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MATERIALS TRANSACTIONS Vol. 46 (2005), No. 8

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. 46 (2005), No. 8

Improvement of Oxidation Resistance of an Fe–Mn–Si–Cr Shape Memory Alloy by Annealing under Vacuum

Hiroyuki Fukai, Shigeru Suzuki, Naoya Masahashi, Shuji Hanada, Tadakatsu Maruyama, Hiroshi Kubo, Yoshio Waseda

pp. 1745-1748

Abstract

Electron microprobe microanalysis (EPMA), secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS) were used for charactering the surface composition of an Fe–Mn–Si–Cr shape memory alloy. The effect of annealing under vacuum on the surface composition of the alloy was studied. It was found that the amount of manganese decreased, while the amount of chromium increased in a surface layer by annealing. The thickness of the surface layer is of the order of ten micrometers, which is comparable to that obtained by conventional plating or coating. As a result, the surface of the Fe–Mn–Si shape memory alloy annealed under a vacuum exhibited better oxidation resistant than that of the as-lapped alloy.

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Improvement of Oxidation Resistance of an Fe–Mn–Si–Cr Shape Memory Alloy by Annealing under Vacuum

Microstructure Stability and Creep Strength in a Die-Cast AX52 Magnesium Alloy

Yukako Mori, Yoshihiro Terada, Tatsuo Sato

pp. 1749-1752

Abstract

Superior creep strength of a heat resistant AX52 magnesium alloy is ascribed to the grain boundary eutectic Al2Ca phase covering the primary α-Mg grains. The eutectic phase is stable in morphology at temperatures below 473 K, while it collapses during long term exposure at temperatures higher than 473 K. The microstructural change of the alloy during high temperature exposure is characterized by the decrease in the grain boundary coverage by the eutectic phase. The creep strength of the alloy decreases with the decrease in the grain boundary coverage, and the correlation between the creep strength and the grain boundary coverage is discussed.

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Microstructure Stability and Creep Strength in a Die-Cast AX52 Magnesium Alloy

Magnetic Field Effect on Structural Property of MnFeP0.5As0.5

Keiichi Koyama, Takeshi Kanomata, Takeshi Matsukawa, Kazuo Watanabe

pp. 1753-1756

Abstract

The magnetic field effect on the structural property of a ferromagnetic compound MnFeP0.5As0.5 was investigated by powder X-ray diffraction measurement in magnetic fields up to 5 T. The compound with the hexagonal Fe2P-type structure shows a field-induced isostructural transformation with a hysteresis by applying magnetic field, accompanied by the metamagnetic transition from the paramagnetic to ferromagnetic state just above the Curie temperature of 284 K. In this transformation, the a parameter expands by 0.5% whereas the c parameter contracts by 1%. However, the cell volume slightly and continuously decreases with increasing magnetic field through the transformation.

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Magnetic Field Effect on Structural Property of MnFeP0.5As0.5

Hydrogen Desorption Properties of Lithium–Carbon–Hydrogen System

Takayuki Ichikawa, Shigehito Isobe, Hironobu Fujii

pp. 1757-1759

Abstract

Hydrogen desorption properties of a mixture of hydrogenated nanostructural graphite CnanoHx and lithium hydride LiH are demonstrated in this paper, where CnanoHx was synthesized from graphite by ballmilling under 1 MPa hydrogen for 80 h. First of all, we clarified the hydrogenated properties of CnanoHx synthesized under four different milling conditions. The hydrogen desorption profile with typical two-peak structure was caused by iron contamination in CnanoHx from steel balls during ballmilling, while the products prepared by zirconia balls showed the broad single peak in hydrogen desorption. The amount of desorbed hydrocarbon gas from the products using a rocking (vibrating) mill estimated by the thermogravimetry was larger than that using a rotating (planetary) one. Next, the destabilization properties of extremely stable LiH was examined, indicating that LiH was destabilized by mixing with another component LiOH or NaOH, and then, the mixture easily released hydrogen gas at lower temperature compared with LiH, LiOH and NaOH themselves. On the analogy of this result, we examined hydrogen desorption properties of the ballmilled mixture of LiH and CnanoHx. The hydrogen desorption started from about 200°C and showed a peak at 350°C, although each product needs more than 400°C to release hydrogen. Since this hydrogen storage system is specially based on lithium, carbon and hydrogen in the mixture, it can be regarded as Li–C–H hydrogen storage system.

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Hydrogen Desorption Properties of Lithium–Carbon–Hydrogen System

Microstructual Characterization of Sputtered Pt–Ir Coatings on Ni-Base Single Crystal Superalloy

Aya Suzuki, Masanori Harada, Yingna Wu, Hideyuki Murakami

pp. 1760-1763

Abstract

Characterization of Pt–Ir alloy coatings on a Ni-base single crystal superalloy was carried out. Pt–Ir alloys with varied composition were sputter-deposited on TMS-82+, which were then subjected to annealing and Al-pack cementation treatments. It was found that all the as-deposited films consisted of Pt–Ir solid solutioned fcc single phase, while the annealing treatment at 1423 K for 1 h drastically changed the microstructure, depending on the composition of coated layers. On the other hand, concentration profiles of alloying elements were not drastically changed by the Al-pack cementation process. It was also revealed that Ir addition increases the surface hardness of all the as-deposited, annealed, and aluminized specimens.

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Microstructual Characterization of Sputtered Pt–Ir Coatings on Ni-Base Single Crystal Superalloy

In Situ TEM Observation of Thermally-Induced First-Order Magnetic Transition in Itinerant-Electron Metamagnetic La(FexSi1−x)13 Compounds

Naoyuki Kawamoto, Yasukazu Murakami, Daisuke Shindo, Shun Fujieda, Asaya Fujita, Kazuaki Fukamichi

pp. 1764-1767

Abstract

Defocus mode of Lorentz microscopy has revealed change in the magnetic microstructure with a first-order magnetic phase transition in La(FexSi1−x)13 compounds (0.86≤x≤0.90). Upon heating specimens from the ferromagnetic phase to the paramagnetic phase, magnetic domains disappear instantaneously at the Curie temperature, concurrent with a substantial change in the volume. The observations are consistent with the feature of the first-order phase transition, which gives rise to extraordinary phenomena of these compounds such as large magnetocaloric effects.

