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Kotoji Ando - One of the best experts on this subject based on the ideXlab platform.
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Self-Crack-Healing behavior in ceramic matrix composites
Advances in Ceramic Matrix Composites, 2014Co-Authors: Toshio Osada, Koji Takahashi, Wataru Nakao, Kotoji AndoAbstract:Abstract: Self-Crack-Healing is one of the most valuable phenomena to overcome the decrease in reliability of ceramics caused by Cracking. This is because self-Healing is triggered by Crack initiation and gives complete strength recovery through the passive oxidation of SiC. Thus, self-Healing ceramics are candidates for high-temperature materials for gas turbine components, i.e., turbine blades and stator vanes. Nano-composite and multi-composite concepts for self-Healing ceramics are described. The design concept is based on ‘damage management’ rather than ‘damage prevention’. The kinetics of self-Crack-Healing of ceramic/SiC composites including the effects of temperature and oxygen partial pressure is introduced. The time for Crack-Healing with low oxygen partial pressure can be estimated. Furthermore, the effects of oxygen partial pressure on self-Healing under tensile stress are discussed. The design stress of ceramic turbine blades with self-Crack-Healing is considered.
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Improvement in Contact Strength of Si3N4/SiC Composite by Crack Healing
Journal of Powder Technology, 2013Co-Authors: Koji Takahashi, Keita Takahashi, Kotoji AndoAbstract:Ceramics have been used as bearing and cutting tool components, which are subjected to contact loading during their operation. The presence of surface Cracks on these components decreases their contact strength. Thus, the reliability of ceramic components can be increased by improving their contact strength through Crack Healing. In the present study, the effects of Crack Healing on the contact strength of a silicon carbide-(SiC-) reinforced silicon nitride (Si3N4) composite subjected to various machining processes were investigated. The contact strength of this composite was evaluated using a sphere indentation test in which acoustic emission was used. The results showed that the contact strength of the composite improved when it was subjected to Crack Healing in combination with rapping; this was true even when the composite had Cracks due to a heavy machining process.
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Strengthening of Ceramics Surface by Crack Healing and Electron Beam Irradiation
International Journal of Applied Ceramic Technology, 2011Co-Authors: Wataru Nakao, Chiba Yohei, Keisuke Iwata, Yoshitake Nishi, Kotoji AndoAbstract:New hybrid surface reinforcement consisting of Crack Healing and low energy electron beam irradiation has been proposed for structural ceramics. Crack Healing was found to make surface Cracks be innocuous. Low-energy electron beam irradiation was found to significantly harden the treated subsurface layer, which includes the matrix layer near the surface as well as the partly or fully covered silica layer formed by the Crack Healing. Moreover, it was found not to break the improved fracture strength due to Crack Healing. These results suggest that the proposed surface reinforcement can actualize to manage the existence of surface Cracks in structural ceramics.
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Crack‐Healing behaviour of ZrO2/SiC composite ceramics
International Journal of Structural Integrity, 2010Co-Authors: Keiji Houjou, Kotoji Ando, Koji TakahashiAbstract:Purpose – Zirconia ceramics exhibit high strength and fracture toughness. The purpose of this paper is to research a possibility of Crack Healing in zirconia ceramics.Design/methodology/approach – ZrO2/SiC composite ceramics are sintered and subjected to three‐point bending. A surface Crack of 100 μm in diameter is formed on each specimen. The Cracks are healed and the specimens are tested under bending.Findings – The paper finds that ZrO2/SiC composite ceramic material had a high Crack‐Healing ability at a considerably low temperature. For example, a Crack of 100 μm in diameter is healed even at 600°C.Research limitations/implications – The paper provides a low temperature Healing and a new mechanism of Crack Healing.Originality/value – The paper shows the Healing temperature and the minimum time required to heal showed a good proportional relation on the Arrhenius plot at temperatures of 600‐800°C. Moreover, the Crack Healing is caused by SiO2 cristobalite produced during the Healing.
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Crack Healing behaviour of zro2 sic composite ceramics
International Journal of Structural Integrity, 2010Co-Authors: Keiji Houjou, Kotoji Ando, Koji TakahashiAbstract:Purpose – Zirconia ceramics exhibit high strength and fracture toughness. The purpose of this paper is to research a possibility of Crack Healing in zirconia ceramics.Design/methodology/approach – ZrO2/SiC composite ceramics are sintered and subjected to three‐point bending. A surface Crack of 100 μm in diameter is formed on each specimen. The Cracks are healed and the specimens are tested under bending.Findings – The paper finds that ZrO2/SiC composite ceramic material had a high Crack‐Healing ability at a considerably low temperature. For example, a Crack of 100 μm in diameter is healed even at 600°C.Research limitations/implications – The paper provides a low temperature Healing and a new mechanism of Crack Healing.Originality/value – The paper shows the Healing temperature and the minimum time required to heal showed a good proportional relation on the Arrhenius plot at temperatures of 600‐800°C. Moreover, the Crack Healing is caused by SiO2 cristobalite produced during the Healing.
