Best Papers Awarded in 2023 in Materials Transactions

Zenji Horita

doi:10.2320/matertrans.MT-M2024076

Abstract

The Japan Institute of Metals and Materials (JIMM) awarded the nine best papers in 2023 presenting cutting edge research. Here, we introduce brief summaries of the awarded papers as current trends in research of Materials Transactions. Among the nine best papers, four were specially selected for young scientists whose ages are 35 or below. The awarded papers cover a wide range of metals and materials such as magnesium-based, aluminum-based and titanium-based alloys including high-entropy alloys, SUS304 stainless steel, Si/solder/Si joints and fine copper powder. In association with all the awarded papers, special issues edited in Materials Transactions are also briefly introduced to show the recent activities of Materials Transactions.

1. Introduction

In 2023, the nine best papers were awarded by The Japan Institute of Metals and Materials (JIMM) from the papers published in 2022 in Materials Transactions [1–9]. Such highly evaluated papers are then introduced as a current trend in research in Materials Transactions. Since 2020, we have announced the awarded papers [10–13] and, in particular, the announcement in 2023 was not only for the papers awarded by JIMM [14–21] but also by The Japan Institute of Light Metals (JILM) [22–24] and The Japan Society for Technology of Plasticity (JSTP) [25–27]. All the awarded papers are based on cutting edge research fulfilling one or more of the following requirements: (a) sufficient originality, (b) highly influential (good potential for significant research advancement), (c) solving long-term problem and (d) being far ahead of others for the evaluation by JIMM together with (e) enormous contribution to application development for the evaluation by JILM. The selection committees of JIMM carefully evaluated the papers recommended by referees of reviewing processes, editorial members of Materials Transactions and board members of the Japan Institute of Metals and Materials including authors’ self-recommendation. Each paper was rigorously scored by about 10 members of the award selection committee representing either of the following six research areas: (1) materials physics, (2) microstructures of materials, (3) mechanics of materials, (4) materials chemistry, (5) materials processing, and (6) engineering materials and their applications. In this year, four out of the nine best papers are for young scientists under age of 35 [6–9] with the encouragement of their future research activity. It is noted that one of the young scientist best paper awards [9] was originally published in Japanese in Journal of The Japan Institute of Metals and Materials [28] and translated to English following the rule of Materials Transactions. Here, we introduce the nine awarded papers below [1–9, 28] with brief summaries provided by the corresponding authors.

2. “Advanced Mg-Al-Ca Alloys with Combined Properties of High Thermal Conductivity, High Mechanical Strength and Non-Flammability” by Yoshihito Kawamura, Kazuki Ougi, Shin-ichi Inoue, Takanori Kiguchi, Makoto Takafuji, Hirotaka Ihara and Donald S. Shih (Vol. 63, No. 2 (2022) pp. 118–127) [1]

In the realm of 3C (computer, communication, and consumer electronics) products, the demand for heightened heat dissipation capabilities and steadfast resistance to fire and explosions has become increasingly urgent [29]. Consequently, the need for lightweight Mg alloys capable of concurrently delivering high thermal conductivity, mechanical strength, and non-flammability has surged. Historically, Mg alloys with substantial strength and thermal conductivity have been achieved through the extrusion of diluted alloy compositions, such as Mg-Zn-Mn, Mg-Zn-Zr, Mg-Zn-Cu-Zr, Mg-Zn-Ca-Zr, Mg-Mn, and Mg-Mn-Ce, albeit with a significant drawback – their susceptibility to combustion [30–33].

We have pioneered the development of Mg-Al-Ca-based alloys possessing noteworthy thermal conductivity, impressive strength, and resistance to combustion, through the hot extrusion of heat-treated cast materials enriched with additional elements exceeding 6 atomic percent. These innovative alloys have demonstrated an outstanding performance profile, boasting a thermal conductivity ranging from 111 to 119 Wm⁻¹K⁻¹, a tensile yield strength of 318 to 363 MPa, and an exceptional resistance to combustion, characterized by a high ignition temperature of 1343 to 1408 K (Fig. 1). The microstructure of these alloys is composed of α-Mg, eutectic C36 and C14 compounds, alongside precipitated C15 compounds exhibiting incoherent interfaces with the α-Mg matrix. The augmentation of thermal conductivity is primarily attributed to the purification of the α-Mg matrix, facilitated by the precipitation of C15 Al₂Ca nano-plates during the heat treatment process. Superior mechanical properties are linked to the grain structure refinement within the α-Mg phase and the uniform dispersion of fine compounds. The remarkable non-flammability of these alloys is attributed to the presence of substantial quantities of Ca and Be, which serve to elevate the ignition temperature [34, 35].

