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MATERIALS TRANSACTIONS Vol. 52 (2011), No. 11

ISIJ International
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ONLINE ISSN: 1347-5320
PRINT ISSN: 1345-9678
Publisher: The Japan Institute of Metals and Materials

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MATERIALS TRANSACTIONS Vol. 52 (2011), No. 11

Formation of Icosahedral Quasicrystals and 1/1 Crystal Approximants in Al-Pd-RE (RE: Rare Earth Metals) Systems

Yeong-Gi So, Takuro Yoshikawa, Fukuaki Saruhashi, Keiichi Edagawa, Ryuji Tamura

pp. 2011-2015

Abstract

We have investigated the formation of an icosahedral quasicrystal (i-phase) and its 1/1-crystal approximant (1/1-phase) in the (Al, Ga)-Pd-RE (Rare earth metals) systems. Consequently, the Ga-Pd-Sc 1/1-phase, the Al-Pd-RE (RE = Yb, Tm and Er) 1/1-phase and the Al-Pd-Yb i-phase have been newly found by the substitution of Al for Ga, or Sc for other RE in the constituent elements of the Al54Pd30Sc16 i-phase previously reported. For the i- and the 1/1-phases studied in this work, the number of valence electrons per atom (ea) ratio is 2.10 and the atomic radius ratio of the rare earth element to that of the other base elements is in the range 1.15–1.24, which fulfilled the formation conditions previously reported for other Tsai-type i-phases. On the other hand, the stability of the i-phases becomes lower with increasing the atomic radii of the RE elements, which indicates that the atomic radius ratio plays important role in the formation of the Al-Pd-RE i- and 1/1-phases.

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Formation of Icosahedral Quasicrystals and 1/1 Crystal Approximants in Al-Pd-RE (RE: Rare Earth Metals) Systems

Morphology and Crystallography of Martensite Plate with Long Period Stacking Structure in Ti-Pd Shape Memory Alloy

Mitsuhiro Matsuda, Shoichiro Yano, Minoru Nishida

pp. 2016-2021

Abstract

The morphology and crystallography of martensite plates with a long period stacking structure in Ti-Pd shape memory alloy were investigated by transmission electron microscopy. In addition to B19 (2H) martensite, an 18R(2\\bar1)6 structure was observed in equiatomic Ti-Pd alloy quenched above 1373 K. Three fundamental plate variant combinations were identified in the plate group in the region consisting exclusively of 18R martensite. These were designated A:B, A:C and A:D types, and their morphologies and crystallographic characteristics are a wedge with type II, a spear with type I and a fork with compound twin relations, respectively. Duplex martensitic phases coexisting in the same area, namely, “two-in-one” structures, were also observed.

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Morphology and Crystallography of Martensite Plate with Long Period Stacking Structure in Ti-Pd Shape Memory Alloy

Formation of Nanotwins in Cold-Rolled Cu-Zn Alloy by Electric Current Pulses

Wenbin Dai, Xinli Wang, Lin Zhao, Jingkun Yu

pp. 2022-2026

Abstract

A significant number of nanotwins was fabricated in a cold-rolled Cu-Zn alloy after an electric current pulse (ECP) treatment in this study. Results showed that the formation of nanotwins was related not only to the α to β phase transformation, but also to the effect of the enhanced directional nucleation along the current direction during the heating caused by the ECP treatment. A theoretical analysis revealed that the nucleation rate of the higher conductivity phase (β phase) was significantly accelerated by the application of an electric current, which provided more nucleation places for the α phase during the subsequent rapid cooling process. Especially, during the cooling process, nanotwins with {111} twin planes in the α phase would be formed due to the stronger internal stress induced by the rapid cooling rate after the ECP treatment.

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Formation of Nanotwins in Cold-Rolled Cu-Zn Alloy by Electric Current Pulses

A Bainite-Ferrite Multi-Phase Steel Strengthened by Ti-Microalloying

Jianfeng Wang, Guangqiang Li, Aida Xiao

pp. 2027-2031

Abstract

Ti-microalloyed bainite multi-phase steels were prepared in laboratory scale. The tensile strength of examined steels are all higher than 775 MPa and the maximum value is 875 MPa, with at least 27 J impact energy at 253 K which shows a good balance of high strength and high toughness. The examined steels have uniform and fine multi-phase structure with bainite as main phase and ferrite as minor phase, the ratio of ferrite phase gradually decreases with the cooling speed of post-rolling increasing. Most of the precipitates are nano scaled particles of TiN and TiC, which disperse at grain boundaries, dislocations and other places, having effect of grain refinment strengthening and precipitation strengthening.

