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

MATERIALS TRANSACTIONS Vol. 57 (2016), No. 8

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

    pp. 1221-1229

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    DOI:10.2320/matertrans.M2015457

    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 influence 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 fine-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.
  • Effect of a High Static Magnetic Field on the Origin of Stray Grains during Directional Solidification

    pp. 1230-1235

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    DOI:10.2320/matertrans.MG201601

    The formation of stray grains in directionally solidified Al-4.5 mass% Cu alloy under an axial high static magnetic field up to 6 T has been investigated. Electron backscattering diffraction (EBSD) was performed to analysis the orientation of the stray grains. The experimental results suggest that the formation of the stray grains are significantly affected by the external magnetic field. The modification of dendrite morphology demonstrates the existence of thermoelectric magnetic effect on dendrite scale. It is implied that the thermoelectric magnetic force (TEMF) gives rise to the pinch-off of the sidebranches. When the fragments form, they will become the souce of the stray grains. Moreover, free dendritic fragment will rotate in melt and tend to align the 〈310〉 crystallographic axis along the direction of the magnetic field. This is because of the magnetic torque induced by the anisotropic susceptibility of α-Al crystal.
  • Evaluating Microstructure and High-Temperature Shear Behavior of Hot Extruded Al-Al13Fe4 Nanocomposite

    pp. 1236-1245

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    DOI:10.2320/matertrans.MG201605

    The microstructure and mechanical properties of extruded aluminum matrix composites reinforced with novel Al13Fe4 complex metallic alloy (CMA) nano-particles were investigated. The large grained structure of the hot pressed matrix was refined after addition of Al13Fe4 CMAs, the effect being more pronounced for Al-5 mass% Al13Fe4 composite. The hot pressed specimens were subjected to uniaxial hot extrusion process (with a 9 : 1 ratio at 400°C). This had a great effect on the microstructural evolution of the composites. High-temperature shear punch test (SPT) was employed to investigate the effects of 1–10 mass% Al13Fe4 additions on the microstructure and mechanical properties of the as-extruded Al/Al13Fe4 composite. The shear behavior of the alloys was investigated in the temperature range of 25–350°C. Al-5 mass% Al13Fe4 nanocomposite had the highest shear strength among all the materials tested at high temperature (150, 250 and 350°C), mainly due to the semi-ideal dispersion of the thermally stable Al13Fe4 nano-particles, and the refined microstructure of the extruded specimen, which results in pronounced enhancement in mechanical properties. These thermally resistant particles are believed to increase the resistance of the composite against the applied shear stress in the deformation zone during the subjection of the material to SPT.
  • Orientation Dependence of Bending Deformation Behavior in Magnesium Single Crystals

    pp. 1246-1251

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    DOI:10.2320/matertrans.MG201613

    Magnesium single crystals with different orientations were subjected to three-point bending tests, and bending deformation behavior was investigated. With the basal plane parallel to the neutral plane, the specimens deformed due to basal slips and showed gull-shape after deformation. Conversely, with the neutral plane and the axis parallel to (1120) and [1100], the specimen deformed due to {1012} twinning. However, the specimens fractured after a few percent of deformation, subsequently displaying V-shape. The specimens, whose neutral plane and axis were (1120) and [0001], also deformed due to basal slips. The relationship between bending yield stress of the specimens and the critical resolved shear stress of the basal slip, or {1012} twin, is discussed.
  • Strain Measurement of Micrometre-Sized Structures under Tensile Loading by Using Scanning White-Light Interferometry

    pp. 1252-1256

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    DOI:10.2320/matertrans.MG201616

    A scanning white-light interferometry (SWLI) technique was used to image the surface topography and measure the in-plane strain in micrometre-sized structures subjected to uniaxial tensile deformation. This technique was applied to observing the macro and local deformation behaviours in micrometre-sized Au specimens. Reproducible stress–strain curves were successfully obtained using SWLI during the intermittent tensile tests. The local strain distribution was also calculated from the movement of natural gauge marks that are characteristic of triangular elements. Combining this micro-tensile test with orientation imaging microscopy enables crystal plasticity of mesoscale structures to be revealed.
  • Brittle Fracture of Electrodeposited Gold Observed by Micro-Compression

    pp. 1257-1260

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    DOI:10.2320/matertrans.MG201612

