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ONLINE ISSN: 1347-5320
PRINT ISSN: 1345-9678

MATERIALS TRANSACTIONS Vol. 61 (2020), No. 12

  • Color Metallography of Characteristic Microstructure in High-Speed Twin-Roll Cast Al–Mn–Si Alloy Strip Using Weck’s Reagent

    Thai Ha Nguyen, Ram Song, Yohei Harada, Shinji Kumai

    pp. 2253-2262

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    DOI:10.2320/matertrans.L-M2020856

    Abstract

    A color metallography using Weck’s reagent was employed to investigate the characteristic microstructure of Al–Mn–Si alloy strip fabricated by high-speed twin-roll casting. The microstructure of the strip consists of two components: solidified shells and a central band. By Weck’s reagent etching, the colorful microstructure was obtained, and doughnut-like patterns were observed in the globular grains. Based on the presence of the patterns, the globular grains were divided into two types: Type-I and Type-II. Type-I grains exhibited the core-like structure. On the other hand, Type-II grains had no color contrasts in the grain. SEM-EDS analysis of Type-I grains revealed the high correlation between the obtained color and micro-segregation of Si. TEM and STEM analyses confirmed the formation of an amorphous film on the surface of Al substrate by the etching. The thickness of the film and the roughness of the Al substrate under the film were different from location to location. The local change of the film’s features resulted in the different color in the optical microscopic image. Based on the microstructure observation, the origin of globular grains observed in the central band in the Al–Mn–Si alloy strip was discussed in detail.

  • Dry Sliding Wear Behavior of 38CrNi3MoV Steel at Elevated Temperatures

    Yong Lian, Wen Gao, Chao Zhao, Minyu Ma, Jinfeng Huang, Jin Zhang

    pp. 2263-2269

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    DOI:10.2320/matertrans.MT-M2020032

    Abstract

    Friction and wear behavior of 38CrNi3MoV steel were investigated from 25–600°C using a pin-on-disc elevated temperature tester. Thereafter, the hot hardness of the pin and disc, tribo-oxides phase composition, worn surface and interface morphology were examined to understand the wear mechanisms. The results show that the 38CrNi3MoV steel presented different wear rates at various temperatures. The ambient temperature is the main factor affecting the formation of tribo-oxides. While, the final morphology of tribo-oxides remaining on the worn surface depended on the difference between the disc’s hot hardness and the pin’s hot hardness (Hdisc − Hpin). Adhesive and abrasive wear, mild oxidative wear, severe oxidative wear, and mild oxidative wear prevailed at 25, 200, 400, and 600°C, respectively.

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  • Texture Formation through Thermomechanical Treatment and Its Effect on Superelasticity in Mg–Sc Shape Memory Alloy

    Keisuke Yamagishi, Daisuke Ando, Yuji Sutou, Yukiko Ogawa

    pp. 2270-2275

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    DOI:10.2320/matertrans.MT-M2020244

    Abstract

    The formation of texture through thermomechanical treatment was investigated in Mg–18.8 at% Sc shape memory alloy to enhance its superelasticity at room temperature. The samples were cold rolled in an α phase or in a β phase and then finally heat treated at 690°C followed by water quenching to obtain a β phase. In the case of cold rolling in the α phase, a basal-plane texture was formed, while no preferential texture was observed along in-plane direction. After the final heat treatment, {011}〈uvw〉β transformation texture was obtained, according to Burgers relationship, indicating no improvement of the superelasticity along in-plane direction. In the case of the cold rolling in the β phase, a weak {111}〈011〉β recrystallization texture was obtained. The sample showed about 0.65% superelastic tensile strain along rolling direction, while that along transverse direction (//∼〈113〉β) showed only about 0.43%. This trend is in good agreement with the orientation dependence of the transformation strain, but, the obtained superelastic strain was much lower than the expected value, which is due to the weak texture and suggests the existence of a strong grain constraint in the Mg–Sc shape memory alloy. This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 84 (2020) 253–259.

