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

MATERIALS TRANSACTIONS Vol. 44 (2003), No. 5

  • Direct Crystallization of the Nd2Fe14B Peritectic Phase by Containerless Solidification in a Drop Tube

    pp. 806-810

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    DOI:10.2320/matertrans.44.806

    Nd2Fe14B molten alloy droplets were containerlessly solidified using a 25 m drop tube. The relationship between the sample diameter and the microstructure was investigated. The diameter of the resultant spherical samples was in range of 150 to 2000 μm. When sample diameter was larger than 500 μm, the microstructure of the spherical sample consisted of the α-Fe phase embedded in matrix of the Nd2Fe14B phase within entire sections. In the spherical sample with diameter of 400 μm, the microstructures consisted of two regions, one was columnar grains of the Nd2Fe14B phase and the other was α-Fe phase embedded in matrix of the Nd2Fe14B phase. The columnar Nd2Fe14B region expanded as the sample diameter decreased from 400 to 350 μm. When sample diameter reduced to 250 μm, the microstructure of a spherical sample consisted of the pure dendritic Nd2Fe14B phase without any α-Fe phase.
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  • Micro-Segregation along the Monovariant Line in a Ternary Eutectic Alloy System

    pp. 811-818

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    DOI:10.2320/matertrans.44.811

    To investigate the solidification after a single-phase dendritic solidification of a ternary alloy or to develop the process for making in-situ composite of a ternary alloy, a micro-segregation model along the monovariant line has been introduced. The solidification mode accompanied with this micro-segregation model is assumed as cellular or dendritic eutectic solidification. This model assumes a partial diffusion in the solid; the diffusion of the first solute element in the first solid phase works completely or finitely but no other diffusions work in either solid. This is also a model of the solidification of an iron-carbon-metallic ternary alloy. Two kinds of formulations are made; the first is the general formulation between the solid compositions or the liquid compositions and the volume fractions of the two solids and the second is with a simplified phase diagram. Comparison of the results between Scheil-type solidification, complete diffusion of the first solute in the first phase and finite diffusion of the first solute in the first phase has been made for three cases of simplified phase diagrams. The affect of the solutal transition in the phase diagram has been demonstrated and the affect of diffusivities in the solid on the micro-segregation along the monovariant line has been illustrated.
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  • Phase-field Simulation of Transient Liquid Phase Bonding Process of Ni Using Ni-P Binary Filler Metal

    pp. 819-823

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    DOI:10.2320/matertrans.44.819

    The transient liquid phase (TLP) bonding process of Ni using a Ni–11 mass%P binary filler metal was simulated by using both a phase-field model (PFM) and a moving boundary model (MBM). The dissolution of the base metal and isothermal solidification behavior during the TLP bonding process were simulated, and the results calculated by using the PFM were compared with those obtained by using the MBM. The results obtained during the isothermal solidification process in the two models were the same. The change in the concentration at the solid-liquid interface during the dissolution of the base metal was examined, and deviation from the local equilibrium concentration occurred in samples with a high heating rate in the phase-field simulation. On the other hand, the local equilibrium was always maintained in the MBM, but the calculation time of the simulation using the MBM was several hundred-times faster than that using the PFM.
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  • Analysis of Growth Behavior of a Cellular and Dendritic Interface under a Constrained Growth Condition using a Phase-Field Model

    pp. 824-828

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    DOI:10.2320/matertrans.44.824

    A phase-field simulation was carried out to investigate the growth behavior of a cellular and dendritic interface of an Fe–C binary alloy in a constrained growth condition. The simulated results were in good agreement with the experimental results. The effect of the magnitude of anisotropy at solid/liquid interface energy was examined, and it was found that the magnitude of anisotropy affected the growth direction when the growth rate was low. Dimensionless growth direction, π′, was used to examine the obtained results, and it was found that π′ increases from zero and approaches unity with increase in growth velocity. A good correlation was obtained between calculated growth velocity and growth direction by using dimensionless growth velocity (VVc), and this correlation was in agreement with the experimental results.
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  • Analysis of Yield Rate in Single Crystal Casting Process Using an Engineering Simulation Model

    pp. 829-835

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    DOI:10.2320/matertrans.44.829

    A 2-D engineering model for grain selection has been developed taking the columnar dendrite growth theory into consideration. After evaluating this model via a unidirectional solidification experiment, the single-crystal casting process was simulated. Since the time required for calculation is rather short, a statistical analysis has been performed for the first time. The yield rate of well-oriented single crystal is increased by increasing the initial number of grains on the chill plate. However, the yield rate does not exceed approximately 90%. A detailed investigation of the formation mechanism of misorientation has revealed two possible processes (Type A and Type B) that may occur during single crystal casting process.
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  • Influence of Carbon Content on Solidifying Shell Growth of Carbon Steels at the Initial Stage of Solidification

    pp. 836-844

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    DOI:10.2320/matertrans.44.836

