Showing papers in "Materials Transactions in 2016"

Design Concept and Applications of Fe–Mn–Si-Based Alloys—from Shape-Memory to Seismic Response Control

Abstract: 1Microstructure Design Group, Structural Materials Unit, Research Center for Strategic Materials, National Institute for Materials Science, Tsukuba 305-0047, Japan 2R&D Group, Awaji Materia Co., Ltd., Tokyo 101-0052, Japan 3Research and Development Institute, Takenaka Corporation, Inzai 270-1395, Japan 4Department of Mechanical Engineering, Faculty of Engineering, Kyushu University, Fukuoka 819-0395, Japan

Corrosion of Ultrafine Grained Materials by Severe Plastic Deformation, an Overview

Abstract: Corrosion of ultra ne grain (UFG) materials by severe plastic deformation (SPD) is reviewed in light of the existing literature and microstructural change. Fortunately, by holistic survey of the literature, it seems likely that grain re nement by SPD, while enhancing mechanical properties, does not compromise the overall corrosion resistance, and in many case, improve it in comparison with coarse-grained counterparts, although there are some contradictory results within the same materials and same environment. The degree of impact of UFG formation on corrosion is highest in stainless steels followed by aluminum and magnesium alloys whereas it is relatively marginal in pure copper and titanium. The effect of UFG formation by SPD on corrosion is imparted by not only grain re nement, but also other microstructural change occurring commonly in SPD in general and unique to each speci c SPD method. In this review, an attention is paid speci cally to the former case, and this includes shuf ing or redistribution of chemical inhomogeneity into a ner scale, deformation-induced grain boundaries and high internal stress stemming from these grain boundaries. The literature on stress corrosion cracking (SCC) of UFG materials are de nitely insuf cient to nd the general trends, more studies are waited. [doi:10.2320/matertrans.M2015452]

Microbially Induced Sand Cementation Method Using Pararhodobacter sp. Strain SO1, Inspired by Beachrock Formation Mechanism

Abstract: To develop an alternative ground improvement technique in coastal areas based on bio-stimulation, we investigated sand cementation using bacteria that have been shown to enhance beachrock formation. We conducted cementation tests using Pararhodobacter sp. strain SO1, a local ureolytic bacteria originating from the sand near beachrock in Okinawa, Japan. Specifically, we attempted to cement sand specimens to unconfined compressive strength (UCS) of several MPa and establish the influence of several test conditions (curing temperature, injection interval of cementation solution, Ca2+ concentration and sodium malate concentration in the cementation solution, and test period) on the UCS. Column specimens were cemented up to UCS of 10MPa after 28 days under the conditions (curing temperature; 30°C, injection interval; 1 day, Ca2+ concentrations in cementation solution; 0.3M). Multiple regression analysis showed that the relevant conditions for UCS were test period, D (days), and Ca2+ concentration of the cementation solution, Cca (M). The prediction formula for UCS, qud (MPa), was experimentally determined to be qud = 48.3Cca + 0.456D 1 19.51. Overall, the results of this study will contribute to the application of a new technique for coastal sand improvement and bio-stimulation. [doi:10.2320/matertrans.M-M2015842]

Densification Behavior of 316L Stainless Steel Parts Fabricated by Selective Laser Melting by Variation in Laser Energy Density

Abstract: 1Powder & Ceramic Division, Korea Institute of Materials Science (KIMS), Changwon 51508, Republic of Korea 2Department of Mining and Materials Engineering, McGill University, Montreal, Quebec H3A 0C5, Canada 3Department of Materials Science and Engineering, University of Ulsan, Ulsan 44610, Republic of Korea 4Metal 3D Printing Convergence Research Team, Korea Institute of Machinery & Materials (KIMM), Daejeon 34103, Republic of Korea

Fabrication and All Solid-State Battery Performance of TiS2/Li10GeP2S12 Composite Electrodes

