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

MATERIALS TRANSACTIONS Vol. 49 (2008), No. 7

  • Microstructures and Fusing Electrical Current of Microelectronic Sn-9Zn-(0.25RE) Solders

    Fei-Yi Hung, Truan-Sheng Lui, Li-Hui Chen, Kung-An Lan

    pp. 1491-1495

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    DOI:10.2320/matertrans.MF200801

    Abstract

    Both Sn-9Zn and Sn-9Zn-0.25RE solders were used to investigate the effect of RE (rare earth elements) addition on their solidification structures and electrical current properties. The results indicate that adding RE not only made the needle-like Zn-rich phases finer, but also caused the Sn-Zn eutectic phases to decrease. RE elements existed mostly in the β-Sn phases and could not form intermetallic compounds. After direct current (DC) testing and electrical conductivity (%IACS) testing, the fusing electrical direct current density of the 0.25RE solder was higher than the Sn-9Zn solder, however, the electrical conductivity had an inverse tendency. Also, the RE element addition restrained electromigration and enhanced diffusion to occur easily in the Sn-9Zn solder.

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  • Influence of Ga addition on Microstructure, Tensile Properties and Surface Oxide Film Characteristics of Microelectronic Sn-9Zn-xGa Solders

    Fei-Yi Hung, Truan-Sheng Lui, Li-Hui Chen, Ping-Hui Chen

    pp. 1496-1502

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    DOI:10.2320/matertrans.MF200802

    Abstract

    The tensile properties of Sn-9Zn-xGa (x=0, 0.4, 0.6, 0.8 mass%) solders at room temperature and 120°C were first explored, and the specimens were then used to investigate the surface thin film characteristics. The results indicate that increasing the Ga content not only promoted needle-like Zn-rich phases to grow, but also caused the tensile strength and hardness to increase. In addition, the Ga was mostly solid solution in both β-Sn phases and bar-like Zn-rich phases. For high temperature tensile testing, the strength of the Sn-9Zn-xGa specimens was higher than the Sn-9Zn specimen. On the surface thin film, the effect of Ga solid solution not only promoted anti oxidation, but also suppressed the growth of the oxidative thin film of the Sn-9Zn solder under reflow or aging.

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  • Estimation of the Thermal Fatigue Resistance and Creep Properties of the Co/Ni-Bearing SAC305 Lead-Free Solders by the Strain Rate Change Tensile Test

    Fangjie Cheng, Hiroshi Nishikawa, Tadashi Takemoto

    pp. 1503-1507

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    DOI:10.2320/matertrans.MF200803

    Abstract

    In the present paper, in order to evaluate the creep properties of Co/Ni-bearing SAC305 lead-free alloys, the strain rate change tensile (SRCT) test was conducted. Two parameters, m0 and k, obtained from the SRCT test could be applied to estimate the thermal fatigue resistance and the creep properties for lead-free solder alloys. The m0 value implied the material’s creep resistance, and the k value revealed the stability of the creep resistance during the whole tensile test process. The Co/Ni-bearing SAC305 solder alloys showed much lower m0 and k values than the conventional Sn37Pb solders which indicated that the Co/Ni-bearing SAC305 solder alloys possessed of excellent thermal fatigue resistance and higher creep resistance. For the lead free solder alloys, high temperature aging led to microstructural coarsening. After aging, the m0 value increased meanwhile the k value decreased for the Co/Ni-bearing SAC305 solders. Furthermore, the two parameters showed a converse change tendency between the conventional Sn37Pb and Co/Ni-bearing SAC305 solders after high temperature aging, which implied that they have different creep mechanism. It can be deduced that, for the conventional Sn37Pb solder, the grain boundary slide is the dominant creep mechanism, whereas the Co/Ni-bearing SAC305 solders showed a dislocation glide/climb creep mode.

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  • Effect of Surface Contamination on Solid-State Bondability of Sn-Ag-Cu Bumps in Ambient Air

    Ying-Hui Wang, Tadatomo Suga

    pp. 1508-1512

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    DOI:10.2320/matertrans.MF200804

    Abstract

    Two solid-state bonding methods, thermocompression bonding (TCB) and surface activated bonding (SAB), were used for studying the effect of surface contamination on the bonding of Sn-Ag-Cu bumps in ambient air. The surface contamination was analyzed by X-ray photoelectron spectroscopy. Correlated to the surface contamination, the influence of Ar-plasma pretreatment time as well as the air exposure time on the shear strength was investigated in SAB process. The bonding of Sn-Ag-Cu bumps was achieved at 25–200°C benefiting from dispersing the surface contamination. With an Ar-plasma activation process prior to the assembly under a low-vacuum background, the carbon contaminants on the bump surfaces in SAB process was removed, and the required bonding pressure or temperature to achieve a high shear strength and bond yield is lower than that in TCB process.

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  • Impact Properties of Lead-Free Sn-Ag-Cu-Ni-Ge Solder Joint with Cu Electrode

    Ikuo Shohji, Hirohiko Watanabe, Takeshi Okashita, Tsutomu Osawa

    pp. 1513-1517

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    DOI:10.2320/matertrans.MF200808

    Abstract

    The impact properties of solder ball joints with Sn-Ag-Cu-Ni-Ge lead-free solders and Cu electrodes were investigated in the aged conditions at 393 K. The impact properties evaluated was compared with Sn-Ag and Sn-Ag-Cu solder joints. The impact properties of Sn-Ag-Cu-Ni-Ge joints were superior to those of Sn-Ag and Sn-Ag-Cu joints. In the cases of Sn-Ag and Sn-Ag-Cu joints, fracture mainly occurred in the intermetallic compounds (IMC) layer formed in the joint interface regardless of aging treatment. On the contrary, main fracture mode was solder fracture in as-reflow Sn-Ag-Cu-Ni-Ge joints. Although the main fracture mode gradually changed from solder fracture to IMC fracture upon aging, Sn-Ag-Cu-Ni-Ge joints had excellent impact reliability compared with Sn-Ag and Sn-Ag-Cu joints even after aging at 393 K for 1000 h.