    A dipping test that a water cooled copper plate was continuously dipped at 14 mm/s was performed in order to investigate solidifying shell growth in initial solidification. Anomalous rough surfaces and uneven shell growth were exhibited for an ultra-low carbon steel (0.005 mass% C) and a hypo-peritectic carbon steel (0.116 mass% C), while for a low carbon steel (0.044 mass% C) and a hyper-peritectic carbon steel (0.304 mass% C), flat surfaces were formed. The carbon content dependence of the anomalous uneven shell growth can be explained by stress caused by solidification shrinkage and δ⁄γ transformation occurring from a fraction solid 0.7, where shell begins to have strength, to 1.0, complete solidification state. Besides the analysis shows that decrease of the cooling rate can reduce the stress in the shell generated during the initial solidification.
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  • Influence of Copper and Iron on Solidification Characteristics of 356 and 380-Type Aluminum Alloys

    pp. 845-852

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    DOI:10.2320/matertrans.44.845

    The influence of copper and iron on the solidification characteristics of two major aluminum foundry alloys was investigated. The thermal history during solidification of each sample was recorded and compared with the solidification path calculated from the multicomponent equilibrium and Gulliver-Scheil solidification models. SEM/EDX analysis and optical microscope were used to examine the microstructure of solidified samples. The amount of phases was also calculated from the latter model and compared with the observed microstructure. Binary interaction parameters were used in calculation for their practicality. Results show that the high content of copper and iron suppresses the liquiduses and final solidification temperatures. Moreover, the crystallization of Al2Cu and Al5FeSi is very sensitive to copper and iron content respectively; Al2Cu increases significantly when copper is added while Al5FeSi does greatly when iron content is higher.
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  • Containerless Solidification and Net Shaping by Splat Quenching of Undercooled Nd2Fe14B Melts

    pp. 853-860

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    DOI:10.2320/matertrans.44.853

    High-speed optical temperature measurement and digital imaging elucidated the solidification behavior of undercooled Nd2Fe14B melt through containerless processing by an electromagnetic levitation method. The Fe phase solidified primarily from the melt. Subsequently, the remaining melt was undercooled below the peritectic temperature and the Nd2Fe14B phase surrounded the primary Fe dendrites, yielding the recalescence. The clear interface of the thermal field propagated and covered the entire sample. Detailed microstructural observation showed that the Nd2Fe14B phase surrounding the different Fe dendrites mutually came into contact with the several points. This suggested that many sites for nucleation of the Nd2Fe14B phase are not necessary for the successive growth of the Nd2Fe14B phase that was maintained by the spread of the Nd2Fe14B phase to the different primary Fe dendrites. This resulted in the macroscopic interface of the thermal field during recalescence. Moreover, the undercooled melt was dropped from the levitation coil and quenched by a pair of copper chill plates with moulds, the shape of which is a hemisphere cap, in order to obtain a small bulk sample for industrial purpose. The spherical sample with the diameter of 5 mm was successively obtained without decreasing the cooling rate. This result suggests the possibility of the net shaping of a small magnet from the melt.
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  • Aluminide Coating on Niobium by Arc Surface Alloying

    pp. 861-865

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    DOI:10.2320/matertrans.44.861

    A new method for surface modification based on the arc surface alloying has been proposed and its feasibility has been investigated performing niobium aluminide coating on a niobium base metal. When tungsten arc was used to melt an aluminum plate placed on a niobium block, the niobium surface was also melted and a melt pool of an Al–Nb binary alloy was formed on the niobium block. The melt pool solidified into niobium aluminides on the surface of the niobium block, forming a thick NbAl3 layer on the top surface of the coating layer. When an Al–Si alloy plate was used instead of the aluminum plate, a niobium almino–silicide layer was formed on the niobium block.
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  • Microstructures and Hardness of Mo Heater Chip Brazed with Au-18 mass%Ni

    pp. 866-869

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    DOI:10.2320/matertrans.44.866

    Microstructures and hardness of Mo heater chips brazed with Au–18 mass%Ni were investigated. The reaction layer of Mo–Ni compounds forms at the brazed interface. Spherical MoNi compounds form initially, and they change columnar ones with increasing brazing time. The reaction layer grows abruptly when the brazing time is more than 5 minutes with the brazing temperature range from 930°C to 970°C. The Vickers hardness of MoNi is evaluated as 682 Hv. That is approximately three and four times those of Mo and the Au–18Ni filler, respectively.
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  • Cold Model Experiment on Dispersion of Melted Ingots in Hot Dip Plating Bath

    pp. 870-876

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    DOI:10.2320/matertrans.44.870

    The dispersion of melted ingots in a continuous hot dip plating bath was investigated using a transparent cold model vessel with a reduced scale of one-tenth. The used tracers were CaCO3 particles with a mean diameter of 1.0 μm and 5.0 mass%KCl aqueous solution. The dispersion of the CaCO3 particles in the bath was observed by eye inspection. The mixing time and the local concentration of the two kinds of tracers were measured with an electrical conductivity sensor and a laser beam sensor. The dispersion of the CaCO3 particles was mainly controlled by the main stream of liquid caused by the motion of the belt in the bath. The mixing time and the local concentration of the tracer were dependent on the measurement position. The mixing time was shortest when the tracer was introduced in the exit region, i.e., the belt out-going region. This fact suggests that the mixing time in the real bath was shortest by introducing ingots into the exit region.
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  • Cold Model Experiment on Melting Phenomena of Zn Ingot in Hot Dip Plating Bath

    pp. 877-884

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    DOI:10.2320/matertrans.44.877

