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MATERIALS TRANSACTIONS Vol. 50 (2009), No. 12

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. 50 (2009), No. 12

Influence of Current Density on the Reduction of TiO2 in Molten Salt (CaCl2 + CaO)

Keiichi Kobayashi, Yuichi Oka, Ryosuke O. Suzuki

pp. 2704-2708

DOI:

10.2320/matertrans.MA200910

Abstract

Titanium dioxide (TiO2) was successfully reduced at 1223 K by calcium, which was deposited due to the molten salt electrolysis of CaO dissolved in CaCl2. The current density and the Ca concentration near the cathode were changed by varying the electrodes’ surface areas and the distances between an anode and cathode, respectively. At the initial stage of reduction, metallic Ti powder with a lower oxygen concentration was obtained at a lower current density; in this case, most of the electrochemically deposited Ca was efficiently used for reduction. Meanwhile, at the final stage of deoxidation, Ti powder with a much lower oxygen concentration was obtained at a higher current density. In order to obtain metallic powder with a low oxygen concentration, the formed Ca should penetrate the inner part of the sintered sample.

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Influence of Current Density on the Reduction of TiO2 in Molten Salt (CaCl2 + CaO)

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Oxygen Distribution in Titanium Single Crystal Fabricated by Optical Floating-Zone Method under Extremely Low Oxygen Partial Pressure

Koji Hagihara, Takahiro Tachibana, Keita Sasaki, Yoshiyuki Yoshida, Naoki Shirakawa, Tohru Nagasawa, Takayuki Narushima, Takayoshi Nakano

pp. 2709-2715

DOI:

10.2320/matertrans.MA200903

Abstract

This study examines the properties of a titanium single crystal fabricated by the floating-zone-melting process in Ar gas flow atmosphere where the partial pressure of oxygen was maintained extremely low at PO2=∼10−23 atm by the newly developed oxygen pump system. The distribution of solute oxygen atoms in the obtained single crystal exhibited a peculiar gradient. In the early stage of the titanium single crystal growth, the oxygen content in the single crystal (approximately 1600 ppm) was higher than that in the mother ingot (980 ppm). However, as the crystal growth progressed, the oxygen content gradually decreases and then reduced to 660 ppm in the final stage of crystal growth. Such a gradient of oxygen composition was not detected in titanium single crystals fabricated under conventional, commercial Ar gas flow atmosphere. Owing to the unique gradient of oxygen content formed under extremely low oxygen partial pressure, the Vickers hardness of the single crystal decreased gradually along the crystal growth direction.

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Oxygen Distribution in Titanium Single Crystal Fabricated by Optical Floating-Zone Method under Extremely Low Oxygen Partial Pressure

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Effect of Oxygen Content on Microstructure and Mechanical Properties of Biomedical Ti-29Nb-13Ta-4.6Zr Alloy under Solutionized and Aged Conditions

Masaaki Nakai, Mitsuo Niinomi, Toshikazu Akahori, Harumi Tsutsumi, Michiharu Ogawa

pp. 2716-2720

DOI:

10.2320/matertrans.MA200904

Abstract

The effect of oxygen content on the microstructure and mechanical properties of the Ti-29 mass%Nb-13 mass%Ta-4.6 mass%Zr (TNTZ) alloy was investigated in this study. The microstructural observation of TNTZ alloys, containing 0.1–0.4 mass% oxygen, subjected to solution treatment shows the presence of a single β phase. With an increase in oxygen content, the hardness, tensile strength, and Young’s modulus of TNTZ alloy increase, but its elongation decreases. Further, the α phase precipitates in TNTZ alloys subjected to aging treatment at 723 K for 259.2 ks. The results of transmission electron microscopy and X-ray diffraction analysis indicate that the size and volume fraction of the α phase increase with oxygen content. Corresponding to the changes in the microstructure, the mechanical properties of TNTZ alloy subjected to aging treatment at 723 K change with oxygen content. The increase in oxygen content leads to enhancement of the age hardening of TNTZ alloy, thereby increasing both tensile strength and Young’s modulus of TNTZ alloy, but its elongation decreases due to the α-phase precipitation. The mechanical properties of TNTZ alloy (Young’s modulus: around 60–100 GPa, tensile strength: around 600–1400 MPa, and elongation: around 5–25%) vary significantly depending on oxygen content and heat treatment.

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Effect of Oxygen Content on Microstructure and Mechanical Properties of Biomedical Ti-29Nb-13Ta-4.6Zr Alloy under Solutionized and Aged Conditions

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Effect of Nb Content on Deformation Textures and Mechanical Properties of Ti-18Zr-Nb Biomedical Alloys

Hirobumi Tobe, Hee Young Kim, Shuichi Miyazaki

pp. 2721-2725

DOI:

10.2320/matertrans.MA200908

Abstract

Recently, β-type Ti alloys composed of non-toxic elements such as Nb, Ta, Zr, Mo and Sn have been studied for biomedical applications. The present author’s research group has also developed these alloys including Ti-Zr-Nb as new biomedical superelastic materials. They reveal strong textures which are formed during thermo-mechanical processing and cause the anisotropy in mechanical properties. In this study, the effect of Nb content on the deformation texture of Ti-18Zr-Nb alloys was investigated. The anisotropy in mechanical properties of Ti-18Zr-Nb alloys was also investigated. Ti-18Zr-(15∼18)Nb (at%) alloy ingots were fabricated by an Ar arc melting method and then homogenized at 1273 K for 7.2 ks. The ingots were cold rolled with a reduction up to 99% in thickness. For the as-rolled alloys, a weak γ-fiber texture was observed in Ti-18Zr-(15, 16)Nb alloys, whereas a well developed {001}⟨110⟩ texture was confirmed in the Ti-18Zr-18Nb alloy. The former alloys revealed weak anisotropy in Young’s modulus due to the weak texture, while the latter alloy exhibited strong anisotropy due to the strong texture.