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  • Effect of Ni or Co Addition to Sn-Ag Solder on Microstructure and Joint Strength at Interface

    Hiroshi Nishikawa, Akira Komatsu, Tadashi Takemoto

    pp. 1518-1523

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    DOI:10.2320/matertrans.MF200851

    Abstract

    Among various lead-free alloys, Sn-Ag(-Cu) system solders are considered the most promising lead-free solders for both wave and reflow soldering technology. Moreover, to improve the characteristics of lead-free solders, the effect of the addition of minor elements to lead-free solders on the properties of solder and interfacial reactions have been studied. The purpose of this research was to investigate the addition of Ni or Co to the Sn-Ag solder on the microstructure and the joint strength of the interface with metallization layer of the substrate. As a metallization layer of the substrate, bare Cu and electroless Ni-P plating were used. For the reflow process, test samples were heated in a radiation furnace at 523 K for 60 s, and for the aging process, some samples were heat-treated in an oil bath at 423 K for 168 h, 504 h and 1008 h. Results show the addition of Ni or Co was effective for the IMC formation and growth at the interface with a Cu pad during reflow and aging process, and the addition of Co, except Ni, affected the pull strength of the solder joint with electroless Ni-P plating during aging process.

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  • Effect of Hold Time on Low Cycle Fatigue Life of Micro Solder Joint

    Yoshihiko Kanda, Yoshiharu Kariya, Yusuke Mochizuki

    pp. 1524-1530

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    DOI:10.2320/matertrans.MF200852

    Abstract

    Effect of holding time and temperature on the fatigue life of micro Sn-Ag-Cu solder joint has been studied with waveform of triangle and trapezoid wave at 298 K and 398 K. Both the microstructural coarsening and the crack propagation occurred simultaneously and therefore the cyclic load decreased rapidly in the trapezoidal wave at 398 K compared with the other conditions. Therefore, under the condition of waveform that includes holding time at high temperature, it is necessary to define fatigue life by considering crack length, although the load drop life definition is typically employed for the low cycle fatigue evaluation. The fatigue life of Sn-Ag-Cu micro solder joints is not strongly affected by temperature and holding time when the crack length is considered to define fatigue life. This is different form the trends in large scale bulk specimen and is attributed to the peculiar microstructure of the Sn-Ag-Cu.

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  • Characteristics of Zn-Al-Cu Alloys for High Temperature Solder Application

    Seong-Jun Kim, Keun-Soo Kim, Sun-Sik Kim, Chung-Yun Kang, Katsuaki Suganuma

    pp. 1531-1536

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    DOI:10.2320/matertrans.MF200809

    Abstract

    Melting range, microstructure, mechanical properties and spreadabililty of Zn-(4∼6 mass%)Al-(1∼6 mass%)Cu alloys were investigated. Liquidus temperature was targeted between 655 and 675 K, and solidus temperature was targeted to 645 K. The liquidus temperature of the Zn-Al-Cu solders increased with Cu contents, but it decreased with Al contents. Microstructures of the Zn-Al-Cu solders consisted of primary ε-phase (CuZn4), η-phase (Zn matrix), α-η eutectic phase (Zn-Al eutectic) and ε-η eutectic phase (Zn-Cu eutectic), irrespective of the Al and Cu contents. Increasing the Al and Cu contents, hardness and tensile strength increased, but elongation decreased. The Al content played an important role in improving the spread ratio, the Cu content had no significant influence on the spread ratio.

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  • Interfacial Bonding Mechanism Using Silver Metallo-Organic Nanoparticles to Bulk Metals and Observation of Sintering Behavior

    Yusuke Akada, Hiroaki Tatsumi, Takuto Yamaguchi, Akio Hirose, Toshiaki Morita, Eiichi Ide

    pp. 1537-1545

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    DOI:10.2320/matertrans.MF200805

    Abstract

    We have proposed a novel bonding process using silver nanoparticles, which can be alternative to lead-rich high melting point solders. The bonding mechanism of silver metallo-organic nanoparticles to bulk materials (gold and copper) is discussed based on the observations of the bonded interface using Transmission Electron Microscope (TEM). At the interface of sintered silver and bulk gold, the crystal orientation of silver corresponded to that of gold. It is thought that the epitaxial layer of silver formed through silver nanoparticles being oriented in the direction of the gold crystal. At the interface of sintered silver and bulk copper, no epitaxial layer of silver on the copper crystal formed. Though the appearance of the crystal structure of silver/copper interface is different from that of the silver/gold interface, copper as well as gold are coherent with silver, and have been successfully bonded using the silver nanoparticles.