    Micro-compression tests were conducted to evaluate micro-mechanical properties of electrodeposited gold. The gold film was electrodeposited on a platinum substrate with a thickness of 40 μm. The gold film was found to be composed of columnar textures along the film growth direction. Two sizes (10 × 10 × 20 μm3 and 20 × 20 × 40 μm3) of micro-pillars with a square cross-section and the long-side parallel to the Pt/Au interface were fabricated by focused ion beam. From the micro-compression tests, brittle fracture was observed. Both of the micro-pillars showed a high compressive strength of about 600 MPa, which are much higher than the strength of the bulk gold. Grain size of the gold film was estimated to be 14.7 nm, which is believed to be the main factor giving the high compressive strength. The strength of the larger micro-pillar was slightly lower than that of the smaller micro-pillar. The results confirmed presence of the size effect in these specimens.
  • The Anneal Hardening and Deformation Softening Behaviors of Nanocrystalline Cu-Zn Alloys

    pp. 1261-1265

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    DOI:10.2320/matertrans.MG201618

    The changes in the mechanical properties and microstructure of nanocrystalline Cu-Zn alloys deformed by cryorolling during low temperature annealing and the post-process deformation were studied. The deformed Cu-Zn alloys exhibited uncommon anneal hardening and deformation softening behaviors. The degree of anneal hardening and deformation softening increased with the addition of the solute atoms. X-ray diffraction analysis and transmission electron microscopy were employed to reveal the microstructure of the samples in different states. The annealing hardening effect is ascribed to the contribution of solute segregation to dislocation and short range ordering.
  • Microstructural Analysis of NdFeB Ternary Alloy for Magnets Fabricated Using a Strip-Casting Method

    pp. 1266-1271

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    DOI:10.2320/matertrans.MG201624

    The microstructural evolution of a NdFeB starting alloy fabricated by a strip-casting method was investigated as a function of the surface roughness, surface velocity, and thermal conductivity of the cooling roll of the strip caster. The nucleation of the solid phase took place preferentially at the edges of grooves machined on the roll and the grain size was inversely proportional to the frequency of nucleation. A higher surface velocity produced thinner strip-cast samples. The growth rate of the solid phase weakly influenced the dendrite sizes compared with the case of a thin plate obtained using mold-casting. Cooling rolls with higher thermal conductivity resulted in alloys with smaller grain and dendrite sizes.
  • Effect of Zn Addition on Interfacial Reactions Between Sn-Bi Solder and Cu Substrate

    pp. 1272-1276

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    DOI:10.2320/matertrans.MD201515

    A comparative study of the formation, growth, and morphology of the interfacial intermetallic compounds (IMCs) of the eutectic Sn-Bi and Sn-Bi-Zn solder joints was conducted, and the shear strengths of the two solder joints were evaluated. The cross-sectional microstructures of the joints were investigated and the fracture surfaces of the joints were examined after the shear tests. The results of the microstructural analysis of the joints indicated that the addition of Zn suppressed the growth of the interfacial IMCs significantly after both reflow and thermal aging. Although the shear-test results indicated that the addition of Zn decreased the shear strength of the Sn-Bi solder joint, the fracture surface examination after the shear tests revealed the cause of the degradation of the shear strength and a possible solution to prevent this degradation is suggested in the paper.
  • Synthesis and Photocatalytic Activity of Bi2Fe4O9 Using KOH as Mineralizer via Hydrothermal Method

    pp. 1277-1281

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    DOI:10.2320/matertrans.M2016043

    Bi2Fe4O9 nanoplatelets were successfully prepared via hydrothermal method using KOH as the mineralizer. The influence of KOH concentration on the morphology of the products was investigated. It is found that the thickness and edge length of as-prepared Bi2Fe4O9 nanoplatelets can be tailored by adjusting the KOH concentration. With increase in the KOH concentration from 3 to 9 M, the thickness of nanoplatelets increases gradually, whereas their edge length exhibits a trend of decrease. A possible influencing mechanism of the KOH concentration on the morphology of Bi2Fe4O9 nanoplatelets is proposed on the basis of experimental results. The photocatalytic activity of Bi2Fe4O9 nanoplatelets was investigated by the degradation of methylene blue under simulated sunlight irradiation, indicating that they possess an appreciable photocatalytic activity. Furthermore, the as-prepared Bi2Fe4O9 nanoplatelets present good photocatalytic reusability. Magnetic hysteresis loop measurement shows that the Bi2Fe4O9 nanoplatelets exhibit weak ferromagnetic behavior at room temperature.
  • Effect of High-Speed Impact Compression on Natural Aging and Subsequent Artificial Aging of a 6061 Aluminum Alloy

    pp. 1282-1286

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    DOI:10.2320/matertrans.L-M2016819