Fig. 1

Comparison of the thermal conductivity and tensile yield strength of the extruded Mg-(x+2)Al-xCa alloys (HT/WC+Ex and HT/FC+Ex) having non-flammability, with various wrought Mg alloys having high thermal conductivity [30–33].

Our work challenges the conventional belief that achieving high strength, exceptional thermal conductivity, and non-flammability in Mg alloys is a daunting task, fostering anticipation for future developments in this domain.

3. “Preferential Dynamic Grain Growth Mechanism Enabling the Control of Microstructure and Texture by High Temperature Deformation: Experimental Evidence and Applicability” by Hiroshi Fukutomi, Kazuto Okayasu, Yusuke Onuki, Makoto Hasegawa, Equo Kobayashi, Bohumir Strnadel and Osamu Umezawa (Vol. 63, No. 2 (2022) pp. 148–156) [2]

The relationship between the mechanism of high temperature deformation and the evolution behavior of the texture and microstructure during deformation of solid solution alloys is clarified. The authors showed that the preferential dynamic grain growth (PDGG) mechanism proposed by the authors [36] can explain the behavior of microstructure change as well as texture change of all studied alloys without exceptions. The essential of the PDGG mechanism is the preferential growth of crystal grains with the orientation stable for deformation and with low Taylor factor in the given deformation mode during high temperature deformation. Physical meaning of Taylor factor is elucidated theoretically: Taylor factor corresponds to the density of uniformly distributed dislocations and hence to the stored energy during the high temperature deformation of solid solution alloys when viscous glide of dislocations is the rate controlling process.

It has been well known that recrystallization texture appears after the recrystallization of cold worked metals and alloys. Although many researches have been conducted in order to elucidate the formation mechanism of recrystallization texture, the mechanism is still not clarified enough. Thus, it has not been possible yet to predict the recrystallization texture. However, the PDGG mechanism can give the prediction irrespective of deformation modes.

In Fig. 2 the texture of Fe-3.0 mass%Si after high temperature plane strain compression is given. At room temperature deformation, usual deformation texture consisting of α and γ fiber components were seen. However, in Fig. 1, γ fiber disappears and the development of {001} ⟨110⟩ is seen, in accordance with the PDGG mechanism. Many experimental results supporting the PDGG mechanism have been reported by the authors [37, 38].

Fig. 2

φ₂ = 45° section showing the orientation distribution after plane strain compression deformation of Fe–3.0 mass%Si at 1173 K with a strain rate of 5.0 × 10⁻⁴ s⁻¹ up to −1.0 in true strain. Formation of {001}⟨110⟩ texture is confirmed, which corresponds with the prediction by the PDGG mechanism.

Because of the importance of the applicability, the possibility of the occurrence of the PDGG mechanism in materials other than solid solution alloys is discussed.

4. “Ultra-High Mixing Entropy Alloys with Single bcc, hcp, or fcc Structure in Co–Cr–V–Fe–X (X = Al, Ru, or Ni) Systems Designed with Structure-Dependent Mixing Entropy and Mixing Enthalpy of Constituent Binary Equiatomic Alloys” by Akira Takeuchi, Takeshi Wada, Takeshi Nagase and Kenji Amiya (Vol. 63, No. 6 (2022) pp. 835–844) [3]

