Showing papers in "Materials Transactions in 2015"

Martensitic Transformation and Superelastic Properties of Ti-Nb Base Alloys

Abstract: Ti-Nb base alloys have been proposed as prospective candidates for Ni-free biomedical superelastic alloys due to their excellent mechanical properties with good biocompatibility, and many kinds of Ti-Nb base alloys exhibiting shape memory effect or superelasticity have been developed up to now. However, typical Ti-Nb base superelastic alloys show a small recovery strain which is less than one third of the recovery strain of practical Ti-Ni superelastic alloys. Over the last decade there have been extensive efforts to improve the properties of Ti-Nb base superelastic alloys through microstructure control and alloying. Low temperature annealing and aging are very effective to increase the critical stress for slip due to fine subgrain structure and precipitation hardening. The addition of interstitial alloying elements such as O and N raises the critical stress for slip and improves superelastic properties. In this paper, the roles of alloying elements on the martensitic transformation temperature, crystal structure, microstructure and deformation behavior in the Ti-Nb base alloys are reviewed and the alloy design strategy for biomedical superelastic alloys is proposed. [doi:10.2320/matertrans.M2014454]

Criticality Assessment of Metals for Japan's Resource Strategy

Abstract: Criticality assessment of metals has been developed to analyze a country’s supply risk and vulnerability to supply restriction. This study presents Japan’s criticality of 22 metals during 2012. Whereas a past assessment focused only on minor metals, evaluation targets here included both common and minor metals. In addition, a new analytic method included mineral interest sufficiency as a criticality component. The evaluation framework developed in this study included 13 criticality components within five risk categories: supply risk, price risk, demand risk, recycling restriction, and potential risk. Weighting factors were used to aggregate components into a single score. This framework reflects a recent government announcement about Japan’s resource strategy. High criticality was found for neodymium, dysprosium, and indium due to a recent increase in demand. Niobium also had high criticality due to production concentration in Brazil. There were few differences in the aggregated criticality scores between the other minor metals and common metals. For minor metals, aggregated criticality was mainly increased by production concentration and recycling difficulty. For common metals, aggregated criticality was increased by short depletion time and growth in global mine production. Compared with a previous study, in 2012 the criticality of tungsten and tantalum were lower due to reduced domestic demand. The analytic methods and results presented in this study will be useful in developing Japan’s resource strategy. [doi:10.2320/matertrans.M2014380]

Coral Sand Solidification Test Based on Microbially Induced Carbonate Precipitation Using Ureolytic Bacteria

Abstract: Artificial beachrock, formed by coral sand solidification through microbially induced carbonate precipitation (MICP), could provide coastal protection instead of concrete structures, and would be eco-friendly as well as help minimize costs. The present study was conducted to solidify coral sand through the MICP method by using an ureolytic bacterium (Parahodobacter sp.) isolated from peripheral beachrock. The goal was to obtain a sample with an unconfined compressive strength (UCS) of 20MPa or more. We also aimed to examine the growth characteristics of this bacterium in the culture medium ZoBell2216E, which is commonly used for marine bacteria. In order to determine the suitability of the MICP test, growth properties of the microbial strain were observed under various culture conditions. A sand solidification test with MICP was carried out in a syringe as well as a PET cylinder. The strength of the resulting specimens was measured with the needle penetration test. The specimen solidified up to 20MPa of the estimated UCS after 21 days of curing. For optimum growth of the bacterium, 1.0 g of the culture was added to100mL culture media and incubated with shaking at 160 rpm. The preferred final concentration in solidification promoting solution of both urea and CaCl2 was 0.5M, with bacterial cell densities of 109 CFU/mL. In order to efficiently induce solidification, the optimum pH was 7.0 or higher, and Ca2+ concentration was maintained at 1.0 g/L. The results were enhanced by re-injecting the culture solution when the pH and Ca2+ concentrations in the specimen were not in the ideal ranges indicated above. [doi:10.2320/matertrans.M-M2015820]

Relation between Vickers Hardness and Bragg-Edge Broadening in Quenched Steel Rods Observed by Pulsed Neutron Transmission Imaging