Koji Takahashi - One of the best experts on this subject based on the ideXlab platform.
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Self-Crack-Healing behavior in ceramic matrix composites
Advances in Ceramic Matrix Composites, 2014Co-Authors: Toshio Osada, Koji Takahashi, Wataru Nakao, Kotoji AndoAbstract:Abstract: Self-Crack-Healing is one of the most valuable phenomena to overcome the decrease in reliability of ceramics caused by Cracking. This is because self-Healing is triggered by Crack initiation and gives complete strength recovery through the passive oxidation of SiC. Thus, self-Healing ceramics are candidates for high-temperature materials for gas turbine components, i.e., turbine blades and stator vanes. Nano-composite and multi-composite concepts for self-Healing ceramics are described. The design concept is based on ‘damage management’ rather than ‘damage prevention’. The kinetics of self-Crack-Healing of ceramic/SiC composites including the effects of temperature and oxygen partial pressure is introduced. The time for Crack-Healing with low oxygen partial pressure can be estimated. Furthermore, the effects of oxygen partial pressure on self-Healing under tensile stress are discussed. The design stress of ceramic turbine blades with self-Crack-Healing is considered.
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Improvement in Contact Strength of Si3N4/SiC Composite by Crack Healing
Journal of Powder Technology, 2013Co-Authors: Koji Takahashi, Keita Takahashi, Kotoji AndoAbstract:Ceramics have been used as bearing and cutting tool components, which are subjected to contact loading during their operation. The presence of surface Cracks on these components decreases their contact strength. Thus, the reliability of ceramic components can be increased by improving their contact strength through Crack Healing. In the present study, the effects of Crack Healing on the contact strength of a silicon carbide-(SiC-) reinforced silicon nitride (Si3N4) composite subjected to various machining processes were investigated. The contact strength of this composite was evaluated using a sphere indentation test in which acoustic emission was used. The results showed that the contact strength of the composite improved when it was subjected to Crack Healing in combination with rapping; this was true even when the composite had Cracks due to a heavy machining process.
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Crack‐Healing behavior of ZrO2/SiC composite ceramics and strength properties of Crack‐Healing specimens
International Journal of Structural Integrity, 2012Co-Authors: Keiji Houjou, Koji TakahashiAbstract:Purpose – The purpose of this paper is to study the Crack‐Healing mechanism of ZrO2/SiC composite ceramics which have a high Crack‐Healing ability at low temperature.Design/methodology/approach – The effects of dispersed SiC and the environment on Crack‐Healing behaviour were investigated. The fatigue strength of Crack‐healed specimens was also investigated.Findings – The main conclusions are that for Crack‐Healing of ZrO2 ceramics, it is necessary to have both a SiC composite and an oxidative environment; and when ZrO2/SiC composite ceramics are heat‐treated in air, a phase transformation attributable to the SiC composite results in Crack‐Healing and improvement of fracture toughness and bending strength.Originality/value – An appropriate heat treatment for ZrO2/SiC composite caused not only Crack‐Healing but also the improvement of fracture toughness, and created a multiplier effect on Crack‐Healing, bending strength and fracture toughness.
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Crack‐Healing behaviour of ZrO2/SiC composite ceramics
International Journal of Structural Integrity, 2010Co-Authors: Keiji Houjou, Kotoji Ando, Koji TakahashiAbstract:Purpose – Zirconia ceramics exhibit high strength and fracture toughness. The purpose of this paper is to research a possibility of Crack Healing in zirconia ceramics.Design/methodology/approach – ZrO2/SiC composite ceramics are sintered and subjected to three‐point bending. A surface Crack of 100 μm in diameter is formed on each specimen. The Cracks are healed and the specimens are tested under bending.Findings – The paper finds that ZrO2/SiC composite ceramic material had a high Crack‐Healing ability at a considerably low temperature. For example, a Crack of 100 μm in diameter is healed even at 600°C.Research limitations/implications – The paper provides a low temperature Healing and a new mechanism of Crack Healing.Originality/value – The paper shows the Healing temperature and the minimum time required to heal showed a good proportional relation on the Arrhenius plot at temperatures of 600‐800°C. Moreover, the Crack Healing is caused by SiO2 cristobalite produced during the Healing.
