Multiscale, Multifunctional and Functionally Graded Materials

Volumes 631-632

doi: 10.4028/

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Authors: De Gang Zhao, Xiao Ya Li, Yan Hong Cai, Wan Jiang, Li Dong Chen
Abstract: Joining of TE material to electrode is the key technique in the construction of TE device for the practical applications. In this study, a suitable alloy electrode was introduced into CoSb3-based element by means of spark plasma sintering (SPS). Finite element analysis showed that the maximum thermal residual stress appeared at the cylindrical surface zone close to the CoSb3/electrode interface. Microstructure of CoSb3/electrode was investigated by EPMA and the intermetallic compound (IMC) layers were found. The shear strength of CoSb3/electrode joints was tested and the results show that the joints have sufficient strength for reliability of TE device. Electrical contact resistance between CoSb3 and electrode was measured by means of four-probe technique. The results show that the contact resistance was minimal and below the 50μΩ.cm2, which meant the joint exhibited a good electrical contact. The high temperature reliability evaluation showed good thermal duration stability of the CoSb3/electrode joints.
Authors: Chang Sheng Ding, Hong Fei Lin, Kazuhisa Sato, Yoshifumi Tsutai, Mabito Iguchi, Toshiyuki Hashida
Abstract: Dense gadolinium doped ceria (GDC) electrolyte thin films were prepared on porous NiO-GDC substrates by spray coating process. Microstructure of the GDC thin films and effect of preparation process on the microstructure were examined. SEM results show that uniform and dense GDC thin films with a thickness of approximately 1 μm were successfully prepared on porous NiO-GDC anodes. Anode-supported single cell with the thin GDC electrolyte film was tested using humidified hydrogen as a fuel, and exhibited relatively high electrical performance at low operating temperature (the maximum power density of 135 mW/cm2 at 600 °C). This means that the thin GDC film may be applicable to an electrolyte for anode-supported SOFCs. The experimental results suggest that the spray coating method developed in this study may offer a useful route for preparing thin and dense electrolytes of SOFCs.
Authors: K. Sakon, Y. Hirokawa, Yasuji Masubuchi, Shinichi Kikkawa
Abstract: Sputter deposited Fe0.7Co0.3 nitride thin film had zinc blende structure. It was thermally decomposed completely back to the ferromagnetic Fe0.7Co0.3 alloy above 400°C. As-deposited nitride thin films obtained in cosputtering of (Fe0.7Co0.3)1-xAlx composite target with nitrogen sputter gas were solid solutions with zinc blende (x≤0.44) and wurtzite (x>0.5) type structure, respectively. The largest magneto resistance ratio of 0.24% was observed on the Fe0.7Co0.3 alloy particles dispersed in AlN thin film obtained by thermal decomposition of the nitride solid solution with x=0.66 at 500°C.
Authors: Mehmet Ali Guler, Yusuf Fuat Gülver, Serkan Dag
Abstract: In this study the contact problems of thin films bonded to Functionally Graded Materials (FGM) are considered. In these problems the loading consists of any one or combination of stresses caused by uniform temperature changes and temperature excursions, far field mechanical loading, and residual stresses resulting from film processing or in the manufacturing process of the graded coating. The primary interest in this study is in examining stress concentrations or singularities near the film ends for the purpose of addressing the question of crack initiation and propagation in the substrate or along the interface. The underlying contact mechanics problem is formulated by assuming that the film is a “membrane” and the FGM an elastic continuum, and is solved analytically by reducing it to an integral equation. The calculated results are the interfacial shear stress between the film and the graded substrate, mode II stress intensity factor at the end of the film and the axial normal stress in the film.
Authors: Tsugumi Hayashi, Yohei Baba, Toshiharu Taga, Shun Yokoyama, Hiroaki Suzuki, Hideyuki Takahashi, Masayuki Niino, Kazuyuki Tohji
Abstract: Objective of study was the development of core-shell type ZnS-CdS photocatalyst with the stratified morphology. To form the stratified morphology, condition of the precursor is extremely important. For this purpose, three types of precursors, thus core-shell type, egg-shell type and uniform type, was tried to synthesize by utilizing the results of the calculation. The size of the synthesized precursor particles was about 40-100 nm. Main phase of the particle was gradually changed from ZnO (pH8.0) to Cd(OH)2 (pH9.5). Detailed analysis of the synthesized precursor was clearly demonstrated that these have the crystalline structure and each metal element was co-existed in one particle. Therefore, it could be concluded that core-shell type or uniform type precursor was successfully synthesized. Core-shell type ZnS-CdS stratified photocatalyst could be successfully synthesized by sulfurization for 1h, and it shows the high photocatalytic activity under visible light irradiation.