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In Situ TEM Observation of Thermally-Induced First-Order Magnetic Transition in Itinerant-Electron Metamagnetic La(FexSi1−x)13 Compounds

Hydrogen Permeation of the Melt-Spun Ni–X–Zr Amorphous Membranes

Shin-ichi Yamaura, Shuhei Nakata, Hisamichi Kimura, Yoichiro Shimpo, Motonori Nishida, Akihisa Inoue

pp. 1768-1770

Abstract

The Ni70−x⁄2Nb30−x⁄2Zrx (x=10, 20, 30, 40 and 60 at%) amorphous alloys were prepared by the melt-spinning technique. The hydrogen permeability of those alloys was compared to derive the principles of the element addition. As the result, it was found that the hydrogen permeability of the Ni–Nb–Zr ternary amorphous alloys increases with increasing Zr content. However, the hydrogen permeation of the Ni40Zr60 binary amorphous alloy was much smaller than that of the Ni50Nb10Zr40 amorphous alloy. This behavior indicates that the Nb addition also improves the hydrogen permeability.
Then, as a next step, we prepared the Ni–X–Zr (X=Y, Ti, Hf, V, Nb and Ta) amorphous alloys to investigate the effect of the additional elements on the hydrogen permeation of melt-spun Ni–Zr binary amorphous alloys. As the result, it was found that the additional element with higher hydrogen affinity was preferable and that the Ni content should be reduced to improve the permeability.

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Hydrogen Permeation of the Melt-Spun Ni–X–Zr Amorphous Membranes

Influence of Purity on Tensile Property of Al–Si Hypo-Eutectic Alloy Castings

Toshifumi Ogawa, Shigeyuki Haruyama, Hidenori Era, Katsuhiko Kishitake

pp. 1771-1774

Abstract

Influence of alloy purity on the tensile properties of Al–Si eutectic alloy castings has been investigated by using two kinds of the melted alloys: L-Alloy of 99.89 mass% purity and H-Alloy of 99.98 mass% purity. Although the base structure in both of alloys was composed of proeutectic α-phase and eutectic structure, the eutectic structure of H-Alloy was finer than that of L-Alloy. Coarse crystals of plate-like silicon were observed in L-Alloy, while were not observed in H-Alloy. Based on the results of Brinell Hardness Test on the solidification structure, it was found that there was little difference of the hardness between the both alloys. Tensile tests were also performed in an atmosphere at room temperature. The elongation of H-Alloy was twice as large as that of L-Alloy, though the tensile strength of L-Alloy and H-Alloy were almost the same.

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Influence of Purity on Tensile Property of Al–Si Hypo-Eutectic Alloy Castings

Effects of Heat Treatment on Microstructures and Physical Properties of Segmented Thermal Barrier Coatings

Hongbo Guo, Hideyuki Murakami, Seiji Kuroda

pp. 1775-1778

Abstract

Highly segmented thermal barrier coatings (TBCs) were produced by “hot” plasma spraying. The effects of heat treatment on the microstructures, mechanical and thermophysical properties were studied. The segmented coatings are denser than traditionally plasma-sprayed TBCs due to its good insplat bonding at high substrate temperature. The segmentation cracks and associating branching cracks hardly propagated or closed during sintering process, indicative of a good stability of crack network. Due to its low porosity, the segmented coatings compromised the property of thermal insulation of TBCs. For the coatings after 24 h heat treatment at 1523 K, the thermal conductivity was improved by around 35%. The segmentation cracks had a strong impact on decreasing the Young’s modulus. Heat treatment could not effectively promote the increase of the Young’s modulus, especially for the case of highly segmented coatings.

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Effects of Heat Treatment on Microstructures and Physical Properties of Segmented Thermal Barrier Coatings

Tempering Treatment Effect on Mechanical Properties of F82H Steel Doped with Boron and Nitrogen

Nariaki Okubo, Eiichi Wakai, Shingo Matsukawa, Hiroyasu Tanigawa, Tomotsugu Sawai, Shiro Jitsukawa, Somei Ohnuki

pp. 1779-1782

Abstract

Effects of tempering treatment on mechanical properties and microstructures have been studied for martensitic steel F82H doped with 60 ppm B and 200 ppm N (F82H+B+N). The tempering treatments were performed at 700–780°C after the normalizing treatment at 1000°C. Yield stress of the F82H+B+N steel tempered at 700, 750 and 780°C was 740, 580 and 500 MPa, respectively, and ductile-brittle transition temperature (DBTT) of the specimens was −55, −85 and −85°C, respectively. The areal density of dislocations decreased from 1.1×1014 to 2.5×1013 m−2 with increasing tempering temperature from 700 to 780°C. The number density of precipitates decreased with increasing tempering temperature from 700 to 750°C, while the number density was almost equivalent as increasing tempering temperature from 750 to 780°C. The results indicate that the change of DBTT, depending on tempering temperature, is related with the change of yield strength, size and number density of carbides. Hardening behavior of the F82H+B+N steel irradiated by 10.5 MeV Fe3+ to 10 dpa at 360°C has been also studied by using a micro-indentator. The micro-hardness of the F82H+B+N steel tempered at 780°C was changed from 3.6 to 4.8 GPa by the irradiation. Because hardening behavior of the F82H+B+N steel was found to be similar with that of F82H non-doped, doping effects of B on irradiation hardening were suppressed by co-doping of B and N.

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Tempering Treatment Effect on Mechanical Properties of F82H Steel Doped with Boron and Nitrogen

Effects of Ion Irradiation on Coherency of Precipitates in Cu–Co Alloy

Z. C. Li, H. Abe, M. Ishikawa, N. Sekimura

pp. 1783-1785

Abstract

Typical precipitation Cu–Co alloy has been selected to investigate the formation and mobility of point defects upon ion irradiation, during which the coherent precipitates lose their coherency and transform to incoherent structures, thus can be served as a detector of point defects mobility.