    The melting process of a Zn ingot in the continuous hot dip plating bath was investigated using an ice prism simulated with Nu number and a transparent cold model vessel with a reduced scale of one-tenth. The ice prism was used as a model for the Zn ingot. The Nusselt number similitude was selected to determine the size of the ice prism. The melting process of the ice prism fixed in the entry region was observed with a high-speed video camera. The local heat transfer coefficient around the ice prism was calculated from the local melting rate of the prism. The mean flow velocity and the root-mean-square (r.m.s.) value of the turbulence component of water flow approaching the ice prism were measured with a hot-wire anemometer. The mean heat transfer coefficient calculated by averaging the local heat transfer coefficients over the entire surface of the ice prism was hardly dependent on the turbulence intensity under the Reynolds number range considered. The turbulence intensity was defined as the ratio of the r.m.s. value of the turbulence component to the mean flow velocity.
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  • Size Effect on Dynamic Behavior of Dross in Model Hot Dip Plating Bath

    pp. 885-892

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    DOI:10.2320/matertrans.44.885

    The motions of top and bottom dross with different diameters in hot dip plating baths were investigated using a transparent cold model vessel with a reduced scale of one-tenth. Polystyrene particles of the same density and diameter were used as models both for the top and bottom dross, and NaCl aqueous solutions with different densities were used as models for the plating melts. The typical streak lines of the top and bottom dross model particles were nearly the same as the main stream lines in the model bath regardless of the dross diameter. The top and bottom dross model particles were enriched in the region enclosed with the belt. Some of the model particles were trapped in the clearances between the sink roll and the belt. As the dross diameter became large, the number of top dross model particles floating on the bath surface increased and that of bottom dross model particles staying on the bottom wall increased.
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  • Processing of Semi-Solid Gray Cast Iron Using the Cooling Plate Technique

    pp. 893-900

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    DOI:10.2320/matertrans.44.893

    A semi-solid processing technique combining a cooling plate and various mold materials is developed to produce high quality gray cast iron components. Flow behavior of semi-solid slurry along an inclined cooling plate is studied to establish the effect of plate orientation on the integrity of cast products. The concept of multiple-stage cooling is discussed by considering cooling rates at different stages of processing along the cooling plate and in sand, graphite and metallic molds to show the significance of cooling rate in determining component microstructure. The morphology of microstructure in cast components is discussed and image analysis results presented. A refined microstructure of primary austenite and graphite, and their characteristics associated with the use of different mold materials are reported. Angle of inclination of plate is shown to influence the morphology and quantity of precipitated phases. Finally, the effects of cooling plate and mold material on Vickers hardness and mechanical strength of cast components are discussed.
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  • THE FORTY-EIGHTH GOLD MEDALIST OF THE JAPAN INSTITUTE OF METALS, 2003 Physical Metallurgy and Micromechanics

    pp. 901-906

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    DOI:10.2320/matertrans.44.901

    This article first reviews a part of my past work. The subjects referred to are work hardening of a dispersion strengthened alloy, diffusional stress relaxation around an inclusion, stress aging, double kink formation in a dislocation, the role of boundary or interfacial sliding in stress relaxation and creep of a composite and a polycrystal. Next, micromechanics is applied to stress induced martensitic transformation. In contrast to a standard method of analysis, a change in the structure of a martensite plate by stress is examined. This change is small at the onset of transformation, but becomes larger as transformation progresses.
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  • Microstructure of Zr-Al-Cu-Ni-Ag Ingot and the Thermal Stability of Corresponding Glass

    pp. 907-910

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    DOI:10.2320/matertrans.44.907

    Zr65Al7.5Ni10Cu12.5Ag5 ingots with different microstructures are obtained by changing the number of the repeated arc melting times. Differential scanning calorimetry (DSC) traces show that when the microstructure of the mother ingot becomes finer, the thermal stability of the glassy alloy improves during the crystallization of the glass. Because of the structure heredity, the finer the mother ingot microstructure is, the smaller the average size of the (Zr,Ag)-rich short-range orders in the glassy alloy is. The decrease of the size of the short-range orders makes the rearrangement of the elements more difficult in the glassy alloy. As a result, the activation energy for precipitation and decomposition of the I-phase becomes higher.
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  • Amorphous Co-Ni-P Alloys with High Saturation Magnetization Produced by Electrodeposition

    pp. 911-916

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    DOI:10.2320/matertrans.44.911