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  • Surface Sink Effects on Void Formation in GaSb and InSb under Ion Irradiation

    Noriko Nitta, Yukari Ohoka, Koichi Sato, Qiu Xu, Yoshihiko Hayashi, Toshimasa Yoshiie, Masafumi Taniwaki

    pp. 1546-1549

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    DOI:10.2320/matertrans.MBW200729

    Abstract

    Cellular defect structure forms on GaSb, InSb and Ge surfaces irradiated with energetic ions. These structures are generated after void formation via the movement of point defects induced by ion irradiation. In this transmission electron microscopic study, void formation by thin foil irradiation (irradiation after polishing for transmission electron microscopy (TEM)) was compared with void formation by bulk irradiation (cross-sectioning after ion irradiation), in order to investigate the effect of surface sinks for the point defects. The voids formed in GaSb and InSb by thin foil irradiation with 60 keV Sn+ at a temperature of 100–150 K were smaller than those formed by bulk irradiation. The diameters and densities of the voids increased rapidly as the ion dose increased from 1×1014 to 2×1014 ions/cm2 under both types of irradiation. Amorphous halos were observed in the selected area diffraction patterns (SAED) of the thin foil irradiation specimens in addition to the main spots of the zincblende structure at a dose of 1×1014 ions/cm2. This finding contrasts with the polycrystalline ring patterns observed in the SAED of the bulk specimen under the same dose. It was concluded that the easy escape of interstitials to the surface assists both void formation and amorphization in thin foil irradiation.

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  • Interdiffusion in Pt-Containing γ-Ni and γ′-Ni3Al Alloys at 1150°C

    Shigenari Hayashi, Daniel J. Sordelet, Larry R. Walker, Brian Gleeson

    pp. 1550-1557

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    DOI:10.2320/matertrans.MRA2008001

    Abstract

    Ternary interdiffusion coefficients in the γ-Ni and γ′-Ni3Al phases of the Ni-Al-Pt system at 1150°C were experimentally determined by applying a Boltzmann-Matano method at a common composition in the time-invariant diffusion paths for a given two couples. The variation of the main-term interdiffusion coefficients of Al, \\ ildeDAlAlNi, with increasing of Pt content was different for the γ and γ′ phases. In γ \\ ildeDAlAlNi generally increased with increasing Pt content, but it decreased with increase in Pt in γ′ phase. By contrast, the main-term coefficients for Pt, \\ ildeDPtPtNi, apparently increased monotonically with increasing Pt content in both phases, but there was little dependency on Al content. The cross-term interdiffusion coefficients, \\ ildeDAlPtNi and \\ ildeDPtAlNi, were negative in both γ and γ′, showing that the chemical interaction between Al and Pt in these phases is negative. \\ ildeDAlPtNi values were larger than those of \\ ildeDPtAlNi; however, there was no clear dependence of \\ ildeDAlPtNi and \\ ildeDPtAlNi on Pt and Al contents within the composition ranges studied. The cross-term interdiffusion coefficients were comparable to the main-term coefficients in γ and within an order of magnitude of each other in γ′. The significance of these findings are discussed and quantitatively assessed.

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  • Effect of Ni Addition on the Glass Forming Ability and Mechanical Properties in Cu60Zr22Ti18 Metallic Glass Alloy

    Dong-Myoung Lee, Seung-Yong Shin, Ju-Hyun Sun, Jin-Kyu Lee, Chi-Hwan Lee

    pp. 1558-1562

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    DOI:10.2320/matertrans.MRA2008041

    Abstract

    This paper investigates the effects of Ni addition on the glass forming ability (GFA) and mechanical properties in Cu60−xNixZr22Ti18 (x=0∼15) metallic glass alloys. Partial substitution of Cu by Ni in the alloys improved the GFA. By increasing Ni content x from 0 to 6, the supercooled liquid region (ΔTx) and crystallization temperature (Tx) were increased, whereas the liquidus temperature decreased to reach the lowest value at x=6. The lowering of liquidus temperature improved the GFA, and the maximum GFA of 6 mm in diameter was obtained at x=6. The compressive strength and micro hardness of the alloys were raised by increasing Ni content, and the Ni containing alloy showed some macroscopic plasticity after yielding.

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  • Kinetic Analysis of the Gasification of Diamond

    Yoshiaki Kashiwaya, Maki Iwasa, Kuniyoshi Ishii

    pp. 1563-1571

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    DOI:10.2320/matertrans.MRA2008069

    Abstract

    Diamond is the ultimate state of carbon crystal. However, a transformation from diamond to graphite during gasification occurs under oxidizing atmosphere. The gasification behaviors of diamond vary with the reaction gas composition and temperature.
    There has been no kinetic study on the diamond gasification. Most of the interest in this area has been related to diamond growth.
    The change of morphology of diamond surface and the crystallographic orientation between the diamond and the graphite formed was presented in a previous study.
    In this study, the gasification of natural diamond was investigated using TG-DTA. Kinetic analysis was performed on the basis of Langmuir-Hinshelwood type equation, in which some rate constant was modified from the previous study for coke gasification. SEM observations of the diamond surface were carried out in order to clarify the change in surface morphology. Moreover, the simultaneous gasification of diamond and graphite was carried out in order to clarify the difference in reactivity between ordinary graphite and graphite formed on the diamond during gasification.