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Effect of Nb Content on Deformation Textures and Mechanical Properties of Ti-18Zr-Nb Biomedical Alloys

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Effect of Nitrogen Addition on Superelasticity of Ti-Zr-Nb Alloys

Masaki Tahara, Hee Young Kim, Tomonari Inamura, Hideki Hosoda, Shuichi Miyazaki

pp. 2726-2730

DOI:

10.2320/matertrans.MA200907

Abstract

Recently, the Ti-Zr-Nb alloys have been developed as Ni-free shape memory and superelastic alloys. In this study, the effects of Nb and nitrogen (N) contents on martensitic transformation behavior, shape memory effect and superelasticity in Ti-18Zr-(12∼16)Nb-(0∼1.0)N (at%) alloys are investigated using loading and unloading tensile tests, optical microscopy and X-ray diffractometry. The shape memory effect is observed in Ti-18Zr-(12∼13)Nb and Ti-18Zr-12Nb-0.5N alloys at room temperature. The superelastic behavior appears by the increase of Nb or N content. The Ti-18Zr-(14∼15)Nb, Ti-18Zr-(13∼14)Nb-0.5N and Ti-18Zr-(12∼14)Nb-1.0N alloys exhibit the superelasticity at room temperature. The martensitic transformation start temperature decreases by 75 K with 1 at% increase of N content for the Ti-18Zr-13Nb alloy. The critical stress for slip deformation and the stress for inducing the martensitic transformation increase with increasing N content. The superelastic recovery strain is also increased by adding N. The maximum recovery strain of 5.0% is obtained in the Ti-18Zr-14Nb-0.5N alloy.

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Effect of Nitrogen Addition on Superelasticity of Ti-Zr-Nb Alloys

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Effect of Cooling Rate on Superelasticity and Microstructure Evolution in Ti-10V-2Fe-3Al and Ti-10V-2Fe-3Al-0.2N Alloys

Yusaku Tomio, Tadashi Furuhara, Tadashi Maki

pp. 2731-2736

DOI:

10.2320/matertrans.MA200909

Abstract

A Ti-10V-2Fe-3Al alloy with a small amount of nitrogen shows superelasticity. Controlling of the cooling rate from β solution treatment temperature improves superelasticity in both Ti-10V-2Fe-3Al and Ti-10V-2Fe3-Al-0.2N alloys. In this study, a wider range of the cooling rate was examined and microstructure change during slow cooling was investigated through examining quenched and aged specimens by means of hardness and resistivity measurement and transmission electron microscopy. Although superelasticity is improved with a decrease in the cooling rate up to 22 K/s for the N-free alloy and up to 50 K/s for the 0.2N alloy, there is no obvious change in microstructure. It is clarified from the observation of specimens quenched and aged at the temperature range where superelasticity is improved that the β phase decomposition occurs through isothermal ω phase precipitation. Therefore, microstructure evolution during slow cooling is considered to be precipitation of isothermal ω phase or its precursor phenomena.

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Effect of Cooling Rate on Superelasticity and Microstructure Evolution in Ti-10V-2Fe-3Al and Ti-10V-2Fe-3Al-0.2N Alloys

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Isothermal Aging Behavior of Beta Titanium–Manganese Alloys

Masahiko Ikeda, Masato Ueda, Ryoichi Matsunaga, Michiharu Ogawa, Mitsuo Niinomi

pp. 2737-2743

DOI:

10.2320/matertrans.MA200902

Abstract

Although titanium is considered to be a ubiquitous element as it has the 10th-highest Clarke number of all the elements, it is actually classified as a rare metal because the current refinement process for the metal is more environmentally damaging than the processes used to refine iron and aluminum. Furthermore, the principal alloying elements of titanium alloys are very expensive, owing to their low crustal abundances; this is especially true of the beta-stabilizing elements. Manganese is also considered to be a ubiquitous element as it has the 12th-highest Clarke number of all the elements. Therefore, manganese is promising as an alloying element for titanium, especially as a beta-stabilizing element. In order to develop beta titanium alloys as ubiquitous metallic materials, it is very important to investigate the properties of Ti-Mn alloys. In this study, the phase constitutions and isothermal aging behaviors of Ti-6.0 to 14.8 mass%Mn alloys were investigated by electrical resistivity and Vickers hardness measurements, X-ray diffraction (XRD), and optical microscopy. In 6.0 mass%Mn alloys quenched from 1173 K, both hexagonal close-packed martensite and the beta phase were identified by XRD, whereas only the beta phase was detected in 8.7 and 14.8 mass%Mn alloys. The resistivity at liquid nitrogen temperature was greater than that at room temperature between 6.0 and 14.8 mass%Mn. The Vickers hardness decreased with an increase in the Mn content up to 11.3 mass%Mn and then increased slightly. On aging at 673 K, the isothermal omega phase was precipitated in 6.0 to 11.3 mass%Mn alloys, while it was precipitated by aging at 773 K in 6.0 and 8.7 mass%Mn alloys. The Vickers hardness increased drastically on isothermal omega precipitation, whereas it increased slightly in the case of direct alpha precipitation with no isothermal omega precipitation.

