MATERIALS TRANSACTIONS
Online ISSN : 1347-5320
Print ISSN : 1345-9678
ISSN-L : 1345-9678
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Displaying 1-14 of 14 articles from this issue
Overview
  • Hiroyuki Iwata, Hiroyasu Saka
    Article type: Overview
    2024 Volume 65 Issue 7 Pages 711-722
    Published: July 01, 2024
    Released on J-STAGE: June 25, 2024
    Advance online publication: April 26, 2024
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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.

    Fig. 20 Giant pseudo Frenkel pair. Upper part is reproduced with permission from Ref. [10]. Fullsize Image
Regular Article
Materials Physics
  • Shinya Kudo, Akihiko Hirata
    Article type: Regular Article
    2024 Volume 65 Issue 7 Pages 723-727
    Published: July 01, 2024
    Released on J-STAGE: June 25, 2024
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    The atomic configurations of the quasicrystal-forming ternary Zr70Cu29Pt1 metallic glass were calculated by the combination of classical molecular dynamics (MD) and ab-initio MD simulations. The binary Zr70Cu30 was prepared by classical MD and then Pt atoms were inserted into the large voids of Zr70Cu30, followed by relaxation using ab-initio MD. The coordination number of Pt atoms increased due to relaxation and reached a level comparable to that of Cu. The obtained structural model of Zr70Cu29Pt1 was analyzed by Voronoi polyhedral analysis modified especially for shell structures. We then compared Pt-centered polyhedra and Bergman-type atomic clusters formed in quasicrystals. The combined method of classical and ab-initio MD simulations is effective for the construction of the complicated structural models for glassy materials.

Microstructure of Materials
  • Bum-Soon Park, Hyoung-Seok Moon, Hyun-Kuk Park
    Article type: Regular Article
    2024 Volume 65 Issue 7 Pages 728-735
    Published: July 01, 2024
    Released on J-STAGE: June 25, 2024
    Advance online publication: April 19, 2024
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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 Fe0.99Nb0.01 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.

  • Ryo Tsukane, Kazuhiro Matsugi, Yong-Bum Choi, Hiroyasu Tamai
    Article type: Regular Article
    2024 Volume 65 Issue 7 Pages 736-743
    Published: July 01, 2024
    Released on J-STAGE: June 25, 2024
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    In this study, a TiC–Ti composite has been synthesized as a novel cermet without using rare elements like W, Co, and Ni. The mechanical properties of the prepared TiC–Ti composite are improved by utilizing Ti and C powders as raw materials in the mechanical alloying process. The effects of the non-equilibrium state during mechanical alloying on the characteristics of the composite have been analyzed. The results indicate that for short milling times, the addition of 25 mol% of C results in the Ti phase size in the sintered compact typically being on the order of several tens of micrometers, and unreacted C remains in the sample. A milling time of ≥21.6 ks affords a TiC–Ti composite containing approximately 80% fine TiC phase with an average size of 1–2 µm. As the milling progresses, the crystalline size of the Ti phase decreases, while the lattice strain increases. Prolonged milling improves the diffusion of C into Ti; a milling time of 36 ks at a low temperature of ∼700 K results in the formation of TiC as well as uniform diffusion of C throughout the Ti phase. Sintering the composite powder milled for 36 ks affords a Vickers hardness of approximately 700 Hv, which is similar to that of a TiC-35% Ni cermet.

    Fig. 10 Schematic of the microstructure evolution during the sintering of the powders milled for (a) short time (3.6 ks) and (b) long times (21.6 and 36 ks). Fullsize Image
Mechanics of Materials
  • Xuanyi Shao, Moriaki Ogido, Taiki Nakata, Bui Phuong Thao, Nan Zhang, ...
    Article type: Regular Article
    2024 Volume 65 Issue 7 Pages 744-753
    Published: July 01, 2024
    Released on J-STAGE: June 25, 2024
    Advance online publication: April 26, 2024
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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.

  • Masahito Omiya, Yohei Sakakibara
    Article type: Regular Article
    2024 Volume 65 Issue 7 Pages 754-762
    Published: July 01, 2024
    Released on J-STAGE: June 25, 2024
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    This study was aimed at examining the effect of the number of grains (representing the total measurement area) on the statistical variation of the area average of the kernel average orientation (KAM), denoted as KAMA, ave, as determined through electron backscatter diffraction (EBSD). Moreover, the number of triple junctions required to obtain statistically valid results was investigated. The results indicated that at least 80–100 grains should be evaluated to reduce the statistical dispersion in plastic-strain evaluation using KAMA, ave. The average triple junction KAM (KAMTJ, ave) values near the random boundary tend to be higher than those near coincident site lattice (CSL) boundaries. There was a correlation between plastic strain and average triple-junction KAM (KAMTJ, ave). This study highlights that KAMTJ is useful parameters for evaluating plastic strain around the triple junctions.

  • Hiroyuki Toda, Hiro Fujihara, Kyosuke Hirayama, Kazuyuki Shimizu, Yafe ...
    Article type: Regular Article
    2024 Volume 65 Issue 7 Pages 763-772
    Published: July 01, 2024
    Released on J-STAGE: June 25, 2024
    Advance online publication: May 10, 2024
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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.