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  • Preparation of TiC-Ti3SiC2 Composites by Mechanical Alloying and Hot-Pressing

    Hitoshi Hashimoto, Zheng Ming Sun

    pp. 1572-1578

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    DOI:10.2320/matertrans.MRA2008013

    Abstract

    TiC-Ti3SiC2 composites having the microstructure of fine Ti3SiC2 grains dispersed in TiC matrix were synthesized by two processes, that is, mechanical alloying of a powder blend of Ti, Si and C followed by hot-pressing (MA-HP process) and hot-pressing of a powder blend of Ti, Si and TiC (MIX-HP process). The microstructure, damage tolerance and 4-point flexural strength of the composites were investigated. It was found that more uniform dispersion of Ti3SiC2 grains in TiC matrix was achieved by MA-HP process than by MIX-HP process, while the flexural strength of the composites synthesized by MA-HP process was lower than that by MIX-HP process, which may be attributed to micropores formed in the composites synthesized by MA-HP process. Preferential orientation of Ti3SiC2(001) and TiC(111) occurred in the composites synthesized by MA-HP process. We proposed two mechanisms of the preferential orientation. We also found that the dispersion of Ti3SiC2 in TiC matrix is effective in improving the damage tolerance of the brittle TiC, evidenced by the fact that no cracks emanated from the corners of Vickers indentations at a load of 9.8 N.

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  • In Situ Observation of Diamond Gasification and the Crystallographic Relationship of Graphite Formed on the Surface of Diamond

    Yoshiaki Kashiwaya, Maki Iwasa, Kuniyoshi Ishii

    pp. 1579-1588

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    DOI:10.2320/matertrans.MRA2008068

    Abstract

    Recently, a property of diamond as a semiconductor is focused on by many researchers. For the mass production, it is important to develop the manufacturing process. As it is thought that the ionic milling process has limitations, the application of gasification reactions with oxidizing gases such as CO2, H2O and O2 is the best option.
    In this study, reaction behaviors of diamond at temperatures of more than 1273 K were investigated under a wide range of oxygen potentials, and the crystallographic relationship from diamond to graphite was clarified.
    A graphite layer was formed on the surface of diamond under both Ar gas with an oxygen potential of less than 100 ppm, and a CO2-Ar mixture (30 vol%). The Raman spectrum consisted of the amorphous carbon and graphite. However, the graphite formed differed from ordinary graphite in the reactivity. Furthermore, the crystallographic relationship between diamond and graphite was determined to be (111)D||(002)G.

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  • Grain Boundary Precipitation in Fe-30Mn-9Al-5Cr-0.7C Alloy

    Yi Hsuan Tuan, Chih Lung Lin, Chuen Guang Chao, Tzeng Feng Liu

    pp. 1589-1593

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    DOI:10.2320/matertrans.MRA2008060

    Abstract

    The as-quenched microstructure of the Fe-30%Mn-9%Al-5%Cr-0.7%C (in mass%) alloy was single-phase austenite. When the as-quenched alloy was aged at 550°C–750°C, fine (Fe,Mn)3AlC carbides were formed within the austenite matrix. In addition, as the aging temperature increased, a M7C3 carbide + D03→M7C3 carbide + B2→M7C3 carbide + α (ferrite) phase transition had occurred on the grain boundaries. This grain boundary precipitation behavior has never before been observed in FeMnAlC and FeMnAlCrC alloy systems.

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  • Effect of Milling on the Carbothermal Reduction of Oxide Mixture for (Ti,W)C-Ni

    Hanjung Kwon, Shinhoo Kang

    pp. 1594-1599

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    DOI:10.2320/matertrans.MRA2007267

    Abstract

    The effect of high-energy milling on the phase transformation and carbothermal reduction was examined using an oxide mixture, TiO2-WO3-NiO-C, with a process to synthesize (Ti,W)C cermets. Due to the high energy involved in the mill raw, anatase TiO2 transformed first to TiO2-II and then to rutile, while WO3 transformed to a high-pressure WO3-HP and hexagonal WO3 phase. The co-existence of WO3 and TiO2 enhanced the formation of a nano-crystalline or amorphous phase. The (Ti,W)C phase was formed mainly at 1150°C from TiC and WC formed in the early stages. These results were further examined using XRD, the Rietveld method and mass spectroscopy.

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    3. Change in Mechanical Properties and Microstructure of ARB Processed Ti during Annealing MATERIALS TRANSACTIONS Vol.49(2008), No.1

  • Plasma Electrolytic Oxidation of AZ91 Mg Alloy in the Sodium Stannate Electrolyte

    Duck Y. Hwang, Jin Y. Cho, Dong H. Lee, Bong Y. Yoo, Dong H. Shin

    pp. 1600-1605

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    DOI:10.2320/matertrans.MC200797

    Abstract

    The effect of sodium stannate on Plasma electrolyte oxidation (PEO) process of AZ91 Mg alloy was systematically investigated. The oxide layer formed on an AZ91 Mg alloy created using an electrolyte containing sodium stannate formed a much thicker layer consisting of: MgO, SnO, Mg2SiO4, and MgF2. The result of EDS analysis shows a tin enriched zone at the oxide layer/substrate interface. Corrosion resistance of the sample coated from the electrolyte containing sodium stannate was determined to be superior to that of the sample coated from the electrolyte without sodium stannate. As a result of salt spray test for 120 hrs, severe filiform corrosion is observed on the thin oxide layer of AZ91 Mg alloy without sodium stannate. However, the sample of the electrolyte containing sodium stannate shows localized pitting corrosion. Tin ions in the electrolyte influence on the growth rate of the oxide layer, especially resulting in a formation of dense barrier layer. The co-existence of dense MgO and SnO in the oxide layer could improve the corrosion resistance of the AZ91 Mg alloy.