  • Estimation of Texture-Dependent Stress-Strain Curve and r-Value of Aluminum Alloy Sheet Using Deep Learning

    Kohta Koenuma, Akinori Yamanaka, Ikumu Watanabe, Toshihiko Kuwabara

    pp. 2276-2283

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    DOI:10.2320/matertrans.P-M2020853

    Abstract

    The deformation of an aluminum alloy sheet is affected by its underlying crystallographic texture and has been extensively studied using the crystal plasticity finite element method (CPFEM). Numerical material test based on the CPFEM enables the quantitative estimation of the stress-strain curve and Lankford value (r-value), which depend upon the texture of aluminum alloy sheets. However, the application of CPFEM-based numerical material test to the optimization of aluminum alloy texture is computationally expensive. In this paper, we propose a method for rapidly estimating the stress-strain curves and r-values of aluminum alloy sheets using deep learning with a neural network. We train the neural network with the synthetic crystallographic texture and stress-strain curves calculated through the numerical material tests. To capture the features of synthetic texture from a {111} pole-figure image, the neural network incorporates a convolution neural network. Using the trained neural network, we estimate the uniaxial stress-strain curve and in-plane anisotropy of the r-value for various textures that contain Cube and S components. The results indicate that the application of a neural network trained with the results of numerical material test is a promising method for rapidly estimating the deformation of aluminum alloy sheets. This Paper was Originally Published in Japanese in J. JSTP 61 (2020) 48–55.

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  • Microstructural Characterization and Wear Behavior of Sintered Compacts Fabricated from Plasma-Nitrided Commercially Pure Titanium Powder

    Shoichi Kikuchi, Shiori Suzuki, Hiroyuki Akebono

    pp. 2284-2291

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    DOI:10.2320/matertrans.Z-M2020854

    Abstract

    The microstructure of commercially pure (CP) titanium having a bimodal nitrogen diffusion phase for biomedical applications, which was fabricated by sintering plasma-nitrided powders, was characterized, and its effect on the wear behaviors was examined. The maximum nitrogen concentration and hardness of CP titanium having a bimodal nitrogen diffusion phase depended on the powder plasma nitriding and sintering temperatures. The grain size of CP titanium made by sintering plasma-nitrided powders is smaller than that of the un-nitrided one. As results of ball-on-disk dry friction tests, CP titanium fabricated from powder plasma-nitrided at 873 K had lower wear resistance than compacts manufactured by sintering as-received CP titanium powder. In contrast, CP titanium fabricated from powder plasma-nitrided at 973 K having a continuous connected network nitrogen diffusion phase had high wear resistance due to the high hardness and differences in the wear mechanism. The wear resistance of CP titanium is dependent on the powder plasma nitriding and sintering temperatures.

  • A Novel Joint of 18-8 Stainless Steel and Aluminum by Partial Welding Process to Ni-Plated Carbon Fiber Junction

    Masataka Tomizawa, Michael C. Faudree, Daisuke Kitahara, Sagiri Takase, Yoshihito Matsumura, Itaru Jimbo, Michelle Salvia, Yoshitake Nishi

    pp. 2292-2301

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    DOI:10.2320/matertrans.MT-M2020199

    Abstract

    A novel joint of 18-8 stainless steel and aluminum (Al) connected by a 20 × 10 × 0.3 mm nickel (Ni)-coated carbon fiber (CF) cross-weave cloth junction utilizing extremely large friction force by broad interface of 6 µm diameter CF has been successfully developed for potential aerospace application. This was done by a partial welding process of the CF junction to 18-8 stainless steel and Al separately taking advantage of the different welding temperatures of 660°C for Al, and about 1400 to 1450°C for 18-8 stainless steel. First, the 18-8 side is fabricated by inserting half the CF junction length (10 mm) into a cut slit in 18-8 rod half length, followed by the welding and rapid solidification. Next, the remaining exposed CF junction half length is inserted into Al rod, also followed by welding and rapid solidification, resulting in the finished [18-8/CF/Al] joint. The partial welding was performed by novel method of spot electron beam allowing capillary action of molten metals into the CF junction for high CF surface contact area. When the carbon fibers were electroplated with Ni prior to the partial welding, tensile stress, σb of Ni-plated carbon fiber [18-8/Ni–CF/Al] joint was 36 MPa, about 2.5 times larger than that without Ni plating [18-8/CF/Al] joint at 14 MPa. Fracture energy estimated by integrated area under the stress-strain curve was substantially improved in [18-8/Ni–CF/Al] over [18-8/CF/Al] joints. This shows the partial welding performed by spot electron beam allows joining metals with different melting temperatures with the carbon fiber junction. XRD (X-ray diffraction) tests revealed improvements in [18-8/Ni–CF/Al] joint are by Ni plating the carbon fibers minimizing typical brittle Al4C3 carbide formation by acting as a barrier, and rapid solution hardening by nickel addition. EPMA (Electron probe microanalysis) showed the Ni coating also acts to protect carbon fibers against impingement from the hot molten metals during welding, along with prevention of mutual diffusion between Al or Fe with carbon fibers increasing strength of the [18-8/Ni–CF/Al] joint.