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Crack Healing behaviour of zro2 sic composite ceramics
International Journal of Structural Integrity, 2010Co-Authors: Keiji Houjou, Kotoji Ando, Koji TakahashiAbstract:Purpose – Zirconia ceramics exhibit high strength and fracture toughness. The purpose of this paper is to research a possibility of Crack Healing in zirconia ceramics.Design/methodology/approach – ZrO2/SiC composite ceramics are sintered and subjected to three‐point bending. A surface Crack of 100 μm in diameter is formed on each specimen. The Cracks are healed and the specimens are tested under bending.Findings – The paper finds that ZrO2/SiC composite ceramic material had a high Crack‐Healing ability at a considerably low temperature. For example, a Crack of 100 μm in diameter is healed even at 600°C.Research limitations/implications – The paper provides a low temperature Healing and a new mechanism of Crack Healing.Originality/value – The paper shows the Healing temperature and the minimum time required to heal showed a good proportional relation on the Arrhenius plot at temperatures of 600‐800°C. Moreover, the Crack Healing is caused by SiO2 cristobalite produced during the Healing.
Wataru Nakao - One of the best experts on this subject based on the ideXlab platform.
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Self-Crack-Healing behavior in ceramic matrix composites
Advances in Ceramic Matrix Composites, 2014Co-Authors: Toshio Osada, Koji Takahashi, Wataru Nakao, Kotoji AndoAbstract:Abstract: Self-Crack-Healing is one of the most valuable phenomena to overcome the decrease in reliability of ceramics caused by Cracking. This is because self-Healing is triggered by Crack initiation and gives complete strength recovery through the passive oxidation of SiC. Thus, self-Healing ceramics are candidates for high-temperature materials for gas turbine components, i.e., turbine blades and stator vanes. Nano-composite and multi-composite concepts for self-Healing ceramics are described. The design concept is based on ‘damage management’ rather than ‘damage prevention’. The kinetics of self-Crack-Healing of ceramic/SiC composites including the effects of temperature and oxygen partial pressure is introduced. The time for Crack-Healing with low oxygen partial pressure can be estimated. Furthermore, the effects of oxygen partial pressure on self-Healing under tensile stress are discussed. The design stress of ceramic turbine blades with self-Crack-Healing is considered.
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Strengthening of Ceramics Surface by Crack Healing and Electron Beam Irradiation
International Journal of Applied Ceramic Technology, 2011Co-Authors: Wataru Nakao, Chiba Yohei, Keisuke Iwata, Yoshitake Nishi, Kotoji AndoAbstract:New hybrid surface reinforcement consisting of Crack Healing and low energy electron beam irradiation has been proposed for structural ceramics. Crack Healing was found to make surface Cracks be innocuous. Low-energy electron beam irradiation was found to significantly harden the treated subsurface layer, which includes the matrix layer near the surface as well as the partly or fully covered silica layer formed by the Crack Healing. Moreover, it was found not to break the improved fracture strength due to Crack Healing. These results suggest that the proposed surface reinforcement can actualize to manage the existence of surface Cracks in structural ceramics.
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kinetics of self Crack Healing of alumina silicon carbide composite including oxygen partial pressure effect
Journal of the American Ceramic Society, 2009Co-Authors: Toshio Osada, Koji Takahashi, Wataru Nakao, Kotoji AndoAbstract:Self-Crack-Healing behavior under a combustion gas atmosphere with a low oxygen partial pressure, , is important for actualizing ceramic gas turbines, but to date only self-Crack-Healing behavior in air has been investigated. In this study, we investigated Crack-Healing behaviors at 1273–1773 K under several levels of. Crack-Healing in atmospheres withgave rise to the complete strength recovery of Cracked specimens, resulting from passive oxidation. Based on the obtained results, the kinetics for strength recovery by self-Crack-Healing was expressed as a function of Healing temperature, TH (K), and(Pa). The strength recovery rate for complete Crack-Healing, vH (s−1), could be expressed as Using this rate equation, one can evaluate the Healing time for complete strength recovery under combustion gas in a gas turbine.
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Kinetics of Self-Crack-Healing of Alumina/Silicon Carbide Composite Including Oxygen Partial Pressure Effect
Journal of the American Ceramic Society, 2009Co-Authors: Toshio Osada, Koji Takahashi, Wataru Nakao, Kotoji AndoAbstract:Self-Crack-Healing behavior under a combustion gas atmosphere with a low oxygen partial pressure, , is important for actualizing ceramic gas turbines, but to date only self-Crack-Healing behavior in air has been investigated. In this study, we investigated Crack-Healing behaviors at 1273–1773 K under several levels of. Crack-Healing in atmospheres withgave rise to the complete strength recovery of Cracked specimens, resulting from passive oxidation. Based on the obtained results, the kinetics for strength recovery by self-Crack-Healing was expressed as a function of Healing temperature, TH (K), and(Pa). The strength recovery rate for complete Crack-Healing, vH (s−1), could be expressed as Using this rate equation, one can evaluate the Healing time for complete strength recovery under combustion gas in a gas turbine.
