellae decreased and the size of prior β grains, the β phase content increased with the increase of Vanadium content. Electrochemical results suggested that Ti–6Al alloy possessed higher corrosion resistance than Ti–6Al–4V. The difference in corrosion behavior could be attributed to grain size and orientation and phase distribution.

This study achieves an increase in Pd concentration on the surface of Ti–Pd alloys using hydrogen peroxide as a green dealloying method, as well as determining the effect of Pd on the hydrogenation of the Ti–Pd alloys. Spontaneous oxidation of Ti in Ti–Pd alloys has been reported to precipitate low-valent Pd on the surface, which can be used for fast δ-TiH₂ formation and as a catalyst for various organic reactions. On the other hand, spontaneous oxidation has limited potential to increase the surface Pd concentration. As most of the Pd remains in the metallic phase, there is a need to increase the utilization of the remaining Pd. H₂O₂ is known to be a green oxidant and also forms complexes with Ti, therefore surface Pd enrichment by dealloying is expected. This study was carried out to investigate the relationship between hydrogenation and surface properties of Ti–Pd alloys by H₂O₂ immersion. The increase in the thickness of Ti oxide layers and the increase in Pd concentration on Ti–Pd alloys were found by H₂O₂ immersion. Model experiments on chip-like specimens showed that the Ti oxide layer retards hydrogen diffusion, while the Pd on the surface has the effect of increasing the hydrogen supply to the metallic phase. Pd on the surface was also found to have an effect on the fast decomposition of H₂O₂. These results indicate that H₂O₂ immersion is effective as a surface treatment to increase the Pd concentration on the surface with reduced Ti dissolution.

Solid electrolytes with high Li⁺ conductivity and excellent electrochemical stability are required for the realization of all-solid-state lithium-ion batteries. In this study, LiCsF₂, which has been proposed to possess a wide electrochemical stability window, was fabricated and its ion-conduction properties were investigated. LiCsF₂ and Mg²⁺–LiCsF₂ were fabricated via ball milling. The dissolution of MgF₂ in LiCsF₂ via variation of the lattice parameters of LiCsF₂ was suggested. The conductivity of LiCsF₂ was of the order of 10⁻⁸ S/cm at room temperature, and the activation energy for ion conduction was estimated as 1.3 eV. Li deposition/dissolution currents were not clearly observed in the cyclic voltammetry (CV) curves of Mg²⁺–LiCsF₂. The conductivity of Mg²⁺–LiCsF₂ significantly increased upon increasing the relative humidity of the measurement atmosphere. Based on the voltage variation in the water vapor concentration cell, it was concluded that the major conduction carrier in Mg²⁺–LiCsF₂ after exposure to moisture was H⁺.

The effect of corrosion status of zinc coating on the hydrogen absorption behavior was investigated. Dry-wet corrosion test was conducted after applying NaCl solution to the zinc coated steel sheets. The permeating hydrogen during the corrosion test was measured by electrochemical technique. It was found that the hydrogen permeation was not observed at early stage of corrosion while significant hydrogen permeation was observed at middle stage of corrosion. Then, the hydrogen permeation decreased gradually at later stage of corrosion. In order to clarify the mechanism of this behavior, surface morphologies of corroded specimens were analyzed by Electron Probe Micro Analyzer. It was found that the hydrogen permeation was observed when the steel substrate was partially appeared, indicating that galvanic corrosion is related to the hydrogen permeation.

This Paper was Originally Published in Japanese in Zairyo-to-Kankyo 71 (2022) 218–224. The description of the second eq. (1) is slightly modified.

In former studied, authors have already succeeded to get chill-free spheroidal graphite iron castings of φ35 × t5.4 mm indicator sample and automobile knuckle, using permanent mold in as-cast condition. The process of melting, molten treatment and pouring were theoretically designed considering both the reduction and increase of free nitrogen (N_F), but it was not analytically proved by actual data yet. In this study, the amount of N_F was analyzed using chill samples, which were taken at critical points like melting and molten treatment. As the results, the processes which reduce and increase N_F were made clear. The increasing N_F was occurred on the process during heating up, carbon addition and temperature slightly increased at near the T_EC. The decreasing N_F was occurred the process of alloy addition, during super-heating and temperature decreased at under the T_EC. Furthermore, as the amount of molten metal decarburization increased, the variation of N_F changed from adsorption to denitrification.