    The effect of high-speed impact compression on natural aging and subsequent artificial aging of a 6061 aluminum alloy was investigated using Micro-Vickers hardness test, differential scanning calorimetry (DSC) analysis and transmission electron microscopy (TEM). The suppression of natural age-hardening was clearly seen in the alloy with high-speed impact compression. TEM observation showed that fine β” precipitates was formed during artificial aging even after high-speed impact compression and natural aging. Maximum hardness of the peak-aged alloys with high-speed compression was almost the same as that without natural aging, showing that negative effect of two step aging was almost overcome by high-speed impact compression.
  • Effects of Nd or Zr Addition on Microstructure and Mechanical Properties of As-Cast Mg-Zn-Y Alloy

    pp. 1287-1295

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    DOI:10.2320/matertrans.M2016035

    The effects of Nd or Zr addition on microstructure and mechanical properties of casting Mg-Zn-RE alloy have been investigated. The results indicate that the optimum contents of Nd and Zr are 0.5% and 0.3% respectively. The less or higher contents all increase grain size and accelerate the formation of shrinkage porosity, and thus decrease tensile properties and change fracture regime from transgranular mode to intergranular mode during tensile tests. The Mg-Zn-RE ternary phases transform from W (Mg3Zn3(Nd,Y)2) in turn into W + Z (Mg12Zn(Nd,Y)) and Z as the Nd content increases and their distribution gradually changes from small discontinuous lath form to continuous network form. The grain bonding strength of an alloy with a certain amount of W phase that distributes in a discontinuous form is high than that of the alloy with the Z phase, and thus the W phase is an ideal strengthening phase. The alloy with 0.5 Nd and 0.3% Zr, named ZW21 alloy, has the smallest grains and highest grain bonding strength, and so has the highest comprehensive mechanical properties.
  • Microstructure and Viscosity of Particles Reinforced 7075 Al Matrix Composites

    pp. 1296-1299

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    DOI:10.2320/matertrans.M2016085

    In-situ TiB2 particle reinforced 7075 Al alloy was produced by molten salt method (LSM). The effects of TiB2 content on the microstructure, the melting behavior and the viscosity of 7075 Al alloy were investigated. The experimental results have shown that the microstructure became uniform rosette grains and the grain size decreased with increasing TiB2 particles. The morphology of grains became bigger with dendritic structure when the TiB2 particles content is more than 4.5%. The liquidus and solidus temperatures of the TiB2/7075 composites were firstly increased and then decreased with the increase of the content of TiB2 particles. The semisolid processing temperature window of 7075 Al alloy became narrow after adding TiB2 particles, and the liquid fraction of TiB2/7075 composites with increasing temperature was more sensitive than 7075 Al alloy. The apparent viscosity of the 4.5%TiB2/7075 composite was the lowest among 3.0, 4.5 and 9.0%TiB2/7075 aluminum matrix composites respectively. The apparent viscosity of the 9.0%TiB2/7075 was less than that of 7075 alloy but was greater than that of 4.5%TiB2/7075 composite under the same conditions. The viscosities of the composites decreased sharply with increasing shear rate, and the change with the shear rate were more sensitive than that of the 7075 alloy.
  • Turning Machinability of Short Carbon Fiber Reinforced Aluminum Alloy Composite

    pp. 1300-1304

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    DOI:10.2320/matertrans.M2016062