  • Effect of Baking on Hydrogen Embrittlement for High Strength Steel Treated with Various Zinc Based Electroplating from a Sulfate Bath

    Makoto Hino, Shunsuke Mukai, Takehiro Shimada, Koki Okada, Keitaro Horikawa

    pp. 2302-2306

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    DOI:10.2320/matertrans.MT-M2020245

    Abstract

    The hydrogen embrittlement of SK85 high-strength steel sheets was evaluated using a three-point bending test. The effects of electroplating each with zinc, zinc–SiO2, zinc–nickel, and zinc–nickel–SiO2 on hydrogen embrittlement were examined by baking the electroplated steel specimen. Each electroplating type caused hydrogen embrittlement, which was promoted by hydrogen, owing to the reduction due to hydrogen ions during electroplating. The hydrogen embrittlement of both zinc-electroplated and zinc–SiO2-electroplated SK85 steel continued after baking for 24 hours at 200°C, but that of the zinc–nickel-electroplated and zinc–nickel–SiO2-electroplated SK85 steel ceased. Furthermore, TDA revealed that the diffusible hydrogen at approximately 200°C, which was caused because of hydrogen embrittlement, was desorbed from all the electroplated specimens before the baking. However, after the baking, this diffusible hydrogen for each specimen was not desorbed. These results indicate that the hydrogen embrittlement for zinc-based electroplated high-strength steel was caused by another factor except for diffusible hydrogen. The hydrogen formed due to the electroplating was incorporated in the steel substrate, following which the hydrogen-vacancy cluster was formed in the substrate. It seems that the zinc and zinc–SiO2 film provided insufficient permeability required for the formation of the hydrogen-vacancy cluster. However, zinc–nickel and zinc–nickel–SiO2 film enabled hydrogen-vacancy cluster diffusion from the substrate. This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 84 (2020) 87–91.

  • Effect of Bonding Temperature on Microstructure and Mechanical Properties of Zircaloy-4/Ti/Ag/304L Diffusion Bonded Joints

    Yinglong Jiang, Yangyang Guo, Baoshuan Liu, Houhong Pan, Yan Liu, Gaofeng Quan

    pp. 2307-2311

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    DOI:10.2320/matertrans.MT-M2020065

    Abstract

    Vacuum diffusion bonding of Zircaloy-4 (Zr-4) and 304L stainless steel by using pure Ti and pure Ag as multiple interlayers was carried out at the bonding temperatures of 800–900°C for the bonding time of 30 min under the bonding pressure of 12 MPa. The effect of the bonding temperature on the interfacial microstructure and mechanical properties of the joints was studied. The results showed that the interface zone of the joints was transited from 304L/Ag/α-Ag+TiAg/Ti/Ti(Zr)/Zr(Ti)/Zr-4 to 304L/Ag/α-Ag+TiAg/Ag(Ti, Zr)2/Ti(Zr, Ag)/Ti(Zr)/Zr(Ti)/Zr-4 with the bonding temperature increased to 900°C while the TiAg content of α-Ag+TiAg layer decreased. Shear strength of the joints increased with the increasing of the bonding temperatures, and the maximum shear strength of 111.2 MPa was reached at 900°C. The fracture occurred in the Ag layer, which was mainly due to the low mechanical properties of Ag.

  • Lap Joining of Titanium to Galvanized Steel by Cold Metal Transfer Technology

    Jinghuan Chang, Yingjie Yan, Rui Cao

    pp. 2312-2319

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    DOI:10.2320/matertrans.MT-M2020226

    Abstract

    In this study, a cold metal transfer method with low heat input and no welding splash is used to weld the pure titanium TA2 and hot dipped galvanized mild Q235 steel with H08Mn2SiA wire. The effect of zinc coating on microstructure and properties of titanium/steel joints was investigated. The results show that an interface reaction layer with Ti–Fe intermetallics was produced between the titanium base metal and weld metal, even when a 2 mm offset distance of the welding torch towards the steel base metal was set. Zinc coating cannot improve mechanical properties of Ti/galvanized steel joint. It is attributed to the vaporization of the zinc coating, Zn element doesn’t react with Fe and Ti elements in the weld metal. The joints were fractured at the Ti–Fe interface reaction layer. It is not feasible to weld titanium and galvanized steel using the H08Mn2SiA wire, even though the cold metal transfer method and the galvanized steel with pure zinc coating were used.

