The mechanical behaviour of materials, including plastic deformation and fracture, is a key issue that is directly related to the strength and safety of mechanical structures. This paper reviews historic research on crack and dislocation theories, focusing on the pioneering contributions of Alan Arnold Griffith, Sir. Geoffrey Ingram Taylor, Keiji Yamaguchi and George Rankine Irwin during the early to mid-20th century. Particular attention is paid to Taylor’s work, highlighting the close relationship between dislocation and crack theories, and their significance in the interdisciplinary field of materials science and solid mechanics.

This Paper was Originally Published in Japanese in J. Jpn. Soc. Heat Treatment 64 (2024) 78–84. The title, main text and caption of Fig. 3 have been slightly modified.

The process of severe plastic deformation under high pressure through high-pressure torsion (HPT) was applied to an Al-Mg-Si alloy containing excess Fe and Si, which was designed as a model alloy for aluminum recycling. It was shown that the tensile strength exceeded 500 MPa with a total elongation to failure more than 20% after HPT processing under 2 GPa for 1 revolution. Microstructure observation was carried out using transmission electron microscopy for grain size and dislocations. Three dimensional image analyses were also carried out using high-energy X-rays in SPring 8 of JASRI for pores and intermetallic particles. Strain rate change tests were further performed for the evaluation of strain rate sensitivity (m). It was found that the m value increases with the imposed strain (the number of HPT revolution). This increase in the m value is attributed to a significant decrease in the activation volume through a reduction in mobile dislocation segments and/or their gliding distances along with the reduction in the grain size to the submicrometer range.

This Paper was Originally Published in Japanese in J. JILM 75 (2025) 464–470.

Two types of low-carbon steels with different Al contents were used, and low-oxygen weld metals with an oxygen content of 10 ppm were fabricated. Bead-on-plate welding experiments were performed with a tungsten-inert-gas welding system and subsequent water cooling using a welding nozzle that prevents oxygen from entering the molten pool with a double shielding gas. The effect of Al content on the composition of inclusions that act as the starting point for acicular ferrite formation in the early and late stages of the austenite-to-ferrite transformation during cooling after welding was clarified. Optical micrographs and images obtained by a scanning electron microscope equipped with an energy dispersive X-ray spectroscopy detector showed that acicular ferrite formed within austenite grains on inclusions with a chemical composition and size that were considered to be ineffective for acicular ferrite formation in low-Al steel. This suggests that in low-oxygen region, Al uniformly dissolved in the austenite grains has a large effect on the formation of acicular ferrite.

This Paper was Originally Published in Japanese in J. Soc. Mater. Sci., Japan 74 (2025) 387–393.

α+β dual phase Ti-(0∼6 wt.%) Fe alloys were prepared via sintering and hot rolling process to clarify the effects of Fe contents and the rolling temperature on their microstructures and crystalline orientation. With an increase in the Fe content, the volumetric fraction of the β-Ti phase, which contains high Fe solutes, drastically increased. When hot rolled at 750°C (α+β dual-phase temperature), each phase grew immediately after rolling and suppressed each other’s grain growth, resulting in fine microstructure formation and uniform residual strain. In Ti-Fe alloys rolled at 1000°C (single β-phase temperature), a very small amount of residual strain was observed, and acicular α-Ti grains with random crystalline orientations were formed due to the phase transformation from β-Ti grains after rolling.

This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 71 (2024) 510–516, https://doi.org/10.2497/jjspm.23-00078.

The effect of initial texture on the formation of deformation twins and its impact on the final heterogeneous nano-structure (HN-structure) and mechanical properties of a Cu-Zn-Sn alloy with an extremely low stacking fault energy during cold rolling were systematically investigated. Specimens with an accumulation of 〈111〉 along the normal direction (ND) were prepared and cold-rolled up to 90% reduction in thickness. Two different rolling directions (RD) were applied: one with a high accumulation of 〈211〉 along RD (211 specimen) and another with a 〈110〉 orientation (110 specimen). The 211 specimens exhibited higher volume fractions of twinned grains in the early stages of rolling (∼50% reduction) than the 110 specimens. In the later stage of rolling (60∼90% reduction), the HN-structure consisting of deformation twin domains, lamellar grains and shear bands was well developed in both specimens. However, the 〈211〉 specimen exhibited a higher fraction of twin domains with {111}〈211〉 orientation, whereas the 〈110〉 specimen contained more {111}〈110〉 twin domains. The highest strength-ductility balance was achieved at an 80% reduction, with the 211 specimen exhibiting a higher strength-ductility balance. The higher strength of the 211 specimen is attributed to the higher fraction of {111}〈211〉 twin domains, which offer greater resistance to plastic deformation compared to {111}〈110〉 twin domains.

