Showing papers in "Materials Transactions in 2009"
TL;DR: In this article, the Vickers hardness, thermal expansion coefficient and thermal conductivity were measured at high-temperatures, and it was verified that the hardness of each synthesized oxide was identical with the naturally formed iron oxide, as observed in the cross-section of oxide scales on steels.
Abstract: The mechanical properties of oxide scales at high-temperature were studied in order to improve the surface quality of commercial Sicontaining high strength steels. Specific oxides of Fe2O3 ,F e 3O4, FeO and Fe2SiO4 were synthesized by powder metallurgy. The Vickers hardness, thermal expansion coefficient and thermal conductivity were measured at high-temperatures. A series of measurements confirmed that the physical properties of the synthesized oxides were different each other. From the Vickers hardness measurements, it was verified that the hardness of each synthesized oxide was identical with the naturally-formed iron oxide, as observed in the cross-section of oxide scales on steels. The influence of the Fe2SiO4 formed on Si-containing steels on the scale adhesion at high temperature and the surface property is discussed on the basis of the physical properties of the oxides. [doi:10.2320/matertrans.M2009097]
210 citations
TL;DR: In this article, the authors developed new FeSiBPCu nanocrystalline soft magnetic alloys with high saturation magnetic flux density (B s ) and a significant increase in material cost.
Abstract: Technically important nanocrystalline soft magnetic alloys and their derivatives always include metal elements such as Nb, Zr, Mo, etc. and/or Cu to realize the nanostructure, which results in a remarkable decrease of saturation magnetic flux density (B s ) and a significant increase in material cost. With the aim to solve the serious problem, we successfully developed new FeSiBPCu nanocrystalline soft magnetic alloys. The melt-spun Fe 83.3-84.3 Si 4 B 8 P 3-4 Cu 0.7 (at%) alloys have heterogeneous amorphous structures including a large amount of α-Fe clusters, 2-3 nm in size, due to the unusual effect of the simultaneous addition of the proper amounts of P and Cu. The hetero-amorphous alloys exhibit higher B s of about 1.67T than the representative amorphous and the nanocrystalline alloys, and the low coercivity (H c ) of 5-10Am -1 . A homogeneous nanocrystalline structure composed of small α-Fe grains with a size of about 10 nm can be realized by crystallizing the hetero-amorphous alloys. The nanocrystalline alloys show extremely high B s of 1.88-1.94 T almost comparable to the commercial Fe-3.5 mass%Si crystalline soft magnetic alloys, and low H c of 7-10Am -1 due to the simultaneous realization of the homogeneous nanocrystalline structure and small magnetostriction of 2-3 × 10 -6 . In addition, the alloys have a large economical advantage of lower material cost and better productivity than the ordinary soft magnetic nanocrystalline alloys now in practical use.
185 citations
TL;DR: The highest value of the dimensionless figure of merit ZT obtainable from a given electronic structure was quantitatively estimated from the linear response theory by considering the normalized spectral conductivity as mentioned in this paper.
Abstract: The highest value of the dimensionless figure of merit ZT obtainable from a given electronic structure was quantitatively estimated from the linear response theory by considering the normalized spectral conductivity. It was found, by calculating ZT from the possible electronic structures, that the bulk materials with the electronic structure consisting of two bands overlapping together near the Fermi level have potential to possess a large ZT-value exceeding unity.
131 citations
TL;DR: In this article, the morphological deviation of ZnO nanostructure (from sheets to micro-flowers) by varying pH of the solution via precipitation method was presented. And the amount of H þ and OHions are found a key to control the structure of studied material and discussed in the growth mechanism.
Abstract: Here we present a systematic study on the morphological deviation of ZnO nanostructure (from sheets to micro-flowers) by varying pH of the solution via precipitation method. In this regard, zinc nitrate hexa-hydrate, NaOH and hydroxylamine hydrochloride (NH2OHHCl) were used. The solution of all three compounds was refluxed at a very low temperature (60 � C) for short time (20 min). The solution pH was calibrated from 6 to 12 by the controlled addition of NaOH and HCl. We have observed from FESEM (field emission scanning electron microscopy) that the morphology of ZnO microballs composed with thin sheets markedly varies from sheet (at pH ¼ 6) to micro-flower composed with sheets of zinc oxide (pH ¼ 10{12). Further the morphology and crystallinity were also studied by the TEM (transmission electron microscopy) and HR- TEM (High resolution transmission electron microscopy) and it's clearly consistent with the FESEM observations. The FTIR spectroscopic measurement also confirms the compositional analysis of ZnO and it comes in the range of 475 to 424 cm � 1 which is a standard peak of ZnO. In addition to this, the amount of H þ and OHions are found a key to control the structure of studied material and discussed in the growth mechanism. (doi:10.2320/matertrans.M2009099)
113 citations
TL;DR: In this paper, transmission electron microscopy showed that an intermetallic compound (IMC) layer formed at the bonding interface of the joints, and it was found that the formation and growth of the IMC were controlled by react diffusion of Mg and Al atoms, instead of the eutectic reaction.