Abstract: TiS2/Li10GeP2S12 composite electrodes were fabricated using a mill pot rotator, and their electrochemical properties were investigated in all solid-state batteries of TiS2 cathode/Li10GeP2S12 solid-electrolyte/In-Li anode. The batteries compressed under a pressure of 19 MPa demonstrated poor cycle stability and rate capability because of the deterioration of physical contact between the TiS2 and the Li10GeP2S12. The battery performance was considerably improved by applying a pressure of 228 MPa throughout the electrochemical cycling while maintaining the contact area. The battery delivered the reversible a capacity of over 160 mAh・g−1 under 1 C operation with high capacity retention. [doi:10.2320/matertrans.Y-M2016804]

Bulk-Type All-Solid-State Lithium Batteries Using Complex Hydrides Containing Cluster-Anions

Abstract: In this study, we incorporated fast lithium ion conducting complex hydrides containing cluster anions, namely icosahedral dodecahydro-closo-dodecaborate anions, [B12H12], into a bulk-type all-solid-state battery. Li2B12H12, TiS2 and Li were used as an electrolyte, a positive electrode active material and a negative electrolyte, respectively, for a battery assembly to investigate its battery performance. “Bulk-type” battery contains high quantity of electrode active materials in the electrode layer, and thereby the enhanced energy-storage density is expected. In addition, non ammable solid-state electrolyte would ensure the safety, which is currently problematic for the conventional lithium rechargeable battery that uses organic liquid electrolyte. Li2B12H12 has a high lithium ionic conductivity of log(σ/S cm−1) = −2.6 at 393 K. It exhibits a relatively higher conductivity of log(σ/S cm−1) = −3.5 at reduced temperatures such as 333 K. These high lithium ionic conductivity allows for the repeated operation of the bulk-type all-solid-state TiS2/Li battery for at least 10 cycles at not only 393 K but also 333 K with the discharge capacities higher than 190 mAh g−1. Li2B12H12 exhibits higher oxidative stability. Thus, our battery realized high coulombic ef ciencies of over 92% during the battery operation. This information will be bene cial for the further development of novel complex hydride-based electrolyte to have high-performance bulk-type all-solid-state batteries. [doi:10.2320/matertrans.MAW201601]

Effects of Grain Boundary Phase on Coercivity of Dysprosium-Free Rare Earth Magnet

Abstract: As a part of the challenge of reducing the use of scarce rare-earth elements in magnets, a Dy-free Nd-Fe-B magnet with the remanence and coercivity of 1370 mT and 1830 kA/m, respectively, was investigated. The grain boundary was composed of mainly two phases, R6T13M and R-rich phases. The R6T13M phase formed at around 750 to 1000 K, and in that temperature range, coercivity improved and remanence decreased. By increasing the amount of grain boundary phases to 17.3 at% R addition, coercivity higher than 1990 kA/m (25 kOe) was realized. [doi:10.2320/matertrans.M2016160]

Real Hydrostatic Pressure in High-Pressure Torsion Measured by Bismuth Phase Transformations and FEM Simulations

Abstract: 1WPI, International Institute for Carbon-Neutral Energy Research (WPI-I2CNER), Kyushu University, Fukuoka 819–0395, Japan 2Department of Materials Science and Engineering, Faculty of Engineering, Kyushu University, Fukuoka 819–0395, Japan 3Commercialization Research Division, Korea Institute of Materials Science (KIMS), Changwon 641–831, South Korea 4Department of Materials Science and Engineering, Pohang University of Science and Technology, Pohang 790–784, South Korea 5Erich Schmid Institute of Materials Science, Austrian Academy of Sciences, Jahnstrasse 12, 8700 Leoben, Austria

Study on Reaction Performances and Applications of Mold Flux for High-Aluminum Steel

