Showing papers in "Materials Transactions in 2012"

XPS and Magnetic Properties of CoFe2O4 Nanoparticles Synthesized by a Polyacrylamide Gel Route

Abstract: Cobalt ferrite CoFe2O4 nanoparticles were prepared via a polyacrylamide gel route and were characterized by XRD, SEM, XPS and VSM. It is demonstrated that the sample (designated S1) prepared without using the cross-linking agent bis-acrylamide has an average grain size of 45nm, while the sample (designated S2) prepared by introducing an amount of bis-acrylamide which is about 1/5 times the amount of acrylamide has an average grain size of 23nm. The two kinds of particles are shaped like spheres. The cation distribution is determined, from Co 2p3/2 and Fe 2p3/2 XPS spectra, to be (Co0.4Fe0.6)[Co0.6Fe1.4]O4 for both the samples, where (Co0.4Fe0.6) and [Co0.6Fe1.4] represent cations in the tetrahedral and octahedral sites, respectively. Magnetic measurement reveals a saturation magnetization of 67.3A·m 2 ·kg ¹1 for sample S1 and 62.3A·m 2 ·kg ¹1 for sample S2, but a similar coercivity of about 87.5kA·m ¹1 for both the samples. [doi:10.2320/matertrans.M2012151]

Accelerated Diffusion and Phase Transformations in Co–Cu Alloys Driven by the Severe Plastic Deformation

Abstract: The cast Co­5.6mass% Cu and Co­13.6mass% Cu alloys were subjected to severe plastic deformation (SPD) by the high-pressure torsion(HPT). The HPT treatment drastically decreases the size of the Co grains (from 20µm to 100nm) and the Cu precipitates (from 2µm to 10nm).The metastable fcc-Co disappeared, and supersaturated Co-based solid solution present in the as-cast alloys completely decomposed after HPT.Only the phases stable below 400°C remained after severe plastic deformation (i.e. almost pure hcp-Co and fcc-Cu grains). The applicability ofthe concept of effective temperature originally developed for materials under irradiation for the SPD-accelerated diffusion is discussed.[doi:10.2320/matertrans.MD201111](Received July 14, 2011; Accepted October 31, 2011; Published December 25, 2011)Keywords: severe plastic deformation, cobalt­copper alloys, phase transformations, driven systems

Synthesis and Characterization of NiO Nanoparticles by Sol­Gel Method

Abstract: Due to the outstanding electrical, magnetic and catalytic properties, nickel oxide (NiO) has been received considerable attention during the past decades. In this study, NiO nanoparticles were prepared by sol­gel method, which is one of the simplest and lowest-cost techniques. The synthesis was accomplished by using Poly(alkylene oxide) block copolymer as the surfactant, and Ni(NO3)2·6H2O as the inorganic precursor. The effect of experimental parameters, such as calcination temperatures and H2O concentration on the NiO nanoparticles formation were investigated. TGA, XRD, SEM, TEM and N2 adsorption­desorption isotherms were used to characterize the microstructure and specific surface area of the samples. TGA and FTIR analyses demonstrated that copolymers were expelled at 573K. The formation of NiO nanoparticles and their structural features were greatly dependent on the calcination temperature. The sample calcined at 923K was composed of pure NiO nanoparticles as shown by XRD. As H2O concentration was increased, the reoxidation process of metallic Ni to form NiO would reduce, but it would not affect the structural type of NiO nanoparticles. In general, the addition of water would weaken and inhibit oxidation effects. The temperature of stable metallic Ni was increased up to 823K. The specific surface area evaluated from the N2 adsorption­desorption indicated that the samples consisting of non-porous NiO nanoparticles. Increasing H2O addition resulted in an increase of specific surface area of nanocrystalline NiO powder. [doi:10.2320/matertrans.M2012244]

Bridge Deflection Measurement Using Digital Image Correlation with Camera Movement Correction