Abstract: The friction stir weldability of a fine-grained high strength AZ31B magnesium alloy to A5083 Al alloy was evaluated at various welding conditions, by using a tool with shoulder diameter of 15 mm, pin diameter of 5 mm and pin length of 3.9 mm. A square butt dissimilar joint without any defect was obtained at the condition of welding speed 100 mm/min, tool rotating speed 500 rpm and offset 0 mm. Higher or lower welding speeds or rotating speeds led to either the formation of defect or lack of bonding in the joint. Defects occurred also in the case that the offset was not 0 mm, i.e. the insertion position of the probe was on either Mg side or Al side, when tool rotating speed was 500 rpm and welding speed was 100 mm/min. The maximum tensile strength of the dissimilar joints in the present study was about 115 MPa, lower than that of Al alloy base metal (about 308 MPa). Transmission electron microscopy showed that an intermetallic compound (IMC) layer, which consisted of Al12Mg17 and Al3Mg2, formed at the bonding interface of the joints, and it was found that the formation and growth of the IMC were controlled by the react diffusion of Mg and Al atoms, instead of the eutectic reaction. The present study demonstrated that the tensile strength of the dissimilar joints was mainly affected by the thickness of IMC layer and the mechanical interlock between magnesium and aluminum alloys. The tensile strength decreased remarkably with the increase in the thickness of IMC layer, which made the mechanical interlock weaker. [doi:10.2320/matertrans.M2009289]
112 citations
TL;DR: In this article, the microhardness and tensile properties of pure Fe were analyzed by high pressure torsion (HPT) using disc and ring samples and it was shown that a subgrain structure containing dislocations develops at an initial stage of straining and the subgrain size decreases with further straining.
Abstract: Pure Fe (99.96%) was processed by high pressure torsion (HPT) using disc and ring samples. When the microhardness and tensile properties are plotted against the equivalent strain, the individual properties fall well on unique single curves, level off at the equivalent strain of � 40. At the saturated level, the tensile strength of 1050 MPa and the elongation to failure of 2% are attained. Transmission electron microscopy showed that a subgrain structure containing dislocations develops at an initial stage of straining. More dislocations form within the grains and the subgrain size decreases with further straining. At the saturation stage, the average grain size reaches � 200 nm, the misorientation angle increases and some grains which are free from dislocations appear. It is suggested that at the saturation stage, a steady state condition should be established through a balance between hardening by dislocation generation and softening by recrystallization. [doi:10.2320/matertrans.MD200812]
110 citations
TL;DR: In this article, the morphology and crystallography of sub-blocks in lath martensite were studied in an interstitial free steel, and the subblocks were classified into dominant and minor subblocks in terms of the volume fraction.
Abstract: The morphology and crystallography of sub-blocks in lath martensite were studied in an interstitial free steel. In each block the sub-blocks are classified into dominant and minor sub-blocks in terms of the volume fraction. The orientation relationship between the dominant and minor sub-blocks is [011]α′/10.5 degrees. Minor sub-blocks have a plate-like morphology and are connected to each other with the habit plane close to {111}γ, and their growth directions close to 〈10\\bar1〉γ.
95 citations
TL;DR: In this article, the authors used transmission electron microscopy (TEM) to characterize the obtained powders and found that adding graphene would hinder grain growth of alumina, making much finer particles.
Abstract: Alumina/graphene composite powders were produced by ball milling alumina and graphite for different times. Transmission electron microscopy (TEM) was used to characterize the obtained powders. 3–4 nm graphene sheets were produced after 30 h milling time. Accelerative effect of alumina to ball milling was also studied. Graphene reinforced alumina-based composites were fabricated by spark plasma sintering (SPS) technique from as-prepared powders. Microstructural observation of fracture surface was conducted using scanning electron microscopy (SEM). It was found that adding graphene would hinder grain growth of alumina, making much finer particles. [doi:10.2320/matertrans.MRA2008458]
85 citations
TL;DR: The magnetic susceptibilities and microstructures of Zr-Nb binary alloys were investigated to develop a new metallic biomaterial with a low magnetic susceptibility for magnetic resonance imaging (MRI) and revealed that the ω phase contributes to the decrease of the magnetic susceptibility.