Abstract: During the continuous casting of high-aluminum steel, important components of the mold flux can be easily reduced by the aluminum in the molten steel. Consequently, the mold flux performance is deteriorated, impeding the smooth running of the continuous casting and affecting the quality of the cast slab. To solve this problem, thermodynamic calculations and laboratorial crucible experiments were performed to investigate the reduction of different mold fluxes by the aluminum in molten steel. Plant trials based on the laboratory studies were performed. It was found that SiO2, MnO, Na2O and B2O3 reacted with the aluminum in molten steel, while CaO, CaF2, MgO, Li2O and BaO did not. Since the composition contents of in CaO-Al2O3-based mold flux were changed only slightly after steel/slag interfacial reactions, a stable CaO-Al2O3based mold flux was tested in industry production. The application effect of this stable mold flux was very good. [doi:10.2320/matertrans.M2015311]

Enhanced Thermoelectric Properties of Silicon via Nanostructuring

Abstract: The effectiveness of thermoelectric (TE) materials at converting heat gradients into electricity, and vice versa, is quantified by the dimensionless figure of merit, ZT. Current TE materials, such as Bi2Te3 and PbTe, have ZT values of approximately 1, but contain highly toxic and/or rare elements, which limits their widespread use. However, Si is a non-toxic, inexpensive, and abundant element. Even though bulk Si exhibits good electrical properties, its lattice thermal conductivity (¬lat) is high (>100Wm11 K11), which results in a ZT value of approximately 0.01 at room temperature. If it were possible to lower the ¬lat of Si without altering the electrical properties, Si would be an ideal TE material. These changes can be realized by nanostructuring Si. In this review, we discuss the recent achievements in the enhancement of the TE properties of Si via nanostructuring. Based on these recent results, we also indicate some potential topics to investigate to enhance the TE properties of Si further. [doi:10.2320/matertrans.MF201601]

Electrochemical Performance of Titanium Hydride for Bulk-Type All-Solid-State Lithium-Ion Batteries

Abstract: 1Graduate School of Advanced Sciences of Matter, Hiroshima University, Higashi-Hiroshima 739–8530, Japan 2Institute for Advanced Materials Research, Hiroshima University, Higashi-Hiroshima 739–8530, Japan 3Graduate School of Integrated Arts and Sciences, Hiroshima University, Higashi-Hiroshima 739–8521, Japan 4Institute for Sustainable Sciences and Development, Hiroshima University, Higashi-Hiroshima 739–8530, Japan

Micromagnetic Simulations of Magnetization Reversals in Nd-Fe-B Based Permanent Magnets

Abstract: Finite element micromagnetic simulation was employed to explain how the microstructure of Nd-Fe-B permanent magnets such as grain size, grain shape, and grain boundary composition in uence the magnetization reversals and coercivity. Micromagnetic simulations showed that local demagnetization factor decreases as grain size decreases, which is attributed to a higher coercivity in ne-grained anisotropic permanent magnets. Lower demagnetization factor is also responsible for a lower temperature dependence of coercivity in the magnets with a smaller grain size. It was also found that the reduction of the magnetization of the grain boundary phase in hot-deformed Nd-Fe-B magnets leads to the coercivity enhancement due to a stronger pinning force against magnetic domain wall motion. The coercivity of Nd-Fe-B magnets cannot be enhanced by the reduction of the grain size alone unless the grain boundary phase become non-ferromagnetic, indicating that the role of the grain boundary phase is more pronounced in the Nd-Fe-B magnets with a smaller grain size. [doi:10.2320/matertrans.M2015457]

Perpendicular Exchange Bias and Magneto-Electric Control Using Cr2O3(0001) Thin Film

Abstract: Antiferromagnets themselves do not generate either stray elds or spontaneous magnetization. However, if an antiferromagnet is coupled with a ferromagnet, unique and useful characteristics appear. Exchange bias is one such characteristic that is utilized in spintronic devices like spin-valve lms. To date, exchange bias has been used to induce static effects in devices; however, the exchange bias has not been switchable in these devices. Recently, switchable exchange bias has been developed using Cr2O3, which exhibits a magnetoelectric effect in an antiferromagnetic layer. The promising features of this effect are (1) the strength of the exchange bias is high and its direction is perpendicular to the lm, and (2) the switching is triggered by an electric eld. In this overview, we will summarize our recent results on the unique temperature dependence of high, perpendicular exchange bias and magnetoelectric switching of the induced perpendicular exchange bias. [doi:10.2320/matertrans.ME201506]