Abstract: When displacement measurement by digital image correlation is performed in outside for the inspection of real structures, the position and the direction of a camera are often changed slightly because of wind, oscillations and the lack of stability of ground. In order to realize the bridge deflection measurement by digital image correlation, a method for correcting the effect of camera movement is proposed in this study. The relationship between images before and after the camera movement is described by an equation of perspective transformation. The unknown coefficients of the equation are determined from undeformed regions of the images. Then, the effect of the camera movement is eliminated by using the perspective transformation. The effectiveness is validated by applying the proposed method to the rigid body rotation and translation measurement of a planar specimen, the deflection measurement of a wide-flange beam, and the bridge deflection measurement. Results show that the effect of the camera movement can be corrected by the proposed method. It is emphasized that noncontact displacement measurement is possible by simple and easy procedure with digital image correlation for the structural evaluation of infrastructures. [doi:10.2320/matertrans.I-M2011843]

Effects of Re Content and Fabrication Process on Microstructural Changes and Hardening in Neutron Irradiated Tungsten

Abstract: The effects of the material fabrication process and rhenium (Re) content on the irradiation-induced changes in the microstructure and hardness of pure tungsten (W) and W­Re alloys were investigated. Neutron irradiation of pure W and W­Re alloys (Re concentration 3­26%) was carried out in the experimental fast reactor JOYO. The irradiation conditions were 0.44 displacement per atom (dpa) at 531°C and 0.47dpa at 583°C for pure W and W­Re alloys, respectively. After irradiation, microstructural observations using a transmission electron microscope (TEM) and Vickers microhardness tests were performed. Voids and dislocation loops were observed in both pure W and W­Re alloys after irradiation. The number density of voids in pure W was higher than that in W­3%Re, W­5%Re and W­10%Re. Only in the case of W­26%Re irradiated to 0.47dpa at 583°C were there no voids observed, but irradiation-induced fine precipitates and a few dislocation loops were observed. The irradiation hardening of pure W was greater than that of the W­Re alloys. It was considered that irradiation hardening of pure W was caused mainly by the higher number density of voids. The addition of Re suppressed void formation and irradiation hardening of the W­Re alloys. Irradiation hardening of W was also suppressed in hot-rolled W compared with arc-melted as-cast W. [doi:10.2320/matertrans.MBW201110]

Bone Loss and Reduced Bone Quality of the Human Femur after Total Hip Arthroplasty under Stress-Shielding Effects by Titanium-Based Implant

Abstract: The present work was aimed at clarifying the stress-shielding effect caused by hip-joint implantation into a femur by using a human cadaver with a cementless hip implant In particular, bone quality was assessed from the standpoint of preferential c-axis orientation of biological apatite (BAp) Comparing the implanted side to the non-implanted side, a finite element analysis (FEA) indicated that artificial hip-joint implantation had a significant stress-shielding effect on the femur The results also showed a marked decrease in the degree of preferential BAp orientation as well as bone loss in the medial-proximal femur This is the first report showing a reduction in the degree of preferential BAp orientation due to a stress-shielding effect after artificial hip-joint implantation Since preferential BAp orientation is an important index for determining bone mechanical function, these findings should be taken into account in future artificial hip-joint designs, especially those involving the stem component [doi:102320/matertransM2011358]

Equal-Channel Angular Pressing and High-Pressure Torsion of Pure Copper: Evolution of Electrical Conductivity and Hardness with Strain

Abstract: Pure Cu (99.99%) is processed by equal-channel angular pressing (ECAP) and by high-pressure torsion (HPT). The electrical resistivity aswell as the microhardness increases with an increase in the equivalent strain at an early stage of straining, but saturates to a steady state at theequivalent strains more than ³20. At the steady state, the samples processed by ECAP and HPT show a significant increase in the hardness(³270%) but little decrease in the electrical conductivity (³12%) when compared to the annealed state. Transmission electron microscopyconfirms that the microstructure does not change at the saturated level with further straining. Evolutions of hardness, electrical conductivity andmicrostructures are also investigated after post-HPT annealing. [doi:10.2320/matertrans.MD201109](Received June 30, 2011; Accepted August 9, 2011; Published September 21, 2011)Keywords: severe plastic deformation, equal-channel angular pressing, high-pressure torsion, ultrafine grain, electrical conductivity

First-Principles Calculations on Elasticity and Anisotropy of Tetragonal Tungsten Dinitride under Pressure