Open-channel aluminum with directional holes is fabricated by extraction of stainless steel wires coated with release agent, boron nitride, which are embedded in solidified aluminum. In order to extract the wires from aluminum, tensile force is necessary. If a number of wires can be extracted simultaneously, the production of open-channel aluminum with many holes becomes feasible. Smaller extraction force is desirable to fabricate open-channel aluminum with holes as many as possible. It was found that the extraction force decreases remarkably by adding magnesium hydride to boron nitride because of forming porous layers between the wires and aluminum during melting of aluminum. Besides, the extraction force is also investigated as functions of diameter and length of stainless steel wires, which decreases with decreasing diameter and length of the template wires. The results show that small contact area of the wire to aluminum results in smaller extraction force, which is attributed to decrease in friction force of the wires to aluminum.

A neural network-based approach is proposed to minimize the maximum axial stress in the powder forming process. The finite element analysis was conducted using a MATLAB code and an ABAQUS python script to generate observations for the neural network training procedure. Powders of three different particle size distributions were mixed, and the mixture fractions were considered as control parameters. The artificial neural network determined the relationship between parameters and objective function. The effect of mixture fractions on maximum axial stress was analyzed. The results showed that the genetic algorithm could effectively determine the optima and the proposed method had strong prediction capability and accuracy.

Extruded profiles of Al–Mg–Si alloys are typically used in automotive applications. In this study, the microstructure of 6000-series alloys was improved in terms of the energy absorption property (bendability) using the shear stress and flow velocity generated during extrusion instead of conventional transition-metal alloying, because the latter presents challenges in reuse and recycling. This was accomplished using dies with different numbers of feeder holes. Furthermore, in a novel step, complementary finite element analysis (FEA) was conducted to investigate the effects of this improvement on microstructure strengthening. FEA results indicated that the profile obtained using the 4-hole die had lower internal shear stress distribution and aluminum flow velocity than using the 5-hole die. Cross-sectional electron backscatter diffraction observations revealed that the microstructure of the profile obtained using the 4-hole die had fine crystal grains and a strong internal cube or Goss preferential orientation, whereas that obtained using the 5-hole die exhibited coarse grains and an increased number of intermediate orientations. Consequently, the profile obtained using the 4-hole die exhibited improved bendability; furthermore, this die maintained the same tensile strength as the other specimen. Reducing the processing shear stress and flow velocity during extrusion allowed grain refinement and improved bendability at the same tensile strength.

In recent years, to reduce manufacturing costs and alleviate the rare-earth supply/demand imbalance in the Nd–Fe–B magnet market, researchers have actively pursued the development of (Nd,Ce)–Fe–B magnets, in which Nd is replaced by Ce. In the present study, we focused on magnetic powders treated by the hydrogenation–disproportionation–desorption–recombination (HDDR) process and explored the relationship between the hydrogen pressure and temperature (P_H2–T curves) in the Ce–Fe–B system, which is essential for the development of (Nd,Ce)–Fe–B magnets. It was confirmed that the disproportionation and recombination reactions of both Ce₂Fe₁₄B and CeFe₂ take place in the Ce–Fe–B system. Furthermore, compared with Nd₂Fe₁₄B, the P_H2–T curve of Ce₂Fe₁₄B was found to be shifted to higher pressure and lower temperature, suggesting a corresponding shift in the HDDR conditions under which good magnetic properties can be obtained.

A Sn–58Bi (SB)/Sn–3Ag–0.5Cu (SAC) composite solder was developed to overcome the challenges, e.g., the low ductility, deterioration of bonding properties and joint reliability, associated with SB eutectic solder and enhance its mechanical bonding properties. Specifically, four types of SB/SAC composite solder samples with different SB/SAC mixing ratios (100:0, 50:50, 20:80, and 0:100) were formulated. Two types of mechanical property investigations, i.e., ball shear and microhardness tests, were conducted to explore the influence of the SB/SAC mixing ratios on the mechanical properties of SB/SAC composite solder joints. The results indicated that the mechanical properties of the joint that containing both SB and SAC were superior to that with only SB or SAC. Furthermore, the mechanical properties of SB/SAC composite solder joint increased linearly with increasing SAC content. This improvement was attributable to the precipitation hardening and dispersion strengthening induced by the presence of fine intermetallic compounds and Bi-rich phase particles dispersed in the SB/SAC composite solder joint.