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Isothermal Aging Behavior of Beta Titanium–Manganese Alloys

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Microstructure and Mechanical Properties of α′ Martensite Type Ti Alloys Deformed under the α′ Processing

Hiroaki Matsumoto, Kazuki Kodaira, Kazuhisa Sato, Toyohiko J. Konno, Akihiko Chiba

pp. 2744-2750

DOI:

10.2320/matertrans.MA200912

Abstract

Microstructure and mechanical properties of cold groove rolled α′ Ti-V-Al and Ti-V-Sn alloys were investigated. Microstructure after solution treatment at 1223 K and quenching into ice water showed the acicular martensitic structure of α′ phase for (Ti-12 mass%V)-2 mass%Al and (Ti-8 mass%V)-4 mass%Sn alloys and (α′+α″) phases for (Ti-12 mass%V)-6 mass%Sn alloy. After cold groove rolling at reduction of 75%, microstructure evolved into the equiaxed refined cell structure having the preferred rolling texture of ⟨10\\bar10⟩ parallel to rolling direction. After cold groove rolling, Young’s modulus decreases to 47.5 GPa, in contrast, tensile strength increases to more than 1000 MPa accompanying with work hardening and grain refinement.

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Microstructure and Mechanical Properties of α′ Martensite Type Ti Alloys Deformed under the α′ Processing

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Cost Effective Pure Titanium with High Mechanical Response by Oxide Dispersion Strengthening

Tomohiro Yoshimura, Hisashi Imai, Thotsaphon Threrujirapapong, Katsuyoshi Kondoh

pp. 2751-2756

DOI:

10.2320/matertrans.MA200905

Abstract

Titanium (Ti) alloys are possible to be applied to various products such as aircraft, automotive and motor cycles industries because of their weight reduction effect, superior mechanical responses and high corrosion resistance. Ti-6Al-4V (Ti64) is one of the most common Ti alloys used in structural components. It shows high tensile strength of 900 MPa or more. On the other hand, its applications are limited to high-performance products because of both its poor plastic formability and high cost due to the addition of vanadium element and difficult melting process.
In this study, the highly strengthened pure titanium has been developed using cheap sponge Ti powders via repeated plastic deformation, avoiding the melting process. The main strengthening mechanism of this material is the oxide dispersion strengthening (ODS) by the in-situ formed TiO2 fine dispersoids during the repetitive plastic deformation of sponge Ti powders. Roll-Compaction (RCP) process, consisting of cold powder rolling and fragmentation, was employed to induce much plastic strain into the matrix of the Ti powders. Subsequently, the grain refinement was also obtained to enhance the mechanical properties. The extruded sponge Ti powder composites reinforced with TiO2 particles indicated high tensile strength of 640 MPa and enough elongation of 17.2% after RCP process with 20 cycles.

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Cost Effective Pure Titanium with High Mechanical Response by Oxide Dispersion Strengthening

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Mechanical Properties of a Titanium Matrix Composite Reinforced with Low Cost Carbon Black via Powder Metallurgy Processing

Thotsaphon Threrujirapapong, Katsuyoshi Kondoh, Hisashi Imai, Junko Umeda, Bunshi Fugetsu

pp. 2757-2762

DOI:

10.2320/matertrans.MA200906

Abstract

A powder metallurgy (P/M) titanium matrix composite (TMC) reinforced with low cost carbon black was prepared by spark plasma sintering (SPS) and hot extrusion. Carbon black particles were added for the in situ formation of TiC dispersoids during the SPS process. Two kinds of titanium (Ti) powders, sponge and fine Ti, were coated with carbon black particles via a wet process using a zwitterionic solution containing carbon black spheres. The distribution of the particles on the Ti powder surface before the consolidation process was imaged using scanning electron microscopy (SEM). We evaluated the microstructure and mechanical properties of extruded pure Ti matrix composites reinforced with TiC particles. The morphology and distribution of the in situ TiC phases were investigated using optical microscopy and SEM with the help of an EDS analyzer. The mechanical properties of these composites were remarkably improved by adding a small amount of carbon black at 0.07∼0.16 mass%. The increases in the yield stress of the extruded sponge and fine TMC were 70.0 and 291 MPa, while the tensile strength increases were 67 and 231 MPa, respectively, compared to those of extruded pure Ti with no reinforcement. Finally, the fractured surfaces of TMC specimens after tensile testing were observed. The benefits of the wet process and the use of carbon black additives are discussed in detail.

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Mechanical Properties of a Titanium Matrix Composite Reinforced with Low Cost Carbon Black via Powder Metallurgy Processing

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Surface Hardening Treatment for Titanium Materials Using Ar-5%CO Gas in Combination with Post Heat Treatment under Vacuum

Y. Z. Kim, Takashi Konno, Taichi Murakami, Takayuki Narushima, Chiaki Ouchi

pp. 2763-2771

DOI:

10.2320/matertrans.MA200911

Abstract

Surface hardening using solute oxygen formed by the dissociation of titanium oxide (TiO2) layer on commercially pure (C.P.) titanium, α+β type Ti-4.5Al-3V-2Fe-2Mo (SP-700) alloy, and β type Ti-15Mo-5Zr-3Al (Ti-15-53) alloy was investigated. This method consists of two steps: surface hardening using Ar-5%CO gas for a short time period and subsequent heat treatment under vacuum. Both treatments were carried out at 1073 K. The maximum surface hardness and hardening layer depth for C.P. titanium obtained by surface hardening in Ar-5%CO gas for 1.8 ks were 420 Hv and 30 μm, respectively. After post heat treatment for 14.4 ks, these values increased to 820 Hv and 70 μm, respectively. The increase of surface hardening achieved by post heat treatment was yielded by solid solution hardening of oxygen via the following steps. Solute oxygen was continuously formed at the oxide layer/titanium interface by the dissociation of the oxide layer formed during surface hardening treatment. Oxygen then diffused into titanium matrix, which resulted in solid solution hardening. The highest and lowest values of the maximum surface hardness were obtained in C.P. titanium and Ti-15-53 alloy, respectively. On the other hand, the hardening layer depth was largest for Ti-15-53 alloy and smallest for C.P. titanium. These results can be explained by the differences in solubility and diffusivity of oxygen between the titanium α phase and β phase. This two-step process appears to be a beneficial industrial surface hardening method for titanium materials because it enables the removal of the oxide layer while yielding surface hardness comparable to that obtained by the one-step process under the same total heat-treating time.

