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MATERIALS TRANSACTIONS Vol. 55 (2014), No. 2

ISIJ International
belloff
オンライン版ISSN: 1347-5320
冊子版ISSN: 1345-9678
発行機関: The Japan Institute of Metals and Materials

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キーワードランキング

22 Dec. (Last 30 Days)

MATERIALS TRANSACTIONS Vol. 55 (2014), No. 2

Development of Multilayer Steels for Improved Combinations of High Strength and High Ductility

Toshihiko Koseki, Junya Inoue, Shoichi Nambu

pp. 227-237

DOI:

10.2320/matertrans.M2013382

抄録

Multilayer steels have been developed to provide a novel route to achieving higher-performance steels by employing a high-strength steel and a high-ductility steel independently in the layer structure. In this article, a background to the development, design, fabrication, properties, and applications of multilayer steels are overviewed. Multilayer steels exhibit improved combinations of strength and ductility compared with existing monolithic steels and also excellent deformation behaviors under high-strain-rate deformation as well as good formability. Those improved performances of multilayer steel are achieved by increased interfacial toughness between the layers and decreased thickness of the brittle steel layers according to the fracture toughness of the brittle steel and the strength of the ductile steel. The concept of multilayer steels is extended by applying different combinations of components, such as Mg-steel multilayer composite.

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Effect of Initial Microstructure on Mg Scroll Forging under Warm Forming Condition

Jonghun Yoon, Junghwan Lee

pp. 238-244

DOI:

10.2320/matertrans.M2013274

抄録

Magnesium (Mg) alloys have attracted considerable interest for various applications, including those in the automotive and electronics industries, because of their high specific strength, excellent thermal conductivity, and recycling capability in comparison with commonly used aluminum alloys and steels for structural materials. One of the core parts in the compressor unit of an automobile is the scroll rotor, which is assembled with two scrolls, a rotating orbit scroll on the fixed scroll, to compress the refrigerant. In this study, we proposed a net-shape forging process and an apparatus with the back-pressure technique for the Mg scroll at a forging temperature of 350°C with an Mg–6Al–1Zn extruded billet. The optimum amount of back-pressure is calibrated by finite element analysis using DEFORM-3D, which enhances the wrap height distribution in the Mg scroll uniformly. To elucidate the effect of the initial texture on the forgeability of the Mg scroll, twin-induced and dynamic recrystallization (DRX)-induced specimens are applied in Mg scroll forging, where the formability of the Mg scroll with the DRX-induced specimen is found to be noticeably improved in terms of the wrap height.

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Visible-Light Photocatalysis of LSMO-Graphene Nanocomposites toward Degradation of Methyl Red

T. Xian, H. Yang, Y. F. Wang, L. J. Di, J. L. Jiang, R. S. Li, W. J. Feng

pp. 245-248

DOI:

10.2320/matertrans.M2013317

抄録

La0.7Sr0.3MnO3 (LSMO) nanoparticles were synthesized by a polyacrylamide gel route. LSMO-graphene nanocomposites were fabricated by mixing LSMO nanoparticles and graphene into absolute ethanol solution followed by thermal drying. SEM observation shows that the synthesized LSMO nanoparticles are uniformly and regularly shaped like spheres with an average size of ∼24 nm. TEM observation reveals that LSMO nanoparticles are well assembled onto graphene sheets. The photocatalytic activity of prepared samples was evaluated by degrading methyl red (MR) under visible-light irradiation. It is demonstrated that LSMO-graphene nanocomposites exhibit an enhanced photocatalytic activity compared to bare LSMO nanoparticles. This can be explained by the fact that the photogenerated electrons are captured by graphene, leading to an increased availability of holes for the photocatalytic reaction. The direct hole oxidation is suggested to be the main mechanism toward the dye degradation.

