PREFACE
Kenji Matsuda, Katsuhiko Nishimura, Ilona Mullerova, Sarka Mikmekova, Shixun Cao, Makoto Shiojiri, Mitsuhiro Murayama
pp. 407-407
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MATERIALS TRANSACTIONS Vol.63(2022), No.4
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02 Nov. (Last 30 Days)
Kenji Matsuda, Katsuhiko Nishimura, Ilona Mullerova, Sarka Mikmekova, Shixun Cao, Makoto Shiojiri, Mitsuhiro Murayama
pp. 407-407
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MATERIALS TRANSACTIONS Vol.63(2022), No.4
Tadayoshi Tsukeda, Takuro Nakagawa, Masaya Moriwaki, Kensei Kikura, Riku Sakurae, Tetsuo Aida, Hironobu Tabata, Hideki Kurihara, Mayumi Suzuki
pp. 408-414
Abstract
Various motor using transportation system in land-sea-air, high speed mobile terminal with 5G specification, and renewable energy storage equipment have required innovative metal rechargeable batteries compared with lithium ones. In particular, magnesium has huge potentialities as an anode material from the standpoint of its theoretical volumetric capacity superior to that of lithium. Secondly, magnesium has been one of the most abundant elements in the Earth’s crust. Moreover, the potential safety by short-circuiting evading with non-dendritic deposition of magnesium. In general, magnesium-based ribbon as an anode has been manufactured by cold rolling which requires multistage process including heat treatment. We have studied rapid liquid quenching process in order to develop low-cost manufacturing technique. On the other hand, we have focused Mg–6 mass%Al–3 mass%Ca alloy due to this unique microstructure which consist of primary crystals and intermetallic compounds along grain boundary. In addition, calcium has affected to prevent of molten magnesium burning in air atmosphere. The structural properties and surface morphology are investigated by XRD and Digital Microscope, respectively. Microstructure has been observed by FE-SEM and FE-TEM. Moreover, these electrochemical properties have been examined by constant current charge - discharge tests using 3 electrodes type cell. Mg–3 mass%Al–1 mass%Zn alloy cold rolled thin plate has been investigated as comparison. The ribbons that exhibited electrochemical properties had a fine microstructure. It is suggested that the grain refinement and dispersion of the second phase are important to improve the charge-discharge properties of Mg–Al–Ca based anode materials.
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ISIJ International Vol.62(2022), No.10
ISIJ International Vol.62(2022), No.10
Tetsu-to-Hagané Vol.108(2022), No.10
P. Czaja, J. Przewoźnik, P. Ozga, M. Marzec, K. Stan-Głowińska, D. Duraczyńska, E. Serwicka, L. Lityńska-Dobrzyńska
pp. 415-421
Abstract
Melt spun Ni70Ga30, Ni70Sn30 and Ni70In30 show different oxidation behaviour following heat treatment at 900°C in air. The Ni70Ga30 ribbon develops a continuous layer of Ga2O3 oxide, which passivates the surface and prevents further oxidation of the Ni3Ga bulk phase. On the contrary, the Ni70Sn30 and Ni70In30 ribbons undergo considerable segregation and decomposition and aside from the Ni and NiO and the primary Ni3Sn and Ni3In also comprise SnO2 and In2O3 phases. Results are conformed from XRD, TEM and XPS analysis. The oxidation behaviour especially in the case of the Ni70Sn30 ribbon is promising with view for development of fine Ni particles on the Ni3Sn support.
Masahiko Hatakeyama, Taiki Tsuchiya, Seung-won Lee, Kenji Matsuda, Yoshifumi Aoi, Masateru Nose
pp. 422-429
Abstract
Radiofrequency (RF) reactive magnetron sputtering was used to deposit thin SiCN and CrSiCN films on high-speed steel or silicon substrates. Nanoindentation, scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM-EDS), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) analyses were used to investigate the changes in the mechanical properties and microstructure of the CrSiCN films after annealing. The CrSiCN (37.6%Cr) film deposited on the Si substrate showed little change (−12%) in the indentation hardness and microstructure after annealing in air at 800°C for 1 h. Comparatively, the hardness of the same films deposited on high-speed steel substrates was greatly degraded (−36% to −50%). The microstructure of the films also changed remarkably after annealing in air or even under vacuum using the same temperature and time conditions. TEM/XPS analyses suggested that the mechanism of degradation of the CrSiCN films involved decomposition of the SiCN phase, induced by CrN and diffusion of Fe from the substrate. The diffusion of Fe formed Fe–Si in the films, while CrN generated Cr–C, which induced grain growth of the CrN phase and degraded the indentation hardness of the films. Thermodynamic calculations were performed to demonstrate the possibility of these reactions. The formation of crater wear faults in the CrSiCN hard coatings used for machining tools was also discussed.