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Surface Hardening Treatment for Titanium Materials Using Ar-5%CO Gas in Combination with Post Heat Treatment under Vacuum

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Effects of Current Density on Elongation of an Electropulsing Treated Zn-Al Based Alloy

S. To, Y. H. Zhu, W. B. Lee, X. M. Liu, Y. B. Jiang

pp. 2772-2777

DOI:

10.2320/matertrans.M2009280

Abstract

Effects of static electropulsing on microstructure and elongation of the ZA 22 alloy were studied by using scanning electron microscopy and transmission electron microscopy techniques. It was found that the current density of electropulsing treatment (EPT) was one of the factors that influenced microstructural changes and dislocation structure in the EPT alloy. The identity of the microstructure and the dislocation density played an important role in plastic elongation of the EPT alloy. The effects of the current density of electropulsing on elongation of the alloy were discussed from the point of view of microstructural evolution and dislocation dynamics.

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Effects of Current Density on Elongation of an Electropulsing Treated Zn-Al Based Alloy

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Isothermal fcc/hcp Transformation in Fe-Si-C-Alloy Thermally Treated at Lower Bainitic Transformation Temperature

Kazuyuki Ogawa, Takahiro Sawaguchi, Setuo Kajiwara

pp. 2778-2784

DOI:

10.2320/matertrans.M2009262

Abstract

High resolution transmission electron microscopic observations have revealed that isothermal fcc (γ) to hcp (ε) transformation accompanies the bainitic transformation from γ austenite to bcc (α) bainite in an Fe-2Si-1.4C (mass%) alloy heated at lower bainitic transformation temperature of 570 K. The ε plates are formed at the ledges of α bainite/γ austenite interfaces. The unit volume of the ε phase with respect to that of the γ austenite increases by as much as 16% when the ε plate has grown from 4 nm to 100 nm in thickness, probably due to enhancement of interstitial carbon. There is no visible stacking fault in the ε phases. These experimental results are interpreted by the concept of bainitic transformation both with shear-type and diffusion-type nature.

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Isothermal fcc/hcp Transformation in Fe-Si-C-Alloy Thermally Treated at Lower Bainitic Transformation Temperature

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Hardening Behavior in Aged Al-4%Cu-0.3%Mg Alloys with 0.5 and 2%Ag Additions

Joel Moreno Palmerin, Héctor J. Dorantes Rosales, Victor M. López Hirata, Nicolás Cayetano Castro, Jorge L. González Velázquez, Angel de J. Morales Ramirez

pp. 2785-2789

DOI:

10.2320/matertrans.M2009233

Abstract

The precipitation characterization of Al-4 mass% Cu-0.3 mass% Mg alloy with additions of 0.5 and 2 mass% Ag during aging treatments was carried out by transmission electron microscopy (TEM) and microhardness measurements. TEM observation of aged samples showed that the Ω phase is the dominant phase and it is in coexistence with the θ′ phase. Additionally, the Ω phase has the morphology of polygonal prism (almost hexagonal) with flat interfaces and a thin thickness. The variation of the cube of mean radius of precipitates, r3, followed a linear relationship, as predicted by the Lifshitz, Slyosov and Wagner (LSW) theory for diffusion-controlled coarsening in both alloys. The coarsening process of the Ω phase was slower in the aged Al-4 mass% Cu-0.3 mass% Mg-2 mass% Ag alloy. The decrease in hardness seems to be related to the coarsening of the Ω phase and the loss of coherency.

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Hardening Behavior in Aged Al-4%Cu-0.3%Mg Alloys with 0.5 and 2%Ag Additions

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Effect of Trace Sodium on High Temperature Embrittlement in Quasi-Static and Impact Deformation of Al-5 mass% Mg Alloys

Hiroyuki Yamada, Keitaro Horikawa, Hidetoshi Kobayashi

pp. 2790-2794

DOI:

10.2320/matertrans.L-M2009824

Abstract

In order to elucidate the mechanism of the high temperature embrittlement of Al-5 mass% Mg alloys containing traces of sodium, microscopic observation of grain boundaries during quasi-static and impact tensile deformation was carried out. The high temperature embrittlement during the quasi-static deformation was caused by a combination of grain boundary sliding and grain boundary serration. On the other hand, the high temperature embrittlement during the impact deformation was caused by the localization of stress concentration at the grain boundaries. This localization was due to planar slips.

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Effect of Trace Sodium on High Temperature Embrittlement in Quasi-Static and Impact Deformation of Al-5 mass% Mg Alloys

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Mechanical Behavior of Au-Based Metallic Glass in Micro-Scale at Ambient and Elevated Temperatures

C. J. Lee, Y. H. Lai, C. W. Tang, J. C. Huang, J. S. C. Jang

pp. 2795-2800

DOI:

10.2320/matertrans.M2009219

Abstract

The Au based amorphous micro-pillars are fabricated by using focus ion beam (FIB) and tested in micro-compression at ambient and elevated temperatures from 300 to 408 K. The room temperature strength of current micro-pillars could reach to 1600–2000 MPa, much higher than the measured strengths for the 3 mm bulk compression specimen. The stress increment can be rationalized by the Weibull statistics. The current Au based micro-pillars maintain inhomogeneous deformation with one (at most two) principal shear band from 300 up to 393 K. At or above Tg (403 and 408 K), the micro-pillars are deformed in a homogeneous manner without the trace of any shear band. For micro-forming, it should be born in mind that there would be apparent stress increment while forming micro- or nano-scaled patterns and pieces.