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Aging Behavior of Ultra-Fine Grained Al–0.5%Si–0.5%Ge Alloy Fabricated by ARB Process

Keiyu Nakagawa, Nobuhiro Tsuji, Daisuke Terada, Toshihiko Nakano, Khairul Nizam, Teruto Kanadani

pp. 249-254

DOI:

10.2320/matertrans.L-M2013842

抄録

The aging behavior of ultrafine-grained (UFGed) Al–0.5%Si–0.5%Ge alloy fabricated using six-cycle accumulative roll-bonding (ARB) processing has been investigated using Vickers hardness measurement and TEM observation.
The hardness of UFGed alloy before aging is about 2.3 times higher than that of the starting specimen without ARB process. The starting UFG specimen showed ultrafine grains with mean size of 156 nm. The hardness of a UFG specimen aged at 473 K decreased monotonously with increasing aging time. From TEM observations of the microstructure of UFG specimen aged at 473 K for long time, results show that the mean size of ultrafine grains increased significantly with increasing aging time. Furthermore, few precipitates exist inside gains, although many coarse precipitates exist at grain boundaries. The hardness of UFG specimen aged at 373 K showed higher value than that aged at 473 K. From TEM observations, results showed many elongated ultrafine grains, with many precipitates formed on the grain boundaries and inside grains of the specimens aged at 373 K.
These results suggest that precipitation hardening strongly affected the hardness in this alloy because many Si–Ge precipitates formed inside grains of the UFG specimen aged at 373 K for long time.

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Dynamic Recrystallization Behavior of Waspaloy during Hot Working

Takanori Matsui

pp. 255-263

DOI:

10.2320/matertrans.M2013376

抄録

Ni base superalloy is one of the most important key materials for hot section parts in various applications. As for cast and wrought material, it is well known that grain size distribution and recrystallization ratio as well as precipitation condition have considerable effect on mechanical properties. The deformation and dynamic recrystallization behavior of representative Ni base superalloy, Waspaloy were revealed through various kinds of hot compression tests and quantitative relationship available for numerical calculation technology was derived. Dynamically recrystallized grain diameter depended on temperature, strain rate and was independent of the initial grain diameter and strain. The grain diameter could be expressed as a function of the temperature compensated strain rate, i.e., Zener–Hollomon parameter quantitatively. Avrami-type equation was available for comprehensive and quantitative expression of dynamic recrystallization transition. The approximation was a function of the given strain and strain for the 50% recrystallization which depends on the initial grain diameter and Zener–Hollomon parameter.

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Microstructure Evolution of Mg–4.3Zn–0.7Y–0.6Zr Alloy during Solution Heat Treatment

Junjie Li, Yacong Zhang, Jincheng Wang, Zhongming Zhang

pp. 264-269

DOI:

10.2320/matertrans.M2013378

抄録

The microstructure evolution in a Mg–4.3Zn–0.7Y–0.6Zr (mass%) alloy was investigated during solution heat treatment from 300 to 500°C for 12 h. In the as-cast and solution-treated at 300°C for 12 h states, the microstructures are consisting of I-phase and α-Mg. After solution treated at 400°C for 12 h, besides I-phase and α-Mg, some long strip precipitates-which are determined as Zn2Zr phase-, also appear in the microstructure. In the solution-treated sample at 500°C for 12 h, small amounts of Zn2Zr and Mg0.97Zn0.03 phases have been found. With the increase of heat treatment temperature, the phase constituents for different states are: α-Mg + I-phase (as-cast) → α-Mg + I-phase (300°C for 12 h) → α-Mg + I-phase + W-phase + Zn2Zr (400°C for 12 h) → α-Mg + Zn2Zr + Mg0.97Zn0.03 (500°C for 12 h).

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Microstructure Evolution of AZ80 Magnesium Alloy during Multi-Directional Forging Process

Qingfeng Zhu, Lei Li, Zhiqiang Zhang, Zhihao Zhao, Yubo Zuo, Jianzhong Cui

pp. 270-274

DOI:

10.2320/matertrans.M2013251

抄録

Grain refinement of a magnesium alloy, AZ80, was studied in multi-directional forging (MDF) with decreasing temperatures from 683 to 573 K. The MDF was carried out up to accumulative true strains of around 7 with changing the loading direction from pass to pass. The structural changes are characterized by the alternate appearance of fine dynamic recrystallized (DRXed) grains (with many dynamic granular Mg17Al12 phases) and coarse DRXed grains (without Mg17Al12 phases) in the sample, the expansion of the fine grains area, and the refinement of (DRXed) grains in the fine grains area during the MDF process. The non-uniform dynamic precipitation of the Mg17Al12 phase may attribute to the inhomogenous Al content distribution in the Mg matrix. These Mg17Al12 phase retards the growth of the DRX grains, which in turn results in the formation and the expansion of the fine grains area during the MDF process with decreasing temperature.