Martin Friák, Martina Mazalová, Ilja Turek, Oldřich Schneeweiss, Jiří Kaštil, Jiří Kamarád, Mojmír Šob
pp. 430-435
Abstract
We have performed an ab initio study of disordered ferrimagnetic Ni1.9375Mn1.5625Sn0.5 martensite. Employing the supercell approach combined with the special quasi-random structure concept for modeling of disordered states we have determined thermodynamic, magnetic, structural, elastic and vibrational properties of the studied material. Its atomic and magnetic configuration is found to exhibit a pressure-induced increase of the total magnetic moment, i.e. the total magnetic moment increases with decreasing volume. This peculiar trend is revealed despite of the fact that the magnitudes of local magnetic moments of atoms decrease (or stay constant) with decreasing volume. The origin of the identified phenomena may be related to (i) the ferrimagnetic nature of the magnetic state when the parallel and antiparallel magnetic moments nearly compensate each other and (ii) chemical disorder that leads to different local atomic environments and, consequently, also to different local magnetic moments and their different response to hydrostatic pressures (the antiparallel moments are more sensitive). The studied state is mechanically and dynamically stable (no imaginary-frequency phonons) but, regarding its thermodynamic stability, it is an excited state.
Matúš Vaňko, Jarmila Müllerová, Milan Dado
pp. 436-441
Abstract
In this paper, we present results of numerical analysis of phase-shifted fiber Bragg gratings aimed at slowing down the group velocity of light propagating through these structures. Using coupled-mode theory and transfer matrix method we model the impact of several parameters such as length of the grating, refractive index modulation depth and phase shift in the periodicity of Brag gratings to calculate transmission spectral properties and to maximize the final group delay. By introducing irregularity into a periodic structure of refractive index, Fabry-Perot like cavity formed in the grating results in a favorable narrow dip in resonance spectra characteristics. Correspondingly, we observe a significant spike in group delay at the same wavelength. Simulations results obtained by numerical approach show a strong need for parameter optimization in process of tailoring gratings behavior. Considerable attention must be put on width of spectral region suitable for large group delay realization and suitable interrogation schemes need to be implemented when adopting studied structures for sensors applications.
Richard Gawel, Łukasz Rogal, Jarosław Dąbek
pp. 442-449
Abstract
This study aims to compare the behaviour of two Ni-rich non-equimolar AlCoCrFeNi high entropy alloys, i.e. Al20Co5Cr20Fe20Ni35 and Al10Co15Cr20Fe20Ni35 (at%) in isothermal high-temperature oxidizing conditions. In both cases, mass gain after 100-hr oxidation at 1173 K in synthetic air atmosphere does not exceed 1 mg/cm2, indicating good resistance against the corrosive environment. Investigations on the morphology, chemical and phase composition of the alloys after the oxidation process indicate that a mixture of Al2O3 and Cr2O3 is responsible for the protective properties of the scale formed on Al20Co5Cr20Fe20Ni35, whereas an additional chromium–iron–nickel–cobalt spinel structure was determined on the Al10Co15Cr20Fe20Ni35 sample after prolonged exposure to the above-mentioned conditions. The oxidation kinetics are slightly better in the case of Al20Co5Cr20Fe20Ni35 and lower amounts of the remaining constituent elements were detected in the protective scale compared to Al10Co15Cr20Fe20Ni35. Furthermore, the Al20Co5Cr20Fe20Ni35 substrate was able to maintain its initial morphology throughout the entire alloy after the corrosion process. From all of the above, it can be concluded that Al20Co5Cr20Fe20Ni35 seems to demonstrate better oxidation properties at a high temperature than Al10Co15Cr20Fe20Ni35.