  • Dependences of Grain Size and Strain-Rate on Deformation Behavior of Commercial Purity Titanium Processed by Multi-Directional Forging

    S. Yamamoto, Y. Miyajima, C. Watanabe, R. Monzen, T. Tsuru, H. Miura

    pp. 2320-2328

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    DOI:10.2320/matertrans.MT-M2020263

    Abstract

    Strain rate dependencies of deformation behavior of commercial purity titanium specimens having different grain sizes were systematically investigated. Ultrafine-grained titanium with an average grain size of 0.07 µm (UFG-Ti) fabricated by multi-directional forging followed by conventional thermo-mechanical processing, and fine-grained (FG-Ti) and coarse-grained (CG-Ti) specimens with an average grain sizes of 0.8 and 12 µm attained by its, respectively, annealing at 773 and 973 K for 1.8 ks were prepared. The FG- and UFG-Ti specimens exhibited strong strain-rate dependence of 0.2% proof stress, while that of CG-Ti ones were almost constant regardless of applied strain-rate. In-situ X-ray diffraction measurements during tensile tests were also conducted at synchrotron radiation facility, SPring-8. Using the modified Williamson-Hall and the modified Warren-Averbach methods, the activated slip systems and change in dislocation density during deformation were estimated. As a result, it was found that 〈a〉 and 〈c + a〉 slips were activated in FG- and UFG-Ti specimens. On the other hand, the activation of 〈c + a〉 slip was never observed in the CG-Ti ones. It can be, thus, concluded that the different strain-rate dependency of deformation behaviors of specimens with different grain sizes were ascribed to the difference in the deformation mechanisms. This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 83 (2019) 465–473.

  • Electrochemical Dy-Alloying Behaviors of Ni-Based Alloys in Molten LiF–CaF2–DyF3: Effects of Constituent Elements

    Kouji Yasuda, Terumichi Enomoto, Yusaku Watanabe, Tetsuo Oishi, Toshiyuki Nohira

    pp. 2329-2335

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    DOI:10.2320/matertrans.MT-M2020200

    Abstract

    The electrochemical Dy-alloying behaviors of Ni–Cr and Ni–Mo alloys were compared with those of Ni–Cr–Mo alloy and pure Ni in a molten LiF–CaF2–DyF3 (0.30 mol%) system at 1123 K. The effects of chromium and molybdenum as constituent elements of the Ni-based alloys were investigated. Cyclic voltammetry and open-circuit potentiometry indicated the formations of Dy–Ni alloys for all the Ni-based electrodes, as well as for the pure Ni electrode. XRD analysis confirmed the formation of DyNi2 and DyNi3 phases for all the electrodes electrolyzed at 0.20 V (vs. Li+/Li) for 60 min. SEM/TEM-EDX analysis of the sample prepared from Ni–Cr–Mo alloy revealed that the Dy-alloyed layer consists of Cr-rich Cr–Mo and Mo-rich Mo–Cr phases, as well as a Dy–Ni(–Fe) matrix phase. The shear stress measurements of the Dy-alloyed samples showed that the Ni–Cr–Mo alloy is the most suitable substrate to improve mechanical strength, which is explained by precipitation strengthening by both the Cr–Mo and Mo–Cr phases.

  • Formation of a Diffusion Barrier Coating on Ni-Based Alloy and Thermal Cycle Oxidation Property

    Shigeru Saito, Shigenari Hayashi, Takuro Narita, Yasumichi Kato, Motohiro Ohtsuka, Mayumi Ara, Toshio Narita

    pp. 2336-2341

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    DOI:10.2320/matertrans.MT-M2020150

    Abstract

    A diffusion-barrier coating layer (DBC) was formed on a Ni–22Cr–19Fe–9Mo alloy by Al-pack cementation at 1000°C followed by heat treatment at 1100°C. The thermal cyclic oxidation behavior of the DBC system was then investigated. The thermal cycle oxidation tests were conducted at 1100°C in air for 45 min, each followed by 15 min at room temperature. Electron probe micro-analysis (EPMA) was performed to determine the microstructure and concentration profile of each element between the substrate and the coating layer.The DBC system showed good thermal cycle oxidation property. The layer structure between the substrate and the coating layer after thermal oxidation cycling is discussed with respect to the composition paths plotted in the Ni–Cr–Fe and Ni–Cr–Al phase diagrams. The coating layer structure after 100 cycles of 45 min at 1100°C consisted of the γ- and α-phases of the Ni–Cr–Fe system and the β-phase of the Ni–Cr–Al system. The coating layer structure after 400 cycles of 45 min at 1100°C consisted of the γ-phase of the Ni–Cr–Fe system and the β-phase of the Ni–Cr–Al system. In contrast, the coating layer structure after 900 cycles of 45 min at 1100°C consisted of the γ-phase of the Ni–Cr–Fe system. This Paper was Originally Published in J. Japan Inst. Met. Mater. 83 (2019) 372–377.