    The composition, structure and magnetic properties of high cobalt-containing Co–Ni–P alloys have been examined by controlling electrodepostion parameters. The alloys were deposited at 323 K from an electroplating solution consisting of nickel and cobalt chlorides and sodium hypophosphite. The current density and pH of the solution were controlled to determine the conditions of forming amorphous films. The alloys prepared at a current density of 150 A/m2 and pH of 5.20 include both amorphous and crystalline phases. The increase of pH to above 5.20 results in the formation of amorphous alloys without crystalline phase. The conditions of 220 A/m2 for current density and 5.24 for pH were optimum to prepare the amorphous alloy at the highest deposition rate of 5.19×10−5 kg/m2/s. These amorphous alloys exhibited high saturation magnetization up to 1.3 T with coercivity of about 20 kA/m.
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  • The Joint Characteristics of Friction Stir Welded AZ91D Magnesium Alloy

    pp. 917-923

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    DOI:10.2320/matertrans.44.917

    This study was carried out to grow an understanding of the microstructural development of friction stir welding on an AZ91D magnesium alloy and to evaluate the mechanical properties of the welds. AZ91D plates with the thickness of 4 mm were used, and the microstructural development of the weld zone was investigated using optical and scanning electron microscopes. Square butt welded joint with good quality was obtained under 187 mm/min of travel speed with the tool rotation speeds range of 115 to 131 rad·s−1. The microstructure near the welds consisted of SZ (Stir Zone) which has fine equiaxed grains with no the original dendrite grain structure, TMAZ (Thermo-Mechanically Affected Zone), HAZ (Heat affected zone) and base metal. The microstructure of each zone showed very different features depending on the thermal and mechanical conditions. The hardness tests showed uniform distributed and slightly increased harness in the stir zone. Tensile strength of the stir zone was remarkably improved due to the fine recrystallized grain structure.
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  • Three-Dimensional Modeling of the Grain Growth by Coalescence in the Initial Stage of Liquid Phase Sintering

    pp. 924-930

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    DOI:10.2320/matertrans.44.924

    A Monte Carlo method was developed to simulate the three-dimensional grain growth by coalescence in the initial stage of liquid phase sintering. The simulated grain, including a cluster of bonded particles, was treated in an appropriate three-dimensional multi-particle arrangement of the powder compact, and each cluster was assumed to be coalesced to reduce the system energy. The probability model also incorporated the energy-misorientation relationship assigned to randomly generated neighboring particles. Simulation results indicate that the size distribution of agglomerated particles are broadened by either an increase in the standard deviation of particle size distributions or a decrease in the volume fraction of the liquid, mainly due to the increasing of the probability of particle contacts. The findings of the simulation are favorably compared with past experimental observations on W–Ni–Fe alloys.
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  • Damping Capacity of Co-Mn System

    pp. 931-934

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    DOI:10.2320/matertrans.44.931

    The damping capacity of Co–Mn system which undergoes fcc → hcp martensitic transformation has been studied as a function of ε volume fraction using an inverted torsional pendulum. The damping capacity increases linearly with increasing ε volume fraction regardless of manganese content, and is represented by δ=0.05+0.27fε where δ is the damping capacity in logarithmic decrement of Co–Mn system and fε is the ε volume fraction. The main damping mechanism of Co–Mn system containing ε martensite is the movement of stacking fault boundaries in ε martensite plates.
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  • Small Dopant Effect on Static Grain Growth and Flow Stress in Superplastic TZP

    pp. 935-939

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    DOI:10.2320/matertrans.44.935

    Static grain growth behavior in 1 mol% of GeO2, TiO2, MgO or BaO-doped ZrO2–3 mol%Y2O3 (3Y-TZP) was examined at 1400°C with a special interest in dopant effect on superplastic flow stress in fine-grained 3Y-TZP. The static grain growth can be described as normal grain growth in single-phase ceramics, and growth constant K for each material is in the order of 10% flow stress of the superplastic flow. The value of K in cation-doped TZP is correlated well with dopant cation’s ionic radius. Assuming activation energy for diffusivity of constituent ion can be given as a linear function of strain caused by difference in the ionic size of dopant cation, the dependence of the growth constant and the flow stress on the ionic radius can be described as a function of the ionic radius of the dopant cation. The activation energy for the diffusivity in cation-doped TZP estimated from the calculation is in good agreement with the experimental data. The small dopant effect on the superplastic flow stress is well described by the activation energy as the function of the dopant cation’s ionic size.
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  • Analysis of Hydrostatic Tube Bulging with Cylindrical Die Using Static Explicit FEM

    pp. 940-945

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    DOI:10.2320/matertrans.44.940

    Tube Hydroforming (THF) is getting an increasing amount of attention in industry. THF has advantages such as weight reduction, high dimensional accuracy, and high rigidity. However, this forming process requires precise control of internal pressure and axial feeding. Additionally, in most cases prebending processes must be performed on the tubes before the hydroforming process can be carried out, and the forming ability of the hydroforming processes is influenced by the outcome of this prebending process. We describe the development of the Finite Element Method (FEM) code for THF analysis and a comparison of experimental and analytical results. The elastoplastic FEM code for THF analysis has been developed based on ITAS3D which is a sheet-metal-forming simulation program using the static explicit method. The algorithm of hydraulic pressure has been newly implemented in ITAS3D. Hydrostatic copper tube bulging with a cylindrical die was calculated with the code, and analytical results show good agreement with experimental ones. In this calculation, there is only a very small difference between the solid element and shell element results.
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  • Experiment and Static Implicit Analysis of Springback in Bend Forming of a Bumper Model

    pp. 946-950

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    DOI:10.2320/matertrans.44.946