Three-Dimensionally Gradient and Periodic Harmonic Structure for High Performance Advanced Structural Materials

Abstract: Creation of a unique “Harmonic Structure (HS)” with controlled bimodal grain size distribution in metals and alloys is a new material design paradigm allowing the improved mechanical performance of structural materials via enhancing strength without sacri cing ductility. A well designed powder metallurgy based processing approach has been developed to create such a controlled microstructure which consists of controlled mechanical milling (MM) of powder particles to create powder particles with bimodal grain size distribution, with a peculiar coreshell structure, followed by their hot consolidation. In the present study, full density compacts with HS were prepared and the effect of such a bimodal microstructure on the mechanical properties of commercially pure Ti with hexagonal close packed (HCP) crystal structure was investigated. The HS pure Ti exhibited considerably higher strength values, without sacri cing ductility, as compared to their coarse-grained (CG) counterparts. The numerical simulation results revealed that the initial stages of deformation and strength of the HS are governed by the characteristics of the interconnected network of the strong ne-grained (FG) shell regions whereas the extent of uniform deformation and overall ductility is governed by the ductile CG core region. It was also demonstrated that the unique HS design promotes uniform deformation very ef ciently by avoiding strain localization during plastic deformation. [doi:10.2320/matertrans.MH201509]

Weathering Steel in Industrial-Marine-Urban Environment: Field Study

Abstract: In the present field study, we report the exposure of weathering steels in the industrial-marine-urban environment at Ennore, located near the east coast of India for 3 years. The Corrosion products viz., iron oxyhydroxides and oxides present in the rust layers were characterized using ATR-FTIR, XRD studies and quantified using TGA analysis. The specific surface area of the rust particles formed during the corrosion process were determined using N2 adsorption isotherm studies. The morphology of the corrosion products were elucidated using SEM. ATR-FTIR and XRD studies showed that the corrosion products formed on the skyward surfaces were highly more crystalline than those on the the earthward surfaces. TGA showed that the iron oxyhydroxides were major corrosion products. N2 adsorption-desorption studies confirmed the formation of compact inner rust layers with high specific surface area (SA). SEM analysis revealed that the skyward surface was smooth and compact while the earthward surface were cracked and porous. SEM images confirmed the formation of characteristic morphological structures such as sandy crystal (lepidocrocite), needle-like (goethite), cotton ball (goethite) and cigar shaped (akaganeite) structures. Further, it revealed the formation of goethite on the skyward surface as a major constituent phase in the rust layer, which was influenced by the presence of SO2 content in the environment. [doi:10.2320/matertrans.M2015345]

Acoustic Emission Monitoring of Laser Shock Peening by Detection of Underwater Acoustic Wave

Abstract: Acoustic Emission (AE) technique is one of the nondestructive methods to evaluate the size, location and generation time of deformation or damage of material in real times. Generally AE sensors are directly attached on the surface of the component to detect AE wave, however this method brings about inconvenient setting to many industrial processes. In the present study, an arrangement of AE sensors was investigated to monitor laser shock peening (LSP). Instead of direct attachment of the sensors on the target, several AE sensors were located in the water layer to detect acoustic wave propagating through the water. The results showed that the sensor arrangement has a good performance to monitor LSP. Impact pressures during LSP process were obtained from detected AE waveforms by deconvolution technique. In addition, with AE measurement, sample surface was observed by high speed camera and investigated phenomena during LSP process. [doi:10.2320/matertrans.M2015401]

Microstructure and Mechanical Properties of ARB Processed Aluminium with Different Purities

