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MATERIALS TRANSACTIONS Vol. 45 (2004), No. 10

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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21 Nov. (Last 30 Days)

MATERIALS TRANSACTIONS Vol. 45 (2004), No. 10

Low Temperature Grain Boundary Diffusion of Chromium in SUS316 and 316L Stainless Steels

Masaki Mizouchi, Yoshihiro Yamazaki, Yoshiaki Iijima, Koji Arioka

pp. 2945-2950

DOI:

10.2320/matertrans.45.2945

Abstract

Grain boundary diffusivity of chromium in SUS316 and 316L stainless steels has been determined in the temperature range between 518 and 1173 K. The magnitudes of the grain boundary diffusivities in four kinds of specimens are in the order of the cold-worked SUS316, the solution-treated SUS316L, the solution-treated SUS316 and the sensitized SUS316. The grain boundary diffusivities in these specimens are remarkably higher than those of previous works. The activation energies for the former are 85—91 kJmol−1, whereas those for the latter are 151—234 kJmol−1.

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Low Temperature Grain Boundary Diffusion of Chromium in SUS316 and 316L Stainless Steels

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Valence Change of Cations in Ceria-Zirconia Solid Solution Associated with Redox Reactions Studied with Electron Energy-Loss Spectroscopy

Shigeo Arai, Shunsuke Muto, Junya Murai, Tsuyoshi Sasaki, Yoshio Ukyo, Kotaro Kuroda, Hiroyasu Saka

pp. 2951-2955

DOI:

10.2320/matertrans.45.2951

Abstract

It has been known that the ceria-zirconia solid solutions (Ce2Zr2O7+x, 0 ≤ x ≤ 1) have an excellent ability for oxygen absorption/release. The local charge states of cations in the CeO2-ZrO2 solid solutions have been studied by means of electron energy-loss spectroscopy (EELS) attached to a transmission electron microscope. The relative intensity of cerium-M4,5 white-line peaks from Ce2Zr2O7, Ce2Zr2O7.5 and Ce2Zr2O8 showed a systematic change, which corresponded to the valence change of cerium; Ce3+ in Ce2Zr2O7, Ce4+ in Ce2Zr2O8. By contrast, the valence of the zirconium ions, which are mainly at the nearest neighbor sites of absorbed or emitted oxygen atoms, remains to be quaternary irrespective of oxygen contents. It was found that the energy-loss near edge structure (ELNES) of the cerium-M4,5 edge in Ce2Zr2O7.5 was well reproduced by the sum of the ELNES profiles of Ce2Zr2O7 and Ce2Zr2O8 with an equal weight, the phenomenon of which is known as the ‘valence fluctuation,’ or ‘mixed valence state,’ often observed in rare earth metal compounds.

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Valence Change of Cations in Ceria-Zirconia Solid Solution Associated with Redox Reactions Studied with Electron Energy-Loss Spectroscopy

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Microstructural Morphology Changes of the Lead-Tin Eutectic Alloy by Different Undercooling Levels

Heesam Kang, Wooyoung Yoon

pp. 2956-2959

DOI:

10.2320/matertrans.45.2956

Abstract

Experimental work is described in undercoolings and microstructures of Pb-Sn eutectic alloy droplets emulsified in oil bath. By controlling experimental variables, the final droplet size produced was in the range of 10 to 300 μm, and measured undercoolings ranged up to about 70 K. Microstructures of the droplets depend strongly on the degree of undercooling before solidification. By increasing undercooling, three major microstructure transitions, which include the morphological changes of eutectic phase from lamellar to anomalous in lower undercooling level and of primary α-Pb phase from dendrite to equiaxed grains in higher undercooling levels, are observed. The phase change from eutectic to primary α-Pb dendrite plus eutectic is also observed. The physical mechanism of these microstructure transitions is analyzed on the basis of the Lipton-Kurz-Trivedi theory for dendrite growth and the Jackson-Hunt theory for lamellar eutectic growth.