Abstract: The magnetic susceptibilities and microstructures of Zr-Nb binary alloys were investigated to develop a new metallic biomaterial with a low magnetic susceptibility for magnetic resonance imaging (MRI). The magnetic susceptibility was measured with a magnetic susceptibility balance, and the microstructure was evaluated with an X-ray diffractometer (XRD), an optical microscope (OM), and a transmission electron microscope (TEM). Zr-Nb alloys as-cast showed a minimum value of magnetic susceptibility between 3 and 9 mass% Nb, and the value abruptly increased up to 20 mass% Nb, followed by a gradual increase with the increase of the Nb content. XRD, OM, and TEM revealed that the minimum value of the susceptibility was closely related to the appearance of the athermal ω phase in the β phase. Since the magnetic susceptibility of Zr-3Nb alloy consisting of an α′ phase was as low as that of Zr-9Nb alloy consisting of the β and ω phases, that of the ω phase was lower than that of the α′ and β phases. When Zr-16Nb alloy was heat-treated, the isothermal ω phase appeared, and, simultaneously, the magnetic susceptibility decreased. Therefore, the ω phase contributes to the decrease of the magnetic susceptibility, independently of the formation process of the ω phase. The magnetic susceptibility of the Zr-3Nb alloy as-cast was almost one-third that of Ti-6Al-4V alloy, which is commonly used for medical implant devices. Zr-Nb alloys are useful for medical devices used under MRI.
69 citations
TL;DR: In this article, a dynamic material flow analysis of aluminum was conducted focusing on Japan, United States, Europe and China, and the recycling of aluminum scrap was optimized using multimaterial pinch analysis.
Abstract: Global aluminum consumption has exhibited significant growth in recent years, because of aluminum's useful properties. As this will result in a large amount of aluminum accumulation in "urban mines", the exploitation of these urban stocks will be an important issue in the future. To examine the recycling potential of urban stocks, a dynamic material flow analysis of aluminum was conducted focusing on Japan, the United States, Europe and China. The concentrations of the alloying elements were also investigated, because carryover of alloying elements during recycling can result in off-specification secondary metals and alloys. The recycling of aluminum scrap was optimized from the results of dynamic material flow analysis using multimaterial pinch analysis. It was estimated that Japan, the United States, Europe and China have the potential to reduce their primary aluminum consumption to 60%, 65%, 30% and 85% of their present levels, respectively. In 2050, it is estimated that 11400 kt of primary aluminum will be required among the four countries, while 12400 kt of obsolete scrap will not be able to be recycled because of high concentrations of alloying elements.
69 citations
TL;DR: In this paper, a new processing technique called high pressure sliding (HPS) was developed as a process of severe plastic deformation (SPD), which can be used for grain refinement of metallic sheets with a rectangular shape.
Abstract: A new processing technique, called in this study as high-pressure sliding (HPS), was developed as a process of severe plastic deformation (SPD). It is then demonstrated that HPS can be used for grain refinement of metallic sheets with a rectangular shape which was difficult with a conventional high-pressure torsion utilizing disk samples. Application of HPS to pure Al (99.99%) showed that the grain refinement is achieved with the extent similar to other SPD techniques.
TL;DR: In this article, the effect of oxygen content on the microstructure and mechanical properties of the Ti-29 mass%Nb-13 mass%Ta-4.6 mass%Zr (TNTZ) alloy was investigated.