Nguyen Duong Nam, Le Thi Nhung, Vu Anh Tuan, Nguyen Hong Hai, Pham Mai Khanh
pp. 450-457
Abstract
In this paper, the changing of microstructures on the surface layer of high manganese steel (HMnS) Mn15Cr2V under the impacted load was investigated. By theoretical calculations based on stacking fault energy (SFE), it was found that at 300 K, the SFE value of this steel was 34.7247 mJ/m2 and at 220 K, the SFE value was 34.72173 mJ/m2. Thus, with this result, the SFE’s value is much larger than the value of the martensitic transformation, which was about 18 mJ/m2. It can be shown that there will be no martensite changes even if the sample is heat-treated with the sub-zero process. The results of the microstructure analysis show that the microstructures were austenite with carbide particles (VC and Cr7C3) that had a small grain size (about 40 nm) and were dispersed in the microstructures. The study’s findings revealed that when the number of impact loads is 3,000 times, the surface layer exhibited twinning, slip, and austenite nanoparticles. When the number of impact loads increases by 10,000 times, the microstructure of the surface steel appears in the amorphous phase. The results of theoretical calculations based on the changing of stacking fault energy (SFE) and experimental results show that there is no appearance of martensite form on the surface layer in research conditions.
Satoru Murata, Tatsuki Noda, Masahiko Hatakeyama, Satoshi Sunada
pp. 458-461
Abstract
To suppress the over-oxidation of solvents, reaction conditions were optimized, and ligands were added to the system to facilitate the oxidation of sulfur compounds with molecular oxygen. The addition of suitable nitrogen ligands led to effective suppression, and 2,2′-bipyridine showed the best performance among the analyzed samples. After the use of the ligand, the yields of by-products from solvent oxidation were reduced by a factor of 15 compared to those from the reaction without any ligands.
J-lin Zhang, Lin Yang, Qian Yan, Ping Zhu, J-kun Xiong, Chang Liu
pp. 462-467
Abstract
In this paper, the reasons for the formation of “white stripe” in the heat affected zone beside low alloy steel of FB2-30Cr1Mo1V dissimilar steel welded joint are analyzed: the microstructure of “white stripe” is tempered sorbite and the grain is fine. The main cause of “white stripe” is composition segregation which hinder grain growth during welding thermal cycle, resulting fine and corrosion-resistant microstructure generated. The peak temperature of welding thermal cycle is main influence factor. Thermal simulation technology was used to reproduce the “white stripe”, which appeared at the peak temperature between 900°C and 1050°C.
Jiao Chen, Kenta Yoshida, Tomoaki Suzudo, Yusuke Shimada, Koji Inoue, Toyohiko J. Konno, Yasuyoshi Nagai
pp. 468-474
Abstract
In situ electron irradiation using high-resolution transmission electron microscopy (HRTEM) was performed to visualize the Frank loop evolution in aluminum–copper (Al–Cu) alloy with an atomic-scale spatial resolution of 0.12 nm. The in situ HRTEM observation along the [110] direction of the FCC-Al lattice, Frank partial dislocation bounding an intrinsic stacking fault exhibited an asymmetrical climb along the 〈112〉 direction opposed to those in the reference pure Al under an electron irradiation, with a corresponding displacement-per-atom rate of 0.055–0.120 dpa/s in a high vacuum (1.2 × 10−5 Pa). We performed theoretical calculations to simulate the asymmetrical climb of the dislocation with Burgers vector b of 1/3〈111〉. The Cu–Cu bonding in Guinier–Preston zones was described as a possible pinning site of the dislocation climb by molecular dynamics simulation.
Thi Dung Pham, Tien Quang Nguyen, Tomoyuki Terai, Yoji Shibutani, Masaaki Sugiyama, Kazunori Sato
pp. 475-483
Abstract
In this paper, the interaction of C with edge dislocations in α-Fe with Burgers vectors of 1/2〈111〉, 〈100〉, and 〈110〉 has been investigated using the classical force-field method in conjunction with the newly-developed Tersoff/ZBL interatomic potential of Fe–C. Here, the potential was constructed from the first-principles database containing force and energy information of various defect complexes with C in body centered cubic (BCC) Fe. The interaction of C and dislocations has been analyzed from the viewpoint of Voronoi volume formed by C and surrounding Fe atoms. It is found that the interaction between dislocations and C is more attractive when the Voronoi volume around C becomes larger. This tendency is similar to the case of grain boundaries reported previously. It is also found that the grain boundaries and dislocations trap C strongly compared to a single vacancy in BCC Fe, and among them more unstable defect structures attract C more strongly. The obtained tendency might offer a useful guideline to analyse the atomistic distribution of C in Fe with extended defects.
