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

MATERIALS TRANSACTIONS Vol. 53 (2012), No. 2

  • PREFACE

    pp. 249-249

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    DOI:10.2320/matertrans.MPR2012902

  • An Attempt to Evaluate Insufficient Supply of Oil in Ball Bearing with Ultrasonic Technique

    pp. 250-255

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    DOI:10.2320/matertrans.I-M2011837

    The purpose of this technique is to estimate the lubrication condition in ball bearing with the variation of ultrasonic echo height reflected from a contact surface of an outer ring and a ball. A part of ultrasonic wave sent from a probe attached on a bearing housing is transmitted to the outer ring of ball bearing through a boundary surface of the outer ring and the bearing housing, and arrives at a boundary surface contacting with the ball, and reflects from there. This reflection echo height is used for an evaluation of insufficient supply of oil in ball bearing. When sufficient oil is supplied to an inlet of contact surface between the outer ring and the ball, the echo height which continued decrease as the ball approaches a sound axis of ultrasonic probe is increased locally. However, degree of its increase becomes lower when oil supply is insufficient, and does not appear at all with running out of oil. Also the time lag between bottom of valley in echo height variation curve and the sound axis of ultrasonic probe decreases gradually as supply of oil becomes insufficient, and becomes zero with running out of oil from a contact surface. This evaluation method has a potential which can evaluate the insufficient supply of oil in the ball bearing by two indexes above.
  • Depth Evaluation of Fretting Fatigue Crack Appearing at Bolt Joints of Aluminum Alloy Plates by Synchronized Surface Acoustic Wave Measurement

    pp. 256-263

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    DOI:10.2320/matertrans.I-M2011838

    The surface acoustic wave (SAW) measurement was carried out for the bolted specimen of aluminum alloy by synchronizing the ultrasonic pulsation with a fatigue cycle in the fatigue testing. The reflection from the crack increased in the loading stage of the fatigue cycle, reached maximum and then decreased in the unloading stage of the fatigue cycle. The sigmoidal intensity change of the reflection from the fatigue crack in a fatigue cycle occurred following opening/closing behavior of the crack, and the intensity took the maximum value when the crack was fully opened. The SAW intensity distribution between the crack and the bolt hole edge was also analyzed to evaluate the depth of the crack: the SAW intensity distribution after the crack root was subjected to the band-pass filtering to recognize the creeping wave (the longitudinal wave) reflected from the crack tip, and then the crack depth was estimated from the propagation time of the creeping wave from the crack root to the crack tip, which was in good agreement with the value measured in the cross section of the specimen and evaluated through the scanning acoustic analysis.
  • Investigation of the Effect of the Roughness-Induced Crack Closure on the Fatigue Crack Propagation Behavior of Hot-Rolled Steels under Mixed-Mode Loading Conditions

    pp. 264-269

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    DOI:10.2320/matertrans.I-M2011839

    It is reasonable to apply crack closure concepts, i.e. roughness-induced crack closure, to understand the crack propagation behavior under mixed mode loading conditions. In this paper, the characteristics of fatigue crack propagation under mixed-mode loading is studied using the concept of roughness-induced crack closure, and a model of the variation of the crack opening ratio is proposed based on multi-variable statistics. In addition, fracture surfaces are examined by C-scan and classified into four stages to quantify the effect of crack closure. The roughness parameter based on the highest intensity reveals the effect of roughness-induced crack closure on the fatigue crack propagation.
  • Characterization of a Humid Concrete by Study of Thermal Impedance

    pp. 270-273

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    DOI:10.2320/matertrans.I-M2011840

    In the paper the thermal characteristics evolution of a humid concrete with water content is determined by study of the relation between the thermal effusivity of concrete and the thermal impedance. At first, the theoretical impedance related the effusivity of material measured is expressed. In certain frequency band, a sample with its enough big thickness can be considered as a semi-infinite system for facilitating determination of the effusivity of material. In the experiment, a sensor which is consist of a plane fluxmeter for measuring the thermal flux and a thermocouple implanted in the fluxmeter for measuring the temperature is disposed below a surface of a humid concrete sample, while a plane electrical resistance for exciting heat signal is disposed below the fluxmeter. The relation of temperature and thermal flux in time is considered a linear system during each test. The experimental impedance is determined by measuring the flux and temperature as the input and output signals of a system. The results of evolution of effusivity with water content are obtained by optimization of parameters in the theoretical impedance while comparing between the theoretical impedance and the experimental impedance. The results of the study show that there is a strong sensibility of the concrete effusivity to water content. This remark allows envisioning the thermal impedance as a possible measure technique of water content. The water content in a humid concrete relates to the porosity of concrete. This thermal characterization method can allow detecting an eventual abnormality in concrete, for example degradation.
  • Using Lamb Waves to Evaluate Debonding of Steel Plate Strengthened Concrete

    pp. 274-278

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    DOI:10.2320/matertrans.I-M2011841