    Experiments on bend forming of a bumper model with a 9.8-MN oil-hydraulic press and FEM analysis with the static code MARC were carried out in order to investigate springback behavior. The materials used were three types of high-strength steel sheets (HSS) of 440–780-MPa class. Experimental springback shapes were investigated using a 3-D measuring machine. The springback of a formed bumper increased with an increase in yield stress (YS) of the material, coinciding with the results of 2-D FEM simulation.
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  • Fragment Size Distribution in Blasting

    pp. 951-956

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    DOI:10.2320/matertrans.44.951

    It is well known that rock is generally treated as a heterogeneous material and the heterogeneity of rock causes sizes distribution of fragmented rocks in blasting. This paper discusses experimental and numerical rock fragment size distribution. To evaluate fines in bench blasting, two test experiments were conducted in the field and fragment sizes of blasted rocks were estimated by sieving analysis and image analysis. The fragment size distributions by image analysis were corrected with the evaluation of the fines. To predict rock fragmentation in bench blasting, a numerical simulation method was developed. Fragment development in bench blasting has been modeled by the numerical simulation method and analyzed for fragment size distributions by image analysis program. The fragment size distributions were corrected with the evaluation of fines, which correspond to compressive fracture zone around a blast hole. This paper discusses the importance of correct evaluation of the fines in bench-blasted rock and shows the possibilities of realistic prediction of fragmentation using a numerical simulation method and image analysis.
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  • Chemical Model of the FeCl3-HCl-H2O Solutions at 25°C

    pp. 957-961

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    DOI:10.2320/matertrans.44.957

    A chemical model was developed to calculate the equilibrium concentrations of chemical species in the FeCl3–HCl–H2O system at 25°C by using chemical equilibria, mass and charge balance equations. The activity coefficients of solutes and the activity of water were calculated with the Bromley equation. The interaction parameters for the individual chemical complexes, which were necessary to calculate the activity coefficients, were obtained from the reported interaction parameters between ions. By applying this model, the distribution of iron species with the electrolyte concentrations was obtained. In the experimental ranges of the ionic strength of solution up to 7.28 m, the experimental pH values were in good agreement with the predicted pH values.
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  • Corrosion Behavior of Ceramics-Coated Hastelloy-XR Alloy in an Ar-SO2 Atmosphere

    pp. 962-967

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    DOI:10.2320/matertrans.44.962

    Glass lining and CVD (chemical vapor deposition) YSZ (yttria stabilized zirconia) coating were applied to improve the corrosion resistance of Hastelloy-XR alloy in an Ar–SO2 atmosphere (PSO2=10 kPa). A glass lining with the composition of 48 SiO2–8 B2O3–6 Al2O3–11 CaO–25 BaO–2 ZnO (mass%) which protected the alloy substrate showed almost no crystallization and mass change below 1073 K, but suffered degradation at temperatures over 1173 K. The YSZ (8 mol% Y2O3) coating had a well-grown columnar structure and showed excellent corrosion resistance at 1273 K.
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  • Computer Simulations of the Aluminium-Silicon Anomalous Eutectic Growth Based on Multiphase Field Method

    pp. 968-972

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    DOI:10.2320/matertrans.44.968

    Aluminium–silicon anomalous eutectic growth has been studied numerically using a phase-field model developed to predict multiple phases. The Si phase grew very slowly in a melt of eutectic composition, but then grew substantially faster when in contact with the solidifying Al phase. The Al-liquid interface was irregular while the Si-liquid interface was flat as a consequence of the low interfacial energy between liquid and Al phases compared with that between liquid and Si. By developing a mathematical nucleation criterion, eutectic growth patterns were predicted and are in good agreement with experimental observations. Two mechanisms were shown to stop locally the growth of the Si phase during solidification. The first is competitive growth between the Al and Si phases, and arises when faster growing Al surrounds the tip of the solidifying Si. The second is due to nucleation and growth of Al ahead of the solidifying Si. It also has been shown that the melt is more likely to be trapped within the Si phase than in the Al phase.
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  • The Effect of Ram Speed on Mechanical and Thermal Properties in ECAE Process Simulation

    pp. 973-980

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    DOI:10.2320/matertrans.44.973

    Mechanical and thermal properties during equal channel angular extrusion (ECAE) process are analyzed by finite volume method simulation. Chronological effective strain behavior during ECAE was visualized by 3-dimensional simulation. Local instability during ECAE was detected by the detailed analyses (named as ‘center-divided points’ and ‘cut-area points’), which are indicative of effective strain, effective stress, effective strain rate and temperature. Different ram speed caused different heat dissipation history and accordingly different mechanical and thermal properties during ECAE. In this simulation work, most of deformation occurred at the slip plane agreeing with theoretical prediction.
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  • In-situ Synthesis of Mg2Si Intermetallics via Powder Metallurgy Process

    pp. 981-985

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    DOI:10.2320/matertrans.44.981