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A Bainite-Ferrite Multi-Phase Steel Strengthened by Ti-Microalloying

Thermodynamic Assessment of the Bi-Mn System

Katsunari Oikawa, Yoshifuru Mitsui, Keiichi Koyama, Koichi Anzai

pp. 2032-2039

Abstract

A thermodynamic assessment of the Bi-Mn binary system was conducted using the CALPHAD approach. Consistent thermodynamic descriptions, which agreed well with the selected experimental data, were obtained using a sub-regular solution model for solution phases and a line-compound model for intermetallic compounds. There are several discrepancies between the phase diagram drawn in a previous study and that calculated in this study. The two-phase separation that appeared in the previous phase diagram was not calculated and the calculated liquidus boundaries at around 1000 K changed smoothly compared with that in the previous diagrams. From the viewpoint of thermodynamic consideration, the calculated phase diagram presented in this study is reasonable.

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Thermodynamic Assessment of the Bi-Mn System

Elastic and Damping Properties of AZ31 Magnesium Alloy Sheet Processed by High-Temperature Rolling

Kazutaka Suzuki, Yasumasa Chino, Xinsheng Huang, Mamoru Mabuchi

pp. 2040-2044

Abstract

Elastic and damping properties of AZ31 magnesium alloy sheet processed by high-temperature rolling were investigated. The specimen rolled at high temperature (798 K) exhibited the significant low basal texture intensity and the wide spread of the basal pole toward the RD and TD, compared with the specimen rolled at 573 K. Young’s modulus of the specimen rolled at 798 K had smaller value at all angles than that of the specimen rolled at 573 K. Besides, the specimen rolled at 798 K exhibited slightly higher internal friction compared with the specimen rolled at 573 K over the strain amplitude range investigated. The suppression of the strong basal texture formation in the specimen rolled at 798 K likely contributed to a reduction of Young’s modulus and an increase in internal friction, because the breakaway stress, which is closely related to the macro-yield stress, decreases with an increase in the Schmid’s factor of basal slip.

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Elastic and Damping Properties of AZ31 Magnesium Alloy Sheet Processed by High-Temperature Rolling

Effect of Eutectic Si Particle Morphology on ECAP Formability and Mechanical Properties of AC4CH Aluminum Casting Alloys

Yoshihiro Nakayama, Tetsuya Miyazaki

pp. 2045-2051

Abstract

AC4CH casting alloys were subjected to the 2-step preheating and the ECAP processing at room temperature. Microstructure change was investigated in terms of size and globularity of the eutectic Si particles and hardness of the primary and the eutectic α-Al. The effects of 2-step preheating, ECAP processing and standard T6 heat treatment on the hardness and the tensile properties were also investigated. The results of this study are as follows. The ECAP formability was significantly improved by the optimum 2-step preheating (1st-step preheating at 560°C and 2nd-step preheating at 350°C). More than 12-times ECAP pressing (equivalent strain of about 5.6) could be made without cracking. The hardness distribution in the primary α-Al suggested that the accumulated plastic strain during the ECAP processing increased gradually toward the eutectic cell regions. The hardness measurement also showed that the accumulated plastic strain of the eutectic α-Al around less-globular Si particles was higher than that around globular Si particles. Concentration of the plastic strain may promote cracking in the eutectic cell regions and deteriorate the ECAP formability. Successive processing by the 2-step preheating, the ECAP processing and the standard T6 heat treatment brought about globularity and homogeneous distribution of the eutectic Si particles. During the tensile deformation, these microstructural features might lead to homogeneous distribution of the plastic strain, suppressions of the cracking of Si particles and the delamination between the Si particle and the matrix. As a result, the 0.2% proof stress and the fracture strain increased about 11% and 47% respectively compared with those of the standard T6 treated sample.