    This is a preliminary study on using the dispersive characteristics of the Lamb wave modes traveling within the steel layer to assess the bonding condition. The dispersive curves are obtained by a multichannel analysis of surface waves. The frequency-phase velocity images obtained from finite-element analyses were constructed based on the phase velocity analysis scheme. These images were compared with the theoretical dispersion curves. The numerical models include pure steel, steel-concrete bi-layered and steel-epoxy-concrete composite plates. The results show the deviation of phase velocity for composite plate can be used to evaluate the bond condition.
  • Measurement Technique of Distribution of Power Generation Current Using Static Magnetic Field around Polymer Electrolyte Fuel Cell by 3D Inverse Problem FEM

    pp. 279-284

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    DOI:10.2320/matertrans.I-M2011842

    A polymer electrolyte fuel cell (PEFC) is a practical clean energy converter. In order to improve power generation state in PEFC is needed. The power generation performance of PEFC depends on mass transfer in it. Thus, it is important to clarify the current distribution that has close relation to the mass transfer. Especially, the measurement of the power generation current in MEA (membrane electrode assembly) inside the PEFC is needed. The power generation current generates the static magnetic field around the PEFC. Therefore, the distribution of power generation current inside MEA can be determined using the static magnetic field around the fuel cell.
    In this paper, non-contacting technique for distribution of power generation current inside the MEA using the distribution of the static magnetic field around the PEFC is examined. The proposed heuristic search method using 3D FEM (finite element method) is used for searching the current distribution inside the MEA. In the proposed heuristic search magnetic field analyzing method, the “ON” (current flow) or “OFF” (no current) of the generation current region only in MEA which consisted of 25 elements in the design variable. The distribution of power generation current in MEA is calculated from the proposed heuristic search analyzing method using the measured values of static magnetic field around the PEFC. By measuring the very small quantity space magnetic field distributed around the PEFC the distribution of power generation current in MEA with the fuel cell can be calculated using the proposed heuristic search method.
  • Bridge Deflection Measurement Using Digital Image Correlation with Camera Movement Correction

    pp. 285-290

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    DOI:10.2320/matertrans.I-M2011843

    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.
  • Variation in Pressure in Liquid-Filled Plastic Film Bags Subjected to Drop Impact

    pp. 291-295

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    DOI:10.2320/matertrans.I-M2011844

    The side-wall pressure in liquid-filled plastic film bags subjected to drop impact was measured using pressure sensors, and the relationship between the variation in pressure with time and the number of heat-sealed sides of the bag was investigated. The two samples A and B [130 × 300 mm2 (width × height)] made of transparent plastic film of 67 µm thickness were used. Sample A was a liquid-packaging bag heat-sealed at four sides, and sample B heat-sealed at three sides. The bags contained about 1,000 mL of liquid. Pressure sensors were placed at 26 positions along the inner wall surface of the bag. The samples were held at a height of 0.5 m and freely dropped onto wood floor, aluminum alloy, rubber and sponge plates on a concrete floor. The bottom drop test was carried out. Results indicate that the propagation speed of pressure is affected by the number of heated-sealed sides of the bag, and the maximum pressure by the type of floor material.
  • Nondestructive Elastic-Wave Tests of Foundation Slab in Office Building

    pp. 296-302

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    DOI:10.2320/matertrans.I-M2011845

    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.
  • Acoustic Nonlinearity of Surface Wave in a Fatigued Aluminum Alloy Specimen

    pp. 303-307

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    DOI:10.2320/matertrans.I-M2011846

    This paper reports a case study for the evaluation of surface fatigue damage by using the acoustic nonlinearity of surface waves. A measurement system using contact angle beam transducers was constructed to measure the acoustic nonlinearity of surface waves based on the harmonic measurement. In order to prove the general properties of acoustic nonlinearity, dependencies of the second harmonic amplitude on the fundamental frequency amplitude and the propagation distance were tested first, where the effect of frequency-dependent attenuation was compensated for. The results showed good agreement with the theoretical expectations. Next, an aluminum 6061 T6 specimen, of which the surface was damaged by a three-point bending fatigue test, was experimented on and magnitudes of nonlinear parameter, measured before and after the fatigue test, were compared. We could see a clear increase in the nonlinear parameter after the fatigue test at the central position of the specimen, where the surface fatigue damage was expected to be concentrated.
  • Mobile Computed Tomography for Inspection of Large Stationary Components in Nuclear and Aerospace Industries

    pp. 308-310

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    DOI:10.2320/matertrans.I-M2011848