Abstract: First-principles calculations of the crystal structure and the elastic properties of tetragonal WN2 have been performed with the plane-wave pseudopotential density functional theory method. The calculated structural parameters and elastic constants at zero pressure and temperature are in excellent agreement with the available theoretical results. The dependence of the elastic constants Cij, the aggregate elastic moduli B, G and the anisotropies on pressure have been investigated. WN2 is a brittle system below about 66GPa, whereas it becomes ductile under high pressure. By the elastic stability criteria, it is predicted that tetragonal WN2 are not stable above 232.1GPa. [doi:10.2320/matertrans.M2011373]

Formation of Black Ceramic Layer on Aluminum Alloy by Plasma Electrolytic Oxidation in Electrolyte Containing Na2WO4

Abstract: The formation of black ceramic layer produced by plasma electrolytic oxidation (PEO) coating has been investigated as a function of coating time. A series of PEO coatings was carried out on aluminum alloy sample in a phosphate electrolyte containing sodium tungstate (Na2WO4) with four different coating times, i.e., 20, 100, 200 and 300 s. As the coating time increased, the amount of tungsten element in the ceramic layer increased, resulting in the black ceramic layer. This phenomenon was discussed based on the electrochemical reaction assisted by micro sparks to form WO3 compounds in the ceramic oxide layer. [doi:10.2320/matertrans.M2011263]

Recovery of Sn, Ag and Cu from Waste Pb-Free Solder Using Nitric Acid Leaching

Abstract: The development of a hydrometallurgical process for the recycling of waste Pb-free solder based on nitric acid leaching, followed by the separation of Ag and Cu through AgCl precipitation or cementation, was investigated Nitric acid dissolved Cu and Ag from the waste material while converting tin to stannic oxide (SnO2), which is very sparingly soluble in the HNO3 solution More than 99% of the Ag and Cu in the waste Pb-free solder were dissol-ved in 2 kmol·m¹3 HNO3 under the leaching conditions of 75°C, 100 kg·m¹3 pulp density and stirring at 400 rpm for 120 min The addition of NaCl or Cu powder was used to separ-ate Ag from Cu in the solution The addition of 2 kg·m¹3 of NaCl or 125 kg·m¹3 of Cu powder to the leaching solut-ion at 30°C led to the successful recovery of 3755 g·m¹3 of Ag Thus, the results showed that Sn, Ag and Cu could be separated and recovered from waste Pb-free solder by the proposed recycling process

Effects of Carbon Addition on Microstructures and Mechanical Properties of Binderless Tungsten Carbide

Abstract: Binderless tungsten carbide (WC) with added carbon was sintered at 1800°C using a resistance-heated hot-pressing machine. Dense binderless WCs were obtained in the range from 0.25 to 0.3mass% C, consisting of only a WC phase. The constituent phase transition with increasing carbon addition was WC + W2C, WC alone, and WC + residual C. Very fine WC grains were formed in the presence of W2C below 0.25mass% C. When binderless WCs consisted of a WC single phase, larger WC grains were observed. While a high hardness value, more than 23.9GPa, was measured for binderless WCs below 0.20mass% C, the hardness decreased markedly in the range from 0.25 to 0.3mass% C, corresponding to significant WC grain growth. A Hall­Petch-like relationship was confirmed between the hardness value and the grain size for dense binderless WC. [doi:10.2320/matertrans.M2012148]

Effects of Grafting Densities of Comb-Like Copolymer on the Dispersion Properties of Concentrated Cement Suspensions

Abstract: Effects of grafting densities of comb-like copolymer on the dispersion properties of concentrated cement suspensions are investigated systemicly in this paper. For comb-like copolymers the adsorbed amount increases at the same dosages as the grafting density decreases, while the efficiency of dispersion is improved by increasing the grafting densities. Based on the theory of Flatt at level of scaling law, the molecule size and the occupied surface area of the comb-like polymers with different grafting densities are calculated. The comb-like polymers with higher grafting density has bigger molecular size. For comb-like polymer dispersant, the steric repulsion provided by the side chains is the main drive of the dispersion, so the Flory energy is employed to explore the relationship between steric repulsion and grafting density. The calculation tells us that higher grafting density results in higher Flory energy which represents stronger steric repulsion. The calculation method based on the scaling law and Flory theory is successfully used to interpret the dispersion mechanism, and it is anticipated that this method can be applied to explain the effect of other parameters of PCE comb-like polymers on the dispersion properties of cement suspensions, ceramics suspensions, slurries and so on. [doi:10.2320/matertrans.M2011344]