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Effect of Eutectic Si Particle Morphology on ECAP Formability and Mechanical Properties of AC4CH Aluminum Casting Alloys

Application of High-Frequency Induction Heating Apparatus to Heat Treatment of 6061 Aluminum Alloy

Fang-ni Shang, Eiji Sekiya, Yoshihiro Nakayama

pp. 2052-2060

Abstract

A high-frequency induction heating apparatus was used for the heat treatment of a commercial 6061 aluminum alloy bar with the objective of improving the mechanical properties and productivity. Heating states of the 6061 alloy bar were examined in terms of temperature distribution, heating rate, overheating and temperature fluctuation; moreover, the mechanical properties of the alloy after heat treatment were also investigated. The results of this study are as follows. When the 6061 alloy bar was rapidly heated to the heat treatment temperature using the induction heating apparatus, temperature distribution and overheating of the sample were small as well as the temperature fluctuations in the holding process. A rapid heating rate of about 21°C/s heated the sample to the heat treatment temperature of 560°C in 26 s. The sample showed equivalent or superior mechanical properties compared with a sample heated by conventional electric furnace. Temperature and time of the heat treatment process greatly influenced the mechanical properties of the 6061 alloy, while there was no significant difference in mechanical properties of the sample heat-treated at various heating rates.

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Application of High-Frequency Induction Heating Apparatus to Heat Treatment of 6061 Aluminum Alloy

Electrochemical Polishing of Metallic Titanium in Ionic Liquid

Tetsuya Uda, Kazuaki Tsuchimoto, Hidekazu Nakagawa, Kuniaki Murase, Yoshitaro Nose, Yasuhiro Awakura

pp. 2061-2066

Abstract

We investigated the electrochemical dissolution of titanium in TMHA-Tf2N ionic liquid in order to develop a new polishing method for titanium. No dissolution of titanium was observed during the anodic potential sweep up to +6.0 V vs. I3⁄I because of the formation of titanium oxide layer during the potential sweep. But when a certain anodic potential was applied instead of the potential sweep, titanium was successfully dissolved to the extent of detectable weight loss. Moreover, TMHA-Tf2N ionic liquid indicated fluorescence X-ray of titanium and the titanium surface showed a shiny metallic silver appearance after experiment. We found that the immersed potential of titanium in the ionic liquid became gradually more negative by increasing the number of mechanical polishings before electrochemical experiments. Using the titanium with an immersed potential of more negative than −0.95 V, the titanium was dissolved anodically at +1.6 V. The potential is within the electrochemical window of TMHA-Tf2N ionic liquid. We believe this technique represents a promising new surface treatment for titanium.

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Electrochemical Polishing of Metallic Titanium in Ionic Liquid

Chemical Dissolution of Iridium Powder Using Alkali Fusion Followed by High-Temperature Leaching

Jaeryeong Lee, Youngjin Kim

pp. 2067-2070

Abstract

The dissolution of iridium has been investigated with an alkali fusion treatment with Na2O2 followed by leaching in HCl solution. Alkali fusion with Na2O2 allows Ir to be easily oxidized to IrO2, which is transformed to a high oxidation state through the binding of Na-Ir-O at 600°C for 4 h. From the fused mixture, with molar ratio of 1:2.0 (Ir:Na2O2), Ir can be leached completely at 130°C using an HCl solution with a concentration above 3 M. Moreover, the leaching with 3 M HCl at 130°C can dissolve Ir from the mixture that was fused at 600°C, regardless of molar ratio of Na2O2. Ir can also be completely dissolved at 70°C or less when the fused mixture has a 1:2.0 ratio.

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Chemical Dissolution of Iridium Powder Using Alkali Fusion Followed by High-Temperature Leaching

Separation of Pt(IV) and Rh(III) from Chloride Solution by Solvent Extraction with Amine and Neutral Extractants

P. P. Sun, J. Y. Lee, M. S. Lee

pp. 2071-2076

Abstract

Solvent extraction experiments were performed to separate platinum and rhodium from mixed chloride solution by using amine and neutral extractants. Effects of extraction conditions on the separation of the two metals were investigated as a function of extractant concentration in the HCl concentration range from 1 to 9 mol/dm3. Alamine304-1, Alamine308, Alamine336, Aliquat336, TBP, TOPO and DOS were tested in our study. The concentration of Pt(IV) and Rh(III) in the mixed solution was fixed at 0.001 mol/dm3 and 0.0001 mol/dm3, respectively. In the extraction with amine, Pt was completely extracted irrespective of HCl concentration, while the extraction percentage of Rh depended on extraction condition. In the extraction with neutral extractants, the extraction percentage of Rh was nearly zero whereas 1 mol/dm3 TOPO completely extracted most of Pt in our experimental range. Separation of Pt from Rh by amines except Alamine336 was possible only from 9 mol/dm3 HCl solution, while complete separation of the two metals by TOPO was possible in the HCl concentration range from 1 to 9 mol/dm3. From the consideration of the economics of the separation process, our results indicate that TBP is better than TOPO in separating Pt and Rh from chloride solution.