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Mechanical Behavior of Au-Based Metallic Glass in Micro-Scale at Ambient and Elevated Temperatures

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Microstructural Variation and Tensile Properties of a Cast 5083 Aluminum Plate via Friction Stir Processing

Chun-Yi Lin, Truan-Sheng Lui, Li-Hui Chen

pp. 2801-2807

DOI:

10.2320/matertrans.M2009049

Abstract

A significant friction stir processed defect of kissing bond accompanied with coarse abnormal growth grains can be recognized where located aside the bottom of advancing side as raised up the rotating speed higher than 1450 rpm. Friction stir processed specimens not only possess refined α-Al phase, the coarse irregular solidification precipitates as breakup Al6(Mn,Fe) and Al6Mn actually could be refined and homogenized in stir zone result in a more stable strain hardening behavior especially from the initial stage of tensile deformation, abovementioned factors significantly benefit the tensile ductility of friction stir processed cast plate, but microstructural refinement did not cause apparent difference in yield strength and hardness performance that might result from the textural feature of friction stir processed fully annealed 5083 casting material.

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Microstructural Variation and Tensile Properties of a Cast 5083 Aluminum Plate via Friction Stir Processing

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Amino Acid Assisted Hydrothermal Synthesis of In(OH)3 Nanoparticles Controlled in Size and Shape

Takafumi Sasaki, Masafumi Nakaya, Kiyoshi Kanie, Atsushi Muramatsu

pp. 2808-2812

DOI:

10.2320/matertrans.M2009236

Abstract

Size and shape controlled indium hydroxide (In(OH)3) nanoparticles are readily obtained by amino acid assisted hydrothermal synthesis from an aqueous system. The shape control is achieved by the utilization of adsorption of amino acid on the growing surfaces of the nanoparticles, and rod- and cubic-shaped In(OH)3 nanoparticles are selectively formed in the presence of glycine and L-aspartic acid, respectively. Furthermore, by utilization of two-step aging technique in L-aspartic acid system, originally developed by the gel-sol method, the cubic-shaped In(OH)3 nanoparticles with narrow size distribution are successfully obtained.

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Amino Acid Assisted Hydrothermal Synthesis of In(OH)3 Nanoparticles Controlled in Size and Shape

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Carbide Phases Synthesised from C/Mo Powder Compacts at Specified Sub-Stoichiometric Ratios by Solar Radiation Heating to Temperatures between 1600°C and 2500°C

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

pp. 2813-2819

DOI:

10.2320/matertrans.M2009167

Abstract

There are a number of distinguishable carbide phases in the binary Mo-C system depending on C/Mo ratio as well as on temperature. In a preceding work published in this journal, carbide formation performance for graphite/molybdenum powder mixtures at specified levels of sub-stoichiometric C/Mo atom ratio (C/Mo = 1/1, 3/4, 2/3 and 1/2) by exposure to concentrated solar radiation in a solar furnace at PROMES-CNRS in Odeillo (France) was reported at a target temperature 1900°C. In the present work, the similar carbide synthesis experiments were carried out at 1600°C as well as at temperature exceeding 2500°C. The target temperature setting was adjusted by controlling the downward deviation of the test piece top surface position from the exact focal spot of the parabolic mirror concentrator located above. In this solar furnace at PROMES-CNRS, temperature of the test piece was raised from ambient temperature to the target temperature within fractions of a second. Reaction products detected were hexagonal η-MoC1−x and β-Mo2C (high temperature sub-carbide phase) depending on the C/Mo ratio in the starting material as well as on the processing temperature. No evidence of formation of cubic α-MoC1−x was detected by X-ray diffraction analysis for any test piece examined.

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Carbide Phases Synthesised from C/Mo Powder Compacts at Specified Sub-Stoichiometric Ratios by Solar Radiation Heating to Temperatures between 1600°C and 2500°C

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Effects of Process Parameters on the Macrostructure of a Squeeze-Cast Mg-2.5 mass%Nd Alloy

Yanling Yang, Liming Peng, Penghuai Fu, Bin Hu, Wenjiang Ding, Baozheng Yu

pp. 2820-2825

DOI:

10.2320/matertrans.MRA2008452

Abstract

The effects of applied pressure, pouring and die temperatures on the macrostructure of a squeeze-cast Mg-2.5 mass%Nd alloy were investigated. The grain size of the Mg-2.5 mass%Nd alloy increased with increasing applied pressure from 60 to 180 MPa when the pouring and die temperatures were 725°C and 330°C. This was attributed to the melting temperature at the time when pressure was applied under the pouring temperature of 725°C, higher than the liquid temperature. Whilst, the pouring and die temperatures are 700°C and 330°C, the grain size of the alloy decreased with increasing applied pressure from 0 to 180 MPa. Lower die and pouring temperatures were favorable to refine grains, but the effects of the die temperature on the distribution and structure of grains were much smaller than those of the pouring temperature.