Effect of Alloying Elements on High Temperature Mechanical Properties for Piston Alloy

Abstract: Recent legislative and environmental pressures on the automotive industry to produce light-weight fuel-efficient vehicles with lower emissions have led to a requirement for more efficient engines. Therefore, combustion pressures of diesel engines have increased up to 20MPa and the more durable alloys for pistons are thus necessary to increase the thermal and fatigue resistance. The demand for more efficient engines is resulting in components operating under severe stress and temperature conditions. During start/stop of engine cycles, LCF (low cycle fatigue) phenomena is generated due to the thermal transient, also HCF (high cycle fatigue) and creep deformation occur under the steady-state engine temperature during operation of engine. A quantitative study of the effect of alloying elements on mechanical behavior of Al­12mass%Si casting alloys for piston has been conducted. In the condition of minimizing casting defects, the influence of compounds features on the high temperature mechanical performance became more pronounced. Depending on Ni and Cu content affecting the strength of the matrix, the tensile strength was increased with Ni and Cu content, whereas the elongation was increased in the reverse case. Also, creep resistance was drastically increased with Ni and Cu contents mainly due to prevention of deformation owing to the increased eutectic and precipitation particles. LCF lives were decreased with alloy contents in Coffin­Manson relation because of the smaller elongation, but the analysis of fatigue lives with hysteresis loop energy which consists of both strength and elongation showed that the fatigue lives were normalized regardless of chemical compositions and test temperature. [doi:10.2320/matertrans.M2011259]

Simultaneous Recovery of Gold and Iodine from the Waste Rinse Water of the Semiconductor Industry Using Activated Carbon

Abstract: This research work focused on the simultaneous recovery of gold (40.5mg/dm 3 ) and iodine (748mg/dm 3 ) from the waste rinse water of the semiconductor industry using activated carbon. A batch study was conducted to optimize process parameters, such as contact time and carbon dose, for the recovery of gold and iodine from the waste water. The loading capacity of the activated carbon for adsorption of gold and iodine was found to be 33.5mg Au/g carbon and 835mg I2/g carbon, respectively. Gold was found to exist on the activated charcoal surface in two forms: ionic gold and elemental gold. Aqua regia was used to convert metallic gold to its ionic form, and the iodine and the small amount of ionic gold were removed from the activated carbon by elution with aqua regia. Gold was recovered from the eluate by reduction with hydrazine. Iodine from the diluted aqua regia was then precipitated by adding sodium hydrosulfite (Na2S2O4). A complete process flow sheet was developed to recover both gold and iodine from the waste water of the semiconductor industry, which conserves the resources while meeting environmental pollution requirements. [doi:10.2320/matertrans.M2012009]

Nondestructive Elastic-Wave Tests of Foundation Slab in Office Building

Abstract: The paper deals with the modern nondestructive elastic-wave testing of concrete in foundation slab in a very important office building put under the ground water level. After the construction water has appeared in lower level of the building. The reason for the tests was to find the place where water gets for building, and also check the technical condition of the foundation slab to take a decision about the range of repairs to be done to the foundation slab or about their strengthening. The primary test methods were: ultrasonic Tomography, Impulse Response and Impact-Echo technique. The auxiliary methods were: the electromagnetic method and the ultrasonic method. About 100 m2 of foundation slab were tested at a time. On the basis of an analysis of the results, in particular the tomography images and the distribution of the amplitude-frequency spectra of elastic waves the damage was found. The damage had the form of cracks running along the foundation slab and delamination of the reinforcement concrete. The depths of cracks were measured, the places of delamination were found, the thickness of slab did not conform to the design and zones of concrete containing honeycombing were identified. The results of the nondestructive tests and the analyses were corroborated by exposures.