Abstract: The effect of oxygen content on the microstructure and mechanical properties of the Ti-29 mass%Nb-13 mass%Ta-4.6 mass%Zr (TNTZ) alloy was investigated in this study. The microstructural observation of TNTZ alloys, containing 0.1-0.4 mass% oxygen, subjected to solution treatment shows the presence of a single β phase. With an increase in oxygen content, the hardness, tensile strength, and Young's modulus of TNTZ alloy increase, but its elongation decreases. Further, the α phase precipitates in TNTZ alloys subjected to aging treatment at 723 K for 259.2 ks. The results of transmission electron microscopy and X-ray diffraction analysis indicate that the size and volume fraction of the α phase increase with oxygen content. Corresponding to the changes in the microstructure, the mechanical properties of TNTZ alloy subjected to aging treatment at 723 K change with oxygen content. The increase in oxygen content leads to enhancement of the age hardening of TNTZ alloy, thereby increasing both tensile strength and Young's modulus of TNTZ alloy, but its elongation decreases due to the α-phase precipitation. The mechanical properties of TNTZ alloy (Young's modulus: around 60-100 GPa, tensile strength: around 600-1400 MPa, and elongation: around 5-25‰) vary significantly depending on oxygen content and heat treatment.
TL;DR: In this paper, a new severe plastic deformation (SPD) technique, namely ECAP-PC, was used to produce ultra-neighbor-grained (UFG) structure in the Al 6061 alloy.
Abstract: The paper focuses on producing of ultrafine-grained (UFG) structure in the Al 6061 alloy by a new severe plastic deformation (SPD)technique, developed recently in our laboratory, namely equal channel angular pressing with parallel channels (ECAP-PC). The evolution ofmicrostructure at ECAP-PC was examined and was proved that the alloy becomes of a homogenous UFG structure after 4 passes. Such astructure increases essentially the alloy’s mechanical properties, specifically strength and ductility. The advantages of this new technique inproducing of UFG alloys over conventional ECAP are considered and discussed as well. [doi:10.2320/matertrans.MD200821](Received August 18, 2008; Accepted October 27, 2008; Published December 25, 2008)Keywords: ultrafine-grained structure, severe plastic deformation, equal channel angular pressing with parallel channels, strength andductility
TL;DR: In this article, the authors evaluated the oxygen permeability of an undoped polycrystalline α-Al 2 O 3 wafer that was exposed to oxygen potential gradients at temperatures up to 1973 K.
Abstract: The oxygen permeability of an undoped polycrystalline α-Al 2 O 3 wafer that was exposed to oxygen potential gradients was evaluated at temperatures up to 1973 K. Oxygen preferentially permeated through the grain boundaries of α-Al 2 O 3 . The main diffusion species, which were attributed to oxygen permeation, depended on oxygen partial pressures (P O2 ), forming oxygen potential gradients. Under oxygen potential gradients generated by P O2 below about 1 Pa, oxygen permeation occurred by oxygen diffusing from regions of higher P o , to regions of lower P O2 . By contrast, under oxygen potential gradients generated by P O2 above about 1 Pa, oxygen permeation proceeded by aluminum diffusing from regions of lower P O2 to regions of higher P o ,. In other words, O 2 molecules were adsorbed onto a surface at higher P O2 and subsequently dissociated into oxygen ions (forming Al 2 O 3 ), while oxygen ions on the opposite surface at lower P O2 were desorbed by association into 0 2 molecules (decomposition of Al 2 O 3 ). The grain-boundary diffusion coefficients of oxygen and aluminum as a function of P O2 were determined from the oxygen permeation constants.
TL;DR: In this article, high purity Al (99.99%) was subjected to severe plastic deformation through twist extrusion at room temperature, and microstructures were examined for 1 pass and 4 passes on the cross section perpendicular to the longitudinal axis of billets using optical microscopy and electron back scatter diffraction analysis.
Abstract: High purity Al (99.99%) was subjected to severe plastic deformation through twist extrusion at room temperature. Microstructures were examined for 1 pass and 4 passes on the cross section perpendicular to the longitudinal axis of billets using optical microscopy and electron back scatter diffraction analysis. It was shown that a vortex-like material flow was observed on the cross section and this became more intense with increasing number of the pressing. After one pass, subgrain structures with low angle grain boundaries were developed throughout the section but after 4 passes, the microstructure consisted of grains surrounded by high angle boundaries with fraction of 70% in the edge parts. The average grain size at the edge parts is refined to1.6μm. © 2009 The Japan Institute of Metals. (Less)
TL;DR: In this paper, high-speed deformation and collision behavior of the metal plates were investigated by using a high speed video camera, and it was clearly observed that a part of the flyer plate which was located along the coil bulged toward the parent plate.