    Mobile Tomographic Computer Aided Radiometry (TomoCAR) is based on the mechanical position control of an X-ray tube in front of an object and the application of a Digital Detector Array (DDA) behind it. Several hundred radiometric projections in small angle steps are acquired during the controlled movement of the X-ray tube along a preselected way. The tomographic or laminographic reconstruction allows the three-dimensional (3D) representation of flaws. A specially designed radiometric detector array with small internal unsharpness and high image contrast was used for visualization and sizing of planar and volumetric defects in austenitic welds in nuclear power plants. A German pilot study was successfully performed on the basis of the European network of inspection and qualification (ENIQ) guidelines. This was the precondition for several applications of TomoCAR in nuclear power stations in Germany and Switzerland.
    A versatile computed tomography (CT) system was developed on basis of the TomoCAR design for in situ inspection of large aircraft components under production conditions. A gate based planar computed tomograph was constructed and tested for inspection of the integrity of CFRP stringers, embedded in aircraft fibre composite shells. A probability of crack visibility >90% could be determined.
  • Application of the “GUCHI” Technique in Radiographic Testing for Flaw Sizing of Pipe

    pp. 311-315

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    DOI:10.2320/matertrans.I-M2011849

    “GUCHI” (Geometric Unravel for Crack Height Image) technique is one of the stereo-radiography methods for flaw sizing in radiographic testing. The AN (Application of Nondestructive Testing techniques for industrial fields) committee in the JWES (The Japan Welding Engineering Society) carried out the experiment on this technique. The results were reported at FENDT 2002 and APCNDT 2003 and 2006 with data on the steel plates and pipes including fatigue cracks and EDM slits. The flaw sizing by RT-GUCHI was performed in a round robin test on 6 inches stainless steel pipe which had circumferential semi-elliptical fatigue cracks with 0.2t, 0.4t and 0.6t height at the OD surface and on plate including a fatigue crack. A trial for flaw sizing of SCC was also performed.
    This paper describes the fundamental of GUCHI technique, the discussion results of the accuracy for flaw sizing which was investigated before 2006 and the results of the round robin tests on test specimens with fatigue cracks.
  • Temperature Distribution Estimated by Optimization and Near-Field Acoustical Holography

    pp. 316-320

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    DOI:10.2320/matertrans.I-M2011850

    We propose a method to estimate temperature distribution non-destructively using combination of near-field acoustical holography (NAH) method and optimization method. NAH method is valid to calculate forward and back propagations of ultrasonic wave in a uniform medium. To estimate of temperature distribution, we proposed a modified method of NAH, called sectional NAH (SNAH), for using NAH in an inhomogeneous medium. In SNAH, a calculation space is discretized into a number of sections, so that the temperature in each section becomes nearly uniform, and NAH calculation is performed in each section. Calculation results using SNAH in the inhomogeneous medium well agreed with the calculation result using finite element method (FEM). By using SNAH, the temperature distribution is estimated as bellows. Firstly, sound fields, which are complex amplitude of harmonic oscillation, in three planes are measured. Next, sound field at one of measured plane is calculated from the other measured sound fields, which are calculated from other measurement planes using SNAH, with an initial sound velocity distribution. Then, difference between calculated and measured sound fields is minimized by optimizing the sound velocity distribution using multi-start downhill simplex method. In this method, a temperature distribution is obtained as the sound velocity distribution. In simulations, temperature distributions given as linear and Gaussian distributions were estimated. Validity of our proposal methods is confirmed by simulations.
  • Material Differentiation by Differential Computed Tomography

    pp. 321-322

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    DOI:10.2320/matertrans.I-M2011851

    This paper presents the study on the feasibility of a differentiation of the individual materials using so called dual energy computed tomography. The individual pixels on tomogram are the results of X-ray attenuation penetrating through the sample from different angles of projections. Attenuation is caused by absorption and scattering of radiation. The contribution of these two main mechanisms is dependent on atomic number, electron density, and also the energy of the X-ray photons. The material characteristics may be quantitatively analyzed when the composition in to atomic number or density information is carried out. Therefore, two different X-ray spectra were used by application of filters. The principle of proposed method results in a numerical approach with the associated detector calibration. We tested first the method on the samples of known composition. From the results it was shown that we are able to obtain removal of “beam hardening” and the estimation of material composition. For further more precise determination of materials, the proposed method will be used with the respect to detector acquisition improvement.
  • Noncontact Deflection Distribution Measurement for Large-Scale Structures by Advanced Image Processing Technique

    pp. 323-329

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    DOI:10.2320/matertrans.I-M2011852

    Ambient unexpected vibration in field experiment for large-scale structures is an essential problem to perform highly accurate displacement measurement. In this paper, an advanced image processing (AIP) technique combining the sampling moiré method and digital image correlation (DIC) method is developed for noncontact measuring deflection distribution of large-scale structures. This technique has demonstrated promising results in both laboratory and field experiments. Experimental results in laboratory show that the artificial vibration can be abated remarkably by DIC using a subset image of background without loading. Experimental results in field show that AIP technique can successfully measure the displacement distribution of a long crane with sub-millimeter deflection under natural vibration environment. The most attractive advantage of AIP technique is only each single image is required before and after deformation. This indicates the noncontact deflection distribution measurement is possible with high resolution and high accuracy by ease setup for the dynamic structural evaluation of infrastructures.
  • Non-Contact Guided Waves Tomographic Imaging of Plate-Like Structures Using a Probabilistic Algorithm

    pp. 330-336

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    DOI:10.2320/matertrans.I-M2011853