Microstructural Evolution during ARB Process of Al–0.2 mass% Sc Alloy Containing Al3Sc Precipitates in Starting Structures

Abstract: Effect of pre-existing precipitates on microstructure evolution during severe plastic deformation was studied. An Al–0.2 mass%Sc alloy was aged at 300 and 400°C for having different sizes of Al3Sc precipitates. The mean precipitate size of Al3Sc was 3.62 and 50 nm for 300 and 400°C aging, respectively. In the as-aged specimens, Al3Sc had coherency with the Al matrix. The three kinds of specimens that were solution-treated (ST), aged at 300°C or aged at 400°C, were then heavily deformed by the accumulative roll bonding (ARB) process up to 10 cycles (corresponding to an equivalent strain of 8.0) at room temperature. After 10 cycles of the ARB process, the specimens showed a lamellar boundary structure having the mean lamellar interval of 0.37, 0.24 and 0.27 µm in the ST, 300°C Aged and 400°C Aged specimens, respectively. Additionally, the fraction of high angle grain boundaries (HAGBs) and the average misorientation between boundaries in the Aged-specimens were both higher than those in the ST specimen ARB processed to the same strain. It indicated that grain refinement during the ARB process was accelerated by the pre-existing precipitates. The reasons for the acceleration in microstructural evolution are considered to be the introduction of shear bands, the enhancement of dislocation multiplication rate and the inhibition of grain boundary migration by the precipitates in the pre-aged specimens.

Grain Size Dependence of Creep in Nanocrystalline Copper by Molecular Dynamics

Abstract: The grain size dependence of creep is critical to understand the plastic deformation mechanism of nanoscale metals. Here we used molecular dynamics to study the stress-induced grain size exponent transition in creep of nanocrystalline copper. The grain size exponent was found to initially increase with increasing stress, then decrease after some critical stress. The derived grain size exponents are in agreement with experimental results for diffusional and grain boundary sliding creep at low stress. While, the founded decreasing grain size exponent with increasing stress for dislocation nucleation creep in nanocrystal is in contrast with conventional materials. We propose a constitutive equation for dislocation nucleation governed creep in nanocrystal to explain its grain size dependence transition with stress.

High-pressure torsion for pure chromium and niobium

Abstract: Two kinds of body centered cubic (bcc) structure refractory metals, pure Cr and Nb, were subjected to severe plastic deformation through high-pressure torsion (HPT) under applied pressures of 2 and 6 GPa for 2, 3, 4 and 5 revolutions at room temperature. Vickers microhardness is plotted as a function of the distance from the disk center and equivalent strain. It is shown that all hardness values fall on a single curve when they are plotted against equivalent strain for both metals. Vickers microhardness increases with increasing equivalent strain at an early stage of straining and then reaches steady state with the grain size of 200–250 nm in Cr and 240–270 nm in Nb irrespective of the applied pressures. In the steady state, there is no changing in hardness even in applying further straining. Tensile and bending tests show that brittle fracture occurs in Cr but in Nb, the strength significantly increases with some ductility after HPT processing.

Effects of Electron Beam Irradiation on Adhesive Force of Laminated Sheet of High Strength Polytetrafluoroethylene (PTFE) and Bio-Adaptable Polydimethylsiloxane (PDMS)

Abstract: The effects of homogeneous low voltage electron beam irradiation (HLEBI) on the adhesive force of peeling ( o Fp) and peeling resistance energy ( o Ep) at each peeling probability (Pp) of laminated sheets of bio-adaptable polydimethylsiloxane (PDMS) with transparency and high strength polytetrafluoroethylene (PTFE) with sterilization were investigated without glue. Although both o Fp and o Ep of peeling at low Pp of 0.06 were 0.2N·m ¹1 and 4.0 © 10 ¹2 J·m ¹1 before treatment, HLEBI enhanced the o Fp and o Ep up to the largest values of 11N·m ¹1 and 2.2J·m ¹1 of the laminated sheets irradiated at 0.13MGy, respectively. They were more than 55 times larger that those before treatment. On the other hand, additional HLEBI reduced the o Fp and o Ep of laminated sheets irradiated at more than 0.22 to 0.86MGy, although they were apparently larger than those before treatment. In order to investigate the influence of EB irradiation on o Fp and o Ep, electron spin resonance (ESR) signals related to dangling bonds were observed. When HLEBI cut the chemical bonds and generated dangling bonds with nonbonding electrons in PTFE and PDMS, the electrons induced the chemical bonding and intermolecular attractive force. HLEBI induced strong adhesive force of laminated sheets was explained by the discussion. Therefore, it was concluded that HLEBI was a useful tool for quick lamination of bio-adaptable PDMS and high strength PTFE. [doi:10.2320/matertrans.M2012124]