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Microstructural Morphology Changes of the Lead-Tin Eutectic Alloy by Different Undercooling Levels

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Effect of Initial Grain Orientation on Evolution of Deformed Microstructure in Hot Compressed Ni-30Fe Alloy

Jae-Young Cho, Tadanobu Inoue, Fuxing Yin, Kotobu Nagai

pp. 2960-2965

DOI:

10.2320/matertrans.45.2960

Abstract

An experimental procedure has been developed to investigate systematically the effect of initial grain orientation on the evolution of deformed microstructure in Ni-30Fe alloy. The investigation of identical grains before and after hot deformation made it possible to trace the evolution of microstructure deformed up to 50% at a strain rate of 1/s in a single pass at 1023 K using a hot compression simulator. The localized inhomogeneous shear bands occurred in almost all grains. On the other hand, the near {110} ‹001› grains have undergone fairly homogeneous deformation even after a high equivalent plastic strain of 1.9.

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Effect of Initial Grain Orientation on Evolution of Deformed Microstructure in Hot Compressed Ni-30Fe Alloy

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Effect of Shear Deformation on Microstructural Evolution of Ni-30Fe Alloy during Hot Deformation

Jae-Young Cho, Tadanobu Inoue, Fuxing Yin, Kotobu Nagai

pp. 2966-2973

DOI:

10.2320/matertrans.45.2966

Abstract

Electron backscattered diffraction analysis has been used to investigate the effect of shear deformation on the microstructural evolution of a Ni-30Fe alloy during hot deformation. The alloy was compressed by 50% or 75% in thickness at a strain rate of 1/s in a single pass at 1023 K using a hot compression simulator. An explicit finite element analysis was carried out to evaluate the inhomogeneous strain distribution introduced in the specimens by hot compression simulator. As the equivalent strain increased, the fraction of high angle grain boundaries with misorientaions between 15° and 30° increased almost in the similar way regardless of the presence of shear strain. The fraction of high angle grain boundaries having misorientations in excess of 30° increased mainly at the expense of low angle grain boundaries with misorientations smaller than 15°. Such the expense occurred at much higher rate with shear strain than without shear strain. The compressive direction changed continuously in the areas with shear strain component during deformation, which was thought to accelerate the subdivision of austenite grain interiors with increased misorientations between subdivided local areas.

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Effect of Shear Deformation on Microstructural Evolution of Ni-30Fe Alloy during Hot Deformation

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Competitive Nucleation and Growth of {111} Ω with {001} GP Zones and θ′ in a Stress-Aged Al-Cu-Mg-Ag Alloy

Shinji Muraishi, Shinji Kumai, Akikazu Sato

pp. 2974-2980

DOI:

10.2320/matertrans.45.2974

Abstract

The stress aging method was conducted for an Al-Cu-Mg-Ag polycrystalline alloy to study the competitive nucleation and growth behavior of GP zones, θ′ and Ω precipitates concurrently existing on different {001} and {111} habit planes. After initial stress aging for 1 h, the preferential nucleation of GP zones against Ω occurred irrespective of the stress direction applied to the grains. With increasing aging time, the density of Ω increased while the GP zones decreased in number to dissolve into the matrix, resulting from competitive nucleation due to the mutual constituent of Cu in GP zones and Ω. With further stress aging, the growth of θ′ plates was enhanced in comparison with the growth of Ω plates. The relative number density change between {001} and {111} precipitates was emphasized especially in grains with the stress direction along [001], which indicated that nucleation and growth of GP zones and θ′ plates were highly sensitive to external stress compared with that of Ω. HREM observation found that low amounts of small Ω plates were nucleated during the initial stress aging indicating retarded Ω nucleation. Two-step aging (stress aging for 1 h followed by the stress-free aging) revealed that preferentially nucleated GP zone against Ω during the initial stress aging determined the successive precipitation sequence of the precipitation of Ω and θ′.