The present study focuses on the entropy of mixing (S_mix), configuration (S_config), and equivalent ideal (S_ideal) of high-entropy alloys (HEAs). Specifically, Co–Cr–V–Fe–(Al, Ru, or Ni) systems [39] were studied to investigate the possibility of non-equiatomic high-entropy alloys (HEAs) that satisfy S_mix > S_config = S_ideal. Three Co₂₀Cr₂₀Fe₂₀V₁₀X₃₀ (X = Al, Ru, or Ni) alloys (referred to as Al₃₀, Ru₃₀, and Ni₃₀ alloys) were studied using conventional arc melting and subsequent annealing. The X-ray diffraction profiles revealed that the Al₃₀, Ru₃₀, and Ni₃₀ alloys annealed at 1600 K for 1 h exhibited B2 ordered, hcp, and fcc structures, respectively. A single structure was verified by scanning electron microscopy observations combined with elemental mapping via energy-dispersive X-ray spectroscopy. As demonstrated in Fig. 3, thermodynamic calculations of S_mix normalized by the gas constant (S_mix/R) revealed that Al₃₀, Ru₃₀, and Ni₃₀ alloys at 1600 K had S_mix/R = 0.833, 1.640, and 1.618, respectively, where the latter two alloys exceeded S_config/R = 1.557. A compositionally optimized Al-containing HEA for S_mix with a single bcc structure was computationally predicted and verified experimentally for the Al₆Co₂₇Cr₃₄Fe₁₉V₁₄ alloy (Al₆ alloy). The non-equiatomic Al₆ alloy with S_config/R = 1.480 exhibited S_mix/R of 1.703 at 1600 K, surpassing S_config/R = ln 5 = 1.609 for the exact equiatomic (EE) quinary alloy. The bcc Al₆, hcp Ru₃₀, and fcc Ni₃₀ alloys were regarded as ultra-high mixing entropy alloys (UHMixEAs) according to S_mix > S_config. Structure-dependent S_mix and the mixing enthalpy of constituent binary EE alloys are useful for future UHMixEAs as a subset of HEAs. The present paper is significant in clarifying the effect of magnetic entropy on the S_mix. This study was a continuation of previous research on hcp-Fe₁₂Ir₂₀Re₂₀Rh₂₀Ru₂₈ UHMixEA [40], and contributed to opening the door for further development of hcp-UHMixEAs [41] of Fe₂₀Mo₂₀Ni₂₀Rh₂₀Ru₂₀ [41] and Fe₁₄Mo₃₅Ni₁₅Rh₁₅Ru₂₁ [41].

Fig. 3

(a) Normalized S_mix/R calculated using Thermo-Calc 2021a and the TCHEA4 database for the Al₆, Al₃₀, Ru₃₀, and Ni₃₀ alloys of bcc, B2, hcp, and fcc structures, respectively. Specific heat at constant pressure (C_p) of Co in the (b) bcc, and (c) hcp and fcc structures.

5. “Crack Tip Deformation during Dwell Fatigue and Its Correlation with Crack/Fracture Surface Morphologies in a Bi-Modal Ti–6Al–4V Alloy” by Yuma Aoki, Motomichi Koyama, Masaki Tanaka and Kaneaki Tsuzaki (Vol. 63, No. 9 (2022) pp. 1232–1241) [4]

Because Ti alloys exhibit creep deformation even at room temperature, the load holding enhances plastic strain evolution; this promotes fatigue failure [42]. Load-holding-assisted fatigue is referred to as dwell fatigue [43]. For fatigue crack propagation, crack tip plasticity is fundamental in understanding the underlying mechanism. As an example of crack tip plasticity, Wang et al. [44] conducted in-situ microstructural strain mapping during displacement holding at room temperature in a fatigue-cracked Ti–6Al–4V alloy, which indicated strain evolution around the crack tip immediately after the holding and continuously progressed with time. Thus, a correlation is necessitated between the four features of crack tip plasticity during dwell fatigue, which are: (1) the crack tip microstructure, (2) crack propagation mode, (3) microstructure-scale strain evolution at the crack tip, and (4) temporal change of the strain under a constant load/displacement.