    A non-contact testing with laser generated ultrasonic transmitter and an air-coupled transducer is very attractive technique in guided wave inspection. It can be used for online inspection and structural health monitoring (SHM) where contact method with embedded sparse sensors can not be applied such as the case of high temperature application. In this paper, tomography based on probabilistic algorithm was employed in conjunction with the hybrid non-contact method. This present approach can be successfully used for detecting, locating and imaging multi-defect in plates. This algorithm is based on the use of signal difference coefficient of guided waves acquired for good and faulty conditions. The simplicity of this algorithm makes it suitable to be implemented to non-contact based online inspection scheme.
  • Simulation of Internal Crack Detection in Shape-Distorted Cast Billets Using Time-of-Flight Measurements of Longitudinal Ultrasonic Waves

    pp. 337-341

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    DOI:10.2320/matertrans.I-M2011854

    To detect cracks in shape distorted cast billets, we newly propose a method that is the use of ultrasonic computerized tomography (CT) in combination with measurements of time-of-flight (TOF) of longitudinal ultrasonic waves at multiple planes as a more robust reconstruction method. The TOF is measured by applying the transmission method, and the measured TOF is used to reconstruct the apparent sound velocity profile. Cracks are identified as a decrease in the apparent sound velocity, which is caused by an increase in the TOF after the diffraction of ultrasonic waves at the cracks. The combination makes it possible to remove the effects of shape distortion to be compensated by the TOF measurements at multiple planes. Therefore, cracks are clearly detected using this method. The detection ability of this method is evaluated by numerical simulations of a shape-distorted billet. The results of this study are validated with help of wave propagation simulations using the transmission line matrix (TLM) method. More specifically, the newly proposed method allowed us to detect cracks that could hardly be distinguished with the use of our previously proposed method owing to fluctuations of the apparent sound velocity caused by shape distortions. In addition, using the new method enables the detection of cracks located near the billet’s surface whose dimensional change is as small as 5%. From the results of this study, we believe that the newly proposed method could be useful for the crack detection in shape-distorted billets.
  • Development of AE Monitoring System with Noise Reduction Function by Spectral Subtraction

    pp. 342-348

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    DOI:10.2320/matertrans.I-M2011855

    In order to monitor acoustic emission (AE) in a noisy environment, an AE monitoring system with a real-time noise reduction function using spectral subtraction (SS) was developed. First, the improvement in the S/N ratio and distortion of the waveform after the process were compare to those in ε-filter and wavelet shrinkage methods. The improvement in the S/N ratio of the waveform processed by SS constantly increased and was observed to be independent of the S/N ratio of the wave before processing. The distortion of the waveform processed by SS was less than the distortions of the waves processed using ε-filter and by wavelet shrinkage. Next, the effect of two parameters in the SS process — frame number (fn) and over-subtraction factor (α) — on the noise reduction performance was studied. The S/N ratio of the signals processed by the SS technique improved with decreasing fn and with increasing α. However, the processed waveform was distorted when α was large. It is necessary to set the value of fn to 16 or less and α to 5 or less so that SS showed an advantage to reduce noise with low waveform distortion.
    Cylindrical wave AE signals produced by the Hsu-Nielsen source (pencil lead breaking) were monitored with the developed system in an environment with artificial noise. The developed system was able to acquire AE signals with a sampling frequency of up to 25 MHz. The noise was reduced and AE signals with S/N ratio of 0 dB before the process could be detected. The S/N ratio of the AE signal was improved by approximately 10 dB using the SS technique.
  • PREFACE

    pp. 349-349

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    DOI:10.2320/matertrans.MPR2012903

  • Fatigue Limit of High V–Cr–Ni Spheroidal Carbides Cast Iron under Rotating Bending Fatigue Test

    pp. 350-353

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    DOI:10.2320/matertrans.F-M2011832

    This study is to find vanadium carbide (VC) effects on fatigue limit of spheroidal vanadium carbide cast iron (SCI-VCrNi) with addition chromium (Cr) and nickel (Ni). The VC is very hard, about 2300 HV in the Vickers hardness and excellent abrasion resistance is possessed. But the shape control of VC is extremely difficult. Then, fatigue limit of SCI-VCrNi was evaluated by rotating bending fatigue test in this study. And, the fatigue tests of FCD500 and FCD700 also were carried out and it was compared with the SCI-VCrNi.
    As a result of rotating bending fatigue testing, the fatigue limit (σw) of SCI-VCrNi has 350 MPa. The fatigue limits of FCD500 and FCD700 have 290 and 300 MPa respectively. A fatigue limit of SCI-VCrNi was higher than all spheroidal graphites cast irons. Then, fracture surface was observed by using the SEM to observe the fatigue mechanism more in detail. As for SCI-VCrNi, a lot of fracture cross sections of VC were observed, it can be guessed that the uniting power of VC and the matrix is strong and the crack progress is delayed by breaking VC.
  • Solidification Microstructures and Quench/Temper Hardness of Tantalum Added High-Carbon High-Speed Steel Type Cast Alloy

    pp. 354-361

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    DOI:10.2320/matertrans.F-M2011836