    The solid-state synthesis of Mg2Si intermetallic compounds has been evaluated in the present paper. The elemental magnesium and silicon powder mixture was employed as starting raw materials. In particular, the influence of the silicon particle by the repeated plastic working (RPW) on the in-situ formation of Mg2Si is discussed, based on the thermal and structural analysis results by DSC thermal analysis and XRD, respectively. Refined Si particles embedded uniformly in the magnesium matrix via RPW, can drive progressing Mg2Si synthesis at extremely low temperature; for example, the ignition temperature, Ts=773 K, to commence the solid-state synthesis of raw powder mixture, was reduced to about 400–430 K. Further plastic working on the mixture causes in-situ formation of Mg2Si intermetallic compounds with a crystallite size of 30–80 nm. However, the ignition temperature to synthesize Mg2Si shifts to a higher temperature again. Regarding to the thermal stability of Mg2Si compounds, the particle size of in-situ synthesized Mg2Si compounds after annealing at 573 K for 900 s is about 30–100 nm, that is, the remarkable coarsening does not occur during annealing.
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  • Plane-Strain Fracture Toughness on Thin AZ31 Wrought Magnesium Alloy Sheets

    pp. 986-990

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    DOI:10.2320/matertrans.44.986

    There are few reports about plane-strain fracture toughness on wrought magnesium alloys. Also, there are a little data, for example plane-strain fracture toughness, that evaluates such as reliability and safety in magnesium alloys. Therefore, in this study, plane-strain fracture toughness, KIC, on thin AZ31 wrought magnesium alloy sheets was analyzed. As a result, appropriate plane-strain fracture toughness was not obtained by plane-strain fracture toughness test. It was because specimens used in this study were too thin to satisfy small scale yielding condition. But, as a result of stretched zone analysis, appropriate plane-strain fracture toughness, KIC, was obtained and the values of KIC were 16.5–18.4 MPam1⁄2. According to the result of this study, it is concluded that stretched zone analysis was one of effective ways to evaluate fracture toughness of AZ31 wrought magnesium alloy appropriately. And the values of fracture toughness on AZ31 wrought magnesium alloys were equal or higher than that of cast magnesium alloy.
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  • Protium Absorption and Desorption Properties of bcc Ti-Fe Solid Solution Alloys Stabilized by Mo Addition

    pp. 991-994

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    DOI:10.2320/matertrans.44.991

    The present study investigates the effect of Mo addition to the TiFe alloys on a stabilization of bcc phase and their protium absorption and desorption properties. Ti0.5Fe0.5 alloys with more than 10 mol% Mo had CsCl phase and bcc phase, which show single plateaus in the PCT curves and were easily hydrogenated without homogenization. The bcc phase has larger lattice parameter than that of the CsCl phase. TiFe–10 mol% Mo annealed alloys with the Ti/Fe ratio of more than 2 had a bcc phase as a main phase and CsCl as a minor one. The alloys had 3 mass% of the maximum protium capacity and desorbed protium only 1 mass%. The phases of the hydrogenated alloy were fcc and orthorhombic structure, which may be caused by di-hydrides of bcc solid solution and mono-hydrides of CsCl phase, respectively. It is found that the Mo addition to TiFe alloys could stabilize bcc phase and enhances the hydrogenation reaction of the disordered bcc Ti–Fe–Mo phase similar to Ti–Cr–X bcc alloys.
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  • Effects of Inclusion Particles on the Microstructure and Mechanical Properties of High Strength Austempered Ductile Iron

    pp. 995-1003

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    DOI:10.2320/matertrans.44.995

    Effects of inclusion particles on the microstructure and mechanical properties of high strength austempered ductile iron (ADI) were investigated in this study. Inclusion particles, especially when their sizes are less than 5 μm, were mostly found in intercellular regions. Whether an inclusion particle can induce the formation of acicular ferrite depends on Mn segregation. In intercellular region, acicular ferrite was hard to form in the vicinity of inclusion particles due to (1) serious Mn segregation, and/or (2) the Mg-enriched inclusions here in halo-like. Consequently the surrounding austenite remained to be blocky type after austempering treatment. The fatigue life cycles of ADIs were affected by the particle counts and the microstructure. Increasing the count of fine inclusions along with the effect of Mn segregation deteriorated the fatigue life and elongation of high strength ADIs.
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  • Thermodynamic Properties of Polybrominated Dibenzo-p-dioxins and Dibenzofurans Calculated by Density Functional Theory

    pp. 1004-1013

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    DOI:10.2320/matertrans.44.1004