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Effects of Ion Irradiation on Coherency of Precipitates in Cu–Co Alloy

Effect of Reinforcement Nonuniformity on Effective Thermal Conductivity of Composite

Yibin Xu, Yoshihisa Tanaka, Masaharu Murata, Kazushige Kamihira, Masayoshi Yamazaki, Koichi Yagi

pp. 1786-1789

Abstract

In composites reinforced by whiskers or fibers, clustering of the reinforcements often occurs. In this work, we studied the effect of these clustering phenomena on effective thermal conductivity of the composites. An analytical model has been developed based on effective medium theory to calculate the effective thermal conductivity of composite with consideration of the nonuniformity of reinforcement distribution. With this model the thermal conductivities of SiC whisker reinforced aluminum matrix composites have been calculated, and the results are in good agreement with the experimental data. The dependences of composite thermal conductivity on parameters such as the shape of the reinforcement cluster, the volume fractions inside and outside cluster, etc. have been investigated.

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Effect of Reinforcement Nonuniformity on Effective Thermal Conductivity of Composite

Effect of Heat Treatment on Microstructure and Mechanical Properties of Ni- and C-Free Co–Cr–Mo Alloys for Medical Applications

Sang-Hak Lee, Eiji Takahashi, Naoyuki Nomura, Akihiko Chiba

pp. 1790-1793

Abstract

The effect of pre-heat treatments, followed by a hot forging process, on the microstructure and strength of Co–Cr–Mo alloys was investigated. Four pre-heat treatments were conducted at 1170, 1200, 1230 and 1260°C for three different time condition: 2, 6 and 15 h and then water cooled to room temperature. Tensile tests and XRD analyses were carried out on both as-cast alloy and heat-treated alloys. The volume fraction of retained γ phase increases with increasing the heat treatment temperature, suggesting that the γ→ε martensitic transformation is suppressed by a higher temperature heat treatment. Tensile strength slightly decreases with increasing the heat treatment temperature and the heat treatment time, whereas the ductility slightly increases. The σ phase completely dissolves into matrix when the alloy is heat-treated at 1260°C for longer than 6 h.

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Effect of Heat Treatment on Microstructure and Mechanical Properties of Ni- and C-Free Co–Cr–Mo Alloys for Medical Applications

Eutectic Anomaly of Compound Forming Bi–Te Liquids Studied by Electrical Resistivity Measurements

Yusuke Nakagawa, Toshio Itami

pp. 1794-1797

Abstract

The electrical resistivity, ρ, of compound forming Bi–Te system in the liquid state was studied by the dc-four probe method. Anomalous behavior of ρ around the intermetallic compound Bi2Te3 in the previous study was not found. Anomalous behaviors of the temperature dependence of ρ, dρ⁄dT, were found both at two eutectic compositions in this system. These behaviors were discussed based on the effective medium theory of electrical conduction. The concentration fluctuation at the eutectic composition (90 at%Te) grows in the homogeneous liquid phase with the approach to the eutectic temperature.

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Eutectic Anomaly of Compound Forming Bi–Te Liquids Studied by Electrical Resistivity Measurements

High-Pressure Synthesis of Novel Hydrides in Mg–TM Systems (TM = Zr, Nb and Mo)

Yasuyuki Goto, Takayuki Hayashi, Riki Kataoka, Hirofumi Kakuta, Atsunori Kamegawa, Hitoshi Takamura, Masuo Okada

pp. 1798-1801

Abstract

New hydrides of Mg–TM–H systems, where TM = Zr, Nb and Mo, have been prepared by using cubic-anvil-type apparatus, and their crystal structure and hydrogen content have been investigated. The high-pressure synthesis was performed at 1073–1173 K under 2–5 GPa. In the Mg–Zr–H system, a new hydride Mg2Zr3Hy with a monoclinic structure (a=0.8591(1) nm, b=0.33539(5) nm, c=0.5816(1) nm, β=103.06(3)°) was obtained by exposing a mixture of MgH2 and ZrH2 to pressure of 2 to 5 GPa at 1073 K for 2 h. In the Mg–Mo system, a new hydride Mg3MoH6 was synthesized by exposing a mixture of MgH2 and Mo to 5 GPa at 1173 K for 2 h. The hydride was found to have a hexagonal structure (a=0.49958(6) nm, c=0.8840(2) nm). In the Mg–Nb–H system, a new hydride Mg4NbHy was also synthesized by exposing a mixture of MgH2 and Nb to 5 GPa at 1073 K for 2 h.

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High-Pressure Synthesis of Novel Hydrides in Mg–TM Systems (TM = Zr, Nb and Mo)

Nanostructure of CoPtCr–SiO2 Granular Films for Magnetic Recording Media

Shunsuke Fukami, Nobuo Tanaka, Takehito Shimatsu, Osamu Kitakami

pp. 1802-1806

Abstract

Structural properties of CoPtCr–SiO2 magnetic recording films grown on Ru or Pt seed layers prepared by UHV-magnetron sputtering were studied by high resolution transmission electron microscopy (HRTEM), electron energy loss spectroscopy (EELS) and energy filtered transmission electron microscopy (EFTEM). CoPtCr grown on Ru seed layers together with SiO2 forms a well-isolated structure composed of CoPtCr fine grains of 10 nm diameter surrounded by amorphous SiO2, whereas CoPtCr grown on Pt seed layers together with SiO2 forms a network structure composed of CoPtCr crystal of 5 nm size. These structural features made differences in their magnetic properties. The HRTEM and EFTEM studies revealed that cylindrical crystalline grains composed of CoPtCr and Ru are formed for CoPtCr–SiO2/Ru samples, whereas SiO2 are aggregated around the boundary between relatively large Pt grains and magnetic layers without obstructing the epitaxial growth of CoPtCr on Pt, not resulting in the cylindrical CoPtCr grains. Lattice spacings of CoPtCr grown on Pt with SiO2 are 0.7% expanded in comparison with CoPtCr grown on Pt without SiO2. The EELS studies suggested that Co and Cr atoms are partly oxidized by SiO2 addition for both samples and Cr atoms are more oxidized for CoPtCr–SiO2/Pt samples.