Abstract: In-situ observation of magnetic pulse welding process using a one-turn coil was performed by using a high-speed video camera. Highspeed deformation and collision behavior of the metal plates were investigated. The flyer plate traveled toward the parent plate with a high speed by the generated electromagnetic force. A collision velocity of the flyer plate to the parent plate was 250 m/s at the representative welding condition (initial gap distance between two plates: 1.0 mm, discharge energy: 2.5 kJ). It was clearly observed that a part of the flyer plate which was located along the coil bulged toward the parent plate. The collision angle between metal plate surfaces was 0 � at the initial collision point, but it increased continuously during the welding. Such a characteristic high-speed oblique collision is considered to result in formation of the wavy interface and gradual changes in its wavelength and amplitude along the welding interface. [doi:10.2320/matertrans.L-M2009816]
TL;DR: In this paper, the volume fraction of ferrite and austenite phase and corrosion resistance of 26.2Cr-6.99Ni-2.37Mo 2.88W-0.35N duplex stainless steel have been studied by the use of optical microscopy, Feritscope, EBSD, SEM and Anodic polarization test after solution treatment at every 20°C at 1050°C∼1200°C for 30min.
Abstract: The volume fraction of ferrite and austenite phase and corrosion resistance of 26.2Cr-6.99Ni-2.37Mo-2.88W-0.35N duplex stainless steel have been studied by the use of optical microscopy, Feritscope, EBSD, SEM and Anodic polarization test after solution treatment at every 20°C at 1050°C∼1200°C for 30min. As the temperature of solution heat treatment increased, the content of ferrite that could be transformed to intermetallics such as σ and χ phase was higher, and besides, grain size increased and the number of grains decreased due to the growth of the phase and thus grain boundary and phase boundary that can be served as precipitation site of intermetallics were reduced, therefore the precipitation of intermetallics was suppressed. When PRE (Pitting Resistance Equivalent) values for the ferrite and austenite phases after solution heat treatment were calculated by weight percents of alloy elements using SEM-EDS, PRE value gap between the two phases was the smallest when heat treated at 1090°C. Because the increase over 1090°C of heat treatment temperature caused larger difference in PRE values between two phases, corrosion resistance between the two phases was out of balance and thus corrosion resistance was reduced when solution heat treated at the temperature over 1090°C.
TL;DR: In this paper, the microstructure and mechanical properties of Inconel 600 subjected to laser-assisted hybrid friction-stir welding (HFSW) were evaluated and it was shown that the increased welding speed and dynamic grain recrystallization caused the average grain size to decrease from 5.5 μm to 3.2 μm.
Abstract: The present study was carried out to evaluate the microstructure and mechanical properties of Inconel 600 subjected to laser-assisted hybrid friction-stir welding (HFSW). In this process, friction-stir welding (FSW) was performed at a constant speed (400 rpm) while a 2-kW YAG laser preheated the material just in front of the rotating tool. We found that HFSW was 1.5 times faster than conventional FSW. In addition, analysis of the grain boundary character distribution by electron back scattered diffraction (EBSD) showed that the increased welding speed and dynamic grain recrystallization caused the average grain size to decrease from 5.5 μm (in the base material) to 3.2 μm (in the stir zone of the welded specimen). This grain refinement led to 30% and 10% improvements in microhardness and tensile strength, respectively.
TL;DR: In this paper, the effect of water vapor on high temperature oxidation was studied based on Wagner's theory of binary alloy oxidation, which was carried out at 1073 K in dry and humid conditions.
Abstract: The effect of water vapor on high temperature oxidation was studied based on Wagner's theory of binary alloy oxidation. The oxidation of Fe-Cr alloys was carried out at 1073 K in dry and humid conditions. The oxidation was conducted in a closed apparatus at 1073 K and the oxygen partial pressure of 1.1 x 10 -14 Pa, which was fixed by a Fe/FeO buffer. To prepare the humid condition, Ar-5% H 2 gas mixture of 3 x 10 4 Pa was filled in the apparatus, which provided the water vapor pressure of 3.3 x 10 2 Pa. The transition of internal and external oxidation was observed in Fe-8Cr in the dry condition and in Fe-12Cr in the humid condition. Interdiffusion experiment of Fe/Fe-16Cr diffusion couples in dry and humid environments showed that the diffusion coefficient of Cr was not influenced by dissolved hydrogen. The oxygen permeability in α-Fe was determined by means of internal oxidation of Fe-5Cr alloy at 1073 K and the oxygen partial pressure of 1.1 x 10 -14 Pa in a dry and two humid conditions with water vapor of 1.1 x 10 2 Pa and 3.3 x 10 2 Pa. The oxygen permeability in humid condition increases by a factor of 1.4. Dissolved hydrogen increases the oxygen permeability, thus increases the minimum concentration of Cr to form external scales in humid conditions. The presence of dissolved hydrogen changes the oxide shape from discrete spherical particle to spike-like precipitates, which enhances the oxygen transport along the metal/oxide precipitates interface.