Abstract: 99.2% Al (2N-Al), 99.99%Al (4N-Al) and 99.999%Al (5N-Al) were deformed to high strains by accumulative roll-bonding (ARB) at room temperature, and microstructure and mechanical properties were systematically characterized. During the ARB process, original coarse grains were subdivided by deformation-induced high-angle boundaries into nano-scale grains, where redundant shear strain introduced in the near-surface layers by friction in the non-lubricated rolling signi cantly accelerated the formation of nanostructures. It was found that spacing and fraction of high-angle boundaries can be explained by total equivalent strain taking the effect of shear strain into account. Quite uniform nanostructures dominated by high-angle boundaries were obtained after 6 cycles of ARB for 2N-Al and 4N-Al, but the boundary spacing was smaller in the 2N-Al than in the 4N-Al. On the other hand, in the case of 5N-Al, recrystallization and grain growth occurred during the roll-bonding process, and nanostructures were not able to be obtained. It was suggested that an increase in the amount of impurities is effective to increase the stability of the nanostructures and to randomize the deformation texture leading to a high fraction of high-angle boundaries. [doi:10.2320/matertrans.MH201519]

Effect of building position on phase distribution in Co-Cr-Mo alloy additive manufactured by electron-beam melting

Abstract: Cobalt-chromium-molybdenum (Co-Cr-Mo) alloys are used for biomedical implants such as arti cial joints because they have excellent wear and corrosion resistance and biocompatibility. Electron-beam melting (EBM) is a type of additive manufacturing technique for metals. We used EBM to fabricate 20 rods of a Co-Cr-Mo alloy with height of 160 mm arranged in a 4 × 5 matrix and observed the phase constitution in the middle part (at a height of 80 mm) of the rods by scanning electron microscopy-electron backscatter diffraction. We found that the rods in the center part of the matrix consisted of more of the face-centered cubic (γ) phase and less of the hexagonal close-packed (ε) phase than rods in the outer part. This happened because even though each rod was fabricated under the same beam condition, the rods at the center had been exposed to higher temperature than those in the outer part, and less thermal dissipation took place because the neighboring rods were also heated by the electron beam. This difference in the thermal histories should be taken into consideration when many objects are fabricated simultaneously. [doi:10.2320/matertrans.Y-M2016826]

Effect of Surface Deposits on Nitriding Layer Formation of Active Screen Plasma Nitriding

Abstract: Austenitic stainless steel SUS 316L was nitrided by active-screen plasma nitriding (ASPN) to investigate the effect of surface deposits from the screen on the nitriding layer formation. ASPN experiments were carried out using a DC plasma-nitriding unit. The sample was placed on the sample stage in a oating potential (bias-off) and a cathodic potential (bias-on). The screen, which was SUS 316L expanded metal with 38% open area ratio, was mounted on the cathodic stage around the sample stage. Nitriding was performed in a nitrogen-hydrogen atmosphere with 25% N2 + 75% H2 for 18–180 ks at 673 K under 200 Pa by the ASPN process. After nitriding, the nitrided samples were examined using scanning electron microscopy, X-ray diffraction, Vickers microhardness and glow discharge optical emission spectroscopy. From the surface observation of the nitrided sample, deposits were observed on the top surface of the sample nitrided with bias-off whereas deposits were not on that nitrided with bias-on. The nitrogen-expanded austenite (S phase) was formed on the surface of both samples. Layer thickness of the S phase increased with increasing the nitriding time. Additionally, the degree of an increase of the layer thickness of the S phase nitrided with bias-on was approximately 2.5 times greater than that nitrided with bias-off. This result suggests that the ASPN treatment with bias-on is effective for the increase of the nitriding layer thickness. [doi:10.2320/matertrans.M2016209]

Surface Composition and Corrosion Resistance of Co-Cr Alloys Containing High Chromium