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Prediction of the Constitutive Equation for Uniaxial Creep of a Power-Law Material through Instrumented Microindentation Testing and Modeling

Hidenari Takagi, Ming Dao, Masami Fujiwara

pp. 275-284

DOI:

10.2320/matertrans.M2013370

抄録

Indentation creep tests and finite element simulations were performed on a model material to show that the constitutive equation for conventional uniaxial creep can be derived using the instrumented indentation testing technique. When the indentation pressure and the indentation creep rate are maintained at constant values of ps and \dot{ε}in(s), respectively, the contours of the equivalent stress and the equivalent plastic strain rate in the region beneath the conical indenter expand according to the increase in the displacement of the indenter while maintaining geometrical self-similarity. These findings indicate that a pseudo-steady deformation state takes place around the indenter tip. The representative point exhibiting the creep behavior within the limited region, which actually determines the indenter velocity, is defined as the location where the equivalent stress \bar{σ}r equals ps/3. The equivalent plastic strain rate \dot{\bar{ε}}r at this point is found to be \dot{ε}in(s)/3.6 in the case when the stress exponent for creep is 3. The stress exponent and the activation energy for creep extracted from the results of Al–5.3 mol%Mg solid-solution alloy indentation tests are in close agreement with those of tensile creep tests reported in the literature. In addition, the values for \bar{σ}r and \dot{\bar{ε}}r agree well with the values for the applied stress and the corresponding creep rate in tensile creep tests at the same temperature. The above results show that the creep characteristics of advanced materials, which are often available in minute quantities or as small-volume specimens, can be obtained from carefully designed indentation creep tests, and furthermore the constitutive equation for tensile creep can be predicted with sufficient accuracy through indentation creep test results.

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In-Situ Observation and Acoustic Emission Analysis for SCC of MgCl2 Droplet in SUS304 Stainless Steel

Mitsuharu Shiwa, Hiroyuki Masuda, Hisashi Yamawaki, Kaita Ito, Manabu Enoki

pp. 285-289

DOI:

10.2320/matertrans.M2013331

抄録

Acoustic emission and optical video microscope monitoring was proposed to investigate the stress corrosion cracking of work-hardened SUS304 stainless steel caused by a small magnesium-chloride droplet. The crack propagation length could measure clearly under the droplet by VMS. The SCC started at 45–82 ks with pitting. The crack velocity was 3.2–4.7 µm/ks and it propagated almost continuously. AE signals were generated at early stage of SCC testing of 55 and 82 ks, after that they were generated discontinuously. With the SEM observations, the detected AE signals were mainly attributed to cracking of the oxidation products and discontinuous crack propagation at the falling-off surface grain.

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High-Temperature Oxidation and Its Kinetics Study of Ti–Al and Ti–V Alloys in Air

Tomoshi Takahashi, Yoritoshi Minamino, Hideyuki Hirasawa, Tadashi Ouchi

pp. 290-297

DOI:

10.2320/matertrans.L-M2013840

抄録

The high-temperature oxidation behavior of Ti–(6–36) mass%Al alloys and Ti–(4–15) mass%V alloys has been investigated in a temperature range of 1123 to 1273 K in air. A kinetic study of the oxidation has been also carried out in Ti–6 mass%Al alloy and Ti–4 mass%V alloy. The growth rate of oxides of Ti–V alloys is larger than that of Ti–Al alloys. The oxidation products have been examined by X-ray diffraction (XRD), electron probe microanalysis (EPMA) and X-ray photoelectron spectroscopy (XPS). The Al2O3 layer is probably formed in the Ti–Al/oxides interface of the Ti–6 mass%Al alloy according to the results by means of EPMA, although only the rutile TiO2 is detected by means of XRD in the oxides of surface layer in Ti–6 mass% Al alloy and Ti–4 mass%V alloy at 1273 K. Furthermore, the TiO2 and Al2O3 are observed by XPS in the surface layer of the above both alloys oxidized at 1123 K for 3.6 ks, but the V2O5 is not observed. It is found that the apparent activation energy (245 kJ/mol) for the oxidation experiment (TG experiment) at a constant heating rate is fairly equal to the activation energy (253 kJ/mol) for the isothermal oxidation in Ti–6 mass%Al alloys.

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Experimental Determination of the Isothermal Section in a Ternary Re–Cr–Nb System at 1500°C

Shigeru Saito, Toshiyuki Takashima, Katsumi Miyama, Toshio Narita, Taiichi Nagata, Ideo Masuda, Kenichi Kajiwara

pp. 298-303

DOI:

10.2320/matertrans.M2013282

抄録

The compositions with tie-lines between the χ, σ, γ, α, and Nb(Cr,Re)2 phases in a ternary Re–Cr–Nb system were investigated at 1500°C by heat-treating various ternary Re–Cr–Nb alloys in vacuum for either 2 or 220 h. The microstructures of the Re–Cr–Nb alloys that had been water-quenched after heating were observed and their Re, Cr, and Nb concentration profiles were measured using an electron probe micro-analyzer (EPMA).
The tie-line compositions (at%) of each phase at 1500°C were experimentally determined, and an isothermal phase diagram was constructed. The χ phase tie-lined with the α phase (26.4 at% Re, 70.0 at% Cr, and 3.6 at% Nb) consists of 42.7 at% Re, 40.8 at% Cr, and 16.5 at% Nb. The α phase tie-lined with the Nb(Cr,Re)2 phase (28.1 at% Re, 41.9 at% Cr, and 30.0 at% Nb) consists of 24.6 at% Re, 71.2 at% Cr, and 4.2 at% Nb. The solubility limit of Re in the γ phase was 44–45 at% Re as the Cr content increased (i.e., Re content decreased) in the γ phase; the Cr content in the χ phase with a tie-line with the γ phase increased from 1.8 at% Cr to 9.8 at% Cr. The solubility limit of Nb in the σ phase tie-lined with the χ phase is 2 at% Nb.

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Entangled Duplex Structure and Polycrystalline Globule Formation through Multistep Liquid-Phase Separation in Cu–Fe–Zr–B Alloys

Takeshi Nagase

pp. 304-310

DOI:

10.2320/matertrans.F-M2013837

抄録

A unique entangled duplex structure was formed in rapidly solidified Cu–Fe–Zr–B alloys with Cu/Fe ratio = 1/1 and 6/1. Polycrystalline globules, embedded in a Cu crystalline matrix, were also observed in Cu35Fe35Zr10B20 and Cu60Fe10Zr10B20 alloys; this rapidly solidified structure was drastically different from that of Cu–Fe–Zr–B alloys enriched in Fe. Multi-step liquid phase separation can lead to unique microstructure formation during rapid solidification.

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Change in Molten Metal Pressure and Its Effect on Defects of Aluminum Alloy Die Castings

Yasushi Iwata, Shuxin Dong, Yoshio Sugiyama, Hiroaki Iwahori

pp. 311-317

DOI:

10.2320/matertrans.F-M2013838

抄録

Surface defects of die castings, such as surface folds, cold shuts and misruns, etc., are thought to occur due to the solidification of molten metal during mold filling. In the die casting process, mold filling and solidification are completed under high pressure. Thus, varying the casting pressure may also have some effects on surface defects.
In this study, we investigated the effects of solidification on mold filling and pressure transmission and elucidated the influences of casting pressure on the quality of die castings.
In the mold filling process of JIS AC4C (A356) alloy (hereinafter called AC4C alloy), flow resistance was found to increase with the increase of the amount of solid phases, and thus decreased the velocity of molten metal flow. Cold shut occurred due to the rapid drop of the temperature of molten metal as a result of the decrease in flow velocity. A similar phenomenon was also observed for JIS AD12.1 (A38X) alloy (hereinafter called AD12.1 alloy), although this alloy showed a skin-formation type solidification. The pressure transmission in molten metal weakened gradually with the increase in the amount of solid phases and eventually stopped completely to cause casting defects as the result. In addition, resistance to molten metal flow due to the back pressure, shape of mold cavities, etc., was also noticed. These results indicate that a high plunger pressure is necessary to obtain die castings without defects.