Abstract: The width of crystal lattice plane spacing (d-spacing) distribution related to microscopic-strain and crystallite size in a martensite phase in a 2 cm thick quenched-ferritic steel sample was quantitatively mapped in real space by a Bragg-edge broadening analysis of spectral data from a pulsed neutron transmission experiment. This analysis was performed under the condition that the instrumental resolution parameters, determined from the data of ferrite in the same sample without microscopic-strain and crystallite size effects, were unchanged over the sample area, and assuming that the d-spacing was distributed according to a Gaussian function in the martensite area. As a result, the full width at half maximum (FWHM) of the Gaussian d-spacing distribution in the martensite was extracted at each position in a sample. Consequently, it was found that the real-space distribution of the FWHM of the d-spacing distribution is closely correlated with a real-space distribution of the Vickers hardness that corresponds to the quantity of martensite. Furthermore, it was indicated that the Vickers hardness was proportional to the FWHM of the d-spacing distribution. The results suggest that it will be possible to measure the Vickers hardness in the martensite non-destructively by using the Bragg-edge neutron transmission method. [doi:10.2320/matertrans.M2015049]

Application of High Pressure Gas Jet Mill Process to Fabricate High Performance Harmonic Structure Designed Pure Titanium

Abstract: Through many years, conventional material developments have emphasized on microstructural refinement and homogeneity. However, “Nanoand Homogeneous” microstructures do not, usually, satisfy the need to be both strong and ductile, due to the plastic instability in the early stage of the deformation. As opposed to such a “nanoand homo-”microstructure design, we have proposed “Harmonic Structure” design. The harmonic structure has a heterogeneous microstructure consisting of bimodal grain size together with a controlled and specific topological distribution of fine and coarse grains. In other words, the harmonic structure is heterogeneous on microbut homogeneous on macro-scales. In the present work, the harmonic structure design has been applied to pure-Ti via a novel powder metallurgy route consisting of controlled severe plastic deformation of the fine-sized powder particles via jet milling and subsequent consolidation by SPS. At a macro-scale, the harmonic structure materials exhibited significantly better combination of strength and ductility, under quasi-static tensile loadings, as compared to their homogeneous microstructure counterparts. [doi:10.2320/matertrans.M2014280]

In-Situ Observation on the Formation Behavior of the Deformation Kink Bands in Zn Single Crystal and LPSO Phase

Abstract: 1Department of Adaptive Machine Systems, Graduate School of Engineering, Osaka University, Suita 565-0871, Japan 2Department of Mechanical Engineering and Science, Graduate School of Engineering, Kyoto University, Kyoto 615-8246, Japan 3Magnesium Research Center/Department of Materials Science, Kumamoto University, Kumamoto 860-8555, Japan 4Division of Materials and Manufacturing Science, Graduate School of Engineering, Osaka University, Suita 565-0871, Japan

Effects of Reducing Solvent on Copper, Nickel, and Aluminum Joining Using Silver Nanoparticles Derived from a Silver Oxide Paste

Abstract: The effects of reducing solvent on copper, nickel, and aluminum joining using silver nanoparticles derived from a silver oxide paste was investigated by thermal analysis, transmission electron microscopy (TEM) observation, and tensile shear testing. A complete weight loss of diethylene glycol (DEG) in a paste occurred during the redox reaction, whereas a polyethylene glycol 400 (PEG) paste retained the PEG solvent until about 300°C due to its longer carbon chains. Residual PEG in the paste reduced the natural oxide film on copper and nickel substrates during bonding, facilitating a direct sinter of silver nanoparticles to these substrates. On the other hand, silver nanoparticles were sintered to the natural oxide film on an aluminum substrate by the DEG paste. The suitability of the reducing solvent for oxide film reduction of the metal substrate during bonding was explained by an Ellingham diagram. [doi:10.2320/matertrans.MI201411]

Influence of Natural Aging Time on Two-Step Aging Behavior of Al-Mg-Si(-Cu) Alloys

Abstract: Nanoclusters formed during natural aging cause the negative effect of the two-step aging in the age-hardenable Al-Mg-Si alloys. The relationship between the clustering behavior during natural aging and the two-step aging behavior was studied using the hardness, differential scanning calorimetry (DSC), electrical resistivity measurements, transmission electron microscopy (TEM) observation in the Cu-free and Cuadded Al-Mg-Si alloys. Three stages during the two-step aging are clearly revealed based on the hardness results. The hardness in the two-step aging with the natural aging time is decreased, increased and then decreased at the initial, middle and final stages, respectively. Si-rich clusters initially formed during natural aging do not transform into the ¢AA phase and are thermally stable during the two-step aging at 170°C. On the other hand, Mg-Si co-clusters formed at the middle stage during natural aging transform into the ¢AA phase and are thermally unstable during the twostep aging at 170°C. Much higher hardness is obtained in the Cu-added alloy than that of the Cu-free alloy during two-step aging when natural aging is performed for 3.6 ks belonging to the initial stage. The higher hardness is also found to be obtained during over-aging regardless of the natural aging time in the Cu-added alloy than that of the Cu-free alloy. The relationship between the clustering behavior during natural aging and the two-step aging behavior is discussed based on the observed age-hardening phenomena. [doi:10.2320/matertrans.L-M2015824]