This Paper was Originally Published in Japanese in the J. Japan Inst. Copper 64 (2025) 13–19.

The microstructure and mechanical properties of Ti-Al-Ni-Cu-Si alloys were evaluated, and the effects of the addition of Ni, Cu, and Si were investigated. Microstructural analysis revealed that the alloy consists of two phases: the α phase and the eutectoid phase, with the precipitation of Ti2(Ni,Cu) as an intermetallic compound (which is identified by SEM and TEM analyses). Tensile tests tested at various temperatures ranging from room temperature to 700°C showed that the Ti-Al-Ni-Cu-Si alloys such as Ti-3Al-0.5Ni-0.5Cu and Ti-3Al-0.5Ni-0.5Cu-0.3Si alloys (in mass%) exhibit a higher strength at room and intermediate temperatures (∼500°C), and a lower stress at high temperatures (≥600°C) compared to conventional Ti-Al-V alloys having similar β phase stability. The results obtained in this study successfully suggest a new type of V-free Ti alloy with high strength from room temperature to 500°C and improved hot working ability (a low flow stress and a high elongation).

This Paper was Originally Published in Japanese in J. JILM 75 (2025) 156–165. The captions (a) and (b) in Fig. 6 have been added.

The creep behavior of pre-tensile strained alpha brass was investigated. The primary creep strain was increased by tensile pre-strain while secondary creep rate was little affected. Based on the stress exponent of 6.32 and the activation energy of 70.2 kJ/mol—obtained from the temperature and stress dependence of the secondary creep rate in the as-received specimen—the dominant creep mechanism was identified as either pipe diffusion-limited dislocation creep or dislocation glide hindered by forest dislocations. By combining the one-variable internal state variable model with creep model and also with back stress, it is suggested that −150 MPa of back stress can explain the increase of primary creep and similarity of secondary creep rate. The calculated results indicate that the back stress introduced by tensile pre-strain increases effective stress and thus creep strain rate in primary region. On the other hand, back stress becomes less significant in secondary region due to creep deformation.

In this research, the microstructure and tensile properties of Cu–7 mass%Al alloy in the α single-phase region and Cu–10 mass%Al alloy in the (α+γ₂) two-phase region on the phase diagram fabricated by laser powder bed fusion (PBF-LB) process and casting were systematically examined, and investigated their microstructure formation mechanism and strengthening mechanism. As a result, in the case of Cu–7 mass%Al alloy, the microfine cellular structures formed by segregation of Al due to the constitutional supercooling by rapid solidification phenomenon in PBF-LB process leaded to high tensile strength and 0.2% proof stress, which were much higher than those of the castings. On the other hand, in the case of Cu–10 mass%Al alloy, the fine β′ martensitic structure with stacking faults formed by rapid solidification phenomena results in lower proof stress and higher tensile strength than the castings. Consequently, it was revealed that the high performance of the Cu–Al alloys is attributed to unique microstructure of the alloys formed by rapid solidification phenomenon in PBF-LB process.

This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 71 (2024) 679–685.

FeB-Ni hard materials were promising alternatives to conventional cemented carbides due to their high hardness, low cost and environmental benefits. In order to optimize the densification and mechanical properties, Al was selected as a functional alloying addition. In this study, 86FeB-10Ni-4Al hard materials were prepared by ball milling and spark plasma sintering under uniaxial applied pressures of 30, 50 and 70 MPa. The effects of uniaxial applied pressures on densification, microstructures and mechanical properties were also investigated. This study demonstrated that at 1373 K for holding 0.9 ks, both apparent relative density and densification rate increased with uniaxial applied pressures. The values of apparent relative density corresponding to the maximum densification rate of the 86FeB-10Ni-4Al hard materials sintered at 30, 50 and 70 MPa were 0.67, 0.74 and 0.78, respectively, falling between those of pure FeB of 0.53 and 71Ni-29Al of 0.88. With increasing uniaxial applied pressures, the equivalent diameter of binder-binder voids decreased from 0.16 to 0.08 µm, and their spheroidization rate increased from 0.44 to 0.64. At the same time, the binder-hard voids exhibited the same trend as the binder-binder voids. The changes in equivalent void diameter and spheroidization rate further promoted densification and fracture toughness. Among them, 86FeB-10Ni-4Al hard materials sintered at 70 MPa demonstrated outstanding mechanical properties, with a hardness of 14.7 GPa and a fracture toughness of 14.5 MPa·m^1/2.