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Separation of Pt(IV) and Rh(III) from Chloride Solution by Solvent Extraction with Amine and Neutral Extractants

Effect of Organic Additives on the Hardness of Ni Electrodeposited from Sulfamate and Watt’s Solutions

Hiroaki Nakano, Hideaki Tsuji, Satoshi Oue, Hisaaki Fukushima, Feng Yang, Wenhuai Tian

pp. 2077-2082

Abstract

Ni electrodeposition was galvanostatically conducted over a current density range 1–5000 A/m2 from unagitated sulfamate (323 K) and Watt’s solutions (313 K) containing polyethylene glycol (PEG) or saccharin to examine the effect of the C and S contents in the deposit and the texture on the hardness of the deposited Ni. The C content in Ni deposited from Watt’s solutions containing PEG was significantly higher than that from the sulfamate solution. The S content in deposits from sulfamate and Watt’s solutions containing saccharin differed slightly, except at 2000 A/m2. The hardness of the deposited Ni increased with increasing C and S contents, and the rate of increase in hardness decreased at S content above 0.02 mass%. The texture of the deposited Ni changed from a field-oriented texture to an unoriented dispersed type when C and S were co-deposited with Ni by the addition of PEG and saccharin. The hardness of the unoriented dispersed type of Ni deposit was greater than that of the field-oriented type of Ni deposit.

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Effect of Organic Additives on the Hardness of Ni Electrodeposited from Sulfamate and Watt’s Solutions

Influence of Colour Filter on Reaction Products from Mo and W Heated to 2000°C by Concentrated Solar Beam in N2 Gas Environment in a Solar Furnace at PROMES-CNRS

Gilles Peraudeau, Fernando Almeida Costa Oliveira, Luís Guerra Rosa, Bernard Granier, Jorge Cruz Fernandes, Teresa Magalhães, Nobumitsu Shohoji

pp. 2083-2090

Abstract

In a preceding work, we reported attempts of synthesizing nitride of d-group transition metals including Ti, V, Nb and Ta using a solar furnace at PROMES-CNRS. In standard solar furnace experimental setup, graphite crucible is used as the sample holder on account of its resistance against high temperature and thermal shock. Plume of C2 radical with high chemical activity a(C) of C was reported to yield from graphite crucible under irradiation of concentrated solar beam. Thus, synthesis of pure metal nitride MN was not successful in the preceding work done in N2 gas environment heated by solar beam irradiation under standard experimental setup. To overcome this problem of undesired carburization in solar furnace, insertion of colour filter in the path of solar beam was tried and it was found that the C2 radical yield from the graphite crucible was effectively suppressed by insertion of Sky blue filter and carbo-nitride M(C,N) with comparatively low C-content was synthesized for Ti, V, Nb and Ta at 2000°C in N2 gas environment while, without the Sky blue filter, M(C,N) with high C-content and low N-content was synthesized under the otherwise comparable conditions of temperature and nitrogen partial pressure. These evidences appeared to suggest that nitride synthesis might be realized in standard solar furnace experimental setup using standard sample holder made of graphite by insertion of Sky blue filter. In the present work, reaction products from Mo and W in N2 gas environment under solar heating to 2000°C were characterized and effectiveness of the Sky blue filter for suppression of C2 radical yield from the graphite crucible was ascertained.

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Influence of Colour Filter on Reaction Products from Mo and W Heated to 2000°C by Concentrated Solar Beam in N2 Gas Environment in a Solar Furnace at PROMES-CNRS

Application of Microwaves for Nondestructive and High-Efficiency Detection of Wall Thinning Locations in a Long-Distance Metal Pipe

Linsheng Liu, Yang Ju, Mingji Chen, Daining Fang

pp. 2091-2097

Abstract

This research aims to find an efficient and nondestructive way of detecting the locations of the pipe wall thinning (PWT) in a long-distance metal pipe at open-end condition. Time domain measurement of microwave signals is adopted in the method since microwaves can propagate a long distance with low attenuation in the pipe and reflection occurs at the PWT section. To carry out the measurement, a vector network analyzer and a self-designed coaxial-line sensor were used to generate microwave signals propagating in the pipe. By analyzing the time domain response of the signals and extracting the time of flight (TOF) that corresponds to the PWT location, the locations are quantitatively evaluated after the group velocity of the signals propagating in the pipe was calibrated. In order to approach a pipe with different PWT degrees and locations, three brass pipes with an inner diameter of 17.0 mm and lengths of 453 mm, 455 mm, and 2000 mm, respectively, were used in the experiment. In addition, five joints, which have the length of 17.0 mm and inner diameters from 17.10 to 18.20 mm were also used. The arithmetical mean error of the evaluation for PWT locations is found to be less than 1.7 mm, i.e. less than 0.068% of the length of the corresponding pipe. It indicates that a quite efficient and precise method to remotely and quantitatively evaluate PWT locations in a long-distance pipe has been established.