Yoji Miyajima, Hiroki Morimoto, Masashi Miyazaki, Takuya Okada, Kazuhiro Ishikawa, Chihiro Watanabe, Hiromi Miura
pp. 484-488
Abstract
In order to reveal the change in electrical resistivity and strengthening due to plastic deformation and microstructural evolution, investigation of mechanical and electrical properties was performed. From microstructural observations, it was found that the heterogeneous-nano structure having “eye”-shaped twin domains was formed of which volume fraction becomes largest at 90% of rolling reduction. Ultimate tensile strength increases with increasing rolling reduction and reaches about 735 MPa at 90% and 95% reductions. The electrical resistivity measured at 77 K changes from about 39.6 nΩ m to about 61.9 nΩ m, and correspondingly, the conductivity at 293 K changed from about 28.0%IACS down to about 19.9%IACS. When compaering the total changes in electrical resistivity before and after reduction of 80%, the latter was larger. The more obvious changes in mechanical and electrical properties over reduction of 80% are associated with the formation of heterogeneous-nano structure in addition to increasing dislocation density. This Paper was Originally Published in Japanese in J. Jpn. Inst. Copper 60 (2021) 56–61. Section 2.1 and 2.5 are slightly modified.
Yoshito Takemoto, Mikiko Yasuno, Masaki Ikemoto, Hiroyuki Ando, Ichiro Shimizu
pp. 489-496
Abstract
The formation mechanism of α′′-martensite (α′′Mt) induced by tempering at 450–550°C for a short time was investigated using Ti–10Mo–7Al alloy. The solution treated and quenched (STQ) sample was composed of β phase and a small amount of α′′Mq, and a large amount of α′′Mt was generated by rapid tempering at 550°C for 3 s using a salt bath. However, α′′Mt was completely transformed into a single β phase by aging at 200°C for 3 min. Reversibility was observed between the α′′Mt transformation and the β reverse transformation. In-situ high-temperature X-ray diffraction measurements revealed that α′′Mq → β reverse transformation occurred at 200°C and that a thermally activated α′′iso was generated at 450°C due to the slow heating rate. In-situ optical microscopic observation of STQ sample with rapid lamp heating revealed that α′′Mt was formed during heating process. However, α′′Mt did not generate under following conditions; that is, a slow heating rate, thin sample plate, and a small temperature difference until tempering by preheating. On the other hand, rapid tempering using thick plate from liquid nitrogen (−196°C) to 250°C was performed to ensure a sufficient temperature difference, but α′′Mt was not generated at all.From the cross-sectional observation of the STQ plate, it was found that α′′Mq was hardly formed on the surface of the sample, but was formed abundantly inside the sample. On the other hand, in the rapidly tempered plate, a large amount of α′′Mt was distributed in the surface layer than inside sample. These results suggest that the thermal compressive stress induced by rapid heat treatment contributes to the formation of α′′M. This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 85 (2021) 405–412.
Yanshuo Li, Norimitsu Koga, Cihiro Watanabe, Hiromi Miura
pp. 497-501
Abstract
The heterogeneous-nano (HN) structure consisting of twin domains, shear bands, and lamellar grains developed by heavy cold rolling of FCC metals with low stacking fault energy is known to provide extremely high strength. In the present study, the effects of the rolling pass schedule on the development of HN structure and the mechanical properties in a Cu–38 mass%Zn alloy were investigated. Rolling was conducted on two different pass schedules; one was conventional unidirectional rolling (1-DR) up to 90% reduction in thickness, and the other was the two-directional rolling (2-DR), in which the specimen was unidirectionally rolled to 25% reduction, then rotated 90° around the rolling direction, and subsequently, unidirectionally rolled up to the total reduction of 90%. At a total reduction of 50%, the number of grains with deformation twins in the 2-DR specimen was higher than that in the 1-DR specimen. Further cold rolling up to 90% produced the HN structure in both specimens. The size of twin domains in the 2-DR specimen was finer and their volume fraction was larger than those in the 1-DR specimen. Also, the 2-DR specimen exhibited a better strength-elongation balance than the 1-DR specimen. It can be concluded that the finer size and larger volume fraction of the twin domains effectively improved the strength-elongation balance in the 2-DR specimen. This Paper was Originally Published in Japanese in J. Japan Institute of Copper 60 (2021) 11–15. The abstract and caption of Fig. 6 have been slightly modified.