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Nanostructure of CoPtCr–SiO2 Granular Films for Magnetic Recording Media

Isotopic Effect on Thermal Conductivity of Diamond Thin Films

Tetsuji Noda, Hiroshi Araki, Hiroshi Suzuki, Wen Yang, Takefumi Ishikura

pp. 1807-1809

Abstract

The thermal conductivities of 99.95%12C and natural diamond films at temperatures from 1.5 to 300 K were studied. The thermal conductivity was measured by a steady heat-flow method. The thermal conductivity of 12C enriched diamond was increased compared to that of natural isotope abundant diamond. Its maximum value was about 1.4 times higher than that of the natural isotope-abundant diamond at around 180 K. The increase in thermal conductivity for the isotope diamond can be explained by Callaway’s model, that is, by lowering the isotope-scattering effect.

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Isotopic Effect on Thermal Conductivity of Diamond Thin Films

Composition-Dependent Thermoelectric Properties of PbTe Doped with Sb2Te3

Pinwen Zhu, Yoshio Imai, Yukihiro Isoda, Yoshikazi Shinohara, Xiaopeng Jia, Guangtian Zou

pp. 1810-1813

Abstract

Although there are many reports on PbTe–SnTe and Bi2Te3–Sb2Te3 systems with improved thermoelectric performance due to reduced lattice thermal conductivity, only few experimental data exist on PbTe–Sb2Te3 system. In this report, the composition-dependent thermoelectric properties of PbTe doped with Sb2Te3 have been studied at room-temperature. It is worth noting that the lattice thermal conductivity is only about 1 W/K·m as the contents of Sb2Te3 is larger than 0.8 mol%. In addition, the figure of merit shows a maximum value of 1.03×10−3 K−1 with the content of Sb2Te3 at 0.8 mol% which is the highest value obtained in doped bulk PbTe samples and is several times higher than that of PbTe containing other dopants with small grain sizes. This confirms that Sb2Te3 is one of the best dopants for PbTe to enhance its thermoelectric performance.

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Composition-Dependent Thermoelectric Properties of PbTe Doped with Sb2Te3

Electron Irradiation Induced Nano-Crystallization in Fe77Nd4.5B18.5 Metallic Glass

Akihiro Nino, Takeshi Nagase, Yukichi Umakoshi

pp. 1814-1819

Abstract

Phase transformation behavior in Fe77Nd4.5B18.5 metallic glass during electron irradiation and thermal annealing was investigated. Crystallization from glassy phase during thermal annealing occurred in multi-stages forming α-Fe and several intermetallic compounds. Electron irradiation induced crystallization occurred at 298 K and nanostructure composed of α-Fe, Nd2Fe14B and Fe17B2 precipitates embedded in amorphous matrix was formed. The electron irradiation induced crystallization behavior was discussed by atomic displacement due to electron knock-on effect and atomic diffusion via free volume in amorphous phase.

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Electron Irradiation Induced Nano-Crystallization in Fe77Nd4.5B18.5 Metallic Glass

Electrical Current Phase Transformation of Sn–9Zn–1Ag Alloy

Fei-Yi Hung, Chih-Jung Wang, Truan-Sheng Lui, Li-Hui Chen

pp. 1820-1824

Abstract

The current load not only easily induces the electromigration effect and thermal strain, but also destroys the effectiveness of solders. As of now, temperature and phase transformation problems caused by the high current load have still not been discussed. This study investigates the structural characteristics of the Sn–9Zn–1Ag alloy under an electrical current test and heat-treatment. The results indicate that the Ag existed mostly in Ag–Zn compounds, and the Zn concentration in the Ag–Zn compounds was higher than in the needle-like Zn-rich phase and Sn–Zn eutectic phase. The Sn–9Zn–1Ag alloy had no transformation during oil heat-treatment, while the structure underwent phase transformation under electrical current testing. After current testing, the needle-like Zn-rich phases had decomposed into finer particle-like features, the Ag–Zn compounds had grown and the Sn–Zn eutectic phases had increased, and the content of Sn-rich phase had decreased. Meanwhile, the current effect also caused the content of Sn to increase but Zn and O both decreased for the Zn-rich (SZO) phases in the relative composition.

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Electrical Current Phase Transformation of Sn–9Zn–1Ag Alloy

Growth Behavior of Au–Sn and Ag–Sn Compounds during Solid-state Reactive Diffusion between Au–Ag Alloys and Sn

Toshio Takenaka, Satoru Kano, Masanori Kajihara, Noriharu Kurokawa, Katsuhiko Sakamoto

pp. 1825-1832

Abstract

The kinetics of the solid-state reactive diffusion between binary Au–Ag alloys and Sn was experimentally examined using Sn/Au0.75Ag0.25/Sn and Sn/Au0.5Ag0.5/Sn diffusion couples. The diffusion couples were prepared by a diffusion bonding technique and then isothermally annealed at temperatures of T=393, 433 and 473 K for various times up to 1272 h in an oil bath with silicone oil. Under the present experimental conditions, AuSn4 and AuSn2 compound layers were observed after annealing. Furthermore, fine particles of Ag3Sn were rather uniformly distributed in the Au–Sn compound layers. The total thickness l of the Au–Sn compound layers is expressed as a power function of the annealing time t as follows: l=k(tt0)n, where t0 is unit time, 1 s. Here, the exponent takes values of n=0.34–0.40. The mean interdistance r of the Ag3Sn particles is also described as a power function of t: r=kr(tt0)p, where p=0.28–0.43. Assuming that the interdistance r varies in proportion to the grain size of the Au–Ag compound during annealing, the rate-controlling process of the reactive diffusion was estimated. If the grain boundary diffusion across the Au–Sn compound layers is the only rate-controlling process, the values of n calculated from the equation n=(1−p)⁄2 become smaller than the experimental values of n=0.34–0.40. Consequently, both the volume diffusion and the grain boundary diffusion should contribute to the rate-controlling process of the reactive diffusion.