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  • Water Drop Erosion on Turbine Blades: Numerical Framework and Applications

    Qulan Zhou, Na Li, Xi Chen, Akio Yonezu, Tongmo Xu, Shien Hui, Di Zhang

    pp. 1606-1615

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    DOI:10.2320/matertrans.MRA2008025

    Abstract

    When small droplets are formed in the wet steam stage of a steam turbine, they may impact the blade surface at a high velocity and repetitive impacts cause water drop erosion, which emerges as one of the primary reliability concerns of the turbine. We propose an effective numerical framework that couples fluid mechanics with solid mechanics. The movements of water drops in a blade channel are analyzed based on the solution of the flow field of water steam in turbine, and impact statistics such as impact frequency, velocity, and position are obtained as the working condition and particle size are varied. A nonlinear wave model is established for high velocity liquid-solid impact, from which the characteristic impact pressure in liquid and peak impact stress in solid are obtained; the solutions are then superimposed with the pathways of water particles, and a fatigue analysis is carried out to elucidate the mechanisms of water drop erosion. The lifetime map on a blade surface with two different materials (1Cr13 and Ti-6Al-4V) under typical working conditions are obtained, in terms of operation hours, and the most dangerous water drop erosion regions and operating conditions of the steam turbine are deduced.

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    3. Change in Mechanical Properties and Microstructure of ARB Processed Ti during Annealing MATERIALS TRANSACTIONS Vol.49(2008), No.1

  • Reactive Infiltration of TiN Powder Preform with Molten Aluminum for the Fabrication of Nitride Ceramics Composite

    Yoshihiro Kobayashi, Makoto Kobashi, Naoyuki Kanetake

    pp. 1616-1620

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    DOI:10.2320/matertrans.L-MRA2008812

    Abstract

    Reactive infiltration of a blended powder preform containing TiN with molten aluminum was attempted at temperatures ranging from 1173 K to 1673 K in order to fabricate nitride ceramics composite. Titanium powder as an infiltration aid was mixed with TiN powder (particle sizes: 53 μm and 1.0∼1.5 μm) by various blending ratios. Spontaneous infiltration of the blended powder with molten aluminum occurred on condition that processing temperature and titanium content in the blended powder were high enough. Spontaneous infiltration took place when processing temperature was 1673 K (TiN: 53 μm) or processing temperature was over 1173 K (TiN: 1.0∼1.5 μm). It was confirmed that Al3Ti and TiN were the main constituents after the infiltration was completed. SiC whisker was added in the blended perform powder (TiN: 1.0∼1.5 μm, Ti: <45 μm) by various blending ratios (4∼30 vol%). The results showed that SiC whiskers were successfully dispersed by up to 10 vol% in the Al3Ti/TiN ceramics composite.

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  • Influence of Casting Defects on Tensile Properties of ADC12 Aluminum Alloy Die-Castings

    A. K. M. Aziz Ahamed, Hiroshi Kato

    pp. 1621-1628

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    DOI:10.2320/matertrans.F-MRA2008814

    Abstract

    Cold flakes, one of casting defects, were observed through acoustic microscopy in aluminum alloy die-cast plates (ADC12), and specimens having a cold flake of different sizes were prepared and subjected to the tensile testing. The tensile strength linearly decreased with the size of the cold flake, and the decreasing rate of the strength was greater for the specimen with the exposed cold flake than that with the embedded cold flake. The in-process ultrasonic measurement was carried out during tensile testing, and it was found that the oxide layer of the cold flake was detached from the matrix to form a crack before final failure. Then by using the linear fracture mechanics, the critical value Kc* at failure was evaluated to be 8–10 MPa·m1⁄2 from the tensile strength, which value was slightly lower than the fracture toughness of the matrix of 11–14 MPa·m1⁄2.

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    3. Change in Mechanical Properties and Microstructure of ARB Processed Ti during Annealing MATERIALS TRANSACTIONS Vol.49(2008), No.1

  • Microstructure and Mechanical Properties of Resistance Spot Welded Advanced High Strength Steels

    M. I. Khan, M. L. Kuntz, E. Biro, Y. Zhou

    pp. 1629-1637

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    DOI:10.2320/matertrans.MRA2008031

    Abstract

    Integration of advanced high strength steels (AHSS) into the automotive architecture has brought renewed challenges for achieving acceptable welds. Resistance spot welding (RSW) is the primary method used in welding automotive structures, which has resulted in a demand to better understand RSW of AHSS. The varying alloy contents and processing techniques used in their production has further complicated this initiative. The current study examines resistance spot welding of AHSS including 590R, DP600, DP780 and TRIP780. HSLA material is also included to represent conventional high strength steels and benchmark AHSS performance. The mechanical properties and microstructure of these resistance welded steel alloys are detailed. Furthermore, a relationship between chemistries and fusion zone hardness is produced.

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    3. Change in Mechanical Properties and Microstructure of ARB Processed Ti during Annealing MATERIALS TRANSACTIONS Vol.49(2008), No.1

  • Surface Coating on Aluminum Flakes with Titanium Nitride Layer by Barrel-Sputtering Techniques

    Satoshi Akamaru, Yuji Honda, Akira Taguchi, Takayuki Abe

    pp. 1638-1643

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    DOI:10.2320/matertrans.MRA2008014

    Abstract

    Flake-shaped fine particles were modified with a thin TiN layer by a hexagonal-barrel-sputtering technique. To determine the optimum sputtering conditions, TiN films were deposited on a glass substrate by the reactive sputtering technique by varying the values of N2 percentage, total pressure, radio-frequency (RF) power, and substrate temperature. From the analysis of XRD patterns, it was determined that a N2 percentage of 25%, a total pressure of 1.2 Pa, a RF power of 200 W, and room temperature were suitable for the preparation of TiN films. Under these optimized conditions, Al flakes were modified with a TiN by the barrel-sputtering technique. The results of optical microscopy, X-ray diffraction measurements, scanning electron microscopy, and energy-dispersive X-ray spectroscopy measurements revealed that the surface of each Al flake was successfully coated uniformly with a TiN layer.