Effect of Minor Sn Additions on the Formation and Properties of TiCuZrPd Bulk Glassy Alloy

Abstract: The minor addition is fundamental to controlling the formation, manufacture and properties of metallic materials by controlling nucleation during solidification. In the present work, we investigated the effect of minor addition of Sn on glass-forming ability, thermal stability and mechanical property of TiZrCuPd bulk glassy alloy system. The substitution of Cu by 2% Sn improves the glass-forming ability significantly. The Ti40Zr10Cu34Pd14Sn2 bulk glassy alloy rod with a diameter of 12 mm was fabricated by copper mold casting. The Ti40Zr10Cu34Pd14Sn2 bulk glassy alloy exhibits higher energy for crystallization activation (334.3 kJ/mol). The addition of 2–4% Sn can enlarge the supercooled liquid region, indicating good thermal stability. TiZrCuPdSn bulk glassy alloys exhibit high compressive strength about 2000–2050 MPa.

Recovery of Rhenium and Molybdenum from Molybdenite Roasting Dust Leaching Solution by Ion Exchange Resins

Abstract: Ion exchange separation of rhenium using Purolite A-170 and Purolite A-172 was carried out from the dust leach solution of molybdenite concentrate. Different parameters such as effect of contact time, equilibrium pH, and solid liquid ratio were investigated. The optimum absorption condition for Purolite A-172 resin was determined, and the absorption efficiency of Re and Mo were obtained to be about 90 and 0%, respectively. From results, it was evident that, the performance of Purolite A-172 resin was more effective than Purolite A-170 resin, towards the selective recovery of Re from the molybdenite dust leach solution. [doi:10.2320/matertrans.M2012208]

New Developments of Hydroforming in China

Abstract: This paper reviews the recent developments of hydroforming technology in China. Limited corner radius, ring hoop tension test and tube bulging test were introduced on fundamentals of hydroforming. New hydroforming and hydro-bending process of ultra-thin tubes were investigated. Ultra-thin Y-shaped parts and complex section components were manufactured and applied in aerospace and aviation industry. Applications of tube hydroforming in automotive industry in China are also presented, including the hydroforming machines and production lines, typical automotive parts and potential market. New sheet hydroforming process with controllable radial pressure was proposed to increase the formability of sheets metals. Warm tube and sheet hydroforming were analyzed and discussed. [doi:10.2320/matertrans.MF201122]

Deoxidation of Ti Powder and Preparation of Ti Ingot with Low Oxygen Concentration

Abstract: In this experiment, we carried out a two-step deoxidation process to obtain Ti ingots with low oxygen concentration from commercial Ti powder. The first step was to primarily reduce oxygen in Ti powder using Ca and the second was to melt the deoxidized Ti powder in Ar atmosphere with added hydrogen using a vacuum arc melting system. We used two types of raw Ti powder, one with a high oxygen concentration of 5,600ppm and average powder size of 35µm, and the other with 2,200ppm and 115µm. The high oxygen of 5,600ppm in the Ti powder was reduced to approximately 1,460ppm by the two-step process of melting after deoxidizing the Ti powder with Ca at 973K. On the other hand, in the case of the Ti powder with low oxygen of 2,200ppm, the Ti ingot with low oxygen of 600ppm could be prepared by the twostep process of melting after deoxidizing at 1,103K. The Vickers hardness and c/a value of Ti ingots decreased as the oxygen concentration decreased. [doi:10.2320/matertrans.M2012004]