    The influence of Ta addition on the solidification microstructure, solute distribution and hardness after quenching and tempering treatments was investigated for a high-carbon high-speed steel type cast alloy (Fe–1.9%C–0.5%Mn–4.9%Cr–5.0%Mo–5.0–7.2%V–0.4–1.4%Ta). The compositions of V and Ta were systematically changed to improve the distribution of hard MC carbides in the hypoeutectic range. Electron probe micro-analysis (EPMA) and X-ray diffraction (XRD) identified an oval microstructure as MC carbides containing mainly V and Ta, and a lamellar structure as M2C carbides containing mainly Fe and Mo among the austenite (γ) dendrites. Redistribution of alloying elements during the solidification sequence of primary γ, γ + MC and M2C eutectic structure could be calculated from the Scheil-Gulliver equation and the initial composition. The macro-hardness of the quenched specimens gradually increased with increasing quenching temperature until a maximum was reached. This indicates that macro-hardness of the quenched specimens depends on both the amount and hardness of martensite matrix. All specimens which were tempered at 723–873 K showed secondary hardening. Furthermore, hardening of the specimens was most apparent when specimens containing large amounts of retained γ were tempered at an optimum temperature. For example, the hardness of specimens with added Ta increased to around 900 HV after tempering at 823 K. These results suggest that the macro-hardness of tempered specimens is governed by the maximum amount of carbon in the γ matrix at quenching temperature, the degree of transformation from retained γ to martensite, and the precipitation and distribution of secondary carbides.
  • Corrosion Properties and Microstructure of a Broad Range of Ce Additions on Mg–Zn Alloy

    pp. 362-366

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    DOI:10.2320/matertrans.F-M2011833

    To launch a new class of Mg alloys based on the Mg–Zn system, the effect of microstructural evolution on the corrosion properties in Mg–Ce–Zn system has been investigated. The alloys were fabricated by using a vacuum induction melting method under an argon atmosphere. Potentiodynamic polarization and hydrogen evolution test were carried out in 3.5% NaCl solution of pH 7.2 at room temperature to evaluate the corrosion properties of Mg–Ce–Zn alloys. The main constituents in Mg99Ce0.5Zn0.5, Mg98Ce1.5Zn0.5 and Mg92Ce7.5Zn0.5 alloys are α-Mg and Mg12Ce phase. On the other hand, Mg41Ce5 and Mg3Ce phases are present in Mg88Ce11.5Zn0.5 and Mg86Ce13.5Zn0.5. Although Ce additions on Mg alloy could tend to ennoble the corrosion potential, the corrosion rate was increased with excessive Ce additions.
  • Multi-Subcenters Solution Search Algorithm for CFD Optimization Problems and Its Application to Die Casting

    pp. 367-373

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    DOI:10.2320/matertrans.F-M2011831

    For die-casting, various approaches to finding the optimal control settings and optimal mold by using a computational fluid dynamics (CFD) simulator have recently been studied and applied. However, the optimal value obtained by using a conventional CFD simulator does not consistently agree with experiment, owing to computational error. Accordingly, we analyze the problem of optimization with a CFD simulator in order to develop an optimization method that can consistently produce suitable results. To assess the effectiveness of the proposed method, it was applied to the optimization of plunger speed in die-casting.
  • Real-Time Radiographic Observation of Solidification Behavior of Al–Si–Cu Casting Alloys with the Variation of Iron Content

    pp. 374-379

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    DOI:10.2320/matertrans.F-M2011834

    Real-time radiography using synchrotron radiation X-ray was utilized to directly observe and investigate the formation behavior of Fe bearing intermetallic phases in Al–Si–Cu alloys. Solidification sequences of two Al–Si–Cu alloys with different Fe content were examined in a specially designed vacuum furnace and chamber in BL20XU of SPring-8. Detailed solidification sequence and resultant phases forming reactions were confirmed by combined analyses of radiography, thermodynamic calculation and SEM-EDS. The formation behavior of primary, eutectic and peritectic β-Al5FeSi as well as α-Al8Fe2Si and α-Al15(Fe,Mn)3Si2 were explained as a function of Fe content. The β-Al5FeSi was found to form as only small eutectic component in the low Fe containing alloy, while that was crystallized as a primary phase as well as α-Al8Fe2Si and α-Al15(Fe,Mn)3Si2 in the high Fe containing alloy.
  • Influence of Alloying Elements on Sulfide Formation in Lead Free Bronze Castings with Dispersed Sulfide Particles

    pp. 380-384

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    DOI:10.2320/matertrans.F-M2011835