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Effects of Tensile Prestress Level on Impact Value of 50 vol% Continuous Unidirectional 0 Degree Oriented Carbon Fiber Reinforced Epoxy Polymer (CFRP)

Yoshitake Nishi, Takumi Okada, Soushi Okada, Mitsuru Hirano, Masumi Matsuda, Atsushi Matsuo, Michael C. Faudree

pp. 318-322

DOI:

10.2320/matertrans.M2013278

抄録

Effects of tensile prestress level on Charpy impact value (auc) of 50 vol% continuous unidirectional 0 degree oriented carbon fiber reinforced epoxy polymer (CFRP) were investigated. Experimental results showed the auc at mid-fracture probability Pf = 0.50 induced by a large prestress of 17.6 MPa (109 kJm−2) was increased 30% over that (84 kJm−2) of slight prestress of 0.25 MPa. The statistically lowest impact value as at Pf = 0 calculated by 3-parameter Weibull equation was raised 26% from 73 to 92 kJm−2 showing increased reliability of part strength. Fracture surface observation showed a flat surface extending through the thickness from the impact side generally extends deeper as prestress level was raised. This may be due to the transition depth in the specimen thickness from compression to tension is deeper during impact as prestress level was increased acting to raise the impact values.

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Impact Value of CFRP/Ti Joint Reinforced by Nickel Coated Carbon Fiber

Yoshitake Nishi, Sho Ishii, Shigehito Inui, Atsushi Kasai, Michael C. Faudree

pp. 323-326

DOI:

10.2320/matertrans.M2013320

抄録

A nickel coated carbon fiber reinforced joint (Ti/NiCF/CFRP) was suggested and developed between carbon fiber reinforced epoxy polymer (CFRP) and titanium (Ti). The most important point of the new joint method are not only extremely large friction force by broad interface of carbon fiber with 6 µm-diameter, but also Ni-coating for suppression of TiC formation and enhancement of contact ability of fiber wrapped by molten Ti. The new joint part was strengthened by impregnated nickel-coated carbon fiber (NiCF) and exhibited the high Charpy impact value (auc). Since carefulness for aircraft parts would be necessary, the lowest impact value (as) was defined. It was calculated by the 3-parameter Weibull equation when the fracture probability (Pf) = 0. The as of Ti/NiCF/CFRP was 2.2 kJ m−2, which was higher than that (0.34 kJ m−2) of the joint sample with glue. Consequently, the new joint method remarkably enhanced the safety level (reliability).

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Discharge-Charge Property of Lead-Acid Battery Using Nano-Scale PbO2 as Cathode Active Material

Masami Taguchi, Toshihiro Sasaki, Hiroki Takahashi

pp. 327-333

DOI:

10.2320/matertrans.M2013343

抄録

In this study, nanoscale PbO2 was obtained by the hydrolysis reaction of Pb(CH3COO)4 in an ethanol solution, and the conventional PbO2 was prepared by the electrolytic oxidation of PbO powder in a H2SO4 solution. The former PbO2 was identified as single phase β-PbO2 with the average crystallite size of about 12 nm that had an excellent electrochemical activity, whereas the latter one was a mixture of α-PbO2, β-PbO2 and PbSO4 of about 41 nm average size. A hybrid lead-acid battery cathode consisting of an inner layer of the conventional PbO2 and an outer layer of the nanoscale PbO2 was also manufactured. The average diameter of the pores in the hybrid cathode was smaller than that of the conventional cathode of the lead-acid battery, which was made from only the conventional PbO2. The mass change in the hybrid cathode during the discharge-charge cycle test was relatively high as compared to that of the conventional cathode. Moreover, the cycle tests clearly showed that the reversibility of the discharge-charge reaction was improved in the hybrid cathode since the electrode mass returned to zero even after repeated charge and discharge. As a result, the hybrid cathode was significantly better than the conventional cathode regarding both the current efficiency and the utilization factor of the active materials of the cathode during the discharge-charge reaction. These results may suggest the manufacturing of a novel lead-acid battery with a higher power density and higher capacity.