Masaki Chiba, Takenori Tanno, Maho Abe, Shuichiro Hashi, Kazushi Ishiyama, Toru Kawamata, Rie Y. Umestu, Kazumasa Sugiyama, Shigeo Sato, Yosuke Mochizuki, Koji Yatsushiro, Tsuyoshi Kumagai, Tsuguo Fukuda, Shun-Ichiro Tanaka, Shigeru Suzuki
pp. 502-507
Abstract
To process ingots of Fe–Ga alloy single crystals into wafers, Fe–17% Ga alloy crystals were cut using multi-wire sawing or electric discharging and rolling. Further, their properties of magnetization and magnetostriction were analyzed using electron backscatter diffraction (EBSD) and X-ray diffraction (XRD). It was observed that the magnetization and magnetostriction curves changed with increasing rolling reduction. Although magnetization was negligibly affected by deformation, the shape of the magnetostriction curve of the as-grown crystal could be modified by a slight reduction in rolling or a slight plastic deformation. EBSD results show that rolling introduced dislocations to form heterogeneous dislocation cell walls and decreased the surface roughness of the wafers. The pole figures obtained by XRD indicate that the samples were single crystals; however, the crystal orientation was different from the ideal orientation after rolling. Residual stress measurements using the cos α method revealed that compressive and tensile stresses remained in the polycrystalline surface layers of the samples cut by multi-wire sawing and electric discharging, respectively. Moreover, the stresses were affected by the tensile strains or magnetic fields when the residual stresses were relatively small in the sample. Although the magnetization and magnetostriction of a single crystal are affected by rolling, they are not significantly reduced by small rolling reductions.
Yoshihiro Matsuura, Hironori Sakai, Chihiro Watanabe, Yuya Sumino, Hiromi Miura
pp. 508-512
Abstract
Effects of pre-aging of Corson alloys with high concentrations of Ni and Si (Cu–4.2 mass%Ni–0.93 mass%Si) followed by heavy cold rolling and full-aging on strengthening were systematically investigated. Especially, development of heterogeneous-nano (HN) microstructure was focused. And the relationship of mechanical/electrical properties was precisely examined. The pre-aged alloys exhibited a considerable strengthening after 90% cold rolling. This was attributed to the increase in the volume fraction of deformation twin domains in the HN microstructure after cold rolling as well as the precipitation strengthening. The sample prepared by a thermo-mechanical process via pre-aging at 723 K, subsequent cold rolling and full-aging at 673 K for 600 s exhibited the best strength/conductivity balance with an ultimate tensile strength (UTS) of 1096 MPa and electrical conductivity (E) of 29% IACS. When examined the effects of solid-solution (SS) temperature on the microstructure and properties, SS at 1223 K derived finer grain size than at 1323 K and the achieved best balance of UTS and E with 1061 MPa and 33% IACS. Therefore, grain refinement prior to pre-aging had no significant effect on strengthening but contributed to modification of electrical conductivity. This Paper was Originally Published in Japanese in J. Japan Inst. Copper 60 (2021) 45–49.
Hiroki Ishii, Rikito Takagi, Naoki Takata, Asuka Suzuki, Makoto Kobashi
pp. 513-521
Abstract
In the present study, we investigated the effects of Cu or Ni additions on the precipitation of intermetallic phases in the heat-resistant aluminum alloy with a ternary composition of Al–5Mg–3.5Zn (mol%). The quaternary alloys with 1 mol%Cu or 1 mol%Ni content were solution-treated at 480°C and subsequently aged at 300°C for different periods. Both Cu and Ni additions have a slight effect on the age-hardening of these alloys at 300°C. The added Cu element partitioned into not only the T-Al6Mg11Zn11 phase but η-Zn2Mg phase precipitated in the α-Al matrix. The observed Cu enrichment in the precipitates of the T phase indicated high stability of the T phase in the Al–Mg–Zn–Cu quaternary system, which was different from the results of thermodynamic calculations using the existing database. The added Ni element enhanced the formation of fine Al3Ni phase located at grain boundaries and slightly influenced the precipitation of T phase in the grain interior. These results provided new insights to design novel heat-resistant Al alloys using the Al–Mg–Zn–Cu–Ni system. This Paper was Originally Published in Japanese in J. JILM 71 (2021) 275–282.