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  • Preparation of WC-SiC Whisker Composites by Hot Pressing and Their Mechanical Properties

    Shigeaki Sugiyama, Daiki Kudo, Hitoshi Taimatsu

    pp. 1644-1649

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    DOI:10.2320/matertrans.MRA2008019

    Abstract

    Composites of WC and SiC whisker (0–30 vol% SiC) were prepared at 1550 to 1800°C by using a resistance-heated hot pressing technique called spark plasma sintering. The composites obtained were examined for reaction products and microstructure, and were characterized for mechanical properties. The addition of small amounts of SiC induced the marked grain growth of WC, and drove the densification of WC. Above 10 vol% SiC, dispersed SiC phases impeded the grain growth of WC. Increasing sintering temperature made SiC whiskers thick and lowered the aspect ratio of whiskers. The hardness of composites decreased with increasing average grain size of WC. The Young’s modulus of dense composites was decreased with the SiC content. The addition of 3 to 5 vol % SiC greatly increased the fracture toughness of WC.

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  • Effects of Pre-Strain and Heat Treatment Temperature on Phase Transformation Temperature and Shape Recovery Stress of Ti-Ni-Nb Shape Memory Alloys for Pipe Joint Applications

    Kazunari Uchida, Naoto Shigenaka, Toshio Sakuma, Yuji Sutou, Kiyoshi Yamauchi

    pp. 1650-1655

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    DOI:10.2320/matertrans.MRA2007266

    Abstract

    Effects of pre-strain and heat treatment on shape recovery stress and phase transformation temperature in Ti-Ni-Nb shape memory alloys with various Nb content (6, 9, and 12 mol%) were investigated by tensile testing. The recovery stress of Ti-Ni-Nb alloys increased with increasing the pre-strain and then decreased after reaching the maximum recovery stress of around 450–500 MPa at about 9% pre-strain. Martensitic transformation temperatures (Ms, As, Af) also increased with increasing the applied pre-strain, while the relation between As and pre-strain did not depend on the Nb contents and Ni/Ti ratio. Moreover, the recovery stress in the Ti-Ni-Nb alloy heat treated at 673 and 773 K after solution treatment was slightly higher than that in the solution-treated alloy. These behaviors were examined relative to the increased defect density due to pre-straining and the elimination of defects by heat treatment.

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  • Effects of Cold Drawing and Annealing on Mechanical Properties and Microstructure of Co-Cr-Mo-Ni-Fe Alloys for Surgical Implants

    Yoshimitsu Okazaki

    pp. 1656-1660

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    DOI:10.2320/matertrans.MRA2007275

    Abstract

    The effects of cold drawing and annealing on the mechanical properties and microstructure of 0.06C and 0.12C-Co-Cr-Mo-Ni-Fe alloys were examined. The 0.2% proof strength (σ0.2%PS) and ultimate tensile strength (σUTS) of the cold-drawn 0.06C alloy increased proportionally as the reduction in area increased, whereas the total elongation (T. E.) decreased linearly. The 45% cold-drawn alloys showed the following σ0.2%PS, σUTS, T. E., and reduction of area (R. A.): for the 0.06C alloy 1174±125 MPa, 1549±23 MPa, 10±1%, and 36±5%; for the 0.12C alloy, 1223±57 MPa, 1623±23 MPa, 12±2%, and 44±4%, respectively. In the 45% cold-drawn 0.12C alloy, M6C carbide precipitates were observed in the dislocation network, which was caused by cold drawing. M6C carbide precipitates were also observed in the grain and grain boundary in the 0.06C and 0.12C alloys annealed from 950 to 1200°C. The matrix was the γ-phase; no ε- or σ-phase was observed. As annealing temperature increased, the σ0.2%PS and σUTS of the annealed alloys decreased gradually, while the T. E. increased linearly. Approximately 70% T. E. was obtained by annealing at 1100°C for the 0.06C alloy, and at 1200°C for the 0.12C alloys.

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  • Susceptibility to Hydrogen Absorption and Hydrogen Thermal Desorption of Titanium Alloys Immersed in Neutral Fluoride Solution under Applied Potential

    Ken’ichi Yokoyama, Katsutoshi Takashima, Jun’ichi Sakai

    pp. 1661-1666

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    DOI:10.2320/matertrans.MRA2008083

    Abstract

    The susceptibility to hydrogen absorption and hydrogen thermal desorption of titanium alloys has been investigated in a neutral 2.0% NaF solution at 37°C under various applied cathodic potentials. Ti-0.2Pd, Ti-6Al-4V and Ti-11.3Mo-6.6Zr-4.3Sn alloys absorb hydrogen under less noble potentials than −1.5 V, −1.9 V and −1.4 V versus a saturated calomel electrode, respectively. The amounts of absorbed hydrogen of Ti-0.2Pd, Ti-6Al-4V and Ti-11.3Mo-6.6Zr-4.3Sn alloys under an applied potential of −2.0 V for 24 h are approximately 1200, 100 and 1100 mass ppm, respectively. Upon immersion in the 2.0% NaF solution under an applied potential, the hydrogen thermal desorption behavior of Ti-0.2Pd alloy differs from those immersed in acid fluoride solutions, whereas the hydrogen thermal desorption behaviors of Ti-6Al-4V and Ti-11.3Mo-6.6Zr-4.3Sn alloys are similar to those immersed in acid fluoride solutions. The present results indicate that in a neutral fluoride solution, the effects of an applied potential on the hydrogen absorption and desorption behaviors of Ti-6Al-4V alloy are considerably smaller than those of commercial pure titanium reported previously, Ti-0.2Pd and Ti-11.3Mo-6.6Zr-4.3Sn alloys.