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Competitive Nucleation and Growth of {111} Ω with {001} GP Zones and θ′ in a Stress-Aged Al-Cu-Mg-Ag Alloy

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Phase Transformation of an Austempered Ductile Iron during an Erosion Process

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

pp. 2981-2986

DOI:

10.2320/matertrans.45.2981

Abstract

Ductile iron specimens of ∼3.5 mass% C and ∼2.8 mass% Si were austempered at 420°C for 0.5 h∼24 h. These upper bainitic austempered ductile iron (ADI) specimens were 90° -eroded by Al2O3 particles of ∼275 μm grit size under the average particle velocity of 73 m·s−1 to understand phase transformation at the erosion surface. According to the experimental results, the retained austenite content and the carbon content of bainitic ferrite decreases through phase transformation during erosion. After erosion, the retained austenite and the high carbon content bainitic ferrite form ε-carbide, another carbide and ferrite. The other austempering carbide of the remaining matrix also transforms into ε-carbide in the erosion process.

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Phase Transformation of an Austempered Ductile Iron during an Erosion Process

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Measurement of the Densities of Nickel-Based Ternary, Quaternary and Commercial Alloys

Kusuhiro Mukai, Zushu Li, Liang Fang

pp. 2987-2993

DOI:

10.2320/matertrans.45.2987

Abstract

The modified sessile drop method (MSDM) and the modified pycnometric method (MPM) have been employed to measure precisely the densities of liquid nickel-based ternary (Ni-Co-Al) and quaternary (Ni-Co-Al-Cr, Ni-Co-Al-Mo, Ni-Cr-Al-Mo) alloys and four commercial superalloys in liquid and mushy states. There was a good agreement between the values measured by the two methods. The measured densities of liquid model alloys and commercial superalloys in liquid and mushy states decreased linearly with increasing temperature for the experimental temperature range. The temperature coefficient of the density of liquid ternary Ni-Co-Al alloys measured in this work can be represented as a quadratic function of the aluminium concentration in the alloys. The density of liquid Ni-Co-Al alloys can be expressed as a function of both temperature and aluminium concentration in the alloys. The recommended equations for the densities of liquid nickel-based ternary and quaternary alloys and four commercial superalloys in liquid and mushy states were obtained by analysing density values measured by both MSDM and MPM. The calculated values from the recommended density equations show good agreement with those measured by both MSDM and MPM.

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Measurement of the Densities of Nickel-Based Ternary, Quaternary and Commercial Alloys

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Solubility of Metal Oxides under Control of Basicity by Electrolysis in Fused Na2SO4

Michihisa Fukumoto, Takahiro Suzuki, Masanori Sano, Masayuki Hirade, Motoi Hara

pp. 2994-2998

DOI:

10.2320/matertrans.45.2994

Abstract

The dissolution behavior of NiO, Co3O4, Fe2O3, Fe3O4, SiO2, Al2O3 and Cr2O3 powders under the control of the O2− activity of fused Na2SO4 by electrochemical polarization was investigated. As a result, the increase in the quantity of electricity for the anodic reaction with increasing polarization potential for the platinum electrode caused an increase in the basicity(−log aNa2O) of the fused Na2SO4, while the increase in the quantity of electricity for cathodic reaction with decreasing polarization potential caused a decrease in basicity of the fused Na2SO4. The solubility of NiO and Co3O4 in fused Na2SO4 increased in the anodic potential region. However, their solubility did not increase in the cathodic potential region. The solubility of Fe2O3 and Fe3O4 slightly increased in the anodic potential region. The solubility of SiO2 did not increase in the anodic potential region, whereas the solubility of SiO2 increased with a decrease in the polarization potential in the cathodic potential region. The solubility of Al2O3 and Cr2O3 increased in the cathodic and anodic potential regions. The solubility of Al2O3 was larger than that of Cr2O3. We found that the resistance of acid and basic dissolution for oxides could be estimated by the electrochemical polarization method.

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Solubility of Metal Oxides under Control of Basicity by Electrolysis in Fused Na2SO4

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High Density Powder Injection Molded Compacts Prepared from a Feedstock Containing Coarse Powders

Guo-Jiun Shu, Kuen-Shyang Hwang

pp. 2999-3004

DOI:

10.2320/matertrans.45.2999

Abstract

Carbonyl iron powders are the most widely used raw powder in fabricating the powder injection molded (PIM) components owing to their high driving forces for sintering. However, the cost of this powder is relatively high. To improve the competitiveness of the PIM process, coarse iron powders, which are much more economical, were mixed with fine carbonyl iron powders in an optimum ratio of 6/4 in this study. This replacement of fine carbonyl iron powders did not change the kneading and molding behaviors significantly. The solvent and thermal debinding rates of the compacts that contain 100 mass% and 40 mass% fine powders also showed little difference. Such debinding results, which are contrary to the general belief, suggest that the particle size is not the critical factor in the debinding of PIM compacts. The debinding rate is more likely controlled by the diffusion of the soluble binder in the solvent (for solvent debinding) and the decomposition rate of the backbone binder (for thermal debinding). High sintered densities can still be attained in the compact with mixed powders after α phase stabilizers, such as P and Mo, are added. These additives prevent the α-γ phase transformation and the accompanying exaggerated grain growth. When 0.7 mass%P or 0.35 mass%P+2.5 mass%Mo is added into a mixed powder that contains 60 mass% coarse iron powders, high densities more than 96% can be attained after the compact is sintered at 1593 K for 3.6 ks. The hardness, tensile strength, and elongation of the Fe-2.5 mass%Mo-0.35 mass%P were HRB68, 520 MPa, and 20%, respectively. The densities, mechanical properties, and comparable processing capability found in this study show that the more economical coarse iron powder can be used in the PIM process.

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High Density Powder Injection Molded Compacts Prepared from a Feedstock Containing Coarse Powders

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Optimization of Thickness Uniformity in Electrodeposition onto a Patterned Substrate

Young-joo Oh, Soon-hyo Chung, Man-seung Lee

pp. 3005-3010

DOI:

10.2320/matertrans.45.3005

Abstract

A numerical simulation based on the finite element method was used to obtain the optimal electrodeposition condition at a patterned cathode. The calculated deposition rates agreed well with the measured ones. Influences of the following parameters on uniformity of electrodeposit have been studied; width of auxiliary electrode, gap between cathode and auxiliary electrode, distance between the inner wall of bath and auxiliary electrode, shape of auxiliary electrode, paddle velocity, gap between cathodes and paddles, anode size.

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Optimization of Thickness Uniformity in Electrodeposition onto a Patterned Substrate

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Characterization and Optimization of Arc Spray Process Parameters for Synthesis of TiO2 Nanoparticles

Liang-Chia Chen, Tsing-Tshih Tsung, Ho Chang, Jen-Yan Sun

pp. 3011-3017

DOI:

10.2320/matertrans.45.3011

Abstract

This article presents the process characterization and optimization of the nanoparticle fabrication process known as the Submerged Arc Spray Nanoparticle Synthesis System (SANSS) by using a developed on-line nanoparticle measurement system and Taguchi method. Without process characterization and optimization, preliminary experimental results indicated that the average secondary diameter of prepared nanoparticles, widely ranging from 45 to 350 nm, are significantly influenced by the process parameters, such as operating pressure, temperature, electrical current and type of dielectric liquids employed. To improve this, an on-line particle sizing system was developed and deployed to measure the particle dimension and analyze the nanoparticle synthesis process. Experiments based on Taguchi method were then conducted to investigate the optimum process parameters for producing nanoparticles with improved properties, such as particle size and uniformity. The experimental results revealed that the pulsed peak voltage and the pulsed peak current have the most significant effect on decreasing the secondary particle size of the TiO2 nanoparticles and that the on-time duration and off-time duration also play an important predominant effect. Using the optimized process parameters, the average secondary diameter of prepared TiO2 particles was reduced from 160 to 65 nm and the range of particle size disparity was narrowed from 300 to 170 nm. The primary particle size observed from TEM results also confirmed a significant reduction of the averaged TiO2 nanoparticle diameter and size disparity.