Harumichi Sato, Hisato Ogiso, Hirotomo Itagaki
pp. 522-528
Abstract
This study investigates the acoustic properties of a metal near its phase-change temperature using laser ultrasonics. A Pb-free solder sample was prepared, and its temperature was increased stepwise from 40°C to 210°C with concurrent measurement of laser ultrasonic waves on the solder surface. Noticeable change in the waveforms was observed at 203°C and 209°C. These sudden changes occurred with a 1°C change in temperature. The change at 203°C was attributed to an acoustic mode transformation from Rayleigh-like to Lamb-like as we also found that part of the solid solder became thin as a result of partial melting from the bottom and rim. Only the sound through the air was detected at temperature of 209°C and higher, where this sound was due to ablations. This phenomenon was responsible for local melting at the laser irradiation point, generating the ultrasonic waves.
Noritaka Yusa, Jiuhao Ge, Mengbao Fan
pp. 529-537
Abstract
This study investigated whether it is really reasonable to insist that being “rich in frequency” represents an advantage of pulsed eddy current testing when compared with conventional eddy current testing. More specifically, this study compared the capabilities of pulsed eddy current testing and conventional eddy current testing in evaluating the thickness of non-ferromagnetic plates with thicknesses of 1–20 mm. To avoid any instrumentation effect, the investigations were performed based on signals obtained by finite element simulations, and the correlations between the thickness and a scalar feature value extracted from measured signals were discussed. This study considered two typical excitation waveforms, a Gaussian pulse and a step function simulating the sudden termination of the excitation currents, and four simple and conventional scaler feature values: peak amplitude, time to peak, time to attenuate the signal into a certain level, and logarithmic slope of the signal attenuation. Narrowing the Gaussian pulse led to difficulty in terms of the thickness evaluation, although it should make the pulse richer in frequency. Subsequent analyses compared the capabilities of the pulsed and conventional eddy current testing to evaluate plate thickness under the assumption that they have the same signal-to-noise ratio. The results revealed that the error in the thickness evaluation using the pulsed eddy current testing was somewhat larger than the error using the conventional eddy current testing with three frequencies. Whereas the target of this study was limited to the thickness evaluation of non-ferromagnetic plates, the results of this study point out that what is important is using frequencies in a proper range as well known in the conventional eddy current testing. They also indicate that it is not reasonable to postulate that “richness in frequency” always leads to a better nondestructive evaluation when using the pulsed eddy current testing.
Yasuhiro Ishijima, Fumiyoshi Ueno, Hitoshi Abe
pp. 538-544
Abstract
The time dependence of the corrosion behavior of tantalum (Ta), which is used in nuclear fuel reprocessing equipment, in sodium hydroxide (NaOH) solutions was investigated by immersion tests, and the mechanism of the time dependence was examined via surface observations and electrochemical measurements. The immersion tests were conducted at room temperature with NaOH concentrations ranging from 1 to 7 mol·L−1 for immersion periods of 24 to 168 h. The corrosion rate increased with the NaOH concentration but peaked with the immersion period and then decreased. The time to peak of the corrosion rate was shorter with higher NaOH concentration. The X-ray diffraction (XRD) patterns and Raman spectra of the surfaces of the specimens immersed in the 7 mol·L−1 NaOH solution for more than 48 h showed Na8Ta6O19 formation. The polarization resistance showed a constant value or an increase after a decrease immediately after immersion. It was suggested that the change in corrosion rate is affected by the formation of film during immersion, since the time dependence of polarization resistance and the sum of film resistance and charge transfer resistance have same tendencies. The film was considered to be mainly Na8Ta6O19 formed by the dissolution of Ta. This Paper was Originally Published in Japanese in Zairyo-to-Kankyo 70 (2021) 192–198.