    Turning machinability of aluminum alloy composites reinforced with carbon fibers was examined using a carbide tool. Pitch-based short carbon fiber was used as the reinforcement. The composites were fabricated by squeeze casting. Optical microscopy revealed that the fibers were randomly arranged in the alloy matrix. The fiber reinforcement decreased the hardness of the alloy. The fiber reinforcement also decreased the cutting resistance of the aluminum alloy, and the resistance values of the composite was lower than that of a composite reinforced with short alumina fibers. The roughness of the machined surface was significantly decreased by the fiber reinforcement under every cutting condition. No carbide tool wear was observed even if the composite underwent a machining of 2 km, whereas the tool wear was clearly observed for the alumina fiber-reinforced composite. These results indicated that the carbon fibers in the alloy act as a solid lubricant. Chips formed by machining the composite were powdery, whereas the chips formed by machining the unreinforced aluminum alloy was long.
  • Effect of Sulfur on Creep Strength of Ni-Base Single-Crystal Superalloy, TMS-1700

    pp. 1305-1308

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    DOI:10.2320/matertrans.M2016032

    We studied the effect of sulfur addition on a Ni-base single-crystal superalloy, TMS-1700, by performing creep tests at 1100℃/137 MPa using specimens doped with 0, 10, 20, and 100 ppm sulfur. The creep rupture life was found to decrease with increasing sulfur concentration. The scanning electron microscopy (SEM) observation of creep-ruptured specimens revealed the coarsening of the raft structure with increasing sulfur concentration. Their transmission electron microscopy (TEM) observation showed the formation of coarser γ/γ' interfacial dislocation networks with increasing sulfur concentration. These microstructural differences may be the cause of the shorter creep rupture life observed in alloys with higher sulfur addition.
  • Chlorination-Volatilization Behavior of Titanium Metal Scraps during Recycling Using Reaction-Mediating Molten Salt

    pp. 1309-1318

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    DOI:10.2320/matertrans.M-M2016818

    In order to develop an efficient and environmentally friendly process for recycling both titanium scrap and FeClx (x = 2, 3) waste, the chlorination-volatilization of titanium metal scraps utilizing a MgCl2-SmCl3 reaction-mediating molten salt was examined. After the thermodynamic analyses on the chlorination behavior of representative elements such as the alloying elements and oxygen, fundamental experiments were carried out at 1100 K by reacting off-grade Ti sponge, Ti-6Al-4V alloy rod, and Ti rod with MgCl2-SmCl3 molten salt. The results indicated that TiCl4 could be effectively produced and volatilized from off-grade sponge and Ti-6Al-4V alloy. It was also confirmed that Fe and Ni in the Ti scrap remain in the molten salt as metal, whereas the Al and V in Ti alloy are chlorinated by SmCl3 and their chlorides volatilized. Oxygen introduced into the reaction system was found to form TiOCl in the molten salt, and therefore does not consume the SmCl3 mediator in the molten salt. These findings confirm that chlorination using a reaction-mediating molten salt is an effective means of recycling both titanium scrap and FeClx waste.
  • Effects of Electrolysis Conditions on the Morphologies and Corrosion Resistances of Polyaniline Films Formed on Fe by Electropolymerization

    pp. 1319-1326

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    DOI:10.2320/matertrans.M2016083

    Polyaniline films were formed on an Fe substrate using the oxidative electropolymerization technique at 288 K in aqueous solutions with pH values ranging from 2 to 10 and containing aniline, p-toluenesulfonic acid and oxalic acid as supporting electrolytes. The effects of the electrolysis conditions on the morphologies and corrosion resistances of the films were subsequently investigated. Although the polyaniline films were partially formed in solutions of pH 2–4, the films completely formed and their surfaces became smooth when deposited in solutions of pH 7–10. Polyaniline films with smooth surfaces and good corrosion resistance were obtained at 8–30 A·m-2, whereas the films obtained at current densities greater than 50 A·m-2 exhibited non-uniform surface morphologies and poor corrosion resistance. Films obtained at anode potentials of 0.4 V and 0.8 V vs. NHE were not formed completely, and the films formed at an anode potential of 2.0 V exhibited very rough surfaces. Films formed from a solution containing only p-toluenesulfonic acid as a supporting electrolyte exfoliated from the Fe substrate after being immersed in a 3 mass% NaCl solution for 3 h. Although the films prepared from a solution containing only oxalic acid as a supporting electrolyte exhibited good adhesion to the substrate, they contained numerous defects and pores; consequently, they improved the Fe's corrosion resistance less than films deposited from a solution containing p-toluenesulfonic acid. In the case of polyaniline films formed in an electrolyte solution containing both p-toluenesulfonic acid and oxalic acid, the Fe exhibited improved corrosion resistance, and the films exhibited good adhesion to the Fe substrate.
  • Recovery of Dy from a Mixture of Nd, Fe, B and Dy by Electrolysis in Molten LiCl

    pp. 1327-1331

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    DOI:10.2320/matertrans.M2016108