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Growth Behavior of Au–Sn and Ag–Sn Compounds during Solid-state Reactive Diffusion between Au–Ag Alloys and Sn

An EBSD and TEM Study on the Microstructural Evolution of in situ Synthesized (TiB+TiC)⁄Ti Matrix Composites during Superplastic Deformation

Min-min Wang, Wei-jie Lu, Di Zhang, Ji-ning Qin, Tongxiang Fan, Bo Ji, Feng Zhu, Sikai Ji

pp. 1833-1838

Abstract

Microstructures of in situ synthesized (TiB+TiC)⁄Ti matrix composites after superplastic deformation at 980°C with a strain rate of 5×10−3 s−1 have been studied. Optical microscope (OM) and scanning electron microcioy (SEM) observations indicate that the mean grain size decreased. Electron back-scattered diffraction (EBSD) and transmission electron microcopy (TEM) observations reveal that the density of sub-grain boundaries and high angle grain boundaries increased during superplastic deformation, clearly indicating that dislocation sliding and climbing are important processes during superplastic deformation. The experiment results indicate the superplastic deformation is controlled by grain boundary sliding and dislocation motion, which is consistent with the result deduced from activation energy.

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An EBSD and TEM Study on the Microstructural Evolution of in situ Synthesized (TiB+TiC)⁄Ti Matrix Composites during Superplastic Deformation

The Role of Retained Austenite on Tensile Properties of Steels with Bainitic Microstructures

Carlos García-Mateo, Francisca G. Caballero

pp. 1839-1846

Abstract

In high-carbon, silicon-rich steels it is possible to obtain a very fine bainitic microstructure by transformation at low temperatures (200–300°C). This microstructure consists of slender ferrite plates, with thicknesses of several tens of nm, in a matrix of retained austenite. Whereas strength is mainly provided by to the fine scale of the ferrite plates (stronger phase), ductility is mostly controlled by the retained austenite (softer phase). Further improvement in ductility is achieved by strain induced transformation of austenite to martensite, the so called TRIP effect. In order to take full advantage of this effect, the mechanical stability of the austenite, i.e., its capability to transform to martensite under strain, must not be too low nor excessively high.
Two main aspects of the mechanical stability of the retained austenite, morphology and chemical composition, have been studied to determine the role that these play on the ductility behaviour of the bainitic steels studied. It is suggested that the chemical composition has the strongest effect on the ductility of these new high strength alloys.

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The Role of Retained Austenite on Tensile Properties of Steels with Bainitic Microstructures

Interfacial Microstructure and Strength of Steel to Aluminum Alloy Lap Joints Welded by a Defocused Laser Beam

Kwang-Jin Lee, Shinji Kumai, Takashi Arai

pp. 1847-1856

Abstract

Lap joining was carried out using a defocused laser beam for 1.2-mm thick A6111 aluminum alloy plate and 1.0-mm thick low-carbon steel (SPCC) plate. The defocused laser beam was applied on the upper surface of the SPCC plate and the beam traveled under various welding conditions. When the depth of the molten SPCC pool was maintained at around 90% of the SPCC plate thickness, the selected area near the upper surface of the A6111 plate melted to form a semi-elliptical molten pool. Consequently, the solid SPCC and molten A6111 came in contact at the interface and joining was achieved through the solid–liquid reaction. The interfacial strength of the lap joint was controlled by the morphology of the Fe–Al intermetallic compound (IMC) layer. Improved strength was obtained when the weld interface was covered with a thin (about 1-μm thick) and continuous IMC layer. The estimated maximum shear stress of the lap joint was about 70% of that for A6111-T4. Welding conditions providing excessive heat input increased the thickness of the IMC layer and caused the formation of needle-like IMC and cracks in the A6111 molten pool. Such microstructures reduced the joint strength. X-ray diffraction analysis for the weld interface revealed that the IMC layer consisted of various kinds of Fe–Al base equilibrium phases (Al13Fe4, Al5Fe2, Al2Fe, FeAl, and Fe3Al) and a non-equilibrium Al6Fe phase.

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Interfacial Microstructure and Strength of Steel to Aluminum Alloy Lap Joints Welded by a Defocused Laser Beam

Ultra-Low Glass Transition Temperatures in Ce-Based Bulk Metallic Glasses

Zan Bian, Akihisa Inoue

pp. 1857-1860

Abstract

New (Ce0.72Cu0.28)100−xyAlx(Ga,Zn)y bulk metallic glasses (BMGs) with ultra-low glass transition temperatures and large supercooled liquid regions (ΔTx) were developed. The addition of Al element into Ce–Cu alloys improves significantly glass formation ability (GFA) of the alloys and the maximum value of ΔTx is 63 K. The lowest glass transition temperature (Tg) was found in the (Ce0.72Cu0.28)97.5Al2.5 BMG alloy and the value is 326 K. The addition of Ga and Zn elements into Ce–Cu–Al alloys has no obvious role in the decrease of Tg. However, Tg has a close relation to Ce content and decreases with increasing Ce content. The activation energies of the glass transition are 136 kJ·mol−1 for the (Ce0.72Cu0.28)97.5Al2.5 glassy alloy and 145 kJ·mol−1 for the Ce62.5Cu15Al12.5Ni10 glassy alloys, respectively. The successful fabrication of Ce-based BMGs with ultra-low Tg and large ΔTx can further extend the potential application of bulk metallic glasses in some special industry fields.

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Ultra-Low Glass Transition Temperatures in Ce-Based Bulk Metallic Glasses

Thermodynamic Study on the Ag–Pb–O System at 1273 K

Shigeru Ueda, Tomomasa Kumagai, Katsunori Yamaguchi

pp. 1861-1864

Abstract

The phase relations for the Ag–Pb–O system saturated with alumina and the activity coefficient of AgO0.5 in the PbO melt were investigated at 1273 K. A chemical equilibrium technique and an EMF method were applied to the measurement. In this system, there is a miscibility gap between a molten Ag–Pb alloy phase and a Pb–Ag–O oxide phase. The solubility of Ag in the oxide phase and that of Pb in the metal phase were studied as a relation of the partial oxygen pressure. These results suggest that component of silver oxide in liquid PbO phase should be represented as AgO0.5. The activity coefficient of AgO0.5 in the PbO based oxide melt at infinite dilution relative to pure solid AgO0.5 is 0.602 at 1273 K.