To investigate the four features, a fatigue test with a Ti–6Al–4V alloy was programmed to include displacement holding for only one cycle at several ΔK using a fatigue test setup equipped with an optical microscope [45, 46]. Through optical microscopy-based digital image correlation and site-specific fractrographic analyses, we found (i) crack tip strain evolved during the displacement holding, (ii) the displacement holding increased fatigue striation spacing, and (iii) the strain increment during the displacement holding was linearly correlated with spacing of the displacement-holding-extended striations. With a help of post-mortem electron channeling contrast imaging beneath the fracture surface [47], the strain evolution and associated striation formations were clarified to result from dislocation emission at the crack tip during displacement holding. These indicate the dwell-loading-assisted the dislocation emission, which opened the crack and accelerated the crack propagation. Furthermore, the observed extra crack tip opening during the displacement holding caused a delay of crack surface contact during the unloading process, resulting in the decrease in the crack closure effect. Figure 4 summarizes these results.

Fig. 4

Overview of the results that clarified the dwell effects on fatigue of the bimodal Ti–6Al–4V alloy.

6. “Fabrication of Al-Based Composite Extruded Plates Containing Cellulose Nanofibers and Their Microstructure and Mechanical Properties” by Seungwon Lee, Shoma Watanabe, Taiki Tsuchiya, Šárka Mikmeková, Ilona Mullerová, Yasushi Ono, Yutaka Takaguchi, Susumu Ikeno and Kenji Matsuda (Vol. 63, No. 11 (2022) pp. 1590–1596) [5]

Aluminum (Al) or its alloy-based composite materials with ceramic particles such as MgB₂ and have been fabricated to obtain superconducting properties of without compromising the properties of the functional composite particles by suppressing the reaction between the composite particles and Al matrix [48]. Carbon fibers and ceramic whiskers have been investigated and proposed for fiber reinforcement for Al-based composites with various fibers to achieve higher strength and weight reduction [49]. However, it is not easy to obtain Al based composite materials because Cellulose Nanofibers (CeNFs) are carbonized at around 200∼400°C. In this research, CeNF/Al-based composites were prepared using CeNFs collected by a non-woven aluminum filter [50], followed by hot extrusion to obtain plates without using molten Al. Gel-like CeNFs were collected by an Al non-woven filter and compacted by a warm press to obtain a compressed form with a lighter specific density than pure Al. The compressed forms were hot extruded to fabricate bars and plates. Both bars and plates were observed in the macro- and microstructural morphology and XRD measurements. They were not significantly carbonized to graphite only, which was inferred to be present as CeNF under the present experimental conditions. Microstructural observations show that CeNFs are aggregated and present in the pores/cracks between the Al filters in the compressed forms. Al filters and CeNF aggregates were more finely mixed when the material was fabricated into hot extruded plates with a higher extrusion ratio. The maximum tensile strength of the CeNF/Al composite extruded plate was about 1.5 times higher than pure Al. In addition, the extruded plates could be cold-rolled by about 30%, and the maximum tensile strength of the extruded sheets was found to be about twice that of pure aluminum. Figure 5 shows the results of tensile tests on extruded CeNF/Al composite sheets with Vf = 16%. The black solid line in Fig. 5 shows the tensile strength of the extruded plate at about 92 MPa, and the chain line shows the tensile strength of the composite after extrusion and 20% cold rolling at about 130 MPa, which is higher than the 70 MPa of the pure aluminum shown in the thin solid line. The pure aluminum shown here is an extruded plate that was cold-rolled 30% and annealed at 400°C for 10 minutes. It offers relatively high strength and low elongation because the Al matrix as Al-filter is probably not fully recrystallized.

Fig. 5

Result of tensile test for each sample.

7. (Young Scientist Best Paper Award) “Nanomechanical Analysis of SUS304L Stainless Steel with Bimodal Distribution in Grain Size” by Viola Paul, Yanxu Wang, Kei Ameyama, Mie Ota-Kawabata and Takahito Ohmura (Vol. 63, No. 4 (2022) pp. 545–554) [6]