    The electrodeposition and recovery of Dy was attempted by chlorinating Dy with Cl2 generated at the anode by electrolysis in molten LiCl, in which Fe, B, Nd and Dy powders were added, then reducing the Dy ions, which were ionized from the dysprosium chloride, at the cathode. When the electrolysis in the LiCl bath was carried out even after the Fe, B, Nd and Dy powders were added to the LiCl bath, the electrodeposition of these metals on the cathode did not occur, thus the metals could not be recovered when the electrolysis in the LiCl bath was carried out even after the Fe, B, Nd and Dy powders were added to the LiCl bath. The mass increase due to the electrodeposition of Dy was observed at the cathode in the LiCl bath in which DyF3 was added. The mass of the material electrodeposited at the cathode was greater in the LiCl bath, in which the Fe, B, Nd and Dy powders were added with DyF3, in comparison to that in the bath with only DyF3. It was found from analyzing the electrodeposited material by an X-ray diffraction technique and an electron probe microanalyzer that the material consisted of a large amount of Dy and a small amount of B. Examination of the cation concentration in the molten salt after electrolysis using an inductively coupled plasma instrument revealed that the molten LiCl, into which DyF3 and the metal powders were added, contained the highest number of Dy ions. Thus, metallic Dy was cationized during the electrolysis in the molten LiCl bath containing DyF3 and the metal powders, then the cationized Dy was reduced at the cathode and precipitated as metallic Dy.
  • Use of Computational Thermodynamics in the Analysis of Hot Metal Desulphurization with Slags Based on Marble Waste and Sodalite

    pp. 1332-1338

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    DOI:10.2320/matertrans.M2016016

    The steel industry is going through transformations aiming at the innovation and use of alternative raw materials. Thus, the use of industrial wastes in synthetic slag production is considered an important alternative to search for new materials and waste reuse. Therefore, the aim of the current study is to study the use of synthetic slags in hot metal desulphurization. It was proposed the use of sodalite instead of fluorspar and the use of marble waste instead of lime. Marble waste was characterized by chemical analysis, X-ray diffraction (XRD) and thermogravimetric analysis. The XRD showed the presence of compounds such as CaCO3, MgCO3 and SiO2. Subsequently, simulations using Thermo-Calc were performed in order to obtain thermodynamic data of the present phases, and to compare them to experimental data. The experimental procedures were carried out at 1400℃. In addition, hot metal tests were performed using an alumina rotor to increase the desulphurization. In hot metal desulphurization, solid CaO phase was responsible for sulfur removal. Furthermore, Ca3O3.SiO2 and Ca3O3.Al2O3 phases limited the reaction, and their concentrations were higher in the slags with marble waste and sodalite, due to the presence of SiO2 and Al2O3 in these raw materials.
  • Machinability of Austempered Spheroidal Graphite Cast Iron Made by Sand Mold and Continuous Casting Methods

    pp. 1339-1344

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    DOI:10.2320/matertrans.F-M2016815

    In this study, the machinability of austempered spheroidal graphite cast iron made by different casting methods was investigated. Spheroidal graphite cast iron samples made by sand mold casting and continuous casting, respectively ADI-S and ADI-C, were used. From the results of cutting tests, the machinability of ADI-C was always excellent compared with that of ADI-S at cutting speeds from 100 to 365 m/min. The feed and thrust forces of ADI-S were higher than those of ADI-C at high cutting speeds, although their-cutting resistance was almost the same at low cutting speeds. In addition, the microstructure of ADI-S chips was found to be greatly deformed near the chip-tool interface for ADI-S compared with ADI-C. It has been reported that there always exists retained austenite in austempered spheroidal graphite cast iron, and that the retained austenite transforms to deformation-induced martensite on the machined surface when the austempered spheroidal graphite cast iron is machined. From the results of the comparative analysis of ADI-S and ADI-C, the average relative volume ratio of retained austenite increased with increasing cutting speed for both ADI-S and ADI-C, and was about double in the case of ADI-S at high cutting speeds such as 365 m/min. From these results, it is clear that the retained austenite in both ADI-S and ADI-C does not transform to deformation induced martensite at high cutting speeds, and that ADI-C can be machined at cutting temperatures and with cutting resistances lower than those necessary for ADI-S, suggesting that the machinability of ADI-C is better than ADI-S.
  • Effect of Powder Calcination on the Cold Spray Titanium Dioxide Coating

    pp. 1345-1350

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    DOI:10.2320/matertrans.T-M2016817