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Recycling of Rare Earth Magnet Waste by Removing Rare Earth Oxide with Molten Fluoride

Osamu Takeda, Kiyotaka Nakano, Yuzuru Sato

pp. 334-341

DOI:

10.2320/matertrans.M-M2013836

抄録

Recycling of rare earth magnet scrap is required for improving resource conservation. Removal of rare earth oxide from off-specification magnet alloy scrap was investigated by remelting the scrap together with fluoride flux, LiF–50 mol% NdF3 and LiF–25 mol% NdF3–25 mol% DyF3, at 1503 K for the development of novel recycling process. As a result, separation of magnet alloy from fluoride flux after remelting was fine, and neither suspension of alloy in the flux nor suspension of flux in the alloy was observed. Oxygen concentration of alloy decreased from 5000 to 160 mass-ppm by charging flux of 1.5 times of equivalent amount for complete dissolution of oxide. Substitution of neodymium in the alloy and dysprosium in the flux was observed. The investigated process should be utilized for mildly contaminated waste such as a used (end-of-life) magnet because of simple process, energy saving and unlimited location.

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Geological Exploration of Beachrock through Geophysical Surveying on Yagaji Island, Okinawa, Japan

Ryosuke Kubo, Satoru Kawasaki, Koichi Suzuki, Shinji Yamaguchi, Toshiro Hata

pp. 342-350

DOI:

10.2320/matertrans.M-M2013839

抄録

This paper describes the knowledge obtained from a study of geophysical prospecting for beachrock. Previous studies on beachrock worldwide have been focused on the geochemistry. However, more knowledge of the chemical and physical properties is needed to elucidate the formation mechanism. In the present study, a direct current (DC) electrical survey and a surface seismic survey were conducted to detect the underground structure of the beachrock on Yagaji Island, Okinawa, Japan. This was a first attempt at conducting multiple geophysical surveys to investigate beachrock. In each survey, one survey line was set perpendicular to the seashore and two survey lines were set roughly parallel to the seashore. The results of each survey were observed in section of resistivity and seismic wave velocity. Furthermore, in order to estimate the effectiveness of the surveys, laboratory tests were conducted on the beachrock samples collected from the study site to measure the porosity, the resistivity, and the velocities of primary- (P-) waves and secondary- (S-) waves. There was a superior correlation between the sections and with the data on the study site. Hence, the features of the beachrock at the site are as follows: the resistivity is about 4–16 Ωm, the S-wave velocity is about 325 m/s, the thickness is about 1 m, and the thickness has a tendency to become greater toward the sea. One beachrock formation mechanism obtained by this study is close a currently accepted mechanism.

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Zn and Fe Recovery from Electric Arc Furnace Dusts

F. F. Grillo, J. L. Coleti, D. C. R. Espinosa, J. R. Oliveira, J. A. S. Tenório

pp. 351-356

DOI:

10.2320/matertrans.M2013385

抄録

Steel production generates dust containing Zn and Fe that can be recovered under certain conditions. The main objectives of the study were to evaluate the recovery of these elements when added in briquette form to liquid pig iron at a temperature of 1500°C and to chemically and morphologically characterize the Electric Arc Furnace Dust (EAFD). In the dust characterization stage, the following techniques were used: granulometric and chemical analyses, Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDS), and X-ray Diffraction (XRD). After characterization, the dust was agglomerated in order to form a briquette, then, placed in liquid pig iron. To perform the tests, a vertical laboratory-scale furnace was used that maintained an inert gas flow (argon) within the furnace during the experiments. All melting tests were performed in this device. Alumina crucibles were used. The zinc was reduced, volatilized and collected by a flue placed on top of the furnace. It was possible to achieve FeO reduction values higher than 98%. The new dust collected during the tests contained iron and 68% of zinc on the average.