  • Corrosion Mechanism of Q235A under 3.5% NaCl Salt Spray

    Jiantao Wang, Bochen Jiang, Jiangdong Cao

    pp. 2342-2347

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    DOI:10.2320/matertrans.MT-M2020053

    Abstract

    Low-carbon steel Q235A is the main material used in marine construction, but it experiences corrosion because of salt spray and seawater exposure. In this study, we investigated the corrosion performance of Q235A in the presence of 3.5% NaCl salt spray. We characterized the microstructure of the material using electron backscattered diffraction, scanning electron microscopy, and specimen weight loss. The phases and morphologies of the corrosion products were then analyzed after salt-fog corrosion testing. The degree of coverage and compactness of surface corrosion products gradually increased from the 24 to 96 hours in the salt spray environment. Under short-term corrosive conditions, surface corrosion products were primarily composed of a loose, porous layer of flocculent γ-FeOOH. With increasing time, the corrosion products gradually changed to a lump-like and block-like dense structure of β-FeOOH and α-FeOOH. The results of electrochemical polarization tests of the corroded steel samples showed that the γ-FeOOH might accelerate corrosion, and that β-FeOOH and α-FeOOH inhibit corrosion.

  • Atmospheric Corrosion Monitoring Sensor in Corrosion Rate Prediction of Carbon and Weathering Steels in Thailand

    Wanida Pongsaksawad, Namurata S. Palsson, Piya Khamsuk, Sikharin Sorachot, Amnuaysak Chianpairot, Ekkarut Viyanit, Tadashi Shinohara

    pp. 2348-2356

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    DOI:10.2320/matertrans.MT-M2020230

    Abstract

    Galvanic type atmospheric corrosion monitoring (ACM) sensors can distinguish wet and dry conditions of a surface by reporting spiked charge when there is an electrolyte film on the sensor. In this study, Fe–Ag type ACM sensor was exposed to monitor time of wetness (TOWACM) on carbon steel and weathering steel coupons at seven test stations in Thailand. Climate parameters were monitored by weather stations. Chloride and sulfur dioxide deposition rates were obtained by dry gauze and lead dioxide cylinder methods, respectively. The objective was to investigate the effects of TOWACM, climate, and aerosols on corrosion rate in Thailand tropical climate under high temperature, high relative humidity, and frequent monsoon-induced rainfalls. Multivariable linear regression model applied on the first-year corrosion rate yielded predictive equations for (1) inland areas-as a function of temperature (T) and relative humidity (RH) and (2) coastal areas-as a function of rainfall (RF) with TOWACM or chloride (Cl−) deposition rate. The first corrosion map of Thailand was proposed based on the predictive equations for corrosion rates of carbon steel and weathering steel.

  • Determination of Gibbs Energies of Formation of Cr3B4, CrB2, and CrB4 by Electromotive Force Measurement Using Solid Electrolyte

    Hiroaki Yamamoto, Yoshitaka Wada, Kazuto Nishiyama, Yoshitsugu Taniguchi, Ai Nozaki, Masao Morishita

    pp. 2357-2362

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    DOI:10.2320/matertrans.MT-M2020247

    Abstract

    The standard Gibbs energies of formation, ΔfG°, of intermediate compounds of Cr3B4, CrB2, and CrB4 in the boron-rich side of the Cr–B binary system were determined by measuring electromotive forces of the galvanic cells using ZrO2–Y2O3 solid electrolyte. The phase equilibria for the Cr–B binary system were clarified to construct the cells using the solid electrolyte. The measured electromotive forces of the cells were evaluated as linear temperature functions under the conditions that the transport numbers of oxide ion in solid electrolyte were regarded as 1.0. The ΔfG° functions determined from the electromotive forces via the Nernst equation were as follows:ΔfG°(Cr3B4)/J (mol of compd)−1 = −264540 − 26.697 T ± 970 (1256–1322 K),ΔfG°(CrB2)/J (mol of compd)−1 = −84572 − 32.442 T ± 790 (1253–1350 K),ΔfG°(CrB4)/J (mol of compd)−1 = −105120 − 57.921 T ± 2200 (1280–1352 K).The present ΔfG° values satisfied the phase equilibria in the Cr–B binary system. Using the ΔfG° values determined in the present study, the composition-oxygen partial pressure diagram of the Cr–B–O ternary system was constructed under the conditions of 1300 K and a total pressure of 1 bar (100 kPa). It is useful to understand the oxidation path of the boron-rich side of Cr–B binary alloys.