    Heat capacities and entropies for 76 polybrominated dibenzo-p-dioxins (PBDDs) and 136 polybrominated dibenzofurans (PBDFs) in the gas state have been computed using the density functional theory. Based on the output data of Gaussian, three methods were employed to calculate enthalpies and Gibbs energies of formation of PBDDs and PBDFs in the gaseous state at 298.15 K and 101.325 kPa. To assess the three methods, thermodynamic properties of 16 brominated arenes compounds were first calculated and compared with experimental values. Among the three methods used, method 2 has the smallest average absolute deviation from the experimental data. All values for the heat capacity, entropy, enthalpy and energy of formation of the 76 PBDDs increase, as the number of substituted bromines increases. For isomers of tetrabromodibenzo-p-dioxins, 1,3,6,8-TeBDD, 1,3,7,8-TeBDD, 1,3,7,9-TeBDD and the most toxic compound 2,3,7,8-TeBDD are more stable than the others, and easier to form during formation process. Comparing with PBDDs, the formation enthalpies and Gibbs energies of PBDF isomers are more variable. The formation enthalpies and Gibbs energies of isomers which have bromine substitutions in 1 and 9 positions are much higher than those of the others.
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  • Transient Liquid Phase Bonding of Nitrogen Containing Duplex Stainless Steel UNS S31803 Using Ni-Cr-Fe-Si-B Insert Metal

    pp. 1014-1023

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    DOI:10.2320/matertrans.44.1014

    Microstructural evolution during transient liquid phase (TLP) bonding of nitrogen containing duplex stainless steel UNS S31803 has been investigated. In order to evaluate mechanical property of joint, tensile strength test was carried out at room temperature. TLP bonding was conducted at the temperature range 1283–1353 K for 0–1000 s under a vacuum of 6.7 mPa using Ni–7 mass%Cr–3 mass%Fe–4.5 mass%Si–3.2 mass%B amorphous insert metal. The results show that the volume fraction of austenite (γ) decreased with increasing bonding temperature and holding time. Particularly, in the case of prolonged holding time, the depleted area of γ phase was observed in the base metal adjacent to joints. There were linear correlations between the width of the remaining liquid phase and square root of holding time at each bonding temperature. In this investigation, the secondary phases formed in the joint area were (Cr, Mo) borides dominantly. For the specimen bonded for longer time up to 1000 s, boron nitride formed at the center and interface of joint area, on the other hand, the amount of borides decreased compared with the case of shorter bonding time. Tensile strength increased with holding time, and the bonding efficiency was ∼94% for the specimen held for 1000 s at 1353 K. Tensile strength of joint depended on, for a short holding time, brittle eutectic and borides, and after completion of isothermal solidification, depended on the boron nitride formed at the joint interface.
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  • Sliding Properties of Composite Sprayed Coating between Bronze Powder and Solid Lubricant

    pp. 1024-1028

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    DOI:10.2320/matertrans.44.1024

    Intake of lead is harmful to the human body. Therefore, it is necessary to substitute other alloying elements for lead in Cu alloys. Using a Cu–9.5 mass%Sn alloy powder and CaF2, which has sliding properties equal to lead, a composite sprayed coating (by flame spraying) was developed. The results were as follows. A composite sprayed coating with the desired characteristics was successfully produced. The area fraction of the CaF2 layer in the composite coating increased with the increase in the blend ratio of CaF2 in the blended powder. The wear resistance of the composite coating containing CaF2 was excellent. As a result it was determined that CaF2 in the composite coating was effective as a sliding material substitute for lead.
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  • Tensile Properties of Mg-8Al-xRE Alloys from 300 K to 673 K

    pp. 1029-1035

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    DOI:10.2320/matertrans.44.1029

    This paper presents the tensile properties of cast and extruded Mg–8Al–xRE (in mass%; x is 0, 1, 2 or 3%) alloys from 300 to 673 K obtained at a strain rate of 8.3×10−4 s−1. Mg–8Al–xRE alloys were prepared by melting and casting in a vacuum induction furnace, and extruded at 633 K with a reduction ratio of 90:1. RE greatly improves the tensile strength of cast and extruded Mg8Al alloys above 473 K. RE negatively affects the elongation of cast alloys at the studied temperature range but considerably enhances that of extruded alloys. Superplasticity of the extruded alloys is observed at 473 K or above. The strengthening mechanisms and the optimal deformation temperature, Tc, of these alloys are discussed in detail.
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  • Formation of Anodic Films on Mg-Al Alloys in NaOH solutions at Constant Potentials

    pp. 1036-1041

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    DOI:10.2320/matertrans.44.1036

    The formation behavior and corrosion characteristics of anodic oxide films on pure magnesium and on Mg–Al alloys were investigated, focusing on the effects of anodization potential, aluminum content, temperature, and NaOH concentration. Pure magnesium and Mg–Al alloys were anodized for 600 s at 3, 10, 40, and 80 V in NaOH solutions. It was found that the anodic film formed at 3 V had the best corrosion resistance, regardless of temperature, NaOH concentration, or aluminum content. An especially high current density was observed at applied potentials of 3–7 V on anodization in alkaline NaOH solutions. XRD analysis detected Mg(OH)2 and MgO peaks in the films on the anodized specimens. The relative intensity of the Mg(OH)2 XRD peaks decreased with increasing applied potential, while those of MgO increased. Mg(OH)2 was generated by an active dissolution reaction with high current density at the specimen surface. Generation of Mg(OH)2 increased with increasing temperature, while that of MgO increased with NaOH concentration. Moreover, the current density after anodization for 600 s at a constant potential decreased with increasing aluminum content in Mg–Al alloys.
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  • Effects of Additional Elements on the Glass Formation and Corrosion Behavior of Bulk Glassy Cu-Hf-Ti Alloys

    pp. 1042-1045

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    DOI:10.2320/matertrans.44.1042