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  • Environmentally Assisted Cracking Behavior of Dissimilar Metal Weldments under High Temperature Water Conditions

    J. Y. Huang, M. C. Young, S. L. Jeng, J. J. Yeh, J. S. Huang, R. C. Kuo

    pp. 1667-1674

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    DOI:10.2320/matertrans.MRA2007336

    Abstract

    The environmentally assisted cracking behavior of Inconel Alloy 52-A508 weldment under simulated BWR coolant conditions was studied. Fatigue and corrosion fatigue crack growth rates of the dissimilar metal weldments were observed to increase with crack extension under the nominally constant ΔK loading mode. It can be accounted for by an increase in the tensile residual stress and a decrease in the crack closure effect with the weld depth. The tensile residual stress measured by hole-drilling strain gauges increased with the weld depth. After PWHT at 621°C for 24 h, the fatigue crack growth rate in the weld did not show to increase with crack length advancement. The crack closure effects in the weld were verified to decrease with the crack increment measured by the strain gauges in front of the crack tip.

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  • Design of Cascaded Oxide Thermoelectric Generator

    Lihua Zhang, Tsuyoshi Tosho, Noriyuki Okinaka, Tomohiro Akiyama

    pp. 1675-1680

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    DOI:10.2320/matertrans.MRA2008085

    Abstract

    This paper describes the design of two- and three-stage cascaded oxide thermoelectric generators (TEGs) for high-temperature heat recovery using reported data to optimize energy conversion efficiency. We used the general intermetallic compounds Bi2(Se,Te)3 and (Bi,Sb)2Te3 for the low-temperature stages and oxides of TiO1.1, La-doped SrTiO3, NaxCo2O4, and Al-doped ZnO for the higher-temperature stages. A two-stage TEG with TiO1.1 as the p-type material and La-doped SrTiO3 as the n-type material was found to have the highest efficiency at heat-source temperatures below 852 K, while the three-stage TEG was slightly more efficient than the two-stage TEG for heat-source temperatures above 852 K. For the three-stage TEG, the optimal boundary temperature of the second and third stages was calculated to be 698 K; at this temperature, the maximum energy conversion efficiency, 13.5%, was obtained at a heat-source temperature of 1223 K. The results showed that the designed two- and three-stage cascaded oxide TEGs have high potential for heat recovery from high-temperature waste.

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  • Froth Separation of Ferrihydrite Slurry Using Microbubbles with Ultrasonic Irradiation

    Etsuro Shibata, Shun Saito, Takashi Nakamura

    pp. 1681-1687

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    DOI:10.2320/matertrans.M-MER2008815

    Abstract

    Here we show the newly developed process of microbubble froth separation enhanced by ultrasonic irradiation for colloidal slurry. In this study, microbubbles were applied to the froth separation of dilute ferrihydrite colloidal suspension. Furthermore, enhancement of the microbubbles froth separation by controlling the motion, aggregation and clustering of microbubbles using the “Bjerknes force” in ultrasonic acoustic fields was investigated. The rate of microbubble froth separation of ferrihydrite colloidal slurry was increased by the ultrasonic irradiation and was more efficient than settling separation. Adjustment of the ultrasonic frequency is important for the microbubble froth separation. With a frequency of 38 kHz producing stronger primary and secondary Bjerknes forces, the motion and clustering of microbubbles are too extreme; the microbubbles abruptly aggregated to form clusters and rose rapidly without carrying the ferrihydrite colloidal particles. However, with ultrasonic irradiation at a frequency of 430 kHz, the motion of microbubbles was moderate and they aggregated widely. In this case, the clear froth separation of ferrihydrite colloidal slurry progressed rapidly, and its rate was increased with increasing output power of ultrasonic irradiation.

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  • High Temperature Properties of AZ91D Magnesium Alloy Composite Reinforced with Short Alumina Fiber and Mg2Si Particle

    Kazunori Asano, Hiroyuki Yoneda

    pp. 1688-1693

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    DOI:10.2320/matertrans.MER2008092

    Abstract

    Short alumina fiber- and in situ Mg2Si particle reinforced magnesium alloy composites were fabricated by squeeze casting. The in situ Mg2Si particles were formed during the infiltration with the melt into the preforms consisting of the fibers having Si particles attached to their surfaces. The microstructure of the composites and their tensile strength and Young’s modulus in the range from 293 K to 523 K were investigated. The effect of the Mg2Si particles on the tensile properties was examined by comparison with the properties of the fiber-reinforced composite without the Mg2Si particles. Fine Mg2Si particles with a grain size of approximately 5 μm were formed due to the rapid solidification in the permanent mold. The dispersion of the Mg2Si having a high Young’s modulus was found to be effective for improving Young’s modulus of the fiber-reinforced magnesium alloy composite. The experimental value of the composite was in good agreement with the calculated value based on a previously proposed model. The tensile strength of the composite with 18 vol% fibers and Mg2Si particles was higher than that of the conventional fiber-reinforced composite at both room temperature and high temperature. Examination of the fracture surfaces indicated that stress transmission between the fiber and the matrix became easy due to the particles, which reduced the fiber-to-fiber contact.