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Application of Microwaves for Nondestructive and High-Efficiency Detection of Wall Thinning Locations in a Long-Distance Metal Pipe

Mechanism for Densification of Yttria-Stabilized Tetragonal Zirconia Powder by Electric Current-Activated/Assisted Sintering

Tatsuo Kumagai

pp. 2098-2105

Abstract

The effect of electric current-activated/assisted sintering (ECAS) on the densification of a mechanically milled 3Y-TZP ceramic powder was investigated. The changes in temperature (T) and relative density (ρ) with time during ECAS under a uniaxial pressure of 90.5 MPa in a closed die were measured for different heating conditions. From the results, densification rate (\\dotρ) vs. T and \\dotρ vs. ρ curves were interpolated for different fixed heating-rates (\\dotT) of 0.1 to 2.0 K/s. Although the values of \\dotρ at fixed temperatures or relative densities increased with increasing \\dotT, the values of T and ρ corresponding to the peaks of \\dotρ were almost constant at 1300 K and 0.8, respectively, irrespective of \\dotT. The stress exponent (n) estimated from log-log plots of \\dotρ and the effective stress (σeff) increased monotonically with increasing T; however, the values of n re-estimated using σeff compensated for threshold stress (σ0) were approximately 2, irrespective of T. In addition, the activation energy (Q) estimated from the (σeff−σ0) vs. 1⁄T Arrhenius plot was 450±20 kJ/mol. These values of n and Q were similar to those for creep experiments reported by Melendo et al., which suggests that densification of 3Y-TZP powder compacts by ECAS proceeds through grain boundary sliding affected by σ0 as well as creep deformation in the intermediate stress region.

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Mechanism for Densification of Yttria-Stabilized Tetragonal Zirconia Powder by Electric Current-Activated/Assisted Sintering

The Effect of Fillers in Nonconductive Adhesive on the Reliability of Chip-on-Glass Bonding with Sn/Cu Bumps

Byeung Gee Kim, Sun-Chul Kim, Wen-Guo Dong, Young-Ho Kim

pp. 2106-2110

Abstract

The effect of a nonconductive adhesive (NCA) on the reliability of chip-on-glass (COG) bonding was studied. Double layer bumps consisting of dome-shaped Sn on Cu columns were formed by electroplating and a reflow process, and were used for this study. COG bonding was performed between the reflowed Sn/Cu bumps on the oxidized Si wafer and an indium tin oxide/Au/Cu/Ti/glass substrate using a thermo-compression bonder. Three types of NCAs were applied during COG bonding: NCA-A with no fillers, NCA-B with fluoropolymer fillers, and NCA-C with silica fillers. Thermal cycling from −25°C to 125°C for 2000 cycles was performed to evaluate the effect of NCA type on the reliability of COG joints. The initial contact resistance values of the COG joints ranged from 32.2 mΩ to 39.3 mΩ. The contact resistance increased during the thermal cycling and the trend of contact resistance increment was different among three NCA types. The failure rate was the highest in NCA-C, followed by NCA-B and NCA-A in descending order. After the thermal cycling, the cross-sections of COG joints were observed with scanning electron microscopy to analyze the failure mechanism. The failures occurred primarily due to trapped fillers and NCAs at the interface between Sn/Cu bumps and the ITO substrate.