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Characterization and Optimization of Arc Spray Process Parameters for Synthesis of TiO2 Nanoparticles

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Optimization of Hot Rolling Process of Gravity Cast AZ31-xCa (x = 0∼2.0 mass%) Alloys

Chang Dong Yim, Bong Sun You, Jin Su Lee, Wan Chul Kim

pp. 3018-3022

DOI:

10.2320/matertrans.45.3018

Abstract

In this study, the effects of Ca content and processing variables on the external surfaces and tensile properties of hot-rolled AZ31-xCa sheets were evaluated systematically. The number and length of side crack were decreased with increasing preheating temperature and decreasing reduction ratio per pass and Ca content. The UTS and YS were not strongly dependent on the Ca content but the elongation decrease with increasing Ca content. The amount of decrease in elongation due to increase in Ca content was least when the sheets were fabricated under preheating temperature of 400°C and reduction ratio per pass of 15%. The sheets had the sound external features with little side cracks by homogenization of gravity cast AZ31-xCa alloys before hot rolling. In the cases of AZ31-xCa alloys containing under 1 mass% Ca, the annealed sheets after homogenization and hot rolling had the similar tensile properties to those of AZ31 sheet.

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Optimization of Hot Rolling Process of Gravity Cast AZ31-xCa (x = 0∼2.0 mass%) Alloys

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Electrical and Optical Properties of IrO2 Thin Films Prepared by Laser-ablation

Yuxue Liu, Hiroshi Masumoto, Takashi Goto

pp. 3023-3027

DOI:

10.2320/matertrans.45.3023

Abstract

IrO2 thin films were prepared by laser ablation using an Ir target at substrate temperatures (Tsub) from room temperature (RT) to 873 K in an oxygen atmosphere. A small amount of Ir metal was contained in IrO2 films prepared at Tsub = RT. The lattice parameters particularly a-axis values decreased with increasing Tsub, and the values were a = 0.452 nm, c = 0.315 nm at Tsub = 873 K in agreement with those of bulk IrO2. The surface roughness increased from 1.2 to 5.2 nm with increasing Tsub. These values imply that the IrO2 films were far smoother than those prepared by MOCVD and sputtering. The electrical conductivity of IrO2 films prepared at Tsub = RT changed from semiconductor-like to metallic behavior after a heat-treatment; on the other hand, those prepared at Tsub > 573 K were metallic without changing after heat-treatment. The IrO2 films prepared at Tsub = 873 K showed the highest electrical conductivity of 37 × 10−8 Ωm at RT. The optical transmittance of IrO2 thin films were mainly dependent on thickness and surface roughness, and were around 10% at a wavelength range from 300 to 800 nm.

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Electrical and Optical Properties of IrO2 Thin Films Prepared by Laser-ablation

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Comparison among Mechanical Properties of Investment-Cast c.p. Ti, Ti-6Al-7Nb and Ti-15Mo-1Bi Alloys

Chia-Wei Lin, Chien-Ping Ju, Jiin-Huey Chern Lin

pp. 3028-3032

DOI:

10.2320/matertrans.45.3028

Abstract

The present study compares castability and mechanical performance among alloys of c.p. Ti, Ti-6Al-7Nb and a newly-developed Ti-15Mo-1Bi in regard to their as-cast state. Experimental results indicate that average cast length of Ti-6Al-7Nb appears a little lower than c.p. Ti and Ti-15Mo-1Bi, although the differences are not significant. C.p. Ti has an hcp α phase of lath-type morphology with serrated, irregular grain boundaries. Ti-6Al-7Nb is dominated by hexagonal α′ phase with acicular martensitic morphology. In particular, Ti-15Mo-1Bi is comprised of equiaxed, metastable bcc β phase. The hardened layer thicknesses of three materials are similar. Ti-15Mo-1Bi has the highest surface microvickers hardness, while c.p. Ti has the lowest. The bulk hardness of c.p. Ti is much lower than the other two alloys which display similar hardness. Notably, Ti-15Mo-1Bi and Ti-6Al-7Nb have similar bending strength which is far higher than c.p. Ti. The bending modulus of Ti-15Mo-1Bi is significantly lower than c.p. Ti and Ti-6Al-7Nb. Ti-15Mo-1Bi also shows a much larger elastic recovery angle than two other materials. Tensile test indicates that Ti-15Mo-1Bi has a similar UTS but much higher YS and elongation along with much lower tensile modulus compared to Ti-6Al-7Nb.