    The influence of the zinc sulfide ratio in the sulfide particle in the lead free bronze castings on the machinability is studied. Also, the influence of alloying elements of the zinc sulfide ratio of the sulfide particle is studied for understanding the mechanism of the zinc sulfide formation during the solidification. The zinc sulfide ratio is evaluated with the analysis of the microstructure in the lead free bronze prepared by the sand mold casting. The condition in which the zinc sulfide stably exists during the solidification is estimated with thermodynamic calculation. The machinability is improved with the decrement of the zinc sulfide ratio. The sulfide is formed as the copper sulfide and the zinc sulfide through eutectic reaction, and also appears as the liquid phase through monotectic reaction. The zinc sulfide is formed with the copper sulfide at the temperature, at which the zinc sulfide was predicted to be unstable by the thermodynamic calculation. The ratio of the zinc sulfide increases with increasing zinc content. Tin does not affect the zinc sulfide ratio when the tin content is less than about 4 mass%. There is no effect of nickel on the zinc sulfide ratio.
  • A Phase Field Model of Sintering with Direction-Dependent Diffusion

    pp. 385-389

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    DOI:10.2320/matertrans.M2011317

    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.
  • Hardness and Micro-Texture in Friction Stir Welds of a Nanostructured Oxide Dispersion Strengthened Ferritic Steel

    pp. 390-394

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    DOI:10.2320/matertrans.M2011226

    The goal of this study is to characterize the hardness distribution and texture evolution in a friction stir welded oxide dispersion strengthened (ODS) ferritic steel. Hardness profiles were plotted by collecting data on the transverse cross section of the joint. The texture evolution and microstructure characteristics were studied by electron backscattering diffraction (EBSD). Results showed that regions near the bottom of the stir zone were the weak points in hardness, as those regions comprise coarser grains compared with the adjacent regions. EBSD results showed that the grain characterization (size, shape, and aspect ratio) varied within different regions and provided important insight into the material flow within the stir zone. EBSD results also revealed that textures within different regions presented some features of rotating coincidence. By suitable rotations of the poles figures, textures within different regions could superpose with each other almost exactly.
  • Dynamic Mechanical Behaviour of Polymer Bonded Nd–Fe–B Composite Materials

    pp. 395-400

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    DOI:10.2320/matertrans.M2011218

    Magnetic composite materials with varied content of Nd–Fe–B particles in epoxy matrix are examined from a dynamic mechanical perspective. Structural, viscoelastic and magnetic properties of composites have been observed using Scanning Electron Microscope (SEM), Dynamic Mechanical Analysis (DMA) and Super Quantum Interference Device (SQUID) magnetometer, respectively. Experimental results show that magnetic properties and corresponding dynamic mechanical behaviour depend on packing density. Also, results observed by predictive mathematical models suggest that maximal packing factor has a direct impact on elastic behaviour of composites.
  • Molecular Dynamics Simulation on Interaction between Screw Dislocation and Pseudo Yttrium Oxide in Bcc-Fe

    pp. 401-406

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    DOI:10.2320/matertrans.M2011276

    For an atomistic insight in oxide dispersion strengthened (ODS) steels, we have performed molecular dynamics simulations on interaction between screw dislocation and nanoparticle of “pseudo” oxide, by using simple Johnson potential. Various dislocation–obstacle interactions are investigated for 2 nm oxides of coherent bcc, incoherent hcp and “hollow” without oxide, on each slip planes of {\\bar{1}10} and {\\bar{1}\\bar{1}2}, respectively. Although it is not a feature of oxide, we have found “Saturn ring” defects around the incoherent oxide and hollow on the {\\bar{1}\\bar{1}2} slip plane, and revealed the mechanism; that is, screw dislocation should leave vacancies to shorten or elongate its length between the incoherent interfaces or surface of hollows. Screw dislocation on the {\\bar{1}10} slip plane doesn’t form such ring due to the cross-slip; however, it forms “entanglement” around the incoherent oxide. On the other hand, the screw dislocation never “splits” against the coherent precipitates so that it leaves little defect around the coherent oxide.
  • Damping Properties of Homogenized and Cold-Rolled Mg–14.3Li–0.8Zn β-Phase Magnesium Alloy

    pp. 407-411

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    DOI:10.2320/matertrans.M2011174