Judd–Ofelt Analysis of Eu 3+ Emission in TiO 2 Anatase Nanoparticles

Abstract: 1College of Sciences, Chongqing University of Posts and Telecommunications, Chongqing 400065, P. R. China 2Institute of Physics, University of Tartu, Tartu 50411, Estonia 3Institute of Physics, Jan Dlugosz University, PL-42200 Czestochowa, Poland 4Institute of Physics, Polish Academy of Sciences, al. Lotników 32/46, 02-668 Warsaw, Poland 5University of Belgrade, Vinča Institute of Nuclear Sciences, P.O. Box 522, Belgrade 11001, Serbia

Production of Nanocrystalline (Fe, Co)-Si-B-P-Cu Alloy with Excellent Soft Magnetic Properties for Commercial Applications

Abstract: With the aim of applying to a magnetic core material, the effect of ribbon thickness on the magnetic properties of a (Fe, Co)-Si-B-P-Cu alloy ribbon was investigated. It is found that the Si addition in (Fe, Co)-Si-B-P-Cu nanocrystalline alloy increased the saturation magnetic flux density (Bs), but degraded the coercivity (Hc), suggesting that the Si addition should be suppressed to a little amount. It is also found that the replacement of Fe with Co is quite effective for obtaining better magnetic properties of Fe-Si-B-P-Cu alloy. Even for the thicker ribbons exceeding 30μm in thickness, the nanocrystalline Fe81.2Co4Si0.5B9.5P4Cu0.8 alloy exhibited low Hc of 7A/m and high Bs of 1.84T. Such excellent magnetic properties were successfully reproduced in 50mm wide ribbons. This regards that the nanocrystallized Co-containing alloy has high applicability to high-efficiency magnetic core material. [doi:10.2320/matertrans.MBW201402]

Titanium Powders via Gas-Solid Direct Reaction Process and Mechanical Properties of Their Extruded Materials

Abstract: In the present study, titanium (Ti) powders containing some nitrogen (N) atoms were prepared by a gas (N2)-solid (Ti starting powder) direct reaction process, and consolidated as an extruded rod with high strength and ductility at ambient temperature. Nitrogen content of the Ti powders via the gas-solid direct reaction process dramatically increased as the treatment time increased while no change in the oxygen content. Ti2N layers were formed at Ti powder surfaces via the above gas-solid reaction, however, no formation of Ti2N compounds was found in the extruded Ti materials. That is, the solid solution of N atoms in ¡-Ti was complete, and expected to enhance the mechanical strength of Ti materials. 0.2% yield strength (YS) and ultimate tensile strength (UTS) of wrought Ti-N materials were proportional to the additive nitrogen content, and the decrease of elongation was very limited. For example, the extruded Ti powder material with nitrogen content of 0.74mass% revealed 974MPa in 0.2%YS, 1120MPa in UTS and 21.7% in elongation. These tensile properties were superior to those of the conventional Ti6Al-4V alloy with the standard specification of ASTM B348-00-GR5 (0.2%YS: 918MPa, UTS: 1047MPa, elongation: 16.6%). [doi:10.2320/matertrans.L-M2015816]

Evaluation of the gas nitriding of fine grained AISI 4135 steel treated with fine particle peening and its effect on the tribological properties