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The Effect of Fillers in Nonconductive Adhesive on the Reliability of Chip-on-Glass Bonding with Sn/Cu Bumps

The Role of Eutectic Phase and Acicular Primary Crystallized Zn Phase on Electrification-Fusion Induced Fracture of Sn-xZn Solder Alloys

Gong-An Lan, Truan-Sheng Lui, Li-Hui Chen

pp. 2111-2118

Abstract

Effect of Sn-xZn solder alloys with varying eutectic phase and acicular primary crystallized Zn phase on the electrification-fusion induced liquidation phenomenon was investigated in this study. The critical fusion current density (CFCD) for liquidation fracture tends to increase with increasing Zn content, the CFCD value required for electrification-fusion induced liquidation are 1457 (×104) A·m−2 (7Zn), 1504 (×104) A·m−2 (30Zn) and 2195 (×104) A·m−2 (70Zn) respectively, which are commonly larger than pure tin (1399 (×104) A·m−2) pertaining to the transformation of current path. Through the in-situ examination of microstructural evolution during electrification-fusion tests, the initial site of electrification-fusion-induced liquidation significantly emerged from Sn/Zn eutectic phase. From the experimental evidences, it should be noted that the pure Sn specimen showing a character that the initiation site for microliquidation were located at the triple junction of electrification induced current path, whereas the Sn-Zn alloy specimens were commonly initiated from the eutectic phase pertaining to the higher conductivity of acicular Zn phase.

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The Role of Eutectic Phase and Acicular Primary Crystallized Zn Phase on Electrification-Fusion Induced Fracture of Sn-xZn Solder Alloys

Hydrothermal Synthesis of Sodium and Potassium Niobates Fine Particles and Their Application to Lead-Free Piezoelectric Material

Kiyoshi Kanie, Yoshiki Numamoto, Shintaro Tsukamoto, Hirofumi Takahashi, Hideto Mizutani, Atsuki Terabe, Masafumi Nakaya, Junji Tani, Atsushi Muramatsu

pp. 2119-2125

Abstract

Cubic-shaped potassium and sodium niobates fine particles with orthorhombic crystal structures were successfully obtained by two-step hydrothermal reaction at 100°C for 24 h and 150–250°C for 3 h using a highly concentrated KOH or NaOH aqueous solution and a niobium pentachloride aqueous solution. The particle mean sizes were gradually controlled by changing the initial KOH and NaOH concentrations. Preheating of the precursor solution at 100°C for 24 h played an important role to obtain the desired alkali metal niobates fine particles with flat and smooth surfaces. The present potassium niobate fine particles exhibited good sintering property keeping with the original particle size and shape. Furthermore, thus obtained KN ceramics showed high piezoelectric properties.

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Hydrothermal Synthesis of Sodium and Potassium Niobates Fine Particles and Their Application to Lead-Free Piezoelectric Material

A Phase Field Model of Surface-Energy-Driven Abnormal Grain Growth in Thin Films

Jie Deng, Srujan Rokkam

pp. 2126-2130

Abstract

A phase field model is established to investigate the surface-energy-driven abnormal grain growth in thin films. It is consistent with sharp interface model and its parameters are connected to material properties. Numerical simulations show that surface energy anisotropy and drag effect are required to motivate the abnormal grain growth. The size of a single abnormal grain increases linearly as a function of time, and it exhibits power-law scaling with film thickness and Arrhenius relationship with temperature. For multiple abnormal grains, their area fraction can be characterized by the Avrami equation with exponent around 2 at large times. These features agree well with the theoretical and experimental results.

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A Phase Field Model of Surface-Energy-Driven Abnormal Grain Growth in Thin Films

Investigation of Mechanical Properties and Elongated Ni Grain Growth in an Al2O3-Ni Composite during Low-Energy Ball Milling

Dong-guk Cho, Seung-Kyu Yang, Jai-Sung Lee, Caroline Sunyong Lee

pp. 2131-2136

Abstract

A composite of 40 mass% Al2O3-60 mass% Ni was fabricated using powder metallurgy. The composite consisted of Ni powders dispersed in an Al2O3 matrix. The morphology of the Ni powders in the composite was monitored during a low-energy ball-milling process over about 10 h. The shape of the Ni particles changed from spherical to elongated shape using this milling method. The aspect ratio of the elongated Ni grains was measured, and 16% of the total Ni grains in the composite were found to have an aspect ratio higher than 3.0. To investigate changes in mechanical properties due to the elongated Ni powders, strength and hardness were measured. The composite having elongated Ni powders with an aspect ratio higher than 3.0 showed improved strength and hardness compared to the composite containing non-milled particles. Low-energy milling of composites is thus an effective way to control the microstructure of particles in order to improve the mechanical properties of the final composite. Because of its low production cost and simplicity, this method could potentially be used in the production of various reinforced composites.

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Investigation of Mechanical Properties and Elongated Ni Grain Growth in an Al2O3-Ni Composite during Low-Energy Ball Milling

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