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Thermodynamic Study on the Ag–Pb–O System at 1273 K

Preparation of Nanometer Cobalt Particles by Polyol Reduction Process and Mechanism Research

Liu Biao, Guan Jian-guo, Wang Qi, Zhang Qing-jie

pp. 1865-1867

Abstract

By the liquid-reduction process, the nanometer spherical cobalt powders with fcc structure and a crystal size of 10 nm, are prepared using the regents of cobaltous salt as precursor and 1,2-propanediol as reducing agent. XRD, TEM are applied to characterize the phase and morphology of the as-prepared products. Both the reaction process and mechanism of the polyol reduction process are discussed preliminary through FT-IR spectra of the systems before and after reduction.

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Preparation of Nanometer Cobalt Particles by Polyol Reduction Process and Mechanism Research

Decomposition and Reaction of Thermal-Formed Alumina in Aluminum Alloy Castings

Teng-Shih Shih, In-Chan Chen

pp. 1868-1876

Abstract

Oxide films are readily entrapped in aluminum alloy castings during the melting, pouring or filling process resulting in defective geometry or quality. The entrapped oxide films may be of different shapes and/or composed of varying constituents (or oxides). It is extremely difficult to directly produce a given type of oxide film with a given thickness, from the aluminum alloy melt. Aluminum alloy castings have a thermally formed aluminum oxide film on their machined surface after being heated. In this study thermally formed aluminum oxide samples were produced from pure aluminum. The intend is to investigate the reaction and decomposition of this oxide in aluminum alloy melts. The reactions of the thermally formed aluminum oxide with aluminum-silicon and aluminum-magnesium alloys are discussed.

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Decomposition and Reaction of Thermal-Formed Alumina in Aluminum Alloy Castings

Measurement of Thermal Transport Properties for Molten Silicate Glasses at High Temperatures by Means of a Novel Laser Flash Technique

Hiroyuki Shibata, Atsushi Suzuki, Hiromichi Ohta

pp. 1877-1881

Abstract

Thermal transport properties; effusivity, diffusivity and conductivity, of six silicate glasses in the molten state have been determined in the temperature range between 1073 and 1673 K. The glass sample was melted in a platinum crucible and heated to the desired temperature. Then, a single laser pulse was flashed on the bottom surface of the platinum crucible, and the infrared ray irradiated from the same bottom surface was measured for obtaining the temperature decay from which thermal effusivity of the sample could be estimated in the molten state. Thermal diffusivity and thermal conductivity were also estimated with available values of specific heat capacity and density of the glasses. Thermal transport properties of six glasses were found to slightly depend on temperature.

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Measurement of Thermal Transport Properties for Molten Silicate Glasses at High Temperatures by Means of a Novel Laser Flash Technique

Corrosion Behavior of Hastelloy-XR Alloy in O2 and SO2 Atmosphere

Rong Tu, Takashi Goto

pp. 1882-1889

Abstract

As Hastelloy-XR alloy is a candidate structural material for the IS (Iodine-Sulfur) process in hydrogen production, oxidation and sulfidation of Hastelloy-XR alloy in Ar–O2 and Ar–SO2 atmospheres were studied by thermogravimetry at temperatures from 1000 to 1300 K. In Ar–O2 atmosphere, the mass change obeyed a linear-parabolic law at oxygen partial pressures (PO2) from 0.01 to 10 kPa. The oxidation scales consisted of inner Cr2O3 layer and outer Mn1.5Cr1.5O4 spinel layer. The surface morphology of the oxide scales changed from island-like to buckled and to porous texture with decreasing PO2. In Ar–SO2 atmosphere, the mass change obeyed a linear-parabolic law at SO2 partial pressures (PSO2) from 0.05 to 5 kPa. The morphology of corrosion scales changed mainly with corrosion temperature. While oxidation was dominant at 1073 and 1173 K forming double-layer scales of inner Cr2O3 and outer Mn1.5Cr1.5O4 spinel, sulfidation was accompanied with oxidation at 1273 K and PSO2<0.5 kPa with scales consisting of Fe3O4, FeCr2O4 and Cr2O3 layers and Ni3S2 dispersed particles together with CrS particles segregating at the grain boundary of Hastelloy-XR alloy.

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Corrosion Behavior of Hastelloy-XR Alloy in O2 and SO2 Atmosphere

A Metallurgical Approach to Metal Dusting of Nickel-Base Alloys

Yoshitaka Nishiyama, Takeo Kudo, Nobuo Otsuka

pp. 1890-1896

Abstract

Preliminary laboratory corrosion tests of two conventional Ni-base alloys were conducted at 650°C for 200 h in various CO–H2–CO2–H2O gas mixtures. For gas mixtures of high ac and CO content, alloy 600 (75 mass %Ni–15%Cr) specimens lost its mass due to metal dusting and deposition of coke was heavy on the surface of the specimen. Meanwhile, any pit formation was not occurred on the alloy 690 (60%Ni–30%Cr) specimens. Microscopic observation indicated that for the corroded Ni-base alloy specimens, inward diffusion of carbon presumably at cracks and flaws in the oxide scale was prominent. Carbon in the diffusion zone reacted with chromium to precipitate carbides in the matrix, followed by the “direct” formation of graphite platelets with a lamellar structure at the revealed metal surface. This direct precipitation of graphite platelets can be considered by a eutectoid reaction, which is similar to the pearlite transformation observed in Fe–C system. In the lamellar structure, the γ matrix thinned with the growth of graphite plates, and small metal particles of Ni and Fe which may catalyze the coke deposition reaction were crumbled and detached from the lamella.

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A Metallurgical Approach to Metal Dusting of Nickel-Base Alloys

Molten Metal Flow through Solid Network in Semi-Solid Al–Si Alloy

Nakornriab Nicom, Hiroyuki Nomura

pp. 1897-1902

Abstract

Based on Darcy’s equation, permeability was measured for the flow of molten metal through solid network in order to evaluate slurry fluidity in semi-solid casting process. An experimental apparatus is constructed to control the morphology of globular and dendrite structure for varied fraction of solid and applied pressure. Semi-solid AC4CH alloys with 7 mass% silicon content have been squeezed by argon gas at pressure of 0.50 MPa to force liquid phase through a filter. The fraction of solid is varied from 0 to as high as 0.55. Filtrate weight ratio and gauge pressure are shown to reach to each constant value with pressurizing time of 20 s. At low fraction of solid, permeability depends strongly upon solid morphology, i.e. dendrite structure yields the lower permeability due to large friction factor. Liquid movement through α solid phase network prevails under the formation of cake layer on the filter surface with most fractions of solid and with the fraction more than 0.33 for the dendritic and globular structure of the slurry, respectively. For the globular structure, on the other hand, liquid motion in the filter becomes important for fraction of solid less than 0.33.