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Hall–Petch Tensile Yield Stress and Grain Size Relation of Al–5Mg–0.5Mn Alloy in Friction-Stir-Processed and Post-Thermal-Exposed Conditions

Chun-Yi Lin, Truan-Sheng Lui, Li-Hui Chen, Fei-Yi Hung

pp. 357-362

DOI:

10.2320/matertrans.M2013334

抄録

Friction stir process (FSP) and post thermal exposure were carried out to a microstructure-thermostable cast Al–5Mg–0.5Mn alloy to examine the grain size dependence of tensile yield stress by using Hall–Petch relation, σy = σ0 + kyd−1/2. The measurement of preferred crystalline orientations and grain boundaries characteristic is used to explain the difference of the Hall–Petch parameters. FSP produces fine grain structure and, for the obtained average grain size from 3.7 to 12.8 µm, near-random crystalline orientations and certain proportion of rigid coincident site lattice boundaries (CSLs) is detected. Two-step post thermal exposure leads to a quick development of rotated ⟨001⟩ type crystalline orientations and the obtained coarse grains with average size from 229 to 508 µm are also commonly surrounded by general high angle boundaries. The calculation of Taylor factor and CSLs proportion reveals that stronger texture and grain boundary hardening effects exist in FSPed specimens than in thermal exposed specimens. These items are the major factors leading to larger σ0 and ky in FSPed specimens than in thermal exposed specimens.

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Effect of Contact Configuration on the Tribological Performance of Micro-Textured AISI 1045 Steel under Oscillating Conditions

Minhaeng Cho

pp. 363-370

DOI:

10.2320/matertrans.M2013214

抄録

The tribological performance of micro-textured AISI 1045 steel was investigated by an oscillating test. This study compared two contact schemes: (1) ball-on-disk and (2) line contact configuration. Texturing fractions of 5, 10, 15, and 20% were used. Results of the ball-on-disk oscillating test revealed that this contact scheme is not appropriate for an ordinary mechanical element in relative contact motion because very high concentrated contact stress is generated. In the case of the line contact test, a load dependency was observed for the coefficient of friction in spite of the lowered contact stress. The coefficient of friction for a load of 50 N was higher than that of the bare specimen over the entire texturing range. However, for a load of 20 N, a reduced coefficient of friction was observed in all cases.

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Effect of Friction Stir Processing on the Microstructural Evolution and Tensile Behaviors of an α/β Dual-Phase Mg–Li–Al–Zn Alloy

Chung-Wei Yang

pp. 371-377

DOI:

10.2320/matertrans.M2013344

抄録

The effect of friction stir processing followed by an aging heat treatment on an extruded α/β dual-phase Mg–8.5Li–2.8Al–1.1Zn (LAZ931) alloy is investigated. The aim of present study is to explore its microstructural characteristic and tensile mechanical properties. The friction stir process reduces the extruded texture and causes a significant grain size refining effect on the coarse Mg-rich α-phase and Li-rich β-phase grains. An apparent decrease in the volume fraction of α-phase is confirmed, and it is resulted from the dissolution and solid solution of the α-phase within the β-phase matrix. The α/β-phase grain size refining and solid solution strengthening effects by the friction stir process can not only improve the microhardness within the stir zone, but also enhance the tensile strength of extruded dual-phase LAZ931-F alloy. With performing an aging heat treatment to friction stirred LAZ931-FSP alloy at 150°C, the microhardness is further increased with an age hardening effect by the precipitation of α-phase and metastable θ-MgLi2Al precipitate in the stir zone. However, the coarsening of precipitated α-phase at β-phase grain boundaries and the phase decomposition of metastable θ-MgLi2Al into a AlLi compound reduces the precipitation strengthening effect to the tensile strength of aged LAZ931-FSP/A alloy. Regardless of being aged state or not, applying a tensile force perpendicular to the stir processing direction causes a decrease in the tensile strength and elongation to friction stirred LAZ931-FSP alloys.