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Enhancement of in situ self-Crack-Healing efficient temperature region by SiC nanosizing
Journal of Intelligent Material Systems and Structures, 2007Co-Authors: Wataru Nakao, Yasuyuki Tsutagawa, Kotoji AndoAbstract:Self-Crack-Healing by oxidation of silicon carbide (SiC) is the most effective method to improve the reliability of ceramics, as this eliminates surface Cracks completely. Furthermore, if the service condition corresponds to the state under which self-Crack-Healing can occur, Cracks introduced during service can be completely healed during service. However, the ceramic composites having Crack-Healing ability exhibit only a small efficient temperature region for Crack-Healing during service. Therefore, the authors have tried to decrease the temperature at which Crack-Healing reaction becomes active, as well as to increase the temperature limit for bending strength by size reduction in the contained SiC particles. The present study adapts the following self-propagating high temperature synthesis (SHS) to fabricate alumina composite containing nanosized SiC particles: 3(3Al2O32SiO2) + 8Al + 6C = 13Al2O3 + 6SiC. The formed nanosized SiC particles have a particle size of 10—30 nm and exist in alumina grain. As...
Shigemi Sato - One of the best experts on this subject based on the ideXlab platform.
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Crack Healing behavior under stress of mullite silicon carbide ceramics and the resultant fatigue strength
Journal of the American Ceramic Society, 2004Co-Authors: Kotoji Ando, Mincheol Chu, Kotokaze Furusawa, Tsuyoshi Hanagata, Kiichi Tuji, Shigemi SatoAbstract:Mullite/SiC composite ceramics were sintered and subjected to three-point bending of specimens made according to the appropriate JIS standard. A semicircular surface Crack 100 to 250 μm in diameter was made on each specimen. We systematically studied Crack-Healing behavior and cyclic- and static-fatigue strengths at room temperature and 1000°C (Crack-Healing temperature) by using three types of specimens (smooth, Cracked, and Crack-healed). The main conclusions are as follows: (i) mullite/SiC composite ceramics have the ability to heal after Cracking; (ii) Crack-healed specimens exhibited higher static and fatigue strengths than those of smooth specimens, which was caused by Crack-Healing; (iii) a sample Crack-healed at 1000°C had a high fatigue strength at 1000°C; and (iv) mullite/SiC ceramics can heal a Crack under stress at 1000°C, and this behavior was considered using Crack-driving force and Crack-Healing force, qualitatively.
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Crack-Healing behavior under stress of mullite/silicon carbide ceramics and the resultant fatigue strength
Journal of the American Ceramic Society, 2004Co-Authors: Kotoji Ando, Mincheol Chu, Kotokaze Furusawa, Tsuyoshi Hanagata, Kiichi Tuji, Shigemi SatoAbstract:Mullite/SiC composite ceramics were sintered and subjected to three-point bending of specimens made according to the appropriate JIS standard. A semicircular surface Crack 100 to 250 μm in diameter was made on each specimen. We systematically studied Crack-Healing behavior and cyclic- and static-fatigue strengths at room temperature and 1000°C (Crack-Healing temperature) by using three types of specimens (smooth, Cracked, and Crack-healed). The main conclusions are as follows: (i) mullite/SiC composite ceramics have the ability to heal after Cracking; (ii) Crack-healed specimens exhibited higher static and fatigue strengths than those of smooth specimens, which was caused by Crack-Healing; (iii) a sample Crack-healed at 1000°C had a high fatigue strength at 1000°C; and (iv) mullite/SiC ceramics can heal a Crack under stress at 1000°C, and this behavior was considered using Crack-driving force and Crack-Healing force, qualitatively.
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Crack Healing Behaviour and High Temperature Strength of Silicon Nitride Ceramics.