A Phase Field Model of Sintering with Direction-Dependent Diffusion

Abstract: A phase field model of sintering with direction-dependent interface diffusion is presented, in which the surface and grain boundary diffusions occur along the tangent of surfaces and grain boundaries, respectively. Compared with previous phase field models of sintering, the proposed model is more consistent with the sharp interface model regarding the directions of interface diffusions. Numerical simulations show that the direction of interface diffusion is critical to model sintering kinetics and morphological evolution, and the performance of phase field model is improved significantly with appropriate interface diffusion directions. The proposed model is able to capture relevant features of sintering such as neck growth and its dependence on particle size, interface energies and mobilities. These features agree well with theoretical predictions. [doi:10.2320/matertrans.M2011317]

Effect of Phase Transition on the Thermoelectric Properties of Ag2Te

Abstract: Ag2Te is well-known as a silver ion conductor. In this compound, a phase transition occurs at around 420K and silver ions jump to interstitial sites repeatedly at the point of starting the phase transition. We consider that the active movement of silver ions would have influence on the scatterings of both charge carriers and heat carrying phonons in Ag2Te. In order to evaluate the effect of the silver ion conduction on the thermoelectric properties of Ag2Te, the Seebeck coefficient, electrical resistivity, thermal conductivity and Hall coefficient of polycrystalline bulk samples of Ag2Te were examined in the temperature range from room temperature to 650K. The electrical resistivity and the Seebeck coefficient dramatically changed at around 420K due to the change of the carrier concentration before and after the phase transition. However, the carrier mobility and the lattice thermal conductivity showed no remarkable change at around the phase transition temperature. These results imply that the thermoelectric transport properties of Ag2Te were affected by the change of the crystal structure rather than the presence or absence of the movement of silver ions. [doi:10.2320/matertrans.E-M2012815]

Thermoelectric Thin Film Device of Cross-Plane Configuration Processed by Electrodeposition and Flip-Chip Bonding

Abstract: Using electrodeposition and flip-chip bonding, a cross-plane thin film device consisting of 242 pairs of the electrodeposited n-type Bi­Te and p-type Sb­Te thin film legs was successfully fabricated. The electrodeposited Bi­Te films with the thickness of 2.5­20.2 μm exhibited the Seebeck coefficients of 152 to 159μV/K and the power factors of 5.5­5.1 © 1014W/m·K2. While the Seebeck coefficient of the Sb­Te film varied from 276 to 485μV/K, the power factor was changed from 81 © 1014 to 50 © 1014W/m·K2 with increasing the film thickness from 2.2 to 20.5 μm. The internal resistance of the thin film device consisting of 242 pairs of the electrodeposited n­p thin film legs was measured as 3.7K3. The open-circuit voltage and the maximum output power of the thin film device were 0.294V and 5.9μW, respectively, with the temperature difference of 22.3K across the hot and cold ends of the thin film device. [doi:10.2320/matertrans.M2012265]

Deformation Behavior in Tubular Channel Angular Pressing (TCAP) Using Triangular and Semicircular Channels

Abstract: In this paper, two different (triangular and semicircular) channel types were investigated in tubular channel angular pressing (TCAP) suitable for deforming cylindrical tubes to large strains without changing the tube dimensions. To examine the effects of the channel geometry on the strain distribution and deformation behavior during the TCAP process, finite element method (FEM) simulations and an analytical model were employed. The FEM results demonstrate that equivalent plastic strains of 2.15­2.9 and 2.35­2.6 were developed after applying one pass TCAP in the triangular and semicircular channels, respectively. The mean values of the equivalent plastic strains were almost identical for both cases, but the strain through the thickness with semicircular channel was more homogeneous than that in the triangular channel. Tube thinning in the early stages of the process was observed as a result of tensile circumferential strains, but this can be compensated by the back pressure effect resulting from the next shear zones and also compressive circumferential strain resulting from the decreasing tube diameter. While the strain values for both channel types were similar, the required load for the semicircular channel was lower than that of the triangular channel. [doi:10.2320/matertrans.MD201107]