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Effects of Process Parameters on the Macrostructure of a Squeeze-Cast Mg-2.5 mass%Nd Alloy

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Effects of Electron Beam Irradiation on Impact Value of Carbon Fiber Reinforced Thermoplastic Polyetheretherketone

Yoshitake Nishi, Hiroaki Takei, Keisuke Iwata, Michelle Salvia, Alain Vautrin

pp. 2826-2832

DOI:

10.2320/matertrans.M2009210

Abstract

Homogeneous low voltage electron beam irradiation (HLEBI) improves the Charpy impact value (auc) of composites sheets of carbon fiber reinforced thermoplastic polyetheretherketone (CFRTP) with 2 mm thickness, although the irradiated depth estimated is 177±32 μm at their both sides surface. The auc values at low fracture probability (Pf) of 0.13 for CFRTP irradiated at 0.43 MGy (kJg−1) is 78 kJm−2, which is 56% higher than that (50 kJm−2) for CFRTP before irradiation. Although the lowest impact values (as) estimated by three parameters Weibull equation is zero for CFRTP before irradiation, HLEBI enhances the as value. The highest as value is more than 55 kJm−2 for CFRTP irradiated from 0.43 to 0.65 MGy. Thus, HIEBL remarkably enhances the as value, as well as the auc value at low Pf value. Since HLEBI enhances the Weibull coefficient (n), it also enhances the reproducibility of CFRTP samples. The maximum n value is found at 0.43 MGy of HLEBI dose. The interfacial friction force, as well as the strengthening of both carbon fiber and polyetheretherketone probably contributes the HLEBI effects to enhance the as value of CFRTP, as well as enhancement of reproducibility.

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Effects of Electron Beam Irradiation on Impact Value of Carbon Fiber Reinforced Thermoplastic Polyetheretherketone

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Effect of Intermetallic Compound Layer on Tensile Strength of Dissimilar Friction-Stir Weld of a High Strength Mg Alloy and Al Alloy

Naotsugu Yamamoto, Jinsun Liao, Shuhei Watanabe, Kazuhiro Nakata

pp. 2833-2838

DOI:

10.2320/matertrans.M2009289

Abstract

The friction stir weldability of a fine-grained high strength AZ31B magnesium alloy to A5083 Al alloy was evaluated at various welding conditions, by using a tool with shoulder diameter of 15 mm, pin diameter of 5 mm and pin length of 3.9 mm. A square butt dissimilar joint without any defect was obtained at the condition of welding speed 100 mm/min, tool rotating speed 500 rpm and offset 0 mm. Higher or lower welding speeds or rotating speeds led to either the formation of defect or lack of bonding in the joint. Defects occurred also in the case that the offset was not 0 mm, i.e. the insertion position of the probe was on either Mg side or Al side, when tool rotating speed was 500 rpm and welding speed was 100 mm/min. The maximum tensile strength of the dissimilar joints in the present study was about 115 MPa, lower than that of Al alloy base metal (about 308 MPa). Transmission electron microscopy showed that an intermetallic compound (IMC) layer, which consisted of Al12Mg17 and Al3Mg2, formed at the bonding interface of the joints, and it was found that the formation and growth of the IMC were controlled by the react diffusion of Mg and Al atoms, instead of the eutectic reaction. The present study demonstrated that the tensile strength of the dissimilar joints was mainly affected by the thickness of IMC layer and the mechanical interlock between magnesium and aluminum alloys. The tensile strength decreased remarkably with the increase in the thickness of IMC layer, which made the mechanical interlock weaker.

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Effect of Intermetallic Compound Layer on Tensile Strength of Dissimilar Friction-Stir Weld of a High Strength Mg Alloy and Al Alloy

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Observation of Magnetic Domain Structure in Fe81B15Si4 Amorphous Alloy by Lorentz Microscopy and Electron Holography

Masahiro Hiraoka, Zentaro Akase, Daisuke Shindo, Yuichi Ogawa, Yoshihito Yoshizawa

pp. 2839-2843

DOI:

10.2320/matertrans.M2009278

Abstract

Effects of heat treatment, with and without an external magnetic field, on the magnetic properties of Fe81B15Si4 amorphous specimens are investigated by Lorentz microscopy and electron holography. These observations are used to clarify the details of magnetizing processes in the specimens. It is found that heat-treatment with an external magnetic field increases the magnetic anisotropy, while that without reduces the magnetic anisotropy. It is considered that this difference results from the alleviation of the strain field by heat treatment and the induced magnetic anisotropy caused by heat treatment with a magnetic field.

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Observation of Magnetic Domain Structure in Fe81B15Si4 Amorphous Alloy by Lorentz Microscopy and Electron Holography

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Development of a New Gravity Separator for Plastics —a Hybrid-Jig—

Kunihiro Hori, Masami Tsunekawa, Masatsune Ueda, Naoki Hiroyoshi, Mayumi Ito, Hideaki Okada

pp. 2844-2847

DOI:

10.2320/matertrans.M-M2009825

Abstract

The development of mechanical methods for plastic-plastic separation is important for recycling of scrapped plastics of office/home appliances and cars. This paper proposes a Hybrid-Jig as a new method for plastic-plastic separation. The Hybrid-Jig was developed based on jigging and flotation, where air bubbles are introduced into the particle bed during jigging to modify the apparent specific gravity of the particles by the attachment of air bubbles to the particles so that particles having different surface properties can be separated by jigging even if their specific gravities are similar.
To demonstrate the performance of the Hybrid-Jig, a laboratory scale TACUB jig was modified to induce air bubbles through the screen under the particle bed, and separation experiments of plastic particle mixtures were carried out under various displacements and frequencies of water pulsation. Feed samples were particle mixtures of two plastics chosen from eight kinds of plastics (3 of polyvinyl chloride (PVC), 4 of polyethylene (PE), and 1 of polyethylene terephthalate (PET)). The particles were cylindrical of 2–3 mm length and diameter, and their specific gravities were 1.05–1.55.
In normal jig operation (without air bubbles), plastic particles with similar specific gravities were difficult to separate, but they were easily separated by the Hybrid-Jig, when air bubbles adsorbed on the surface of the more hydrophobic plastics, and the plastic particles with air bubbles were recovered as top product due to the decrease in apparent specific gravity. Because the differences in the hydrophobicity of the plastics cause the selective bubble attachment, high grade plastic products over 99.9 mass% were recovered by the Hybrid-Jig even for plastic mixtures having the same specific gravity.