TL;DR: In this paper, a part of a flyer plate along the longitudinal direction of a coil bulged toward a parent plate and hit the parent plate, and two parallel seam-welded areas were formed along the side edges of coil.
Abstract: In order to investigate interfacial morphology and their welding condition dependency, Al/Al and Cu/Cu lap joints were fabricated by magnetic pulse welding under various discharge energies. A part of flyer plate along the longitudinal direction of the coil bulged toward a parent plate and hit the parent plate. Two parallel seam-welded areas were formed along the side edges of coil, but the area between them was left unwelded. The welding interface exhibited characteristic wavy morphology, which was similar to that of explosive welding. Wavelength and amplitude of the interfacial wave were not uniform, but gradually changed through the interface. In addition, the maximum wavelength and amplitude increased with increasing discharge energy. Both macro- and microscopic features of interfacial morphology are considered to be due to the oblique collision behavior between the plates, in which traveling velocity, collision angle and collision pressure of the plates gradually change during the welding for a few microseconds. [doi:10.2320/matertrans.L-MRA2008843]
TL;DR: In this article, the surface properties, fluidity, flowability and floodability of untreated ground calcium carbonate (GCC) powder and treated GCC powder with stearic acid (SA) using a dry process coating system were examined.
Abstract: This study examined the surface properties, fluidity, flowability and floodability of untreated ground calcium carbonate (GCC) powder and treated GCC powder with stearic acid (SA) using a dry process coating system. The surface of GCC powder is generally hydrophilic, but was changed to a hydrophobic surface when coated with SA. The contact angle of water on the coated GCC powder surface increased with increasing concentration of SA. The contact angle and hydrophobicity on the GCC powder treated with 1.0 mass% SA was 105° and 100%, respectively. The dispersive component of the surface free energy, γ D S of the untreated GCC powder determined using inverse gas chromatography (IGC) was 103 mJ·m -2 at 100°C. However, that of the GCC powder treated with 1.0 mass% SA was 34.8 mJ·m -2 . Kawakita's equations were used to characterize the properties of the powder. The fluidity index was increased from 18.60 to 30.39 when the surface of GCC powder was modified with SA. On the other hand, the characterization based on the method suggested by Carr showed that the flowability and the floodability of the GCC powder treated with SA increased from 45 to 53 and from 30 to 69, respectively. Therefore, the flowability and floodability of the GCC powder treated with SA were superior to the untreated GCC powder.
TL;DR: In this article, a 100 mm-diameter ring sample of high purity Al (99.99%) was processed by high pressure torsion (HPT) and the results of hardness measurements were consistent with those obtained using disk samples and demonstrated that scaling-up the HPT process was feasible using the ring-shaped sample.
Abstract: A 100 mm-diameter ring sample of high purity Al (99.99%) was processed by high-pressure torsion (HPT). It was confirmed that the results of hardness measurements were consistent with those obtained using disk samples and demonstrated that scaling-up the HPT process was feasible using the ring-shaped sample. Evaluating the advantage of using ring sample, the potential for the scaling-up arises from the fact that the ring diameter can be increased by the amount corresponding to the inner central area of disk sample. Furthermore, the applied load is entirely used for the introduction of intense strain and thus for the development of a homogeneous microstrcuture throughout the ring sample. [doi:10.2320/matertrans.MD200822]
TL;DR: In this paper, high-resolution transmission electron microscopy (HRTEM) and high-angle annular detector (HAADF-STEM) was used to study the Mg-0.99 at%Sm (Mg 99.01 Sm 0.99 ) alloy aged at 200°C.