Abstract: The effect of fine particle peening (FPP) on the gas nitriding of AISI 4135 chromium-molybdenum steel was investigated. Surface microstructures of nitrided specimens pre-treated with FPP were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD) and glow discharge optical emission spectroscopy (GDOES). The nitrided layer formed on the fine grained specimen treated with FPP was thicker than that on the nitrided-only specimen, because the fine grains created by FPP accelerate the formation of iron nitride during the nitriding process. Furthermore, FPP reduces the concentration of chromium near the nitrided surface, which suppresses the formation of cracks and pores in the compound layer. Therefore, a nitrided specimen pre-treated with FPP has higher hardness than a nitrided-only specimen. Reciprocating ball-on-disk friction tests were performed at room temperature to investigate the tribological properties of the nitrided AISI 4135 steel. The nitrided specimen pre-treated with FPP had a lower friction coefficient and exhibited less wear loss due to the presence of a thick compound layer without cracks and pores. Therefore, a hybrid surface modification that employs FPP as a processing step prior to gas nitriding is effective for improving the tribological properties of AISI 4135 steel. [doi:10.2320/matertrans.M2014448]

Environment-Sensitive Thermal Coarsening of Nanoporous Gold

Abstract: In order to investigate environmental effects on the ligament/pore coarsening of nanoporous gold (NPG), we studied the thermal coarsening of NPG both in air and vacuum by ex situ observation, and found that it has high structural stability against heat treatment in vacuum. To clarify the nature of this phenomenon, we investigated the thermal coarsening of NPG by in situ environmental transmission electron microscopy. At an elevated temperature (400°C), the coarsening of ligaments/pores was triggered by introducing either pure N2 or O2 gas into the transmission electron microscopy (TEM) chamber (but not by Ar gas). We thus conclude with a discussion on the mechanism for thermal coarsening of NPG. [doi:10.2320/matertrans.MF201403]

Intermetallic Compound Nanoparticles Dispersed on the Surface of Oxide Support as Active and Selective Catalysts

Abstract: Preparation of nanoparticles of intermetallic compounds and their application to various catalytic reactions are summarized. On the surface of silica support, single-phase nanoparticles of intermetallics with various combinations of elements were obtained by co-impregnation and/or successive impregnation procedures. On alumina support, its strong interaction with metal species requires another preparation procedure, liquidphase reduction, to obtain intermetallic nanoparticles with high phase purity. Most of the particles formed on both supports had diameters of 3³20nm. Thus prepared intermetallic nanoparticles were used as catalysts for various reactions such as H2-D2 equilibration, selective hydrogenation, dehydrogenation, oxidation and isomerization. The catalytic activity and selectivity of nanoparticles differed from each other depending on the combination and composition of two elements. In some cases, the intermetallic catalysts gave much higher activity and/or selectivity than their component monometallic catalysts. The unique catalytic properties of intermetallic compounds were discussed in terms of the electronic and geometric factors compared with pure metals. [doi:10.2320/matertrans.MF201408]

Joining of Pure Copper Using Cu Nanoparticles Derived from CuO Paste

Abstract: A paste containing CuO particles and polyethylene glycol 1000 as a reducing solvent has been applied to joining pure Cu in electronic applications, and the bondability of the joints and bonding mechanism were investigated. Based on a combination of thermogravimetric and differential thermal analysis, pressurization in the bonding process was determined to be started at temperatures near the exothermal peak of 320°C. Pressurization started at a temperature of 320°C, with the 11 MPa shear strength of the Cu-to-Cu joint being 2.4 times greater than a joint pressed at room temperature. During the bonding process, CuO particles were not directly reduced to Cu, but were instead first reduced to Cu2O nanoparticles, which were subsequently reduced to Cu nanoparticles, and an oxide film of a Cu substrate was also reduced, thus ensuring a direct connection between a sintered Cu layer and substrate. The shear strength increases with holding time. Moreover, the shear strength of a joint created with CuO paste and a holding time of 15 min (20 MPa) is in fact higher than what can be achieved using a conventional lead-rich Pb-5Sn solder, thus making it well-suited for use in electronic applications.

High Sensitive Surface Plasmon Resonance (SPR) Sensor Based on Modified Calix(4)arene Self Assembled Monolayer for Cadmium Ions Detection

Abstract: In this work, a new chromogenic calix(4) arene was functionalized onto self assembled monolayer (SAM) of cysteamine for cadmium ions detection and tested by using SPR measurement. The functionalization of modified SPR sensor is based on the oxidation of calixarene-SAM alcohol group to quinone. Four interfering ions were used Cu2+, Co2+, Mg2+ and Ca2+. pH of sensor in which the sensitivity of sensor is higher was optimized for cadmium ions and detection of ions was made in basic solution. Detection limit reached for Cd2+ is lower than 10(-11) M with a dynamic response time of about 16 s when changing from 10(-6) M cadmium to 10(-5) M.