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Development of a New Gravity Separator for Plastics —a Hybrid-Jig—

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Conductivity Percolation on a Square Lattice with Two Different Sizes of Particles

Kazuhito Shida, Ryoji Sahara, MN Tripathi, Hiroshi Mizuseki, Yoshiyuki Kawazoe

pp. 2848-2851

DOI:

10.2320/matertrans.M2009202

Abstract

Electric conductance of percolation clusters is calculated by means of the random circuit approximation, under a binary distribution in the size of the conducting particles. Although we have already investigated the same size distribution model in terms of the percolation threshold, the electric transport conductance of this model is never reported before. The size distribution of conducting particles induces a clear difference in the ensemble of random circuit. However, the observed critical behavior and critical exponents are closely matched to those reported for monodisperse cases.

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Conductivity Percolation on a Square Lattice with Two Different Sizes of Particles

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Effects of Different Hydroxyapatite Binders on Morphology, Ca/P Ratio and Hardness of Nd-YAG Laser Clad Coatings

C. S. Chien, T. J. Han, T. F. Hong, T. Y. Kuo, T. Y. Liao

pp. 2852-2857

DOI:

10.2320/matertrans.M2009245

Abstract

Hydroxyapatite (HA) is a well known biocompatible coating material used to improve the bonding quality between metallic substrates and the surrounding bone tissue following implantation. In this study, HA is mixed with two different binders, namely water glass (WG) and polyvinyl alcohol (PVA), respectively, and is then clad on Ti-6Al-4V substrates using an Nd:YAG laser beam. The results show that for both binders, the weld surface width, penetration depth and heat affected zone decrease with an increasing travel speed. The PVA binder increases the number and severity of the cracks in the transition layer of the weld bead, whereas the WG binder increases the porosity. In each coating layer, the middle level has the lowest Ca/P ratio, while the lower level has the highest value. Moreover, the Ca/P ratio reduces with an increasing travel speed. The microstructure of the transition layers is mainly composed of CaTiO3, Ca2P2O7, TiP2, Ti, and HA phases. SiO2 and Si2Ti are additional phases found in the specimen used WG as binder material. The WG binder yields a higher hardness of the coating layer and transition layer than the PVA binder. However, for both binders, the hardness of the transition layer is generally far higher than that of the substrate or the coating layer.

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Effects of Different Hydroxyapatite Binders on Morphology, Ca/P Ratio and Hardness of Nd-YAG Laser Clad Coatings

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Constitutive Relation for Ambient-Temperature Creep in Hexagonal Close-Packed Metals

Tetsuya Matsunaga, Tatsuya Kameyama, Kohei Takahashi, Eiichi Sato

pp. 2858-2864

DOI:

10.2320/matertrans.M2009223

Abstract

This paper reports creep tests on three kinds of polycrystalline hexagonal close-packed metals, i.e. commercially pure titanium, pure magnesium, and pure zinc, in the vicinity of ambient temperature even below their 0.2% proof stresses. These materials showed significant steady state creep rates around 10−9 s−1 and had stress exponents of about 3.0. Arrhenius plots in the vicinity of ambient temperature indicate extremely low apparent activation energies, Q, of about 20 kJ/mol, which is at least one-fourth of the Q of dislocation-core diffusion. Ambient-temperature creep also has a grain-size effect with an exponent of 1.0. These parameters indicate that ambient-temperature creep is a new creep deformation mechanism in h.c.p. materials.

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Constitutive Relation for Ambient-Temperature Creep in Hexagonal Close-Packed Metals

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Intragranular Deformation Mechanisms during Ambient-Temperature Creep in Hexagonal Close-Packed Metals

Tetsuya Matsunaga, Tatsuya Kameyama, Kohei Takahashi, Eiichi Sato

pp. 2865-2872

DOI:

10.2320/matertrans.M2009224

Abstract

Intragranular deformation mechanisms were investigated for ambient-temperature creep of pure hexagonal close-packed (h.c.p.) metals, i.e. commercially pure titanium, pure magnesium and pure zinc, by transmission electron microscopy and electron back-scatter diffraction pattern mapping analysis. First, straightly aligned dislocation arrays were observed in all of the specimens. Second, although the Burgers vectors of ⟨a⟩ and several slip systems were observed, only one slip system was activated inside of each grain. Third, the deformation twins that form during creep hinder creep strain. Therefore, the dominant intragranular deformation mechanism of ambient-temperature creep is a planner slip of dislocations inside of a grain.

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Intragranular Deformation Mechanisms during Ambient-Temperature Creep in Hexagonal Close-Packed Metals

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New Method for Production of Solar-Grade Silicon by Subhalide Reduction

Kouji Yasuda, Kunio Saegusa, Toru H. Okabe

pp. 2873-2878

DOI:

10.2320/matertrans.M2009260

Abstract

In this study, a new method for producing Si, called “halidothermic reduction”, was investigated with the purpose of producing solar-grade silicon (SOG-Si); by this method, SiCl4 was reduced by gaseous subhalide used as the reductant. Si was produced by reacting SiCl4 with Al subhalides, which were produced by reacting AlCl3 with metallic Al. Fibrous Si with diameters ranging from submicrons to several tens of micrometers was deposited as a result of halidothermic reduction of SiCl4 by an Al subchloride (AlClx) reductant at 1273 K. The size of Si deposits and the reaction rate were increased by simultaneously supplying AlCl3 and SiCl4 vapors to a reaction tube holding Al metal. The impurity level of the obtained Si was found to be lower than the detection limit of X-ray fluorescence. Halidothermic reduction is suitable for producing high-purity Si since all reactants and byproducts exist in the vapor phase. Further, this process has high productivity since the overall reaction is a highly scalable metallothermic reduction reaction.