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Molten Metal Flow through Solid Network in Semi-Solid Al–Si Alloy

Effect of Low-Frequency Magnetic Fields on Microstructures of Horizontal Direct Chill Cast 2024 Aluminum Alloys

Zhihao Zhao, Jianzhong Cui, Hiromi Nagaumi

pp. 1903-1907

Abstract

The horizontal direct chill (HDC) casting process is a well-established production route for wrought aluminum alloy ingots. However, the ingots may suffer from heterogenous microstructures due to the unbalanced cooling condition and gravitational effect. In order to minimize the casting defects, a low frequency electromagnetic field was applied in the HDC casting process and its influence on solidified microstructure was studied. The results show that the low frequency electromagnetic field can effectively reduce heterogenous microstructures in HDC ingot; and two main parameters of electromagnetic field, i.e., intensity and frequency, significantly affect the microstructures and solute distribution from the center to the periphery of the ingot. In the range of ampere-turns and frequency employed in the experiments, the ampere-turns of 10000 At and frequency of 30 Hz were found to be optimum.

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Effect of Low-Frequency Magnetic Fields on Microstructures of Horizontal Direct Chill Cast 2024 Aluminum Alloys

Epitaxial Growth of Vanadium-Doped ZnSe by MOVPE

Masahiro Tahashi, Shinsuke Ito, Toshiyuki Ido, Hideo Goto

pp. 1908-1910

Abstract

Vanadium-doped ZnSe, which is theoretically predicted to induce ferromagnetism above room temperature without carrier doping, was epitaxially grown on (100)GaAs substrate by metal-organic vapor phase epitaxial method in an atmospheric pressure. Vanadium concentration in the film obtained under the condition where the substrate and the vanadocene temperatures are 500 and 140°C, respectively, was 6.0 at% at maximum. The full width at half maximum (FWHM) of the peak diffracted from ZnSe(400) face increased with the increase of a vanadium concentration.

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Epitaxial Growth of Vanadium-Doped ZnSe by MOVPE

Influence of Target Material on the Microstructure and Properties of Ti–Si–N Coatings Prepared by r.f.-Reactive Sputtering

Masateru Nose, Yutaka Deguchi, Eiji Honbo, Wen-An. Chiou, Takehiko Mae, Kiyoshi Nogi

pp. 1911-1917

Abstract

We examined the effects of sputtering conditions and target materials on the microstructure and mechanical properties of Ti–Si–N coatings prepared by r.f.-reactive sputtering. We used composite targets consisting of a Ti (99.99%) plate and Si3N4 chips as well as the target consisting of a Ti plate and Si chips. Thin films were synthesized by an r.f. sputtering machine in a facing target-type (FTS) on the substrates of high speed steel. During the deposition, the substrate was heated from room temperature up to ∼300°C and a d.c. bias up to −100 V was applied. Without substrate heating and bias, the hardness of the films increased from 30 GPa for a binary system, reaching a maximum of 37 GPa for a ternary system with a small amount (3–8 at%) of Si. It then decreased to values lower than those of binary systems when Si was more than 10 at%. The hardness of high Si films (containing ∼20 at%Si) showed a lower value of 20 GPa. The hardness of high Si films deposited from the Ti–Si target increased and reached to a maximum value of 40 GPa around at a bias of −30 V, but the crystallite size of the film increased to ∼30 nm. On the other hand, the hardness of the films (containing ∼20 at%Si) deposited from the Ti–Si3N4 target increased with increasing negative bias voltage, being saturated at 38 GPa over −80 V. Although the crystallite size of the films increased gradually with increasing negative bias, it still remained at about 7 nm at −80 V. The characteristics of the latter film could be attributed to the formation of a nano-composite structure defined by Vep\\v{r}ek et al.

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Influence of Target Material on the Microstructure and Properties of Ti–Si–N Coatings Prepared by r.f.-Reactive Sputtering

Effects of the Intensity and Frequency of Electromagnetic Vibrations on Glass-Forming Ability in Mg–Cu–Y Bulk Metallic Glasses

Takuya Tamura, Rudi S Rachmat, Yoshiki Mizutani, Kenji Miwa

pp. 1918-1922

Abstract

The present authors reported that a new method for producing Mg–Cu–Y bulk metallic glasses by using electromagnetic vibrations is effective in forming the metallic glass phase, and disappearance or decrement of clusters by the electromagnetic vibrations applied to a liquid state is presumed to cause suppression of crystal nucleation [Nature Materials 4 (2005) 289]. This paper aims to investigate the effects of the intensity and frequency of electromagnetic vibrations on apparent glass-forming ability in the Mg–Cu–Y bulk metallic glasses. It was found that the apparent glass-forming ability of Mg65Cu25Y10 alloys increases with increasing the frequency of electromagnetic vibrations up to 5000 Hz. The effects of frequency more than 5000 Hz could not be investigated because of alternating current power devices. Moreover, it was found that the apparent glass-forming ability of Mg65Cu25Y10 alloys increases with increasing the intensity of electromagnetic vibrations by an electric current or a magnetic flux density. However, increasing excessively the electric current was found to weaken the enhancement of the apparent glass-forming ability by using the electromagnetic vibration process because the crystalline particles grow larger by the Joule heat.