Abstract: Precipitates in an Mg-0.99 at%Sm (Mg 99.01 Sm 0.99 ) alloy aged at 200°C were studied by the combination of high-resolution transmission electron microscopy (HRTEM) and high-angle annular detector dark-field scanning transmission electron microscopy (HAADF-STEM). Fine precipitates of a meta-stable phase, which is called γ here, in the alloy aged at 200°C for 4 h have a thin lens-shape with a thickness of 2-5 nm and a diameter of 20-60 nm. The γ precipitate has an incommensurate structure with an orthorhombic unit cell of α = 2a 0 = 0.64 nm, b˙=. 6a 0 3 = 3.334 nm and c = c 0 = 0.52 nm, where a 0 and c 0 are lattice constants of a hexagonal unit of the Mg-matrix. In the early stage of aging at 200°C for 0.5 h, isolated structure units forming the γ structure are dispersed in an Mg hexagonal lattice. By annealing at 200°C for 100h, coarse precipitates of a stable Mg 3 Sm phase are formed along grain boundaries and inside grains of the Mg-matrix, and wide γ precipitate-free zones appear around them.
TL;DR: In this article, a 14H-type long period stacking (LPS) phase and relatively thick bands of LPS were precipitated in α-Mg crystalline grains by annealing at low temperatures.
Abstract: Mg-0.7 at%Zn-1.4 at%Y alloys annealed at low temperatures after quenching in water from 520°C were studied by high-resolution transmission electron microscopy (HRTEM) and high-angle annular detector dark-field scanning transmission electron microscopy (HAADF-STEM). Stacking faults, thin bands of a 14H-type long period stacking (LPS) phase and relatively thick bands of LPS were precipitated in α-Mg crystalline grains by annealing at 300°C, 400°C and 500°C, respectively. The precipitation of stacking faults, LPS phase and a supersaturated solid solution without any precipitates were reversibly transformed by annealing at low temperatures. It can be concluded that the stacking faults and LPS phase are stabilized by the segregation of Zn and Y from a supersaturated solid solution.
TL;DR: In this paper, anodic polarization behavior of Pd-M (M = Fe, Co, Ni) alloys in H 2 SO 4 solution is investigated for the preparation of nanoporous palladium by dealloying.
Abstract: Anodic polarization behaviors of Pd-M (M = Fe, Co, Ni) alloys in H 2 SO 4 solution are investigated for the preparation of nanoporous palladium by dealloying. For Pd 0.2 Co 0.8 alloy, the current monotonically increased with the increase in potential. However, anodic polarization curves for Pd 0.2 Fe 0.8 and Pd 0.2 Ni 0.8 alloys showed passive regions at high potentials, although the standard electrode potentials for Fe, Co, Ni are similar. As a result, nanoporous Pd was successfully fabricated via electrolysis under a constant potential (= +0.5 V vs standard calomel electrode) only when the starting alloy was Pd-Co. Passivation, as well as standard electrode potentials, must be considered for the efficient production of nanoporous Pd. The preparation of nanoporous structure on the surface of bulk Pd was also demonstrated using alloying/dealloying process involving Co electrodeposition, thermal alloying and subsequent dealloying.
TL;DR: In this article, the effects of basicity (the ratio between CaO and SiO2) and FeO content on softening and melting temperatures of direct reduced iron residual, otherwise known as slag, were investigated.
Abstract: The effects of basicity (the ratio between CaO and SiO2) and FeO content on softening and melting temperatures of direct reduced iron (DRI) residual, otherwise known as slag, were investigated. Sample slag pellets were prepared for two target compositions, CaO-SiO2-10%MgO-5%Al2O3 and CaO-SiO2-5%MgO-10%Al2O3. Two sets of experiments were conducted on the pellets: one varied basicity values between 1.83 and 0.55, and the other varied the FeO contents between 10% and 50% at constant basicity. The softening and melting process under elevated temperature was recorded using an optical softening-melting temperature measuring device and the temperature points were recorded at the four distinct shape changes of the sample pellets: initial deformation, sphere and hemisphere formation, and complete melting. The lowest softening and melting temperatures of the CaO-SiO2-5%MgO-10%Al2O3 samples occurred at a basicity of 0.55 while for the CaO-SiO2-10%MgO-5%Al2O3 samples it occurred at 0.70. This corresponds to the liquidus temperatures on the CaO-SiO2-MgO-Al2O3 quaternary phase diagram. At constant basicity, the deformation temperature of CaO-SiO2-10%MgO-5%Al2O3 samples was found to be higher than that of CaO-SiO2-5%MgO-10%Al2O3 samples. Lastly, the addition of FeO below 20% to the CaO-SiO2-MgO-Al2O3 system significantly decreased the softening and melting temperatures of the slag samples. However, further addition of FeO beyond 20% produced inconclusive results. [doi:10.2320/matertrans.MRA2008372]
TL;DR: In this paper, the microstructural and mechanical properties on friction stir welded Inconel 625 alloy were evaluated at a tool rotation speed of 200 rpm and a traveling speed of 100 mm/min.