An improved combination of strength and ductility generally involves a trade-off relationship, and it remains a major research topic in the field of structural materials. A bimodal grained microstructure, consisting of a coarse-grained “core” and a surrounding fine-grained “shell”, exhibits a good balance between strength and ductility [51]. Conventional macro-mechanical tests cannot distinguish the contributions of each grain to the mechanical properties, making the individual strengthening mechanisms unclear. In this study, the strengthening factors have been successfully investigated using the nanoindentation technique to measure the elastic-plastic deformation behavior of individual grains and grain boundaries in SUS304L. The nanoindentation technique was applied locally in the “grain interior” to evaluate the matrix strength and “on the grain boundary” and “near the grain boundary” to assess the grain boundary effect associated with the k value in Hall–Petch relation. As a result, it quantitatively revealed that the resistance to plastic deformation within grains is relatively high in coarse grains, while the resistance at grain boundaries is higher in fine grains. Remarkable innovative methods that enabled quantification of grain boundary strength, include the transformation of load (P)–displacement (h) curve into P/h–h [52–54] (Fig. 6) and the measurement of the critical stress for dislocation generation in grains and grain boundaries through pop-in analysis [55]. Furthermore, a Hall–Petch plot was constructed using nanohardness, Vickers hardness, and grain size to estimate the k value. The plot showed a higher k value in fine grains, which is consistent with the higher strengthening effect of the shell grain boundary that is evaluated independently in the local region. These achievements represent significant progress in understanding the strengthening mechanisms of bimodal structured materials and offer the potential for the development of new guiding principles for strengthening through grain boundaries.

Fig. 6

P/h–h curves for grain interior and near grain boundary in (a) shell and (b) core. SPM images in the insets show indentation marks on the shell and core near grain boundary, respectively. Black arrow indicates grain boundary.

8. (Young Scientist Best Paper Award) “Temperature Independences of Fatigue Crack Growth in Ti-0.49 mass%O” by Yelm Okuyama, Masaki Tanaka and Tatsuya Morikawa (Vol. 63, No. 4 (2022) pp. 600–606) [7]

The temperature dependence of fatigue crack growth in stage IIb was investigated in Ti-0.49 mass%O with an alpha single phase. It was found that the fatigue crack growth rate in stage IIb was temperature-independent at temperatures above 300 K. Figure 7(a) and (b) show an EBSD map along a fatigue crack with respect to the tensile direction and a deviation map showing the [0001] direction from the average orientation of [0001] in each grain, respectively. It indicates that the [0001] directions along the crack wake rarely deviate from the average [0001] orientation. This result indicates that the dominant slip planes for the fatigue crack growth are prismatic planes with a-dislocations even at 673 K. It was reported [56, 57] that prismatic slip with ⟨a⟩ dislocation was dominant at low temperatures while other slip systems such as prismatic slips were activated at temperature higher than 673 K in tensile deformation, employing the same materials with the initial strain rate of 4.17 × 10⁻⁴ s⁻¹, where the strain rate is much lower than that corresponds at the crack tip. However, Fig. 7(b) indicates that the dominant slip system in fatigue crack growth is the prismatic system with ⟨a⟩ dislocations even at 673 K. It suggests that the slip systems other than prismatic with ⟨a⟩ dislocations were somehow restricted from being activated at the crack tip. The reason why the prismatic slips were dominantly activated is discussed with numerical crystal plasticity analysis [58, 59]. It was shown that the local strain rate at the notch tip was higher than the macroscopic strain rate, which leads to the suppression of non-prismatic slips at the fatigue crack tip.

Fig. 7

(a) Orientation map with respect to the tensile direction (y direction) along the wake of a fatigue crack. The crack extended toward the x direction. (b) Colour map showing the deviation of the [0001] direction from the average orientation of [0001] in each grain. The colour key is shown at the bottom-right corner. (c) Relationship between active dislocations and the rotation of -axis. (c1) Prismatic slip plane with ⟨a⟩ dislocations. (c2) Schematic illustration showing the rotation axis in the case of prismatic slip with ⟨a⟩ dislocations. (c3) Pyramidal slip plane with ⟨a + c⟩ dislocations. (c4) Schematic illustration showing the rotation axis in case of pyramidal slip with the ⟨a + c⟩ dislocations.