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Comparison among Mechanical Properties of Investment-Cast c.p. Ti, Ti-6Al-7Nb and Ti-15Mo-1Bi Alloys

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The Effect of Strain Distribution on Abnormal Grain Growth in Cu Thin Films

Miki Moriyama, Kentaro Matsunaga, Toshifumi Morita, Susumu Tsukimoto, Masanori Murakami

pp. 3033-3038

DOI:

10.2320/matertrans.45.3033

Abstract

The effect of intrinsic strain on grain growth in Cu thin films was studied by both plan-view and cross-sectional scanning ion microscope in a focused ion beam system. Significant grain growth with bimodal grain size distribution was observed during room temperature storage in the Cu films which were deposited on the Si3N4 substrates by a sputter-deposition technique. In the thick Cu films, a non-uniform grain size distribution was observed along a direction normal to the film surface: the large grains were observed at the location close to the substrate surface. This grain size distribution coincided with inhomogeneous strain distribution normal to the film surface. We concluded that the grain growth in the Cu thin films was facilitated by the strain intrinsic in the Cu films deposited on the rigid substrates, and that strain (or stress) introduced in the films was a primary factor to induce the grain growth in the Cu films at room temperature.

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The Effect of Strain Distribution on Abnormal Grain Growth in Cu Thin Films

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Transmission Electron Microscopic Study of Whisker Formation on Tetracalcium Phosphate in Hydrochloric Acid

Kuan-Liang Lin, Jiin-Huey Chern Lin, Chien-Ping Ju

pp. 3039-3043

DOI:

10.2320/matertrans.45.3039

Abstract

The present study investigates the changes in microstructure and microchemistry (particularly Ca/P ratio) during whisker formation on the surface of TTCP powder in hydrochloric solution. XRD results indicate that the as-fabricated (non-treated) powder has a monolithic TTCP crystal structure. When the powder is treated for 10 min in HCl, a DCPD phase appears on TTCP surface, which increases in intensity with treating time. When treated longer than 4 h, the DCPD intensity decreases. When treated for 24 h, the DCPD phase disappears. TEM results indicate that, when TTCP is treated for 10 min, fine globular-shaped DCPD crystals are observed to precipitate on the surface of TTCP particles. When treated for 1 h, hexagonal Ca-deficient apatite whiskers with an average Ca/P ratio of 1.5 form. With treating time the apatite whiskers continue to grow in size and increase in Ca/P ratio. When treated for 24 h, the length and thickness of the apatite whiskers can reach >500 and >50 nm, respectively, with an average Ca/P ratio of 1.8. The microchemical data indicate that the apatite whiskers grown on the surface of TTCP particles are substantially non-stoichiometric in nature. Compressive strength data indicate that apatite whiskers grown on TTCP surface under a favorable condition can largely improve the properties of the resulting CPC.

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Transmission Electron Microscopic Study of Whisker Formation on Tetracalcium Phosphate in Hydrochloric Acid

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Effect of Gold Coating on Interfacial Reaction between Dental Porcelain and Titanium

Eri Miura, Tatsuo Tabaru, Jie Liu, Yasuhiro Tanaka, Takanobu Shiraishi, Kunihiro Hisatsune

pp. 3044-3049

DOI:

10.2320/matertrans.45.3044

Abstract

Cross-sectional microstructure observation of the titanium firing porcelain inserted ion-coated gold layer was performed by SEM-EDX that can analyze light elements from boron. Two gold-coated samples applied to mirror finished titanium surface were prepared; one was applied only degassing treatment, and the other was applied firing after degassing treatment. In addition, in order to investigate effect of the gold coating, titanium/porcelain samples without coating were also observed. From SEM-EDX observation of the specimen, approximately 2.5 μm thickness titanium oxide layer appeared across the gold film in the first sample. In the titanium firing porcelain after degassing treatment, two obvious reaction layers appeared across the gold coating. One included mainly titanium and oxygen, and another included titanium, gold and aluminum. Thickness of the reaction layers was approximately 2.5—3 μm. From the results, it is suggested titanium was diffused into porcelain through a gold coating, and titanium oxide was formed at an interface. Titanium/porcelain without gold coating had two reaction layers at the interface, however, many cracks and crevices were exhibited in the layer and between the layers. Effect of gold coating on interfacial layer formation was discussed by the comparison with titanium/porcelain interface without gold coating. Thickness of the reaction layers decreased by gold coating, and cracks and crevices in the layer disappeared. The results suggested that oxygen diffusion became lower due to existence of the coating, and titanium-gold reaction changed layer's microstructure. It is also suggested that gold diffusion into the reaction layer and restriction of oxygen diffusion contribute to the reaction layer formation, consequently gold coating on titanium substrate contributes to improvement of adhesion between titanium and porcelain.