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Improving Recycled Fiber by Applying In-Situ Aragonite Calcium Carbonate Formation Process

Joobeom Seo, Jong Gyu Lee, Thenepalli Thriveni, Chul Seoung Baek, Ji-Whan Ahn

pp. 378-382

DOI:

10.2320/matertrans.M2013369

抄録

Needle-shaped aragonite, a thermodynamically metastable polymorph of CaCO3, was synthesized in a deinked old newspaper pulp (ONP) slurry, otherwise known as the in-situ aragonite formation process, in order to improve the optical properties such as the brightness and ERIC value (effective residual ink concentration) as well as to preserve the strength properties such as the breaking length of the resultant handsheet. The brightness and ERIC value of the handsheet obtained from pulp that was subjected to the in-situ aragonite formation process was improved by 20.4% (from 56.8 to 68.4%) and 55.4% (from 292.1 to 130.4 ppm), respectively, relative to a raw ONP sample. The effects of the in-situ aragonite formation process on the resultant handsheet were compared with the results obtained from a similar process in which rhombohedral-type calcite was synthesized instead of the needle-shaped aragonite. From the comparison, it can be concluded that the in-situ aragonite formation process provides better optical and strength properties to the resultant handsheet than that of calcite, and this is attributed to the needle-shaped morphology of aragonite.

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Effects of Stress Triaxiality on Damage Evolution from Pre-Existing Hydrogen Pores in Aluminum Alloy

Hiroyuki Toda, Hideki Tsuruta, Keitaro Horikawa, Kentaro Uesugi, Akihisa Takeuchi, Yoshio Suzuki, Masakazu Kobayashi

pp. 383-386

DOI:

10.2320/matertrans.L-M2013841

抄録

It has recently been reported that aluminum alloy ductile fracture is dominated by micropore growth, whereas the particle fracture mechanism operates incidentally. The effects of stress triaxiality in front of a notch or crack were here investigated by employing microtomography observations. A fractional dimple pattern area originating in micropores increased with the increase in stress triaxiality on fracture surfaces. This implies that the effects of micropores on mechanical properties are more pronounced in notched and cracked materials.

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Evolution of Texture in a 2.8%Si Non-Oriented Electrical Steel Annealed at 1100°C

Na Li, Liang Ma, Li Xiang, Shengtao Qiu, Pei Zhao

pp. 387-390

DOI:

10.2320/matertrans.M2013339

抄録

The evolution of texture in a 2.8% Si non-oriented electrical steel annealed at 650, 750 and 1100°C was investigated. It was found that, comparing 650°C annealing, Cube and Goss textures in the specimen annealed at 1100°C are strengthened during the early stage of recrystallization. However, the {111}<110> and {111}<112> textures are weakened. Annealing at 1100°C, grains grow rapidly with annealing time in the grain growth stage, Goss and Cube textures are strong and {111}<110> and {111}<112> textures are weak. Cube texture component is strengthened with the growth of grains, Goss texture component is weakened markedly. There is no significant change in the {111}<110> and {111}<112> textures. These characteristics could be attributed to the less recovery before recrystallization and the difference in grain boundary mobility related to the annealing temperature and crystal orientation during grain growth.

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Pulsed Current Activated Synthesis and Consolidation of Nanostructured MoSi2–NbSi2 Composite and Its Mechanical Properties

Hyoung-Gon Jo, In-Jin Shon

pp. 391-394

DOI:

10.2320/matertrans.M2013341

抄録

Nanopowders of Mo, Nb, and Si were fabricated by high-energy ball milling. A dense nanostructured MoSi2–NbSi2 composite was rapidly synthesized and sintered by the pulsed current activated heating method within four minutes using mechanically activated powders of Mo, Nb, and Si. A high-density nanostructured MoSi2–NbSi2 composite was produced under simultaneous application of an 80-MPa pressure and a pulsed current. The sintering behavior, mechanical properties, and microstructure of the composite were investigated. These fracture toughness and hardness values of the nanostructured 0.5MoSi2–0.5NbSi2 composite are higher than those of monolithic MoSi2 or NbSi2.

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