9. (Young Scientist Best Paper Award) “Fatigue Life Prediction of Die-Attach Joint in Power Semiconductors Subjected to Biaxial Stress by High-Speed Thermal Cycling” by Hiroki Kanai, Yoshiharu Kariya, Hiroshige Sugimoto, Yoshiki Abe, Yoshinori Yokoyama, Koki Ochi, Ryuichiro Hanada and Shinnosuke Soda (Vol. 63, No. 6 (2022) pp. 759–765) [8]

A method for predicting the lifetime of fatigue crack network formation in die-attach joints is considered through experiments on high-speed thermal cycling using a Si/solder/Si joint specimen and the mechanism is identified [1]. Equibiaxial stresses are generated in the solder layer because thermal deformation of the solder is constrained by the Si, which causes continuous initiation and propagation of crisscross-shaped cracks. When the crack density is sufficiently high, crack growth is arrested by collisions between cracks, and the formation of the fatigue crack network is completed [60]. Based on these results, development of the damaged area and arrest of the development by collisions between the cracks is expressed in terms of extended volume theory [61–63] incorporating crack initiation and propagation functions for solder as well as considering the damage rate equation. The experimental result for the relationship between the damage ratio in the die-attach joint and the number of cycles under each thermal condition are reproduced by the damage rate equation (Fig. 8).

Fig. 8

Relationships between damage ratio and number of cycles.

10. (Young Scientist Best Paper Award) “Low-Temperature Oxidation–Sintering Behaviors of Cu Fine Particles” by Nobuaki Takeuchi, Daisuke Ando, Junichi Koike and Yuji Sutou (Vol. 64, No. 4 (2023) pp. 931–938) [9]

Recently, wearable devices have been attracting attention in the health field [64]. Flexible printed circuit substrates are used for these devices, but their heat resistance is low at around 400°C. Therefore, interconnects obtained by sintering metal paste need to be formed at lower temperatures. Currently, a paste containing Ag particles is mainly used, but it is very expensive. In recent years, it has been reported that it is possible to sinter an inexpensive Cu paste even at below 300°C by the oxidation-reduction heat treatment [65]. However, the mechanism is still unclear. In this paper, we aimed at clarifying the low-temperature oxidation-sintering mechanism of Cu particles.

Cu particles with a diameter of about 1 µm were subjected to isothermal heat treatment using a thermogravimetry (TG), and the dominant oxidation processes were identified. Electron microscopes were used to observe the microstructure. Then, the low-temperature oxidation-sintering model was proposed.

From XRD analysis, the oxidized sintered bodies were found to be composed of Cu and Cu₂O. TG analysis indicated that mass change curve could be divided into Region I and Region II. The dominant oxidation processes in each region were determined to be the surface reaction (Region I) and the diffusion of Cu in the Cu₂O grain boundaries (Region II) [66, 67]. However, at 200°C, it was suggested that the parabolic law is followed only in the later stage of region II, but the cube law [68] is followed in the early stage. As shown by Fig. 9, Cu₂O (shell) were formed around Cu particles (core) during oxidation process. Although there was a gap between them, a bridge structure was formed, and oxidation progressed continuously [69, 70]. TEM observation revealed that Cu₂O growing from adjacent Cu particles collided with each other to form complex boundaries, indicating that low-temperature oxidation sintering was related to physical bonds between Cu₂O.

Fig. 9

(a) Transmission Electron Microscope micrograph of the oxidized Cu fine particles at 300°C for 10 min. Diffraction patterns taken from (b) Cu core and (c) Cu₂O shell.

11. Editor’s Remarks

As readers recognize, all nine papers introduced above are based on cutting-edge research and well deserve the awards. Most of them were carried out using common metals and materials such as magnesium-based [1], aluminum-based [2, 5] and titanium-based [4, 7] alloys including high-entropy alloys [3], SUS304 stainless steel [6], Si/solder/Si joints [8] and fine copper powder [9].

The work by Kwamura and colleagues demonstrated that Mg can enhance its functionality with additions of Al and Ca in terms of not only mechanical strength but also thermal conductivity and non-flammability. Their paper has good impact for the application of aerospace and automotive industry. Because Mg alloys are popular materials, there are many papers published in Materials Transactions within the last two years [71–94]. Among them, some review/overview papers are available for biocompatibility [88], hydrogen storage [89, 90] and creep properties [94].