    New bulk glassy (Cu0.6Hf0.25Ti0.15)98M2(M = Mo, Ta and Nb) alloys with high thermal stability were synthesized and the effects of additional elements Mo, Ta and Nb on the glass formation and corrosion behavior were examined. The maximum diameter for glass formation of the 2 at%Mo, 2 at%Ta and 2 at%Nb alloys was 1.5 mm, 3.5 mm and 4.0 mm, respectively. The corrosion behavior of the Cu–Hf–Ti–(Mo, Ta and Nb) glassy alloys was examined by weight loss and electrochemical measurements. By substitution of 2 at%Mo, Ta or Nb for the Cu60Hf25Ti15 alloy, the corrosion rates of the alloys decreased to 1⁄2 in 1 N HCl and two orders of magnitude in 3% NaCl solution. It was also found that substitution of elements Mo, Ta and Nb for the Cu60Hf25Ti15 glassy alloy was effective on decreasing anodic passive current density in 3% NaCl solution.
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  • Galvanic Dissolution Behavior of Magnesium-1 mass%manganese-0.5 mass%calcium Alloy Anode for Cathodic Protection in Fresh Water

    pp. 1046-1048

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    DOI:10.2320/matertrans.44.1046

    Magnesium–1 mass%manganese–0.5 mass%calcium (Mg–1 mass%Mn–0.5 mass%Ca) alloy was used as sacrificial anode. This work was performed to investigate the galvanic dissolution behavior of the alloy anode for cathodic protection in fresh water. The microstructure and dissolved surface of the alloy anode were analyzed with an electron probe micro analyzer, a scanning electron microscope with energy dispersive X-ray spectrometer and a microscope. The current efficiency of the anode has been measured by laboratory test method of galvanic anodes for cathodic protection. It was found that calcium is present uniformly at the grain boundaries as Mg2Ca or Mg–Ca–Si compounds. Calcium compounds dissolve preferentially compared to the matrix of magnesium, as a result the anode uniformly dissolve compared to Mg–1 mass%Mn alloy anode. The current efficiency of the anode for the dissolution was higher than that of Mg–1 mass%Mn anode. On the other hand, manganese is added in order to decrease the local cathode to magnesium alloys, however the part of manganese compounds act as the local cathode in the alloys.
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  • Al-Sc Master Alloy Prepared by Mechanical Alloying of Aluminum with Addition of Sc2O3

    pp. 1049-1052

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    DOI:10.2320/matertrans.44.1049

    Al–Sc master alloy was prepared by the powder metallurgy route from the initial composition of Al90(Sc2O3)10 mixture. Aluminum powder was mechanically alloyed with addition of Sc2O3, which is much less costly than the metallic Sc, and fine Sc2O3 particles became uniformly dispersed in the matrix of Al. During consolidation by SPS at 873 K for 3.6 ks of mechanically alloyed powder mixture, Sc2O3 was decomposed and Al3Sc and Al2O3 are formed by solid-state reaction. Subsequently, SPS billets were hot-extruded at 773 K with a reduction of 1/12. Obtained extruded P/M material of Al–Sc master alloy was added to Al–4.5%Cu alloy melt and cast into the copper mold in order to attest its grain refining effect. Apparent grain refining was attained in the ingot of Al–4.5%Cu–0.55%Sc alloy and thus effectiveness of extruded P/M material from mixture of Al90(Sc2O3)10 as the Al–Sc master alloy was clearly attested. However, break down of covered oxide film of each powder particle by large plastic deformation is considered to be necessary to complete melting of added Al–Sc master alloy in the Al alloy melt.
    x

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  • Effect of Superplastic Deformation on Thermal Expansion Behavior of Tetragonal Zirconia Polycrystals

    pp. 1053-1056

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    DOI:10.2320/matertrans.44.1053

    Three mol% yttria stabilized tetragonal zirconia polycrystals (3Y-TZP) were superplastically deformed under various conditions and microstructural evolution was characterized. Thermal expansion properties of the 3Y-TZP specimens were then measured by a push-rod type dilatometer in a temperature range from 300 K to 1473 K. Experimental results showed that the mean coefficient of linear thermal expansion, α, decreased with an increase in the volume fraction of cavities. The cavity dependence of α value was dependent on temperature and was weakened with an increase in temperature. Changes in the average grain size and grain aspect ratio due to the superplastic deformations were found to have little effect on the thermal expansion property within the present experimental range.
    x

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