Abstract: The present study was carried out to evaluate the microstructural and mechanical properties on friction stir welded Inconel 625 alloy. For this work, friction stir welding was performed at a tool rotation speed of 200 rpm and a traveling speed of 100 mm/min. As a result, the grain refinement was achieved from 10.3 μm in the base material to 2.1 μm in the stir zone at an average grain size, accompanied by the dynamic recrystallization. This grain refinement has an effect on the increase of mechanical properties so that microhardness and tensile strength were significantly increased than that of the base material, more than 40% and 15% in fraction, respectively.
TL;DR: In this paper, Zhao et al. investigated the PEO behavior of AZ91 Mg alloy in the electrolytes with/without potassium fluoride and found that the inner barrier layer in the oxide layer coated from the electrolyte with potassium fluoride had a good influence of the corrosion resistance of Mg Alloy.
Abstract: Plasma Electrolyte Oxidation (PEO) behavior of AZ91 Mg alloy was investigated in the electrolytes with/without potassium fluoride. Growth rate of coating thickness in the electrolyte containing potassium fluoride (Bath B) was much higher than that in the electrolyte without potassium fluoride (Bath A). The oxide layer formed on AZ91 Mg alloy in electrolyte with potassium fluoride and sodium silicate consisted of MgO, MgF2 and Mg2SiO4. Corrosion current density of oxide layer coated from the electrolyte with potassium fluoride was much lower than that of oxide layer coated from the electrolyte without potassium fluoride. From the result of EIS analysis, it was known that inner barrier layer in the oxide layer coated from the electrolyte with potassium fluoride had a good influence of the corrosion resistance of Mg alloy. The corrosion resistance curves of Bath B were similar to the thickness curves, indicating that the thickness of the oxide layer played an important role in corrosion resistance of AZ91 Mg alloy. The oxide layer in the Bath B containing potassium fluoride was found to be a compact barrier-type passive film in presence of fluoride ions. The existence of the dense MgO and MgF2 in the barrier layer had a favorable effect on the corrosion resistance of the AZ91 Mg alloy formed from Bath B by PEO process. [doi:10.2320/matertrans.MER2008345]
TL;DR: In this article, the influence of applied pressure on temperature distribution in punch/die/graphite/sample assembly during SPS current control mode operation was systematically investigated by coupling experiments and computer modeling.
Abstract: The influence of applied pressures on temperature distribution in punch/die/graphite/sample assembly during SPS current control mode operation was systematically investigated by coupling experiments and computer modeling. Combined experimental and numerical results showed that the peak temperature and the temperature difference existing between the sample and the die outer surface progressively decreased with increasing of applied pressure from 5 to 80 MPa. This behavior was attributed to the strong change of the electric and thermal contact resistances at the punch/die interface due to punch Poisson deformation. [doi:10.2320/matertrans.M2009148]
TL;DR: In this paper, a self-consistent thermodynamic description of the Si-Ag-Al-As-Au-B-Bi-C-Ca-Co-Cr-Cu-Fe-Ga-Ge-In-Li-Mg-Mn-Mo-N-Na-Ni-O-P-Pb-S-Sb-Sn-Te-Ti-V-W-Zn-Zr system was developed for use within the composition space associated with SoG-Si materials.
Abstract: The fabrication of solar cell grade silicon (SOG-Si) feedstock involves processes that require direct contact between solid and liquid phases at near equilibrium conditions. Knowledge of the phase diagram and thermochemical properties of the Si-based system is therefore important for providing boundary conditions in the analysis of processes. A self-consistent thermodynamic description of the Si-Ag-Al-As-Au-B-Bi-C-Ca-Co-Cr-Cu-Fe-Ga-Ge-In-Li-Mg-Mn-Mo-N-Na-Ni-O-P-Pb-S-Sb-Sn-Te-Ti-V-W-Zn-Zr system has recently been developed by SINTEF Materials and Chemistry. The assessed database has been designed for use within the composition space associated with SoG-Si materials. The thermochemical database has further been extended to calculate the surface tensions of liquid Si-based melts. In addition to thermochemical and phase equilibrium calculation, several surface-related properties (temperature and composition gradients, surface excess quantity etc.) are able to simulate simultaneously using the database. The databases can be regarded as the state-of-art equilibrium relations in the Si-based multicomponent system.