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New Method for Production of Solar-Grade Silicon by Subhalide Reduction

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Dye-Sensitized Solar Cells Made with TiO2-Coated Multi-Wall Carbon Nanotubes and Natural Dyes Extracted from Ipomoea

Ho Chang, Tung-Jung Hsieh, Tien-Li Chen, Kouhsiu-David Huang, Ching-Song Jwo, Shu-Hua Chien

pp. 2879-2884

DOI:

10.2320/matertrans.M2009203

Abstract

This paper reports the fabrication of photoelectrode of dye-sensitized solar cells (DSSCs) using TiO2-modified multi-wall carbon nanotubes (MWCNTs). The self-developed nanofluid synthesis system is employed to make TiO2 nanofluid which has good roundness and uniform size, at an average particle size of 40 nm. The self-prepared TiO2 nanoparticles, after being mixed with TiO2-nanoparticle-modified MWCNTs (TiO2-CNT) by sol-gel method, are deposited in an indium tin oxide (ITO) conductive glass by electrophoretic deposition method, thus forming a thin film of TiO2/CNTs of 14 μm thick. As seen from the FE-SEM image and Raman spectra, the CNTs adhere well to the TiO2 nanoparticles. In addition, the developed DSSCs make use of the natural dye extracted from ipomoea. The TiO2-nanoparticle-modified MWCNTs prepared by sol-gel method can improve the performance of DSSCs by increasing the short-circuit current density (Jsc). The enhancement of Jsc is attributed to the increased adsorption area of thin films and the improved interconnectivity among TiO2 particles and TiO2-CNTs. Experimental results show that TiO2-modified MWCNTs prepared using natural dye extracted from ipomoea could enhance the light-to-electricity efficiency of DSSCs by as high as 30% (0.278% to 0.359%).

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Dye-Sensitized Solar Cells Made with TiO2-Coated Multi-Wall Carbon Nanotubes and Natural Dyes Extracted from Ipomoea

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Precompaction Effects on Density and Mechanical Properties of Al2O3 Nanopowder Compacts Fabricated by Magnetic Pulsed Compaction

S. J. Hong, J. M. Koo, J. G. Lee, M. K. Lee, H. H. Kim, C. K. Rhee

pp. 2885-2890

DOI:

10.2320/matertrans.M2009265

Abstract

In this study, the effects of precompaction on the density, microstructure, mechanical and electrical properties of α-Al2O3 bulks fabricated by the combined application of magnetic pulsed compaction (MPC) and a sintering process were reported. The obtained density of the α-Al2O3 bulks prepared by the combined processes increased with the increasing MPC pressure and precompaction pressure. The resultant higher hardness and breakdown voltage of the consolidated bulks following combined application of the magnetic pulsed compaction, precompaction and sintering process could be attributed to the homogeneously distributed ultra-fine microstructure than that of general processing, suggesting that the grain growth was remarkably reduced during the MPC processes.

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Precompaction Effects on Density and Mechanical Properties of Al2O3 Nanopowder Compacts Fabricated by Magnetic Pulsed Compaction

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Formation Mechanism of Microchannels and Lining Layers in Sintered Iron Powder Compacts with Copper Sacrificial Cores

Tatsuya Ohmi, Takuhiro Kodama, Manabu Iguchi

pp. 2891-2896

DOI:

10.2320/matertrans.M2009252

Abstract

The formation mechanism of microchannels with Fe-Cu alloy lining layers in iron bodies produced by a powder-metallurgical microchanneling process has been investigated. Copper wire was used as a sacrificial core that gives the shape of the microchannel and supplies the alloying element for the lining layer. An iron powder compact containing the sacrificial core was heated and sintered at temperatures between the melting points of copper and iron. Quenching experiments showed that the microchannel was produced just after melting of copper. In a quenched specimen with a newly-formed microchannel, fine copper-rich regions were observed between the iron powder particles in the lining layer. These results established that infiltration of molten copper into the iron powder is the dominant mechanism for the Fe-Cu microchanneling process. It was also found that the liquid copper infiltrated via preferential flow pathways between the iron powder particles.

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Formation Mechanism of Microchannels and Lining Layers in Sintered Iron Powder Compacts with Copper Sacrificial Cores

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Synthesis of TiN Nanoparticles by Explosion of Ti Wire in Nitrogen Gas

Wonbaek Kim, Je-shin Park, Chang-yul Suh, Sung-wook Cho, Sujeong Lee, In-Jin Shon

pp. 2897-2899

DOI:

10.2320/matertrans.M2009297

Abstract

Nano-sized Titanium nitride powders were synthesized by electrical explosion of Ti wire under nitrogen atmosphere ranging from 0.2 to 1.5 atm. Electron microscopy and X-ray diffraction studies revealed that the reaction products are cube-shaped single phase TiN nanoparticles. The lattice parameter of TiN nanoparticles increased with nitrogen pressure in the chamber. The nitrogen content of nanoparticles was estimated from their lattice parameter being comparable to the stoichiometric composition of TiN. Small amount of TiN0.3 phase was formed when nitrogen pressure in the chamber was low.

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Synthesis of TiN Nanoparticles by Explosion of Ti Wire in Nitrogen Gas

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