All composite materials with Al₂O₃ as the matrix, TiC as the reinforcing phase, and Ti₃SiC₂ as the lubricating phase were synthesized in this study. The composites were prepared by using the in-situ reaction of the raw powders of Ti, Si, graphite, Al and Al₂O₃ through spark sintering technology. Three peaks for both Al₂O₃-TiC-10 and 20 vol% Ti₃SiC₂, in densification rate curves corresponded to plastic deformation and power law creep deformation of Al₂O₃, Ti₃SiC₂ and TiC, respectively. The Al₂O₃-TiC-10, 20 vol%Ti₃SiC₂ compacts showed homogeneously localized Ti₃SiC₂ as a lubricating phase between the TiC and Al₂O₃ hard phases. Pin-on-disc friction and wear tests on Al₂O₃-TiC-0, 10, 20 vol%Ti₃SiC₂/ Ti-6Al-4V combinations revealed that the introduction of Ti₃SiC₂ phase could effectively improve the damage morphology of the worn surface, and the optimal wear resistance was exhibited when the content was 20 vol%. Al₂O₃-TiC-20 vol%Ti₃SiC₂ tool exhibited superior intermittent cutting performance to WC-7Co tools, particularly in terms of wear resistance and tool life. Judging from the Hv, K_IC, cutting and friction-wear properties, it may be believed that Al₂O₃-TiC-20 vol%Ti₃SiC₂ compact is replace candidate for the WC-7Co under the rare metal element strategy.

Various environmental factors (temperature, humidity, light/salt exposure, etc.) act in complex ways to degrade the corrosion protection performance of coating films. However, it is difficult to evaluate the individual and combined effects of all these factors. On the other hand, corrosion protection performance has a strong correlation with the impedance of coating films, which corresponds to the resistance to the flow of electrical charges in the coating. Therefore, the effects of light irradiation on the penetration behavior of moisture and salt into the coating films were investigated. As a result, it was found that material changes due to light irradiation accelerated the penetration of water and/or salt, thus decreasing the impedance. When water and/or salt penetrated into the coating films, a peak in the DRT (Distribution of Relaxation Times) spectrum was observed at relaxation times less than 10⁻¹ s.

This Paper was Originally Published in Japanese in Zairyo-to-Kankyo 74 (2025) 124–132.

To investigate the starting points and progression directions of ant nest corrosion, semi-immersion test was conducted using oxygen-free copper. A formic acid solution was used as the test solution. The results revealed that the starting point of pores was primarily formed at grain boundary triple junctions. Furthermore, EBSD was used to measure the crystallographic misorientation in the areas around the pits induced by ant nest corrosion. The average of crystallographic misorientation at grain boundary triple junctions was most frequently observed at 53°, followed by a peak at 45°. On the other hand, ant nest corrosion occurred most frequently at approximately 33°, which is considered to have the highest grain boundary energy. Therefore, it was clarified that the starting point of ant nest corrosion is grain boundary triple junctions with high grain boundary energy.

During the recovery of nickel from laterite ores, scandium is recovered from sulfuric acid leachates as a byproduct using an ion-exchange resin method. The efficient recovery of scandium requires the kinetic and thermodynamic behaviors of the scandium adsorption reaction to be elucidated. In general, the calculation of the standard Gibbs free energy change (ΔG°) for the adsorption of metal ions from solution onto ion exchange resins is complex. Therefore, the use of the Langmuir model to derive the equilibrium constant has been widely discussed. Calculation of the equilibrium constant, which represents the ratio of the activities of the reactants to those of the products at equilibrium, requires the determination of the activity coefficients. In this study, we performed a thermodynamic analysis of the adsorption isotherms to investigate in detail the adsorption reaction of Sc³⁺ from the sulfuric acid solution onto the chelating resin. As a portion of Sc³⁺ forms complexes with sulfate ions, we calculated the concentration and activity coefficient of uncomplexed Sc³⁺ using chemical equilibrium calculations and constructed adsorption isotherms. In this study, we fitted the Sc³⁺ adsorption isotherms using both the Langmuir model, which assumes a homogeneous surface, and several modified models that account for surface heterogeneity. Our analysis indicates that the Langmuir model accurately describes the adsorption behavior of Sc³⁺ under the experimental conditions. Based on the equilibrium constant obtained from the Langmuir adsorption isotherm and on the standard enthalpy change (ΔH°) value of approximately 30 kJ mol⁻¹ determined by using the van’t Hoff equation, we concluded that the adsorption of Sc³⁺ onto the chelating resin is an endothermic process. Our findings are expected to contribute to improving the efficiency of the recovery of scandium from leachates.