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Effect of Gold Coating on Interfacial Reaction between Dental Porcelain and Titanium

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Pressure Dependence of Hydrogen-Induced Transformations in C15 Laves Phase DyCo2

Haiwen Li, Kazuhiro Ishikawa, Kiyoshi Aoki

pp. 3050-3055

DOI:

10.2320/matertrans.45.3050

Abstract

Structural changes in C15 Laves phase DyCo2 heated in a hydrogen atmosphere between 0.1 and 5.0 MPa were investigated using a pressure differential scanning calorimeter (PDSC) and were compared with those of DyFe2. Four exothermic reactions resulting from 1) hydrogen absorption forming crystalline and amorphous hydrides, 2) hydrogen-induced amorphization (HIA), 3) the precipitation of BiF3-type DyH3 in the amorphous hydride and 4) the decomposition of the remaining amorphous hydride into DyH3 + β-Co were observed with increasing temperature. HIA in DyCo2 occurred for every hydrogen pressure in contrast to DyFe2, because the pressure dependence of it is small. The mechanism of the phase transformations for DyCo2 in a hydrogen atmosphere was discussed on the basis of the experimental results such as the pressure dependence of Tp and Tp/Tm (the peak temperature/the melting point of DyCo2), the enthalpy change ΔH, the activation energy EA and so on.

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Pressure Dependence of Hydrogen-Induced Transformations in C15 Laves Phase DyCo2

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Critical Current Densities of Powder-In-Tube (PIT)-Processed MgB2 Tapes

H. Kumakura, A. Matsumoto, H. Kitaguchi, H. Hatakeyama

pp. 3056-3059

DOI:

10.2320/matertrans.45.3056

Abstract

We fabricated MgB2 tapes by a powder-in-tube method. Reacted MgB2 powder (ex situ method) or Mg(MgH2)+B mixed powder (in situ method) were used as the starting powder. We used stainless steel, carbon steel, Cu-Ni, and Cu tubes for the ex situ method. Jc and the anisotropy in Jc with respect to the field orientation of ex situ-processed tape rapidly increased with increasing mechanical hardness of the tube. Annealing after cold rolling significantly enhanced the Jc values for the stainless steel and carbon steel tubes. For the in situ process, pure Fe tubes were used as a sheath material. The superconducting properties, such as Tc, Jc, and Birr, of in situ-processed tapes were sensitive to oxygen contamination during heat treatment. Heat treatment under a closed Ar gas atmosphere was effective in suppressing the oxidation of the tapes and enhancing the Jc values. The Jc value at 4.2 K of the in situ-processed tape was significantly enhanced by SiC doping. At 20 K, on the other hand, little Jc increase was observed due to the degradation of Tc by SiC doping. Typical Jc values of 108 A/m2 at 4.2 K in 12 T and 1.4 × 108 A/m2 at 20 K in 4 T were obtained for in situ-processed tapes heat-treated under a closed Ar gas atmosphere. Birr of in situ-processed tape was much higher than that of the as-rolled ex situ-processed tape.

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Critical Current Densities of Powder-In-Tube (PIT)-Processed MgB2 Tapes

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Effect of Long-Term Formalin Preservation on Bending Properties and Fracture Toughness of Bovine Compact Bone

Hisao Kikugawa, Takashi Asaka

pp. 3060-3064

DOI:

10.2320/matertrans.45.3060

Abstract

To precisely determine the mechanical properties of a bone, the effects of the preservation method on its mechanical properties need to be minimized. It seems likely that prolonged exposure to formalin (formaldehyde solution) will have some affect the mechanical properties of bone. This study investigated the effect of the formalin fixation method on the bending properties and fracture toughness of bovine cortical bone after short-term and relatively long-term preservation. To determine the elements and the quantities eluted from bone into formalin solution (the preservation medium), qualitative and quantitative analyses were performed by inductively coupled plasma atomic emission spectroscopy (ICP-AES). Formalin fixation augments the bending stiffness of the cortical bone while diminishing its fracture toughness. As the bending strength diminishes concurrently with removal of Ca2+, this implies that inorganic components of bone contribute to its bending strength.