    The agglomeration of nanoparticles is usually undesirable in the formation of powder. However, a coating process using the cold spray method only allows the usage of micrometer-sized feedstock powder in a regular powder feeder. In this study, TiO2 coatings on ceramic tiles were prepared by a cold spray process using agglomerated TiO2 powders synthesized via a simple hydrolysis method. XRD analysis showed that TiO2 powders, composed of anatase phase and calcination at 200℃ to 400℃, resulted in enhanced crystallinity and crystallite size of the anatase TiO2 powders. SEM micrographs revealed that the obtained powders were in spherical-like agglomerates with the tertiary particles having diameters of 5–20 µm. TEM image revealed that the obtained TiO2 powders were composed of nanometer primary particles. XPS analyses showed that TiO2 powders without calcination and calcined at different temperatures were formed through the Ti-O bonds. The influences of post treatment at low calcination temperatures of the as-synthesized TiO2 powders were studied on powder deposition. The results of this study indicated that a post treatment on TiO2 powder improved powder deposition on ceramic tile substrate via the cold spray method. The cross-section of the obtained coating which was observed using SEM showed that nanoparticles TiO2 powders in the agglomerated form were able to be deposited on the substrate and formed a thick coating. A stacking of agglomerated TiO2 powders was found on the cross-section observation which is due to the breaking up of ceramic particles which was induced by porosity in the powder and is believed to be responsible for the formation of the coating.
  • Effect of Process Parameters of Backward Extrusion by Servo Press on Purification of A7075 Alloy under the Semisolid Condition

    pp. 1351-1356

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    DOI:10.2320/matertrans.M2016010

    The aggregation of tramp elements in repeated recycling processes is a growing problem and an effective technology for the separation of tramp elements from aluminium alloy scrap is necessary to produce new alloy products from old scrap. In this study, backward extrusion was conducted under the semisolid condition using a servo press (Komatsu- H1F110) to investigate the industrial-scale purification of A7075 wrought aluminium alloy. and, process parameters such as the semisolid temperature, backward extrusion ratio and initial extrusion speed were investigated. From optical microscopic images and the results of scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS), it was confirmed that the aluminium was significantly purified and distributed homogeneously in the unextruded part for suitable combinations of the specific extrusion temperature, extrusion ratio and initial extrusion speed.
  • Development of High Strength Tungsten/Oxide Dispersion Strengthened Ferritic Steel Joints by Innovative Thermal Stress Relaxation Technique Based on Phase-Transformation-Induced Creep Deformation

    pp. 1357-1362

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    DOI:10.2320/matertrans.M2016119

    The realization of fusion reactors rests on the function of the blanket systems with high thermal efficiency consisting of armor and structural materials. The fabrication of the blanket requires upgrade of bonding technology which makes the components reliable. The combination of tungsten and oxide dispersion strengthened ferritic steel (ODS-FS) is considered to be adequate for the application to the fusion diverter components. The issue of diffusion bonding of tungsten with ODS-FS is to reduce thermal stresses caused by a large difference in thermal expansion coefficient between the two materials. In this study, an innovative thermal stress relaxation methodology during cooling has been newly proposed as a key technology in joining, which is based on the phenomenon of γ→α phase transformation-induced creep deformation of low carbon steel inserted between tungsten and ODS-FS. In the cooling pattern where the joint was slowly cooled at a rate of approximately 1.6℃/min from 800℃ to 600℃. The application of the technology to the diffusion bonding of tungsten/ODS-FS resulted in a very high bonding strength of 480 MPa, which has never been achieved so far by the conventional bonding methodologies.
  • Change in Microstructure, Mechanical Strength and Corrosion Resistance of Ti-8Mo-xNi Alloys through Various Sintering Temperatures

    pp. 1363-1369

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    DOI:10.2320/matertrans.M2016044