    As-homogenized β-phase Mg–14.3Li–0.8Zn (LZ141) alloy exhibits a P1 peak and a conspicuous high-temperature damping background (HTDB) in the heating internal friction Q−1 curves. Cold-rolled LZ141 alloy with 80% thickness reduction exhibits a significant P2 peak in the Q−1 curves due to the recrystallization process during heating. The activation energy (H) of the HTDB for as-homogenized LZ141 alloy is 1.44 eV, decreasing to 0.91 eV after 80% cold-rolling. These H values for β-phase LZ141 alloy are lower than those for α-phase AZ80 alloy. Cold-rolled LZ141 alloy exhibits extremely high damping capacity at temperatures around the P2 peak.
  • Atmospheric Corrosivity Estimation at Electrical Control Unit Room by Multichannel Quartz Crystal Microbalance Corrosion Sensors

    pp. 412-416

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    DOI:10.2320/matertrans.M2011238

    In order to evaluate the atmospheric corrosivity in an electrical control unit room in a steelmaking plant by using quartz crystal microbalance (QCM) sensors, the temperature, relative humidity and corrosion rates of metals on QCM were monitored for five months. The metals employed for sensing corrosive gases were silver, copper and cobalt. The concentrations of the corrosive gases were estimated from the data of corrosion rates for these metals considering relative humidity. The temperature, relative humidity, and the corrosion rates in a given day were distributed according to the normal probability law. The concentrations of H2S, SO2 and NO2 were estimated from the mean values of the relative humidity and the corrosion rates of silver, copper and cobalt, which derived from the normal probability plots. The concentrations thus obtained were roughly close to those analyzed by conventional analytical methods. The atmospheric corrosivity will be able to estimate based on the monitoring of the corrosion rate with multichannel QCM sensors.
  • Detectability of Holes in SiC Particulate-Reinforced Al–Si Alloy Composite by Means of Ultrasonic Measurement

    pp. 417-424

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    DOI:10.2320/matertrans.M2011190

    For the development of nondestructive detection method of casting defects in SiC particulate-reinforced Al–Si alloy composite (the MMC castings), plates of the alloy composite and the Al–Si alloy were cast, and holes of different diameters were introduced at different depths. Then the ultrasonic measurement was carried out in water with the longitudinal waves of 5 and 10 MHz in frequency by the normal incidence, and also with the surface acoustic wave (SAW) of 5 MHz in frequency. The hole of 2 and 1 mm in diameter or larger was detected at a depth of 2 to 10 mm below the surface of the MMC castings and the Al–Si alloy castings, respectively, by the normal incidence. And the hole of 2 mm in diameter or larger was detected at a depth less than 1 mm below the surface of the MMC castings by the SAW measurement. The reflection intensity from the hole in the MMC castings took a far lower value than the DGS curve. The DGS curve was modified in consideration of scattering of the ultrasonic wave by cast structures and casting defects, and took a similar tendency with the reflection intensity form the hole. Then, plates of MMC castings were subjected to X-ray radiography and ultrasonic measurement, and the depth of pores and shrinkage cavities of more than 2 mm in size were estimated by the ultrasonic measurement successfully.
  • Preparation of Ultra-High Purity Cylindrical Mo Ingot by Electron Beam Drip Melting

    pp. 425-427

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    DOI:10.2320/matertrans.M2011319

    A cylindrical Mo ingot with ultra-high purity was obtained by electron beam (EB) drip melting process using a Mo rod. The Mo rod as a bar feeder was prepared from Mo powder by vacuum sintering and swaging processing. Most of impurities excluding W in the Mo ingot were removed down to below ppm level by three-times EB drip melting, where the purity of the Mo ingot except W was improved from the initial Mo powder purity of 3N (99.95%) to 5Nup (99.9998%). Furthermore, the gaseous impurities C, N and O in the Mo ingot were removed to a level below 5 ppm from the initial level of around 460 ppm by repetitive EB drip melting.
  • Fabrication and Mechanical Properties of Al-Based In Situ Nano-Composites Reinforced by Al2O3 and Intermetallic Compounds

    pp. 428-434

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    DOI:10.2320/matertrans.L-M2011847

    The Al-based ex situ and in situ composites are fabricated by totally same staring materials. No pore was observed on their cross sections. The fabricated Al-based ex situ and in situ composites are reactive hot pressed with continuously applied pressure of 60 MPa at 620 and 700°C for 5 min respectively. The reactive hot pressed ex situ composites contain homogeneously distributed metal oxides such as ZrO2, Ta2O5, Nb2O5, WO3 and MoO3 with nano or submicron sizes. On the other hands, the reactive hot pressed in situ composites contain homogeneously distributed θ-Al2O3 and intermetallic compounds such as Al3Zr, Al3Ta, Al3Nb, Al5W, Al12W and Al12Mo. It was found that the ex situ composites have a limited range of the mechanical properties such as Young’s modulus and hardness even they contain homogeneously distributed metal oxide particulates with nano or submicron sizes. However, the reactive hot pressed in situ composites present relatively various range of the mechanical properties. It was experimentally confirmed that the in situ composites fabricated by the reactive hot pressing technique is useful for fabricating a high performance structural materials.
  • Mass Gain of Carbon Fiber Reinforced Polyimide (CFRP) by Dipping in Hot Distilled Water

    pp. 435-439

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    DOI:10.2320/matertrans.M2011215