The paper by Fukutomi et al. [2] is concerned with an Al-based alloy, demonstrating that the preferential dynamic grain growth (PDGG) mechanism proposed earlier by the author’s group [95, 96] is applicable to predict texture evolution during high-temperature deformation regardless of FCC and BCC structures so long as a thermal stress component (effective stress) exists in the alloys such as an Al-5 mass%Mg and Fe-3 mass%Si. They also showed the PDGG mechanism worked in a Ti-37 mol%Nb alloy [97]. It should be noted that there are many papers published in Materials Transactions on the subjects of texture evolution and the effects on mechanical properties [98–112].

The paper by Lee et al. [5] is also concerned with an Al-based alloy and has demonstrated the fabrication of a composite with cellulose nanofiber (CeNF). Despite the density became less than pure Al, the tensile strength increased by 1.5 times after extrusion and by twice after further cold rolling. Many articles regarding Al and its alloys have been published in Materials Transactions. In particular, a special issue was edited in 2022 under the title of “Aluminium and its Alloys for Zero Carbon Society” [113], including one overview paper [114], two review papers [115, 116] and 24 regular papers [117–140] based on the presentations made in The 18th International Conference on Aluminium Alloys (ICAA 18), Toyama, Japan on September 4–8, 2022.

The papers by Aoki et al. [4] and Okuyama et al. [7] dealt with fatigue of Ti alloys: while the former elucidated the mechanism of dwell fatigue (so-called load-holding-assisted fatigue) in a Ti-6Al-4V alloy, the latter investigated the temperature dependence of fatigue crack growth in stage IIb in a Ti-0.49 mass%O alloy. Readers also find an investigation on fatigue crack propagation behavior using FEM analysis [141]. Because Ti and its alloys are popular metallic materials in terms of not only light weight, high strength and high corrosion resistance but also nontoxicity and good biocompatibility, many research articles have been published. In fact, a special issue was edited in Materials Transactions under the title of “Recent Research and Development in the Processing, Microstructure, and Properties of Titanium and Its Alloys” [142]. This special issue includes four review articles [143–146] and 17 regular articles [147–163].

The paper by Kanai et al. [8] also reported an investigation on fatigue life prediction of Si where a die was attached between two Si layers and high-speed thermal cycles were applied. This paper appeared in a special issue entitled “Frontier Research on Bonding and Interconnect Materials for Electric Components and Related Microprocessing -Part III-” where 11 papers in total [164–174] was edited by Shoji and Kariya [175].

The paper by A. Takeuchi et al. [3] concerning high-entropy alloys (HEA) received the best paper award following the two best paper awards given to the same authors’ group in 2020 [176, 177]. As introduced in 2022 as a current trend in research [11], the HEA and related subjects are hot research topics in these days. It is noted that a comprehensive summary by Inui et al. [178] for the papers published in the special issue on “Materials Science on High-Entropy Alloys” is available in Materials Transactions. In the coming September 2024, Materials Transactions is planning to publish a latest version of the special issue entitled “Materials Science on High-Entropy Alloys II”.

In the study by Paul et al. [6], a nanoindentation technique was employed to clarify the mechanism for a simultaneous improvement of the strength and ductility in SUS304L stainless steel with a bimodal grained structure. The advantage of the nanoindentation technique was fully utilized in this study to bring them the award. It is noted that readers will find several studies using the nanoindentation technique, which were published in Materials Transactions [179–182].

Investigation by N. Takeuchi et al. [9] revealed the sintering process of Cu fine particles occurring at low temperature for application to flexible electronics devices. In their study, not only thermal gravimetric analysis (TGA) but also scanning and transmission electron microscopy were used. It should be noted that Materials Transactions published a special issue under the title of “Structural Analysis and Measurement of Physical Properties on Advanced and Fundamental Materials” [183]. This special issue focused on materials which are important for intelligent society by IoT and their processing, nano-/micro-analysis, measurements of physical properties and application of data science. Readers may find the related articles published in Materials Transactions [184–195].

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