Authors: Naoya Hayashi, Tatsuya Ohmi, Manabu Iguchi
Abstract: A microchanneling process utilizing microscopic reactive infiltration produces microchannels and alloy lining layers in metal bodies. We examined the composition and structure of a Ni-Al intermetallic lining layer with a peculiar porous structure produced by Ni-Al reactive infiltration. The Ni-Al lining layer is a thick film consists of multiple sub-layers and has many micropores. Such a porous structure and the heat resistance of Ni-Al intermetallic compound are appropriate for a catalyst support in high-temperature use. Image analysis and EPMA revealed that both aluminum concentration and voidage in the Ni-Al lining layer show a graded distribution along the thickness direction of the lining layer.
Authors: Zhang Jian Zhou, Yong Jin Yum, Chang Chun Ge
Abstract: Two kinds of W/Cu functionally graded material based high heat flux components, including monoblock concept and flat tile concept, are designed and fabricated. Thermally induced stresses and strains under operation conditions in these components are analyzed using finite element analysis. The effect on stress and strain of using different graded structures to join Cu to W is examined and compared. There has no obvious difference on operation thermal stress mitigating between monoblock design and flat tile design. The component with monoblock concept was fabricated by a one step fast resistance sintering, and the component with flat tile concept was fabricated by infiltration-welding method successfully.
Authors: Hiroyuki Y. Suzuki
Abstract: Compaction behavior of two component slurry during High-speed Centrifugal Compaction Process (HCP) was observed. Slight amount of iron oxide powder is mixed into alumina slurry, then the slurry was sedimented in a centrifuge under rotational speed of up to 11,500 rpm. A “Y” letter shaped flow pattern was emerged in the cross section of the compact. The pattern was clearer with higher rotational speed, but indifferent to acceleration rate of rotation. A similar pattern was simulated when we presume bidirectional initial flow in centrifugal field, which indicated that the combination of Corioli’s force and bidirectional flows of powder and dispersing medium caused such flow pattern.
Authors: Tatsuya Ohmi, Manabu Iguchi
Abstract: The solidification structure and hardness distribution in aluminum alloy duplex pipes produced by a two-step centrifugal casting have been investigated. In this process, two kinds of molten metals, i.e., the first melt and the second melt with a higher liquidus temperature were cast in sequence at a given interval into a rotating mold of a centrifugal caster. An Al-12mass%Si alloy was used for the first melt, and an Al-30mass%Ni or Al-32mass%Si-0.1mass%P alloy was used for the second melt. The second melt was cast after the solidified shell of the first melt had formed. The resultant cast pipes consisted of an outer side layer and a composite layer containing fine primary crystals. The outer side layer was a portion of the solidified shell of the first melt that survived after the contact with the higher-temperature second melt. The composite layer consisted of one or two layer(s). When the volume of the remelted part of the solidified shell was large, all the second melt mixed into the first melt and the resulted mixed melt formed the composite layer. On the other hand, the composite layer formed only from the second melt when the temperature of the solidified shell was low. In the intermediate case, the composite layer consisted of these two types of the layers.
Authors: Shimaa El Hadad, Hisashi Sato, P.D. Sequeira, Yoshimi Watanabe, Yoshihito Oya-Seimiya
Abstract: Formation of the compositional gradient in FGMs fabricated by centrifugal casting method depends mainly on the processing temperature and the applied centrifugal force. According to the initial state of the dispersed second phase at the processing temperature, CCM-FGMs can be classified into two categories. One is the FGM fabricated by centrifugal solid-particle method, and the other one is the FGM made by centrifugal in-situ method. In previous study, it has been reported that microstructure of Al-Al3Ti FGMs by centrifugal in-situ method was different from that by centrifugal solid-particle method. However, difference of mechanical property due to processing method is still unclear. In this study, mechanical properties, such as hardness and wear property of Al-Al3Ti FGMs fabricated by centrifugal solid-particle method and in-situ method were evaluated.

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