Low Temperature Nitriding of Commercially Pure Titanium with Harmonic Structure

Abstract: Commercially pure titanium with harmonic structure, which consists of a coarse-grained structure surrounded by a network structure of fine-grains, was produced by sintering mechanically milled powders to achieve high strength and high ductility. The effect of subsequent nitriding on the commercially pure titanium with harmonic structure was investigated. Nitriding was performed at relatively low temperatures of 773, 873 and 973K (500, 600 and 700°C). The surface microstructures of the nitrided specimens with harmonic structure were characterized using optical microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), electron backscatter diffraction (EBSD), and a noncontact scanning white light interferometry. The nitrided titanium specimen with harmonic structure had higher hardness than a nitrided-only titanium specimen because the fine-grained structure in the harmonic structure accelerated the formation of titanium nitrides during nitriding. Furthermore, fine grains created by mechanical milling were not coarsened during the nitriding process. These results indicate that low temperature nitriding is effective to increase the surface hardness of commercially pure titanium with harmonic structure while grain-coarsening is also suppressed. [doi:10.2320/matertrans.Y-M2015822]

Deformation behavior of long-period stacking ordered structured single crystals in Mg 85 Zn 6 Y 9 alloy

Abstract: Microtension tests were performed on single crystals with different crystallographic orientations, which were prepared using an 18R-type long-period stacking ordered (LPSO) structure in a directionally solidified Mg85Zn6Y9 alloy. Anisotropic plasticity was observed for the LPSO phase specimens. Cleavage cracking occurred on the prismatic planes in a crystal with its loading direction parallel to the basal plane. The cleavage stress for the prismatic plane was determined to be approximately 460MPa. A crystal that was oriented favorably for gliding on the basal plane exhibited a critical resolved shear stress of approximately 9.4MPa. When a crystal was loaded along [0001], a sudden load drop was observed at a stress of approximately 250MPa in the initial linear region of the stress­strain relation. Transmission electron microscopy results after the load drop showed that the deformation microstructure contained a twin-like boundary with a rotation axis along 1⁄211 20 . [doi:10.2320/matertrans.MH201415]

Precipitation Behaviors and Strengthening of Carbides in H13 Steel during Annealing

Abstract: 1State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, 30 Xueyuan Rd., Haidian District, Beijing 100083, China 2School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, 30 Xueyuan Rd., Haidian District, Beijing 100083, China 3Department of High Temperature Materials, Central Iron and Steel Research Institute, No. 76 Xueyuan Nanlu, Haidian District, Beijing 100094, China 4Department of Special Metal, Chongqing Materials Research Institute Co., Ltd., 400707, China

Deformation Analysis of the Long-Period Stacking-Ordered Phase by Using Molecular Dynamics Simulations: Kink Deformation under Compression and Kink Boundary Migration under Tensile Strain

Abstract: The long-period stacking-ordered (LPSO) phase discovered in magnesium alloys is deformed upon the generation of a large number of unique deformation zones, which have no distinct orientation relationships at the deformation boundaries. These deformation zones are considered kink bands, but the mechanisms underlying their generation are not well understood. It has been suggested that the kink bands are responsible for the deformation of the LPSO phase, while simultaneously strengthening the material. In this study, the kink deformation process of the LPSO phase under compressive deformation was investigated through molecular dynamics (MD) simulations. The MD simulations showed that numerous prismatic ©aa dislocations were nucleated first, which led to cross-slips towards various basal planes and caused kink deformation. This was followed by the nucleation and motion of a large number of basal dislocations, as well as kink deformations in tandem with the formation of kink bands, which occurred through another process. In addition, the individual dislocations were indistinguishable at kink boundaries. In other words, sharp boundaries were formed. Next, a simulation was performed that applied tensile strain to the model after the compressive deformation described above was implemented on it. This revealed that while kink boundaries with large misorientation angles intermittently migrated because of the tensile strain, the kink bands were not easily removed. [doi:10.2320/matertrans.MH201408]

Damage Evaluation in Lithium Cobalt Oxide/Carbon Electrodes of Secondary Battery by Acoustic Emission Monitoring