Electrostatically Controlled Enrichment of Lepidolite via Flotation

Abstract: We first report flotation of lepidolite by using stearyl trimethyl ammonium chloride (STAC), one of the quaternary ammonium salts, without adding any depressant to get an insight on further advanced separation. X-ray diffraction patterns showed that the ores obtained from Boam mine, Uljin, South Korea were mainly composed of lepidolite, muscovite, quartz, calcite and albite. Zeta potential results showed that the isoelectric points (IEP) were about 2.5, 2.3 and 9.7 for quartz, albite and calcite, respectively, and that for lepidolite was determined to be less than 2. Based on the results for the electrokinetic properties of the minerals included in lepidolite ores, 3-stage flotation for the lepidolite was carried out in Denver Sub-A cells. Rougher flotation was first conducted at ca. pH 9 to separate calcite minerals, followed by first cleaner flotation over a pH range of 6.3­8.0 to find the maximum separation point of calcite gangue and second cleaner flotation over a pH range of 2­4 to maximize the removal of quartz/albite gangues. The results for the first cleaner showed that Li2O grade increased with decreasing pH while Li2O recovery tended to slightly increased with increasing pH. The trend for Li2O grade and recovery after second cleaner flotation was similar with that for the products after first cleaner flotation. Overall, Li2O grade increased with decreasing pH while the recovery slightly increased with increasing pH. Maximum Li2O grade (i.e., 2.77), which was about 3.8 times greater than the grade in the feed and around 36% of maximum threshold value (i.e., theoretical value, ³7.7), was achieved at ca. pH 2.0. The increase in Li2O grade with decreasing pH could be attributed to the enhanced selectivity of lepidolite with decreasing pH due to the more favorable interaction of STAC with lepidolite (IEP of lepidolite < 2) relative to albite or silica (IEP of albite and silica = 2.3 and 2.5, respectively). [doi:10.2320/matertrans.M2012235]

Investigation of Flotation Parameters for Copper Recovery from Enargite and Chalcopyrite Mixed Ore

Abstract: A flotation pre-treatment study for the separation of enargite (Cu3AsS4) from chalcopyrite (CuFeS2) ores of different origins was investigated in this work. The copper ore bearing enargite mineral contained 5.87mass% As and 16.50mass% Cu while the chalcopyrite bearing ore contained 0.32mass% As and 21.63mass% Cu. The two ore samples were mixed at 7 : 3 (enargite : chalcopyrite) by weight ratio to prepare a mixed ore sample with As content at 3.16 and 18.25mass% Cu for the flotation study. Effect of particle size, slurry pH, flotation time, collector type, collector addition or dosage and depressants were investigated to evaluate efficiency of enargite separation from chalcopyrite and recovery of both minerals as separate concentrates. For enargite single ore flotation, the 38­75µm size fraction showed that over 98% of enargite was selectively recovered within 5min at slurry pH of 4 and As content in the final tailings was reduced to 0.22mass%. In mix ore (enargite + chalcopyrite) flotation, 97% of enargite was first removed at pH 4 followed by chalcopyrite flotation at pH 8, and over 95% recovery was achieved in 15min flotation time. The As content in the final tailings was reduced to 0.1mass%. [doi:10.2320/matertrans.M2011354]

Effect of Deformation-Induced ω Phase on the Mechanical Properties of Metastable β-Type Ti–V Alloys

Abstract: A series of metastable ¢-type binary Ti­(18­22)V alloys were prepared to investigate the effect of deformation-induced products (deformation-induced ½ phase transformation and mechanical twinning) on the mechanical properties of metastable ¢-type titanium alloys. The microstructures, Young’s moduli, and tensile properties of the alloys were systemically examined. Ti­(18­20)V alloys subjected to solution treatment comprise a ¢ phase and a small amount of athermal ½ phase, while Ti­22V alloy subjected to solution treatment consists of a single ¢ phase. Ti­(18­20)V alloys subjected to solution treatment exhibit relatively low Young’s moduli and low tensile strengths as compared to cold-rolled specimens. Both deformation-induced ½ phase transformation and {332}¢h113i¢ mechanical twinning occur in all of the alloys during cold rolling. The occurrences of {332}¢h113i¢ mechanical twinning and deformationinduced ½ phase transformation are dependent on the ¢ stability of the alloys. After cold rolling, all of the alloys comprise a ¢ phase and an ½ phase. The Young’s moduli of Ti­(18­22)Valloys increase because of the formation of a deformation-induced ½ phase during cold rolling. The significant increase in tensile strength is attributed to the combined effect of the deformation-induced ½ phase transformation and workhardening during cold rolling. [doi:10.2320/matertrans.M2012116]