Alloys formed by laser power bed fusion (LPBF) contain high residual stress and strain due to the cyclic heating process, which decreases ductility. Therefore, many researchers have investigated heat treatments to improve ductility by removing residual stress and forming α+β phase structures. However, in this study the ductility of some heat-treated samples was found to decrease below that of as-built samples. This study investigated the heat treatment of LPBF at different temperatures to decompose α′ grains to α grains and understand the resulting microstructure and mechanical properties. Specifically, the influence of microstructural factors on ductility was examined. In the samples heat treated at 500°C, α′ was found to decompose into α with elevated strain and finer β grains, which increased yield strength at the cost of ductility. Meanwhile, in the samples heat treated at 700°C, coarser β phase was precipitated, and greater ductility was supported by the transfer of the slip deformation between α phase grains.

This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 72 (2025) 79–84.

High-entropy alloys (HEAs) have attracted attention as promising candidates for nuclear fusion reactor materials owing to their superior mechanical properties and irradiation resistance. In our previous research, we predicted the existence of metastable small vacancy cluster configurations in the TiVTaW HEA, attributed to its chemically heterogeneous atomic environment. In this study, molecular dynamics simulations were conducted on TiVTaW and its constituent pure elements (Ti, V, Ta, W) to investigate the defect behavior under cascade damage conditions. The temporal profiles of Frenkel pair counts showed distinct differences among these material systems, which can be explained by two main factors: element-specific intrinsic properties, such as thermal conductivity and displacement threshold energy, and the thermodynamic stability of defects. Notably, TiVTaW exhibited a prolonged thermal spike and generated a greater number of Frenkel pairs than the average of its constituent elements. Furthermore, the defect clusters in TiVTaW were generally smaller in size compared to those in its individual elements. This small defect cluster size can be attributed to two characteristic features of HEAs: the presence of metastable defect and defect cluster sites, and sluggish defect mobility. These findings enhance the understanding of how HEA composition influences irradiation resistance.

Outdoor exposure tests were conducted on reinforced concrete samples with cracks less than 0.1 mm in width. The corrosion behavior of the reinforcing bars was evaluated by measuring the potential difference between the two bars within each specimen and by weighing the specimens. A temporary increase and decrease in the potential difference of the reinforcing bars was observed during the outdoor exposure tests. Upon dismantling the samples, traces of reinforcing bar corrosion were confirmed. Furthermore, since the increase in potential differences progressed during periods of heavy rainfall, it is inferred that this resulted from the carbonation of the environment due to massive water ingress into the cracks, leading to de-passivation of the reinforcing bar. Conversely, the decrease in potential difference is thought to result from the re-passivation of the reinforcing bar due to the creation of an alkaline environment caused by the leaching of unhydrated cementitious components into the water retained within the cracks. These results indicate that in reinforced concrete with micro-cracks of 0.1 mm or less in width, the integrity of the reinforced concrete may be maintained through self-healing.

This study examines technologies for manufacturing aluminum components and proposes a framework for selecting appropriate manufacturing methods from a lifecycle economics perspective. Both conventional manufacturing and additive manufacturing are analyzed. Additive manufacturing can manufacture intricate geometries that are difficult to achieve using conventional methods. However, its low productivity and high cost have limited its implementation into the industry. In addition, there is no clear consensus on the environmental impact of additive manufacturing. To address these issues, we examined the hypothesis that a life cycle cost analysis, which considers environmental impact when selecting a manufacturing method, would enable users to make more reasonable decisions. The study compared the life cycle costs of manufacturing methods for power semiconductors cooling components in electric vehicles and bracket components in aircraft. The results show that GHG emissions are higher during the use phase than the manufacturing phase for both applications. Replacing conventional manufacturing with additive manufacturing can reduce overall GHG emissions. Although additive manufacturing has a higher manufacturing cost compared to conventional manufacturing, the life cycle cost analysis reveals an economic advantage in replacing conventional manufacturing with additive manufacturing in aircraft engine brackets when running costs and carbon pricing are taken into consideration.

This Paper was Originally Published in J. Jpn. Soc. Powder Powder Metallurgy 71 (2024) 649–659. The citation Fig. 1 is modified. Figures 5, 6 are corrected. Figure 7 is slightly modified.

Nickel electrodeposited films with a black appearance were produced by adding nitrate ions to a nickel sulfate (Watt’s) bath. The blackening of the deposited films was attributed to both the formation of a Ni₂O₃ layer on their surface and the refinement of their structure. The addition of nitrate ions increased the pH in the vicinity of the cathode through their reduction reaction, thereby promoting the formation of nickel hydroxide. This hydroxide suppressed Ni²⁺ diffusion during Ni deposition and induced refinement of the deposited films.

This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 89 (2025) 322–326.