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Effects of the Intensity and Frequency of Electromagnetic Vibrations on Glass-Forming Ability in Mg–Cu–Y Bulk Metallic Glasses

Effects of Dual-Ion Irradiation on the Swelling of SiC/SiC Composites

Hirotatsu Kishimoto, Kazumi Ozawa, Sosuke Kondo, Akira Kohyama

pp. 1923-1927

Abstract

Silicon carbide (SiC) matrix composites reinforced by SiC fibers is a candidate structural material of fusion gas-cooled blanket system. From the viewpoint of material designs, it is important to investigate the swelling by irradiation, which results from the accumulation of displacement damages. In the fusion environment, (n, α) nuclear reactions are considered to produce helium gas in SiC. For the microstructural evolution, a dual-ion irradiation method is able to simulate the effects of helium. In the present research, 1.7 MeV tandem and 1 MeV single-end accelerators were used for Si self-ion irradiation and helium implantation, respectively. The average helium over displacement per atom (dpa) ratio in SiC was adjusted to 60 appm/dpa. The irradiation temperature ranged from room temperature to 1400°C. The irradiation-induced swelling was measured by the step height method. Helium that was implanted simultaneously with displacement damages in dual-ion irradiated SiC increased the swelling that was larger than that by single-ion irradiated SiC below 800°C. Since this increase was not observed above 1000°C, the interaction of helium and displacement damages was considered to change above 800°C. In this paper, the microstructural behavior and dimensional stability of SiC materials under the fusion relevant environment are discussed.

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Article Title

Effects of Dual-Ion Irradiation on the Swelling of SiC/SiC Composites

Effect of Hydrostatic Pressure on P-14M-2M and P-2M Martensitic Transformations in Single Crystalline Ni–Mn–Ga Ferromagnetic Shape Memory Alloys

Jae-hoon Kim, Tomoyuki Taniguchi, Takashi Fukuda, Tomoyuki Kakeshita

pp. 1928-1932

Abstract

Effect of hydrostatic pressure on martensitic transformation temperature has been investigated in single crystalline Ni2.14Mn0.84Ga1.02 and Ni2.14Mn0.92Ga0.94 ferromagnetic shape memory alloys, which exhibit P-14M-2M and P-2M transformations, respectively, where P stands for a parent phase. We found that all the martensitic transformation temperatures increase linearly with increasing hydrostatic pressure; their increasing rates against hydrostatic pressure are 3 K/GPa (P→14M), 13 K/GPa (14M→2M) and 7 K/GPa (P→2M). The volume changes associated with the transformations are calculated to be −0.04% (P→14M), −0.04% (14M→2M) and −0.15% (P→2M) by using the Clausius–Clapeyron equation. In addition, Curie temperature of the parent phase of Ni2.14Mn0.84Ga1.02 increases linearly with increasing hydrostatic pressure; its increasing rate of about 4 K/GPa is well explained by using the Ehrenfest equation.

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Effect of Hydrostatic Pressure on P-14M-2M and P-2M Martensitic Transformations in Single Crystalline Ni–Mn–Ga Ferromagnetic Shape Memory Alloys

Magnetostriction of Polycrystalline Strong-Textured Fe–17 at%Ga Laminates

Chihiro Saito, Yasubumi Furuya, Teiko Okazaki, Mamoru Omori

pp. 1933-1937

Abstract

Magnetostrictive bulk Fe–17 at%Ga alloy was fabricated by combining laminates of rapid-solidified ribbons (80 μm in thickness) using the spark plasma sintering/joining (SPSJ). The SPSJ is characterized by a short time, low temperature heating and sintering process. The laminated sample made by the SPSJ maintained a unique metallurgical microstructure of polycrystalline texture of columnar grains, as well as the almost non-equilibrium metastable phase with little evidence of the precipitates of the ordered phases as found in the as-spun ribbons. An excellent sintered sample exhibiting large magnetostriction was obtained under a condition of compressive stress of 100 MPa at a temperature of 973 K. The magnetostriction depended on compressive pre-stress level for each specimen and reached about 100 ppm, which was half the value obtained for the ribbon sample. Furthermore, by subjecting this specimen to a short annealing process, the magnetostriction increased to 170 ppm, comparable to the value for the ribbon.

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Magnetostriction of Polycrystalline Strong-Textured Fe–17 at%Ga Laminates

Numerical Analysis of Thermoelectric Properties on Bi88Sb12

Kazuhiro Hasezaki, Masaki Itoh, Hiroyuki Kitagawa, Hiroyuki Noguchi, Shigetoshi Sota, Yasutoshi Noda

pp. 1938-1941

Abstract

The large maxima of thermopower as functions of the temperature observed for Bismuth Antimony alloy is studied theoretically based on the Boltzmann transport theory of single carrier. The Fermi statistics is fully taken into account, with the chemical potential being calculated self-consistently at each temperature from experimental Hall coefficients. It stays constant at lower temperatures, but starts to rise at T=70 K, where the maximum of the thermopower is observed. The temperature dependence of the calculated thermopower agrees well with the measurements. The occurrence of the maxima is thus shown to be associated with the extrinsic-to-intrinsic transition, thus providing theoretical confirmation to the known empirical rule.

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Numerical Analysis of Thermoelectric Properties on Bi88Sb12

Enhancing the Sensitivity of Oxygen Sensors through the Photocatalytic Effect of SnO2/TiO2 Film

Hsiao-Ching Lee, Weng-Sing Hwang

pp. 1942-1949

Abstract

This paper investigates the effect of photocatalysis on the sensitivity of oxygen sensors constructed with SnO2/TiO2 thin films. An R.F. magnetron sputtering system is employed to fabricate SnO2/TiO2 double-layer films. The thin films are deposited with SnO2/TiO2 thickness ratios of 250/50, 200/100, 150/150, 100/200, and 50/250 nm, respectively. During deposition, the Ar:O2 flow rate is fixed at 4:1. To stabilize the material properties, the films are annealed for four hours at a temperature of either 550 or 650°C. The increase in sensitivity of the SnO2/TiO2 thin films when irradiated by UV light with a wavelength of 365 nm is investigated. The results indicate that the annealed samples have higher oxygen sensitivities than the as-deposited samples. The sensitivity of the non-annealed samples increases from 0.70 to 1.15 under UV irradiation, while the sensitivity of the annealed samples increases from 7.17 to 10.60. Therefore, it is clear that UV irradiation causes the sensitivity of the SnO2/TiO2 thin films to increase significantly. Finally, it is found that the oxygen sensitivity of the SnO2/TiO2 thin films increases as the SnO2/TiO2 ratio is reduced.

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Enhancing the Sensitivity of Oxygen Sensors through the Photocatalytic Effect of SnO2/TiO2 Film

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