Abstract: Air-formed surface oxide lms on four types of Co-Cralloys were characterized using X-ray photoelectron spectroscopy (XPS) and ve types of Co-Cr alloys were anodically polarized, to identify the effects of the addition of N, Mo, and W to Co-Cr alloys containing high Cr on the surface composition and corrosion resistance. Co-20Cr-15W-10Ni (ASTM F90), Co-30Cr-6Mo, Co-33Cr-5Mo-0.3N, and Co-33Cr-9W0.3N were employed for XPS and the above four alloys and another Co-30Cr-6Mo (ASTM F75) were employed for anodic polarization. The surface oxide lm on the Co-Cr alloys consisted of oxide species of Co, Cr, Mo, W and/or Ni contains a large amount of OH− with a thickness of 2.6–3.2 nm. Cations existed in the oxide as Co2+, Cr3+, Mo4+, Mo5+, Mo6+, W6+ and Ni2+. Cr and Mo are enriched and Co and Ni are depleted in the surface oxide lm. W was enriched in the case of Co-20Cr-15W-10Ni but depleted in the case of Co-33Cr-9W-0.3N. On the other hand, Cr, Mo, W and Ni were enriched and Co was depleted in the substrate alloy just under the surface oxide lm in the polished alloy. During rapid formation of the surface oxide lm, Cr was preferentially oxidized and the oxidation of Co and Ni delayed, according to the oxidation and reduction potentials of these elements. The Co-Cr alloys essentially have high localized corrosion resistance that is not easily affected by a small change of composition. Co-33Cr-5Mo-0.3N shows higher corrosion resistance compare than conventional Co-Cr alloys. [doi:10.2320/matertrans.MI201514]

Effect of Anomalous Crystal Structure of Iron Aluminides Fe2Al5 and Fe4Al13: Low Phonon Thermal Conductivity and Potentiality as Thermoelectric Materials

Abstract: Iron Aluminide Fe2Al5 has a rigid framework of both fully occupied aluminum and iron sites and channels of partially occupied aluminum sites. On the other hand, Fe4Al13 possesses a large unit cell with 102 atoms. These complex and peculiar crystal structures bring a low phonon thermal conductivity. Here, we report the thermoelectric properties and discuss how the proposed chain structure and large unit cell can lead to a low phonon thermal conductivity. The calculated room-temperature phonon thermal conductivity by using the Wiedemann-Franz law is approximately 1.5 W/mK and 0.8 W/mK for Fe2Al5 and Fe4Al13, respectively. From the comparison with other Fe-Al alloys, which have neither plural partially occupied sites nor a large unit cell, we found that (1) the speci c heat does not decrease at high temperature, i.e. aluminum atoms at partially occupied sites seem to be xed rather than liquid behavior. (2) the speed of sound for Fe2Al5 and Fe4Al13 are almost identical among Fe-Al alloys, i.e. the average phonon group velocity of acoustic modes for Fe2Al5 and Fe4Al13 are not slower than that of Fe-Al alloys, (3) the electrical conductivities of Fe2Al5 and Fe4Al13 are lower than those of the other Fe-Al alloys. These results suggest that the low phonon thermal and electrical conductivities are brought by short relaxation times of both phonons and electrons due to chemical disorder such as the partially occupied sites. [doi:10.2320/matertrans.MF201607]

Effect of Deformation Temperature on Low-Cycle Fatigue Properties of Fe-28Mn-6Si-5Cr Shape Memory Alloy

Abstract: Effect of deformation temperature on low-cycle fatigue properties of an Fe-28Mn-6Si-5Cr shape memory alloy was investigated. Cyclic push-pull loadings at a total strain range of 0.02 were applied to the alloy at various deformation temperatures ranging from 223 to 523 K. The microstructures and fracture surfaces in the fatigue tested samples were analyzed by means of X-ray diffraction, scanning electron microscopy and electron backscattering diffraction. The highest fatigue life of 22,400 cycles was obtained at 423 K. Increasing or decreasing the deformation temperature resulted in a decrease in fatigue life to several thousand cycles. The specimens deformed to fatigue fracture at temperatures below 298 K exhibited microstructures with ε-martensite and brittle characteristics of the fracture surface, while the specimens deformed above 473 K exhibited the single γ-phase and ductile characteristics of the fracture surface. The deformation at 423 K resulted in a moderate amount of the ε-martensite and a mixed brittle/ductile fracture surface patterns. It is suggested that the highest fatigue life can be obtained when the fatigue temperature lies between Ms and Md. [doi:10.2320/matertrans.MBW201503]