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MATERIALS TRANSACTIONS Vol.63(2022), No.4
Viola Paul, Yanxu Wang, Kei Ameyama, Mie Ota-Kawabata, Takahito Ohmura
pp. 545-554
Abstract
An improved combination of strength and ductility is generally 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 region “core” and a surrounding fine-grained region “shell”, exhibits a good balance between strength and ductility. Therefore, the exact reason for the strengthening mechanism needs to be investigated. In the present study, we conducted nanomechanical characterization to evaluate the individual strengthening factors, including matrix strength (σ0), and grain boundary effect (k), in the Hall–Petch model for each region of the core and shell to clarify the strengthening mechanism in the bimodal grained microstructure. The nanoindentation technique was applied locally in the “grain interior” to evaluate σ0, and “on grain boundary” and “near grain boundary” to assess the grain boundary effect associated with the k value. The grain interior nanohardness was found to be higher in the core region than that in the shell, which is explained by the higher pre-existing dislocation density in the core region. The nanomechanical characterization of the “on grain boundary” and the “near grain boundary” regions show a higher barrier effect due to the grain boundary in the shell than that in the core, which is presumably dominated by the higher internal strain at the shell grain boundary. 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 the shell, which is consistent with the higher strengthening effect of the shell grain boundary that is evaluated independently in the local region. Therefore, the macroscopic strength of the shell region is significantly affected by both grain boundary effect as well as fine grain size.
Atsushi Omori, Saya Ajito, Hiroshi Abe, Kuniki Hata, Tomonori Sato, Yoshiyuki Kaji, Hiroyuki Inoue, Mitsumasa Taguchi, Hajime Seito, Eiji Tada, Shunichi Suzuki, Eiji Akiyama
pp. 555-561
Abstract
To evaluate the effect of oxidants, which are formed by radiolysis of water under gamma-ray irradiation, on the corrosion of a carbon steel in a humid environment, ozone was introduced as a model oxidant into humidity-controlled air at 50°C in a thermo-hygrostat chamber. Corrosion monitoring of carbon steel was performed by using an Atmospheric Corrosion Monitor-type (ACM) sensor consisting of a carbon steel anode and an Ag cathode, and a Resistmetric Corrosion Monitor (RCM) sensor consisting of carbon steel sheets. The corrosion rates obtained from the outputs of the sensors were increased with the increase in relative humidity and were obviously increased with the increase in the introduced ozone concentration at each relative humidity, indicating that ozone accelerates the corrosion of the carbon steel. The effect of ozone on the corrosion acceleration is attributed to its easy reduction reaction and/or fast dissolution reaction into water compared to that of oxygen. This Paper was Originally Published in Japanese in Zairyo-to-Kankyo 70 (2021) 358–364.
Kazushige Tokuno, Masatoshi Mitsuhara, Shinnosuke Tsuchida, Ryo Tsuboi, Junji Miyamoto, Masahiro Hagino, Takashi Inoue, Kouki Nishidate
pp. 562-569
Abstract
Tangled dislocation structures inside the dislocation channels of rapid-cooled and tensile deformed aluminum single crystals were investigated by using BF-STEM. Inside the dislocation channels, arrays of the prismatic dislocation loops belonging to the primary slip system, i.e., (1 1 1)[1 0 1], were mainly formed. Dislocations of the primary coplanar slip systems such as (1 1 1)[0 1 1] and (1 1 1)[1 1 0] were activated due to the internal stresses caused by the primary dislocations pile-up inside the cleared channels. The activated primary coplanar dislocations leave the dislocation loops elongated along the edge dislocation directions behind them. Inter-dislocation-loop interactions take place especially at the arrays of the prismatic dislocation loops of the primary slip systems and produce “butterfly shape” dislocation loops. Since the “butterfly shape” dislocation loops have “sessile” junctions, they should act as “obstacles” against the following multiplications and glides of the dislocations. As the interactions proceed, the arrays are stabilized and grow as “tangles”.
Tomohiro Sannomiya, Daisuke Nakamura, Jinta Arakawa, Tadashi Kado, Tomohito Tsudo, Seiya Takahashi, Masashi Hiraoka, Hiroyuki Akebono, Atsushi Sugeta
pp. 570-578
Abstract
In this study, to clarify the weld area shape that achieves excellent fatigue properties in laser welded joints, an ϕ-shaped weld, which is a combination of a circular weld and a linear weld, was selected for evaluation. Joints with a linear weld having three different linear weld angles with respect to the load axis were fabricated and fatigue tests were conducted. The results showed that the effect of the linear weld angle was remarkable in a relatively high loading amplitude range, and the fatigue life increased as the angle increased. In addition, three-dimensional observation of fatigue cracks was carried out to investigate the fracture mechanism and the factors causing the difference in fatigue strength. It was clarified that the crack propagation life is increased because the crack propagates in the thickness direction not only at circular weld area but also at the linear weld area, when the linear weld angle respecting to loading direction are 45°, 90°. Furthermore, three-dimensional FEM analysis was carried out to recognize the stresses field around the linear weld area. It was clarified that the stresses around the weld area were distributed as the linear weld angle increased, which delayed crack initiation, leading to excellent fatigue properties. Therefore, the fatigue life in the high test-force amplitude region can be improved by providing a weld area shape that distributes the stress and allows the crack to propagate in the thickness direction.