Transactions of the Japan Society of Mechanical Engineers Series A, 1999Co-Authors: Kotoji Ando, Mincheol Chu, Yasuyoshi Kobayashi, F. Yao, Shigemi SatoAbstract:Crack Healing behaviours of silicon nitride have been investigated as a function of sintering additives and Crack Healing condition, systematically. The semicircular Crack (average diameter is 110 μm) was made in the center of specimen using Vickers hardness indenter. Some of the Cracked specimens were heat-treated at 800°C∼1 400°C, 1∼150 hour in air atmosphere. Bending strength was measured at room and elevated temperature up to 1 400°C. Bending strength of Cracked specimen reduced to about 48% of that of smooth specimen. However, the bending strength of pre-Cracked specimens recovered completely up to that of smooth specimen by the heat treatment. And in several specimens, failure occured from the outside of pre-Cracked area even at 1 300°C. This strength recovery was caused by Crack Healing. By analysing the test results, the following conclusion was obtained. The silicon nitride which has the highest Crack Healing ability within this experiment is silicon nitride with 20 wt.% SiC and 8 wt.% Y2O3. The best Healing condition for the specimen is 1 200°C∼1 300°C, 1 h in air. The Crack healed member at the condition has enough bending strength and low sensitivity to static fatigue up to 1 400°C.
Kotokaze Furusawa - One of the best experts on this subject based on the ideXlab platform.
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Crack Healing behavior under stress of mullite silicon carbide ceramics and the resultant fatigue strength
Journal of the American Ceramic Society, 2004Co-Authors: Kotoji Ando, Mincheol Chu, Kotokaze Furusawa, Tsuyoshi Hanagata, Kiichi Tuji, Shigemi SatoAbstract:Mullite/SiC composite ceramics were sintered and subjected to three-point bending of specimens made according to the appropriate JIS standard. A semicircular surface Crack 100 to 250 μm in diameter was made on each specimen. We systematically studied Crack-Healing behavior and cyclic- and static-fatigue strengths at room temperature and 1000°C (Crack-Healing temperature) by using three types of specimens (smooth, Cracked, and Crack-healed). The main conclusions are as follows: (i) mullite/SiC composite ceramics have the ability to heal after Cracking; (ii) Crack-healed specimens exhibited higher static and fatigue strengths than those of smooth specimens, which was caused by Crack-Healing; (iii) a sample Crack-healed at 1000°C had a high fatigue strength at 1000°C; and (iv) mullite/SiC ceramics can heal a Crack under stress at 1000°C, and this behavior was considered using Crack-driving force and Crack-Healing force, qualitatively.
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Crack-Healing behavior under stress of mullite/silicon carbide ceramics and the resultant fatigue strength
Journal of the American Ceramic Society, 2004Co-Authors: Kotoji Ando, Mincheol Chu, Kotokaze Furusawa, Tsuyoshi Hanagata, Kiichi Tuji, Shigemi SatoAbstract:Mullite/SiC composite ceramics were sintered and subjected to three-point bending of specimens made according to the appropriate JIS standard. A semicircular surface Crack 100 to 250 μm in diameter was made on each specimen. We systematically studied Crack-Healing behavior and cyclic- and static-fatigue strengths at room temperature and 1000°C (Crack-Healing temperature) by using three types of specimens (smooth, Cracked, and Crack-healed). The main conclusions are as follows: (i) mullite/SiC composite ceramics have the ability to heal after Cracking; (ii) Crack-healed specimens exhibited higher static and fatigue strengths than those of smooth specimens, which was caused by Crack-Healing; (iii) a sample Crack-healed at 1000°C had a high fatigue strength at 1000°C; and (iv) mullite/SiC ceramics can heal a Crack under stress at 1000°C, and this behavior was considered using Crack-driving force and Crack-Healing force, qualitatively.
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In Situ Crack-Healing Behavior of Mullite/SiC Composite Ceramics
Journal of the Society of Materials Science Japan, 2003Co-Authors: Kotokaze Furusawa, Naoki Furumachi, Koji Takahasi, Sinji Saito, Kotoji AndoAbstract:Three point bending specimen was made from mullite/SiC composite ceramics. A semi-elliptical surface Crack of 75μm or 100μm in diameter (aspect ratio ≈0.9) was introduced on the specimen. Basic Crack-Healing behavior of the Cracked-sample was studied systematically as a function of Crack-Healing temperature, time, environment and cyclic stress applied. Followings are main conclusion obtained; (1) Mullite/SiC composite ceramics are able to recover strength of Cracked sample by heat treatment in air. (2) The recovery was caused by the Crack-Healing behavior, and the activation energy was evaluated as Q=413kJ/mol. (3) This sample was able to heal a Crack even under cyclic stress at service temperature. This behavior was defined as in situ Crack-Healing. (4) The Crack-healed sample from 1273K to 1473K exhibited same level bending strength to Crack-healed sample at 1573K just at the healed temperature. This behavior was defined as in situ bending strength of in situ Crack-healed sample.