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  • Effects of Annealing Temperature on the Properties of Strontium Copper Oxide Prepared by Radio Frequency Reactive Magnetron Sputtering Method

    Jui-wen Liu, Shih-chin Lee, Chih-hao Yang

    pp. 1694-1697

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    DOI:10.2320/matertrans.MER2008099

    Abstract

    Electrical, structural and optical properties of annealed transparent strontium copper oxide (SCO) films were studied in this paper. These SCO films were first deposited by reactive radio frequency magnetron sputtering technique on glass substrates at room temperature with ultra highly pure oxygen and a 100 W sputtering power, and then annealed at different temperatures ranging from 373 to 723 K in an atmosphere of oxygen controlled at 101 Pa. Results showed that the resistivity increased first as the annealing temperature raised from 373 to 473 K, and then decreased when annealed at 623 K. Carrier density of an annealed film increased from 7.09×1020 cm−3 to 1.21×1021 cm−3 as the annealing temperature increased. Results also showed that the resistivity of a SCO film was highly correlated to the carrier mobility. The highest carrier mobility observed by annealing a SCO film at 623 K was 4.0×10−5 m2 V−1 S−1. The optical transmittance of an annealed SCO film in the visible range at 550 nm fell between 52.6% and 58.2%. The Hall coefficient measured at room temperature indicated the nature of the annealed films was p-type.

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  • Effects of Friction Stir Welding Parameters on Microstructures and Mechanical Properties of Brass Joints

    G. M. Xie, Z. Y. Ma, L. Geng

    pp. 1698-1701

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    DOI:10.2320/matertrans.MRP2008089

    Abstract

    5 mm thick brass plates were successfully friction stir welded at the tool rotation rates from 400 to 1000 rpm for a constant traverse speed of 100 mm/min. The nugget zone (NZ) consisted of the incompletely and completely-recrystallized regions. With increasing rotation rates, the fraction of the non-recrystallized grains decreased and the size of the recrystallized grains increased. The hardness values in the NZs were higher than those in the parent material (PM). Increasing the rotation rate did not exert a noticeable effect on the tensile and yield strengths of the welds, but increased the elongation. The tensile and yield strengths of the welds reached up to ∼99 and 80% of the PM, respectively. The fracture occurred in the heat affected zone that had the lowest hardness.

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  • Recrystallization Behavior of Zr-xNb Alloys

    Yoon-Soo Lim, Hyun-Gil Kim, Yong-Hwan Jeong

    pp. 1702-1705

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    DOI:10.2320/matertrans.MRP2008020

    Abstract

    The effect of Nb contents on the recrystallization behavior of a binary Zr-xNb was studied. The specimens of Zr-xNb alloys containing 0.2, 0.4, 0.8 and 1.0 mass % Nb were prepared under various heat-treatment conditions for a cold rolled sheet. The recrystallization behavior was evaluated by using a polarized optical microscope, TEM, and a Vickers hardness tester. The recrystallization temperature of the binary alloys was slightly increased with the Nb content. It was caused by an increment of the activation energy due to an increasing Nb content. The grain growth at the high temperature region was decreased with the Nb content, because the fraction of the beta-phase, which is determined by the Nb content, was increased by increasing the Nb content. Because the minimum hardness value was observed in the temperature range between 600 and 700°C, the annealing was performed in this range to obtain a good ductility in a high Nb-containing Zr alloy.

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  • Hydrothermal Crystallization of TiO2 Gel Films on Ti Substrates and Formability of Hydroxyapatite

    Masato Ueda, Ryoichi Matsunaga, Masahiko Ikeda, Michiharu Ogawa

    pp. 1706-1709

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    DOI:10.2320/matertrans.MRP2008132

    Abstract

    The crystallization of chemically-synthesized TiO2 gel films by hydrothermal treatment was investigated. Pure Ti substrates were chemically treated with H2O2/HNO3 to form a TiO2 gel layer. The specimens were then hydrothermally treated with distilled water or an aqueous NH3 solution in an autoclave at 453 K. By using NH3, an adhesive and sufficiently crystallized TiO2 could be synthesized on the Ti surface. TiO2 greatly enhanced the deposition of hydroxyapatite on the surface during immersion in simulated body fluid.

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    1. Deformation Mechanism of Severely Deformed CP-Titanium by Uniaxial Compression Test MATERIALS TRANSACTIONS Vol.49(2008), No.1
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    3. Change in Mechanical Properties and Microstructure of ARB Processed Ti during Annealing MATERIALS TRANSACTIONS Vol.49(2008), No.1

  • Tensile Properties and Stretch Formability of Mg-1.5 mass%-0.2 mass%Ce Sheet Rolled at 723 K

    Yasumasa Chino, Kensuke Sassa, Mamoru Mabuchi

    pp. 1710-1712

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    DOI:10.2320/matertrans.MEP2008136

    Abstract

    Mg-1.5 mass%Zn-0.2 mass%Ce alloy was hot-rolled at 723 K and its tensile properties and stretch formability were investigated by conducting tensile and Erichsen tests at room temperature. The rolled Mg-Zn-Ce alloy exhibits greater balance of tensile elongation and stretch formability than the commercial Mg alloy, and the balance almost corresponds to that of typical structural Al alloys. This may be attributed to a texture modification, resulting from a synergistic effect of Ce addition and high temperature rolling.

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    3. Change in Mechanical Properties and Microstructure of ARB Processed Ti during Annealing MATERIALS TRANSACTIONS Vol.49(2008), No.1
  • © 2008 The Japan Institute of Metals and Materials

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