  • Influence of Nb and V Addition on Abrasive and Impact Wear Properties of 16%Cr–3%Mo White Cast Iron

    Ngo Huynh Kinh Luan, Koreaki Koizumi, Tetsuya Okuyama

    pp. 2363-2370

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    DOI:10.2320/matertrans.F-M2020852

    Abstract

    Investigations were conducted on the microstructure and behaviors of abrasive wear and impact wear of 16%Cr–3%Mo white cast iron without and with 2.7%Nb–1%V addition heat-treated at 1253 K followed by forced-air cooling to clarify the difference between two kinds of wear mechanisms. Microstructures were analyzed by means of scanning electron microscope equipped with energy dispersive X-ray spectrometer, X-ray diffractometer and ferrite meter. Results reveal that since MC spheroidal carbides are formed by addition of Nb and V, the other primary carbides are refined and martensite in the matrix becomes more stable. Such microstructure improves abrasive wear resistance, but deteriorates impact wear resistance. Under the severe test condition, self-tempering softening of martensite in the matrix caused by the impact energy of abrasive media and it increases the impact wear rate.

  • Viscosity Properties Prediction of Semi-Solid Aluminum Alloys Using Finite Element Analysis Based on Quenched Solidified Structure, and Experimental Validation

    Naofumi Takatori, Mami Amano, Ryousuke Miyachi, Yoshihiro Nagata, Muhammad Khairi Faiz, Makoto Yoshida

    pp. 2371-2377

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    DOI:10.2320/matertrans.L-M2020855

    Abstract

    For predicting hot tearing during casting process, viscosity properties and constitutive equations in the semi-solid region are required. In this research, viscosity properties of two alloys, which are Al–5 mass%Mg alloy with Ti–B grain-refiner and Al–2 mass%Cu alloy with Ti–B grain-refiner, are estimated using the image-based modelling method as suggested by Matsushita et al. As to the mechanical properties of the solid phase in semi-solid region, it is found that by using the temperature dependent value rather than the value just below the solidus temperature, the prediction accuracy of the viscosity value in semi-solid region has increased. By comparing the obtained numerical properties with the experimental properties, it is found that the method can predict the viscosity properties of Al–5 mass%Mg alloy and Al–2 mass%Cu alloy in the semi-solid region at the solid fraction where hot tears are likely to occur. This Paper was Originally Published in Japanese in J. JILM 70 (2020) 187–193.

  • Simulation and Experimental Study on Temperature and Flow Field in Friction Stir Welding of TC4 Titanium Alloy Process

    Yiming Qi, Junping Li, Yifu Shen, Wentao Hou

    pp. 2378-2385

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    DOI:10.2320/matertrans.MT-M2020017

    Abstract

    In this study, numerical simulation method was used to investigate the temperature field and the flow field of FSW for TC4 titanium alloy. According to the contact condition between the tool surface and the weld piece, a scientific heat source calculation method was built and its reliability has been verified by experiments. The temperature distribution characteristics of welding zone were investigated. The simulation results shows that the welding materials around the friction head flows like funnel-shape in a whole, similar to the shape of the friction head. The flow condition of welding materials is asymmetric with respect to the weld line, and the flow velocity increases with the greater distance from the center of the weld. As the depth of the weld increases, the flow capacity of the material gradually becomes weaker.

  • Floating Grain Characterization and Its Effects on Centerline Segregation of Direct-Chill Cast Al–Mg–Si Alloy Billets

    Qipeng Dong, Xiaming Chen, Jun Xia, Xinzhong Li, Bo Zhang, Hiromi Nagaumi

    pp. 2386-2392

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    DOI:10.2320/matertrans.MT-M2020229

    Abstract

    Microstructure and microsegregation analysis were performed on a direct-chill (DC) cast Al–Mg–Si alloy billet, aiming to quantitatively investigate the microscopic features of floating grain and its contribution to the negative centerline segregation. Microstructure results show some irregular grains, whose grain size and secondary dendrite arm spacing (DAS) are two times larger than that of the regular fine grains, appear only in the billet central region. The duplex grain structure, a mixture of internal coarse and peripheral finer dendrites within one grain, was clearly shown by the EPMA results, exhibiting special microsegregation features. The coarse dendrites are more solute-depleted than the nearby finer-DAS structure, in which the average concentration of solute Mg nearly equals to the nominal content. Based on the microscale features and solidification information of the alloy, the irregular grains exhibiting duplex dendrite feature are confirmed to be floating grain, which internal coarse dendrites are believed to mainly contribute to the negative centerline segregation. And the resulting segregation degree is quantitatively evaluated to be ∼0.041 for solute Mg considering the floating grains in the billet center as against with the assumed 100% fine-DAS microstructure.