    In this study, three different powders are mixed and used to produce Ti-8Mo-xNi alloys in three different proportions: Ti-8Mo-4Ni, Ti-8Mo-6Ni and Ti-8Mo-8Ni. The Ti-Mo-Ni alloys simultaneously undergo various vacuum sintering temperatures of 1125, 1150, 1175 and 1200℃, respectively. The experimental results show that the Ti-8Mo-8Ni alloys acquire a higher sintering density (98.9%) and hardness (52.1 HRC) after sintering at 1175℃ for 1 h. However, due to the grain growth and increased amount of nickel in the Ti-8Mo-8Ni alloys, the transverse rupture strength (TRS) shows an obvious decrease (as compared with Ti-8Mo-6Ni, the TRS value decreasing from 1177 to 685 MPa). Consequently, the suitable Ni content of the Ti-8Mo-6Ni alloys which proves advantageous to the TRS results from the uniform distribution of the TiNi intermetallic compound precipitates within the β matrix. The sintered Ti-8Mo-8Ni alloys also possess the lowest corrosion current (Icorr = 1.87 × 10-7 A·cm-2) and highest polarization resistance (56084 Ω·cm2) in 3.5 mass% NaCl solutions. This result confirms that sintered Ti-8Mo-8Ni alloys effectively improve corrosion resistance.
  • Synthesis, Crystal Structure, and the Ionic Conductivity of New Lithium Ion Conductors, M-Doped LiScO2 (M = Zr, Nb, Ta)

    pp. 1370-1373

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    DOI:10.2320/matertrans.Y-M2016816

    New lithium ion conductors of M-doped LiScO2 (M = Zr, Nb, and Ta) were synthesized by a solid-state reaction method. Peak shifts of the X-ray diffraction patterns revealed the formation of solid solutions with aliovalent cation doping. In addition, increase in the ionic conductivity by M doping is indicated. The highest total conductivity of 7.94 × 10-6 S cm-1 at 623 K with an activation energy of 88 ± 5 kJ mol-1 was observed for the Zr4+ doped sample in the systems. The Zr4+ doped system showed the largest solid solution limit in Li1-xSc1-xZrxO2 (x ≈ 0.1) and continuous increase of the conductivity with increasing x. Structural analysis by Rietveld refinement indicated that the lattice expansion and lithium-ion vacancy formation by the Zr doping in the structure, which could contribute to the increase in the ionic conductivity.
  • Effect of Sulfur on the Sintering of Nickel Particles

    pp. 1374-1377

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    DOI:10.2320/matertrans.M2015464

    Sintering behavior of fine nickel powder with various surface sulfur content have been systematically investigated. The nickel powder with 150 ppm sulfur demonstrated the greatest density of the sinters, while the nickel powder with 300 ppm sulfur showed the lower density than the others. It was found that the appropriate content of surface sulfur enhanced the densification of fine nickel powder, which is mainly attributed the existence of solid solution sulfur in the nickel crystal structure. However, the excess sulfur beyond the solubility limit in nickel posed the formation of nickel sulfides, and resulted in the lower density of nickel sinters.
  • Hydrochloric Acid Treatment: An Effective Method to Enhance the Catalytic Performance of TiO2 Stellerite Composite Photocatalyst on Methyl Orange

    pp. 1378-1383

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    DOI:10.2320/matertrans.M2016023

    Stellerite (a natural zeolite) was used as substrate for titanium dioxide deposition. Stellerite was treated at 363 K with hydrochloric acid solutions of different concentrations (0.2–1.0 mol L-1) for 4 hours. The resulting composite samples were characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDX), Fourier transform infrared spectroscopy (FT-IR), BET surface area analysis and X-ray diffraction (XRD). The hydrochloric acid treatment caused the creation of micropores with ~1 nm diameter. The result illustrates that stellerite possesses strongly acid-resistant property in hydrochloric acid solutions with a concentration no higher than 0.4 mol L-1. The photocatalytic degradation activity of TiO2/stellerite changed remarkably when stellerite supports treated with different concentrations of hydrochloric acid were used, giving the optimum hydrochloric acid concentration of 0.4 mol L-1. The recycling of the TiO2/stellerite photocatalyst was also investigated, and the methyl orange degradation rate was 75.0% of the initial rate after four cycles.

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