    Influence of isothermal dipping in hot distilled water for 200 ks on the mass gain of carbon fiber reinforced polyimide (CFRP) was investigated. Dipping in distilled water raised the mass gain. Based on the kinetics equation, both reaction index (n) and kinetic constant (k) were obtained. Since the n value is approximately 0.6 from 333 to 373 K, the reaction mode was independent on the absorption temperature. Based on the results and discussion, the water absorption was probably the directional mass transport through the fiber/polyimide cylindrical interface. On the other hand, Arrhenius linear relationship between logarithmic k (log k) and reciprocal dipping temperature (1/T) was obtained. The apparent activation energy estimated by the slope of water absorption in the CFRP was approximately equal to the activation energy of self-diffusion coefficient of water molecule. Mass gain of CFRP (CF/PI) dipped in distilled water for 100 ks at 373 K probably enhanced the molecules’ density induced by water molecules’ intrusion among polyimide polymers, resulting in enhancement of (dσ/dε)max and fracture stress. On the other hand, the mass gain by dipping for 200 ks at 373 K enriched the water concentration in polyimide matrix. Thus, it was assumed to enhance the intermolecular distance of polyimide polymers and then to reduce the intermolecular force among polyimide polymers, resulting in a drop of (dσ/dε)max of CFRP dipped for 200 ks. On the other hand, the dipping for 200 ks probably raised the intermolecular force between water molecules and polyimide polymers, resulting in remarkable enhancements of the fracture strain, fracture energy and impact value of the CFRP.
  • Discharge Characteristics of Plasma Display Panels with SrCaO Protective Layer Manufactured Using “All-in-Vacuum” Process

    pp. 440-445

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    DOI:10.2320/matertrans.M2011181

    Plasma display panels (PDPs) with a SrCaO protective layer of high secondary electron emission coefficient were manufactured using the “all-in-vacuum” process, whereby the protective layer deposition and panel sealing were performed continuously in high vacuum in order to keep the surface of the protective layer as clean as possible. The PDP with the SrCaO protective layer manufactured using the “all-in-vacuum” process (“all-in-vacuum” SrCaO-PDP) for Ne–20 vol% Xe exhibited a luminance 2.1 times larger, a luminous efficacy 1.7 times larger, and the same discharge time lag, compared with the PDP with the MgO protective layer manufactured using the conventional process (conventional MgO-PDP) for Ne–4 vol% Xe, which had almost the same discharge voltage.
  • Effects of γ′ Precipitation on the Structure and Properties of 713LC Superalloy via HIP Treatment

    pp. 446-452

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    DOI:10.2320/matertrans.M2011287

    This study aimed to examine the TEM observation of γ′ precipitate morphology on 713LC superalloy via HIP treatment, and evaluate the effects of HIP treatment on the 713LC alloy. The experimental results showed that an obvious distribution of γ′ precipitations appeared in the γ matrix for 713LC superalloy after HIP treatment. It also demonstrated that the grain sizes are uniform and the porosity of the structure is improved. The strengthening mechanism of the γ′ phase was Ni3Al precipitates, and it increased the strengthened phase and mechanical properties of 713LC superalloy. Meanwhile, the porosity decreased to 60.3%, hardness increased to 40.5 HRC, and density enhanced to 7.92 × 103 kg/m3. Thus, this study confirmed that tensile strength and elongation of 713LC superalloy can be increased through HIP treatment.
  • Reliability Enhancement of Thick Al–Cu Wire Bonds in IGBT Modules Using Al2Cu Precipitates

    pp. 453-456

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    DOI:10.2320/matertrans.M2011277

    The reliability enhancement of Al wire bonds used in the insulated gate bipolar transistor (IGBT) modules is crucial to raise their reliability at the high operating temperatures of the motor vehicles in which the modules are widely used because cracking can occur in the Al. We investigated the bonding reliability of thick Al–0.5 mass% Cu wires, inside of which very fine Al2Cu phases precipitated in both grain boundaries and the Al matrix. We found the reliability of the aged Al–Cu wire bonds was much better than the reliabilities for Al–Cu wire bonds without aging and conventional Al–Ni wire bonds for temperature change ΔT of 50 K. We also found from thermal cycle test results that Al2Cu precipitates prevented crack propagation due to thermal expansion mismatch between Al wires and Si substrate.
  • Editor’s Announcement

    pp. 458-458

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    DOI:10.2320/matertrans.EAM2011603

  • Editor’s Announcement

    pp. 457a-457a

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    DOI:10.2320/matertrans.EAM2011601

  • Editor’s Announcement

    pp. 457b-457b

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    DOI:10.2320/matertrans.EAM2011602

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