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Effect of Long-Term Formalin Preservation on Bending Properties and Fracture Toughness of Bovine Compact Bone

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Interfacial Characterization of Porcelain Veneered on the Pure Titanium under Vacuum Firing

Tsung-Nan Lo, Truan-Sheng Lui, Edward Chang

pp. 3065-3070

DOI:

10.2320/matertrans.45.3065

Abstract

The interfacial characteristics between porcelain coating and titanium under vacuum firing at 800°C have not been well documented. The cross-sectional variations in microstructures and compositions at the porcelain/Ti interface were investigated with a SEM and an EPMA equipped with WDS. The phase constituents of the porcelain bulk coating and the nearby porcelain/Ti interface were analyzed by X-ray and thin-film X-ray diffractometry respectively. In addition, a TEM equipped with EDS was used to examine the porcelain/Ti oxide interface. The experimental results revealed that the oxidation of Ti occurred at the porcelain/Ti interface, and it is reasonable to deduce that the Ti reduces the SnO2 and SiO2 components of the porcelain and becomes Ti oxide. Furthermore, redox reactions and chemical bonding occur at porcelain/Ti interface during firing and thus prevent the initiation of fracture from occurring at this interface. Subsequently, the fracture initiation tends to be located near the interface of newly formed Ti oxide and Ti substrate and/or slightly inside the Ti.

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Interfacial Characterization of Porcelain Veneered on the Pure Titanium under Vacuum Firing

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In-situ Measurement and Control of Electric Discharge on Submerged Arc Synthesis Process for Continuous TiO2 Nanoparticle Fabrication

Liang-Chia Chen, Sheng-Hsin Pai

pp. 3071-3078

DOI:

10.2320/matertrans.45.3071

Abstract

This article presents electrical properties measurement and control of the nanoparticle preparation process known as the Submerged Arc Nanoparticle Synthesis System (SANSS) for continuous fabrication of TiO2 particles with nano-scale size and good uniformity. Since the dielectric liquid used in the process was limited quantity of deionized water, the electrical conductivity of the liquid can be drastically varied during the process. Under this circumstance, the electrical discharge breakdown voltage was significantly influenced and varied during the submerged process and the process may become unstable when the electrical properties fluctuate beyond system control capability. Consequently, the prepared particle size could differ with a substantial variance range from 20 nm up to one micrometer. Therefore, an effective approach was proposed to control the electrical discharge properties so that the variation in particle size could be decreased and the fabricating process could be continuously operated to achieve desirable particle size and uniformity. Our experimental results showed that the developed in-situ measurement and control method decreased significantly the disparity of TiO2 particle size from 1000 to 80 nm and reduced effectively the mean secondary particle size to 25 nm.

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In-situ Measurement and Control of Electric Discharge on Submerged Arc Synthesis Process for Continuous TiO2 Nanoparticle Fabrication

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An Evaluation of Superplastic Anisotropy after Processing by Equal-Channel Angular Pressing

Genki Sakai, Zenji Horita, Terence G. Langdon

pp. 3079-3081

DOI:

10.2320/matertrans.45.3079

Abstract

Experiments were conducted to evaluate the superplastic properties in three orthogonal directions after processing by equal-channel angular pressing (ECAP). Using an Al-3% Mg-0.2% Sc alloy pressed to a strain of ∼8 through route BC, miniature tensile specimens were cut inthe pressing direction perpendicular to the transverse plane and perpendicular to the flow and longitudinal planes. The results show that similar tensile elongations are obtained in each direction. It is concluded there is no significant anisotropy in the superplastic properties after processing by ECAP.

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An Evaluation of Superplastic Anisotropy after Processing by Equal-Channel Angular Pressing

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