  • Fumiyoshi Yoshinaka, Nobuo Nagashima, Takahiro Sawaguchi
    Article type: Regular Article
    2024 Volume 65 Issue 7 Pages 773-779
    Published: July 01, 2024
    Released on J-STAGE: June 25, 2024
    Advance online publication: April 26, 2024
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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., ΔGγ→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, ΔGγ→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 ΔGγ→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.

    Fig. 1 Relationship between the total strain amplitude and fatigue life. Fullsize Image
Materials Chemistry
  • Yoshiharu Murase, Hideki Katayama
    Article type: Regular Article
    2024 Volume 65 Issue 7 Pages 780-789
    Published: July 01, 2024
    Released on J-STAGE: June 25, 2024
    Advance online publication: April 19, 2024
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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.

  • Qi Kong, Yasushi Shibuta
    Article type: Regular Article
    2024 Volume 65 Issue 7 Pages 790-797
    Published: July 01, 2024
    Released on J-STAGE: June 25, 2024
    Advance online publication: May 13, 2024
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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.

Materials Processing
  • Heng Li, Kai Xu, Yuerong Qian, Wenchao Shi, Xiaoyong Zhu, Yucheng Wu
    Article type: Regular Article
    2024 Volume 65 Issue 7 Pages 798-804
    Published: July 01, 2024
    Released on J-STAGE: June 25, 2024
    Advance online publication: April 12, 2024
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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.

    Fig. 1 Process flow and parameter chart. Fullsize Image
Engineering Materials and Their Applications
  • Yuji Okada, Kohei Ikeno, Yoshihiro Terada
    Article type: Regular Article
    2024 Volume 65 Issue 7 Pages 805-809
    Published: July 01, 2024
    Released on J-STAGE: June 25, 2024
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    The binary Mg–14Ca (mass%) hypoeutectic alloy exhibits a fine lamellar structure of α-Mg and C14 (Mg2Ca) phases with the lamellar spacing of 0.9 µm, together with a small amount of the primary α-Mg phase. Tensile creep tests were conducted for the alloy at temperatures between 473–523 K and stresses between 30–50 MPa. The overall creep rate vs. time in a log–log diagram for the alloy shows a downward curvature from stress application until creep rupture. A well-defined steady-state is barely evident. The decrease in the creep rate during the transient stage is emphasized at lower temperatures and lower stresses. The coarse lamellar structure with the lamellar spacing between 1.5–2.5 µm is evident at colony boundaries during the accelerating creep stage. It is found that the stress exponent of the minimum creep rate, n, is 7, and the activation energy for creep, Qc, is 146 kJ/mol. The value of Qc is close to that for the lattice self-diffusion of magnesium (136 kJ/mol). It is deduced that the creep for the alloy is controlled by dislocation climb.

     

    This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 88 (2024) 53–57.

    Fig. 5 FE-SEM image of the Mg–14Ca alloy creep-ruptured at 498 K under a stress of 40 MPa. The rupture life is 180 h (6.5 × 105 s). Fullsize Image
  • Dang Tuyen Nguyen, Thi Hong Nhung Nguyen, Quoc Hoan Tran, Thanh Tung D ...
    Article type: Regular Article
    2024 Volume 65 Issue 7 Pages 810-816
    Published: July 01, 2024
    Released on J-STAGE: June 25, 2024
    Advance online publication: April 19, 2024
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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.

Environment
  • Hiroshi Ogasawara, Yoshihiro Mima, Akimasa Ishida, Siyanda Mngadi, Mit ...
    Article type: Regular Article
    2024 Volume 65 Issue 7 Pages 817-823
    Published: July 01, 2024
    Released on J-STAGE: June 25, 2024
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    It is difficult to implement routine mine-wide programs to measure absolute stress in deep and over-stressed mines because the drilled holes and cores are often damaged during and immediately following the drilling. We evaluated the use of the Diametrical Core Deformation Analysis (DCDA) method, developed by Funato and Ito, to overcome this problem. This non-destructive method can evaluate the absolute shear stresses and measurement errors in the planes orthogonal to the core axes by precisely measuring the ellipticity of the core section orthogonal to the borehole axis. The five readings required to evaluate a single core take only about ten minutes to make. The measurement system is compact enough for a single regular courier parcel or can be checked-in as luggage on a flight. Absolute shear stresses were determined for thirty-five core specimens from fourteen holes drilled in a range of directions in the highly stressed rock mass surrounding a deep South African gold mine. Using the DCDA method we were able to determine the absolute 3D shear stress field averaged over an area of interest. It was consistent with the 3D stress field measured in-situ with an overcoring method, with the maximum principal stress larger than 100 MPa, with a root mean square of residuals of several MPa. Interestingly, the results represent relaxation in shear stress near the fault intersected by the boreholes. The DCDA measurements require a core diameter larger than approximately 40 mm, and a core that is longer than approximately 10 cm. The method assumes that there is no significant inelastic deformation and that the rock is isotropic.

     

    This Paper was Originally Published in Japanese in J. Soc. Mater. Sci., Japan 71 (2022) 259–265. All contexts are identical to those published in Japanese, except for (1) the use of “absolute shear stress” with additional explanation instead of “absolute differential stress”, which has the same physical meaning, to avoid the inconsistency of “absolute differential”; (2) the use of Fig. 29 of Tucker et al. instead of Fig. 1 of our paper to better illustrate drilling in mines; and (3) the citation of Funato (2021), the co-author’s latest report, in a summary section. Acknowledgement is added.

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