Song Zhenya, Jin Shenchao, Shen Yueming, Teng Jiabin, Lu Bing, Zhang Lincai
pp. 579-585
Abstract
In the present study, the effects of copper and zinc addition on the microstructure and indentation creep behaviors of SnSb8Cu4 Babbitt alloy were systematically investigated. An indentation creep testing device with a flat tip indenter was used to characterize the creep behaviors of the Babbitt alloys at ∼100°C with different loads. By increasing the copper content from 4 wt% to 8 wt%, coarser and shorter Cu6Sn5 dendrites with larger volume fraction were observed. The corresponding Brinell hardness increased from 21.9 to 28.1 at room temperature. However, the improvement in creep resistance was not obvious. After adding 0.72 wt% zinc, large number of small-sized SnSb particles precipitated along the grain boundaries of tin matrix. The total volume fraction of intermetallics, i.e., Cu6Sn5 and SnSb particles, increased from 15.1% to 20.9%. Although, the increment of Brinell hardness was not remarkable at room temperature, dramatic improvement in creep resistance was observed. The addition of zinc caused the decrement of the solid solubility of Sb in tin matrix, while more network-like SnSb particles precipitating in tin matrix were found, giving rise to the pinning effect against grain boundary sliding during creep deformation. However, increment of copper content showed no obvious effect on the solid solubility of Sb in tin matrix. Meanwhile, an exponential relationship between indentation creep rate and indentation stress at the steady creep stage was found. Based on the measured data, the indentation stress exponent of SnSb8Cu4, SnSb8Cu8 and SnSb8Cu4Zn was deduced to be 2.949, 2.865 and 2.743, respectively.
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Abstract
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Abstract
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Abstract
In zinc hydrometallurgical processes, copper was removed as copper precipitate powder by a cementation process, and, in the present study, leaching medium using Cu2+ and O2 in sulfuric acid solution was proposed to enhance the leaching rate of Cu from the cementation Cu precipitate powder. The leaching efficiency of Cu increased with increasing agitation speed, temperature, and initial Cu2+ concentration and decreasing pulp density. When the effect of gas type on the leaching was examined, the leaching efficiency was faster in the order of O2, air, and N2. The leaching efficiency of Cu increased to 100% in 1 mol/L sulfuric acid solution at 70°C and 600 rpm with 2% pulp density, 10000 mg/L Cu2+ and 1000 mL/min O2. In the kinetic study, the leaching behavior of Cu followed the reaction-controlled model, and the activation energy was determined to be 19.2 kJ/mol. Therefore, these results suggest that the addition of Cu2+ and O2 could enhance the leaching rate of Cu from the cementation Cu precipitate.
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Abstract
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Abstract
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In this study, the CoCrNi medium entropy alloy (MEA) coating was firstly fabricated on 5083Al alloy by the resistance seam processing (RESP) method. After processing, the CoCrNi MEA powders were transformed into a simple face-centered cubic (FCC) structural coating with an average thickness of 381 ± 4 µm, and the heat-affected zone was rarely found in the Al alloy matrix. Furthermore, a certain amount of Al element penetrated into gaps of coating and Co, Cr and Ni elements were homogeneously distributed. The average hardness of the coating was 775 ± 68 HV0.2, which was higher than the similar MEAs prepared by other reported methods. To evaluate its wear properties, the wear behaviors of CoCrNi MEA coating and 5083Al alloy were studied in detail. Although the main wear mechanisms of both materials were adhesive wear, the high hardness and plastic deformation ability of the MEA coating effectively improved its wear performance. Practically, the average wear rate was ∼10 times lower than 5083Al alloy. The RESP method was proved to be an effective method for preparing the high wear-resistance MEA coating on Al alloy.
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Abstract
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