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  • Reduction of Blister Occurrence after Plating in Zinc Alloy Die Casting by Optimization of Gating System

    Takuya Sakuragi, Daiki Fuwa, Ichiyou Nakayama, Takumi Nagamori

    pp. 2393-2401

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    DOI:10.2320/matertrans.MT-M2020222

    Abstract

    In die casting, laminations are a serious problem because they cause blisters, stripping defects and zinc deposition on the mold surface. Blisters and stripping defects reduce the quality of the product, and zinc deposits on the mold surface reduce productivity. Therefore, the analytical prediction of the risk of lamination formation and the optimization of the gating system for reducing the occurrence of defects due to laminations are very important before designing a mold. To optimize the gating system, we used an evaluation criterion formulated using the shear rate of the molten metal flow in a die casting simulation. In this study, we proposed a coupling analysis method consisting of mold temperature and mold filling analyses, and applied it to the optimization of a gating system based on the evaluation criterion. Using this method, we eliminated the occurrence of blisters due to laminations after plating.

  • Development of High-Performance Solid-State Thermal Diodes Using Unusual Behavior of Thermal Conductivity Observed for Ag2Ch (Ch = S, Se, Te)

    Keisuke Hirata, Takuya Matsunaga, Singh Saurabh, Masaharu Matsunami, Tsunehiro Takeuchi

    pp. 2402-2406

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    DOI:10.2320/matertrans.E-M2020847

    Abstract

    Thermal diodes are a kind of new device which controls the direction and magnitude of heat flow. The performance of thermal diode is evaluated by thermal rectification ratio (TRR) defined as |Jlarge|/|Jsmall|. Solid-state thermal diodes are made with two materials possessing different temperature dependence of thermal conductivity. Their performance is improved by the significant variation of thermal conductivity with temperature. In this study, therefore, we employed Ag2Ch (Ch = S, Se, Te) because these materials are characterized by a drastic change in thermal conductivity due to a structural phase transition in the temperature range of 373 < T < 473 K. We prepared Ag2Ch samples by means of self-propagating high-temperature synthesis method. The phases involved in the samples were identified using powder X-ray diffraction. We measured temperature dependence of thermal conductivity for prepared samples by means of laser flash method, and consequently observed 200–300% change in their thermal conductivity. The thermal diode consisting of Ag2S and Ag2Te was designed using the measured thermal conductivity. We experimentally confirmed that the developed thermal diode showed TRR = 2.1 ± 0.1 when it was placed between two heat reservoirs kept at TH = 473 K and TL = 405 K. This Paper was Originally Published in Japanese in J. Thermoelec. Soc. Jpn. 16 (2019) 3–7.

  • Chalcostibite Single-Crystal CuSbS2 as High-Performance Thermoelectric Material

    Akira Nagaoka, Manato Takeuchi, Yusuke Shigeeda, Koki Kamimizutaru, Kenji Yoshino, Kensuke Nishioka

    pp. 2407-2411

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    DOI:10.2320/matertrans.E-M2020850

    Abstract

    Chalcostibite CuSbS2 has attracted attention as an environmentally friendly material in thermoelectric (TE) field. Our investigations into the TE properties of high-quality p-type CuSbS2 single crystals revealed that they exhibit a uniquely low thermal conductivity caused by the active lone-pair electrons in Sb3+ ions. The electrical conductivity was improved by the high density of shallow acceptor Cu vacancies and the absence of potential barriers to carrier transport. Consequently, the figure of merit for the Cu-poor CuSbS2 single crystal reached 0.5 at 700 K, which is 25 times higher than that of the reported polycrystalline sample.

  • Novel Fatigue Crack Propagation Analysis of Solder Joint Using Singularity of Strain Energy Density in the Crack Tip Near Field

    Yuta Nakajima, Yoshiharu Kariya, Keisuke Ono

    pp. 2412-2418

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    DOI:10.2320/matertrans.MT-M2020207

    Abstract

    This study investigated a singularity parameter of strain energy density by which the path-independent property is guaranteed in the analysis of fatigue crack propagation in a solder joint by using the finite element method. When plastic deformation was dominant, an inverse relationship obeying the HRR singularity theory held with the strain range ΔW, which was calculated using the volume average of the element solutions in an area of arbitrary size around the crack tip and the size of the area Larea. Therefore, the path-independent property was guaranteed using the proportional constant ΔWc of the inverse relationship. In contrast, the path-independent property of ΔWc was lost under elasto-plastic deformation where the unloading effects could not be ignored or under creep deformation where the generalized Garofalo law was used for the constitutive equation. In this study, ΔWNear field, which was calculated by extrapolation from ΔW obtained in the first field around the crack tip and the second field inside the first field, was proposed as a new parameter in fatigue crack propagation analysis. ΔWNear field exhibited the path-independent property for various loading conditions and it was demonstrated by FEM analysis using the fatigue data of Sn–5.0Sb measured in a past study that highly accurate fatigue crack propagation analysis of solder joints is possible using ΔWNear field.