Abstract: Acoustic Emission (AE) technique was employed for evaluating charge/discharge damage in a lithium-ion battery. A coin-type battery of lithium cobalt oxide/carbon electrodes was used for acoustic monitoring during accelerated charge/discharge cycle test. A number of AE signals were successfully detected during charge/discharge. Microstructural observation of the electrodes after the cycle test revealed mechanical damage such as micro-cracking of the cathode and chemical damage such as solid electrolyte interphase (SEI) layer formed on the anode. The detected AE signals were classified into two distinct types (i.e., type 1 and type 2) based on the AE waveform parameters (i.e., duration and amplitude). The main frequency component of the type 1 signal with short duration and high amplitude was in the range of 121­160 kHz, whereas the frequency of type 2 signals with long duration and low amplitude was between 81 and 120 kHz. Active AE source of type 1 and type 2 signal was attributed to micro-cracking in cathode and gas bubble accompanied by SEI layer formation on anode, respectively. These results demonstrate the feasibility of the AE technique for the evaluation of charge/discharge degradation of secondary battery. [doi:10.2320/matertrans.M2014396]

Temperature Dependent Current-Voltage and Capacitance-Voltage Characteristics of an Au/n-Type Si Schottky Barrier Diode Modified Using a PEDOT:PSS Interlayer

Abstract: The temperature dependence of the current-voltage (I-V) and capacitance-voltage (C-V) characteristics of an Au/n-type Si Schottky barrier diode (SBD) with a PEDOT:PSS interlayer was investigated. The SBD parameters, such as Schottky barrier height ()B), ideality factor (n), saturation current (I0), doping concentration (ND), and series resistance (Rs), were obtained as a function of temperature. The Richardson constant (A**) obtained from the In(Io/T 2 ) versus 1000/T plot was much less than the theoretical value for n-Si. The mean Schottky barrier height ( � � bo) and standard deviation (·0) calculated using the apparent Schottky barrier height ()ap) versus 1/2kT plot were 1.26eVand 0.15eV, respectively. From a fit of the modified Richardson plot of ln(I0/T 2 ) ¹ (q·) 2 /2(kT) 2 versus 1000/T, the A** was extracted as 134A/cm 2 K 2 , which was close to the theoretical value of the n-Si. The interface state densities obtained from the Au/PEDOT:PSS/n-Si SBD decreased with increasing temperature. Furthermore, the conduction mechanism dominating the reverse-bias leakage current in Au/PEDOT:PSS/n-Si SBD was described and discussed. [doi:10.2320/matertrans.M2014263]

Alloying Effects on Hydrogen Solubility and Hydrogen Permeability for V-Based Alloy Membranes

Abstract: The alloying effects of chromium, molybdenum, tungsten, iron and cobalt on the hydrogen solubility of vanadium have been investigated systematically. The addition of iron or cobalt into vanadium decreases the hydrogen solubility more significantly than chromium, molybdenum and tungsten. Thus, the addition of iron or cobalt into vanadium improves the resistance to hydrogen embrittlement of the vanadium alloy itself effectively. It is also found that, in view of the new description of hydrogen permeation based on hydrogen chemical potential, these alloying elements enhance the hydrogen flux through the vanadium alloy. This is because the PCT factor, fPCT, increases by the addition of iron or cobalt. Thus, alloying these elements into vanadium improves not only the resistance to hydrogen embrittlement, but also the hydrogen permeation ability. [doi:10.2320/matertrans.MAW201511]

Crystal Plasticity Analysis of Development of Intragranular Misorientations due to Kinking in HCP Single Crystals Subjected to Uniaxial Compressive Loading

Abstract: The mechanism and the effective factors for the development of intragranular misorientations due to kinking is studied by a crystal plasticity finite element method. A single crystal with hexagonal close-packed (HCP) structure in which only basal slip system is activated is used as a model material. To activate basal slip system, the initial crystal orientations are set to be the ones whose basal planes are slightly deviated from the compressive direction. The result shows that basal slip and the development of intragranular misorientations are sometimes localized near the center of the specimen depending on the initial deviation angle, strain hardening rate, and strain rate sensitivity. The mechanism is discussed in terms of the nonuniform stress distribution and lattice rotation. The effect of slight changes in the boundary conditions shows significant effect on the positions of slip localization. In summary, the present numerical results suggest that there are a number of effective factors for the development of the intragranular misorientations due to kinking including initial crystal orientation, material parameters, and boundary conditions. [doi:10.2320/matertrans.MH201403]