  • Effect of Acetic Acid on Wear Properties of Ferrous and Titanium-Based Materials under Ethanol Lubrication

    Yuko Hibi, Hiroki Mano

    pp. 2419-2427

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    DOI:10.2320/matertrans.MT-M2020103

    Abstract

    Disks of ferrous and titanium-based material were immersed and unidirectionally slid against a stainless steel pin in ethanol with or without acetic acid to evaluate the effect of acetic acid on wear. The disks were made of cast iron, stainless steel, titanium metal and particulate-reinforced titanium metal matrix composite sintered from mixed powder of Si3N4 (5 mass%), TiN (10 mass%) and Ti (85 mass%). In the absence of sliding, the stainless steel, titanium and composite showed good corrosion resistance but the cast iron exhibited galvanic corrosion. With sliding, the addition of acetic acid to the ethanol increased the wear of the ferrous materials but had little effect on the titanium-based materials. Morphological and chemical analyses of the worn surfaces revealed that acetic acid promoted anodic dissolution of iron on the sliding surfaces of the ferrous materials in ethanol. The results also indicated that titanium and the composite in ethanol with and without acetic acid primary underwent mechanical wear and chemical wear, respectively. The composite exhibited good corrosion and wear resistance in ethanol regardless of the presence of acetic acid.

  • Analysis on the Utilization of Opinion of Bridge Inspection Results Using Topic Model for Maintenance and Management

    Fukutsugu Ogawa, Yasuo Chikata

    pp. 2428-2434

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    DOI:10.2320/matertrans.Z-M2020851

    Abstract

    Utilization of collected and accumulated data of bridge inspection results is required for maintenance. Although the qualitative evaluation items of bridges have frequently been used in the past, this research focuses on the opinions of technical experts during bridge inspection. Topic models consist of probabilistic modeling of term frequency occurrences in documents, which can be used to classify documents containing opinions of bridge inspections. A topic model can be applied to the text data to detect the characteristics of bridge damage not recorded as database evaluation items. The topics corresponding to the characteristic damage condition of the bridge can then be organized. In this study, topics have been organized by high probability words about deterioration due to ASR (Alkali-Silica Reaction), which is a characteristic deterioration in the Hokuriku region. By focusing on the opinions from bridge inspections associated with high probability topics, early detection and preventative maintenance are possible. Although effective results were obtained, some topics were organized by the characteristic writing of the inspection company. This means that in order to accumulate the inspection data while maintaining quality, it is necessary to consider the method and writing style that was used in creating the contents of the opinion in the bridge inspection report. This Paper was Originally Published in J. Soc. Mater. Sci., Japan 69 (2020) 197–203.

  • Recent Progress in Nanostructured Functional Materials and Their Applications

    Tomoyuki Yamamoto, Masato Yoshiya, Hoang Nam Nhat

    pp. 2435-2441

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    DOI:10.2320/matertrans.MT-M2020302

    Abstract

    A current research trend for nanostructured functional materials and their applications are summarized in this paper, for which a recently published special issue in Materials Transactions, Vol. 59, No. 7, is mainly surveyed here. Among the progresses of the functional materials, several important topics were covered in this special issue, which are advanced atomic or nano-meter scale analysis, advanced ab initio simulations, highly correlated electron system, advanced spectroscopy and advanced processing. In addition, contents of some related special issues are introduced.

  • Interconnection Mechanism of Ni-Reinforcement Particle Filled Solderable Polymer Composites with Low-Melting-Point Alloy Filler

    Hee Jun Youn, Jeong Il Lee, Jong-Min Kim, Byung-Seung Yim

    pp. 2442-2445

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    DOI:10.2320/matertrans.MT-M2020265

    Abstract

    A novel bonding material system and its interconnection mechanism using a Ni-reinforcement particle filled solderable polymer composites (SPCs) with a low-melting-point alloy (LMPA) filler was proposed to enhance the mechanical properties of the SPC joints. To confirm the feasibility of the proposed interconnection mechanism of Ni-reinforcement particle filled SPC, two types of wetting test (e.g., flat and line pattern wetting test) were conducted. The Ni-reinforcement particle filled SPC exhibited better wettability compared with those of SPC without Ni particle. In the microstructure inspection, ternary Cu–Ni–Sn intermetallic compound (IMC) was formed at surface of the Ni particles within the LMPA region and bonding interface between Cu metallization and LMPA. Additionally, the flow, coalescence and selective wetting behaviors of molten LMPA filler was not hindered by incorporated Ni particles.
  • © 2020 The Japan Institute of Metals and Materials

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