Development of Manufacturing Technology for Direct Recycling Cemented Carbide (WC-Co) Tool Scraps

Abstract: The objective of this research was to develop a sustainable industry manufacturing method for direct recycling cemented carbide tool scraps combining a hydrothermal and electrolysis process (CHEP). The research methodology was performed by studying the current recycling carbide tools, scrap industry and associated recycling technologies. A tungsten carbides (WC) recycling technology was designed by using an electrochemical cell comprising of a titanium cathode, titanium anode and hydrochloric acid (HCl) electrolyte under controlled temperature. Finally, the speed of binder phase removal, key process variables, WC leached and recovered WC purity rates were examined and identified. The results of this research indicated that this recycling process was effective in recycling cemented carbide from industrial cutting tools scraps. This technology can be used to purify the recovered WC rate to near virgin material, resulting in a more environmentally friendly process and reducing natural tungsten material usage. [doi:10.2320/matertrans.M2014213]

Flotation Behavior of Arsenopyrite and Pyrite, and Their Selective Separation

Abstract: This study investigated the effect of pH and pulp potential (EH) on the floatability of arsenopyrite and pyrite, which are single minerals, in Hallimond tube, by using xanthate as a collector On this basis, the study further investigated the selectivity index of arsenopyrite and pyrite, using a mixed sample of arsenopyrite and pyrite To examine the flotation behavior of each mineral by pH change, flotation was carried out at pH 4 and pH 10 The test results showed arsenopyrite had higher floatability at pH 4, regardless of the potassium ethyl xanthate (PEX) concentration This is because xanthate ion was oxidized to be stable dixanthogen, which was well adsorbed onto arsenopyrite surface, due to the high EH of pulp Meanwhile, arsenopyrite had relatively lower floatability at pH 10 than at pH 4, which was because the dixanthogen remained unstable, and was not adsorbed onto the arsenopyrite surface, due to the relatively low EH of pulp Pyrite had low floatability at both pH 4 and pH 10 Just as for arsenopyrite, the result for pH 10 was caused by the low EH of pulp Yet, interestingly enough, different from the case of arsenopyrite, pyrite at pH 4 had low floatability, despite its high EH FTIR analysis was performed, to examine the reason for such contradictory behavior The analysis result showed that this was caused by poor adsorption with xanthate, due to sulfate ion (SO4) that was generated by the oxidation of pyrite surface in reaction with oxygen in pulp at pH 4 To further investigate the selectivity index (ie, the pyrite recovery/ arsenopyrite recovery ratio) of arsenopyrite and pyrite, additional flotation tests were carried out on mixed sample of the two minerals Different from the flotation behavior of single minerals, the results showed that the recovery of arsenopyrite was lower than that of pyrite, and the selectivity index of arsenopyrite and pyrite was the highest when the PEX concentration was the lowest Such a different trend in flotation behavior of the mixed sample from the flotation behavior of the single minerals was because the surface oxidation reaction of arsenopyrite, which was more affected by EH among the mixed arsenopyrite and pyrite, generated ferric arsenate, a hydrophilic compound, on the surface of arsenopyrite, resulting in poor adsorption with xanthate; in turn, this depressed the floatability of arsenopyrite [doi:102320/matertransM2014369]

Silicate Covering Layer on Pyrite Surface in the Presence of Silicon–Catechol Complex for Acid Mine Drainage Prevention

Abstract: In this paper, prevention of pyrite oxidation by carrier microencapsulation (CME) was investigated. A possible layer structure was suggested following analysis with electrochemical and surface analysis techniques. Electrochemical study of treated pyrite samples showed that treatment with silicon­catechol (Si-Cat) for 6 h at an initial pH of 9.5 gave the best barrier properties and suppression of the samples. Scanning electron microscopy with energy-dispersive X-ray, and Fourier transform infrared (FTIR) analyses confirmed the presence of a silicate layer on the surface of treated pyrite. X-ray photoelectron spectroscopy indicated that the coating layers on the treated pyrite samples consisted of a network of Fe-O-Si and Si-O-Si units bonded to the surface of pyrite. The Si-O-C asymmetric stretching mode was also observed in FTIR spectra. Detailed spectroscopic analyses confirmed the formation of a silicate polymer on a silica­quinone layer, which resulted in the effective suppression effect shown by Si-Cat-treated pyrite at increasing pH. [doi:10.2320/matertrans.M-M2015821]