The Experts below are selected from a list of 294 Experts worldwide ranked by ideXlab platform
Koji Hagihara - One of the best experts on this subject based on the ideXlab platform.
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Inducement of kink-band formation in directionally solidified Mg/Mg17Al12 eutectic alloy - Inspired by the deformation behavior of the long-period stacking ordered (LPSO) phase
Materials Science and Engineering: A, 2020Co-Authors: Koji Hagihara, Kyohei Hayakawa, Kosuke MiyoshiAbstract:Abstract Kink-band formation has received significant attention, especially in the Mg-based long-period stacking ordered (LPSO) phase which increases the strength and ductility of Mg alloys. However, its formation criteria are not understood. Recent studies suggested that unique LPSO crystal structure, which is constructed by alternative stacking of soft and hard layers, is a plausible factor governing the kink-band formation. To confirm this assumption, we examined the deformation behavior of a directionally solidified Mg/Mg17Al12 eutectic alloy with Lamellar microstructure as a model material. Consequently, kink-band formation was indeed confirmed when stress was applied parallel to the Lamellar Interface. Interestingly, the hard Mg17Al12 phase rather than the soft Mg phase was found to predominately govern the kink-band formation behavior, contrary to the expectation. This must be because the easiest slip plane in Mg17Al12 is nearly parallel to the Lamellar Interface, which is not the case in Mg. The obtained results show that restricting the shear deformation direction in the material is the most important factor to induce kink-band formation. Furthermore, the distribution of a kink band could be controlled by introducing primary Mg17Al12 grains. The results provide new insight into a strategy for the aggressive use of kink band to improve the mechanical properties of structural materials.
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Outstanding compressive creep strength in Cr/Ir-codoped (Mo 0.85 Nb 0.15 )Si 2 crystals with the unique cross-Lamellar microstructure
Scientific reports, 2017Co-Authors: Koji Hagihara, Takaaki Ikenishi, Haruka Araki, Takayoshi NakanoAbstract:A (Mo0.85Nb0.15)Si2 crystal with an oriented, Lamellar, C40/C11b two-phase microstructure is a promising ultrahigh-temperature (UHT) structural material, but its low room-temperature fracture toughness and low high-temperature strength prevent its practical application. As a possibility to overcome these problems, we first found a development of unique “cross-Lamellar microstructure”, by the cooping of Cr and Ir. The cross-Lamellar microstructure consists of a rod-like C11b-phase grains that extend along a direction perpendicular to the Lamellar Interface in addition to the C40/C11b fine lamellae. In this study, the effectiveness of the cross-Lamellar microstructure for improving the high-temperature creep deformation property, being the most essential for UHT materials, was examined by using the oriented crystals. The creep rate significantly reduced along a loading orientation parallel to the Lamellar Interface. Furthermore, the degradation in creep strength for other loading orientation that is not parallel to the Lamellar Interface, which has been a serious problem up to now, was also suppressed. The results demonstrated that the simultaneous improvement of high-temperature creep strength and room temperature fracture toughness can be first accomplished by the development of unique cross-Lamellar microstructure, which opens a potential avenue for the development of novel UHT materials as alternatives to existing Ni-based superalloys.
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mechanisms of cr segregation to c11b c40 Lamellar Interface in mo nb si2 duplex silicide a phase field study to bridge experimental and first principles investigations
Intermetallics, 2014Co-Authors: Toshihiro Yamazaki, Yuichiro Koizumi, Akihiko Chiba, Koji Hagihara, Takayoshi Nakano, Koretaka Yuge, Kyosuke Kishida, Haruyuki InuiAbstract:Abstract Cr segregation at Lamellar Interfaces in the MoSi 2 /NbSi 2 duplex silicide was examined using a newly developed phase-field model to elucidate the mechanism of interfacial segregation, which is believed to improve the thermal stability of Lamellar structures as well as creep resistance. This is because Lamellar structures can improve the high-temperature strength, and the stabilization of the Lamellar structures improves creep resistance. The model takes into account the segregation energy determined using first-principles calculations to reflect the chemical interaction between the solute atoms and the Interface, in addition to the elastic interaction. Cr segregation occurs at the Interface when the segregation energy is considered, whereas no segregation occurs in the case where only the elastic interaction is considered. However, the extent of segregation was much smaller than that observed experimentally when the segregation energy was evaluated using first-principles calculations without considering lattice vibrations (i.e., the calculations were performed for 0 K). A simulation that took into consideration the segregation energy with the lattice vibrations at 1673 K resulted in segregation similar to that observed experimentally, where the Cr-added MoSi 2 /NbSi 2 duplex silicide was equilibrated at 1673 K, namely, the temperature at which the segregation energy was calculated. Thus, it was revealed that the solute-Interface chemical interaction and its temperature dependence are responsible for the interfacial segregation of Cr. These results suggest that the segregation energy needs to be taken into account in the search for more effective additive elements for improving the thermal stability of Lamellar structures as well as the creep resistance.
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Interface migration with segregation in mosi2 based Lamellar alloy simulated by phase field method
Advanced Materials Research, 2014Co-Authors: Toshihiro Yamazaki, Yuichiro Koizumi, Akihiko Chiba, Koji Hagihara, Takayoshi Nakano, Koretaka Yuge, Kyosuke Kishida, Haruyuki InuiAbstract:MoSi2–based alloys are attracting attention as ultra-high temperature structural material for super-high efficiency gas turbine power generation systems. In this study, the effects of Cr-and Zr-addition on Interface migration in MoSi2/NbSi2 Lamellar silicide were examined by phase field simulations employing the segregation energies evaluated by the first principles calculation in addition to thermodynamic free energy in order to take into account the chemically-driven interfacial segregation. The simulation results indicate that both Cr and Zr can segregate at the Lamellar Interface to suppress its migration, and the Zr-addition is more effective to lower the Interface migration rate than the Cr-addition owing to its higher segregation energy.
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Mechanisms of Cr segregation to C11b/C40 Lamellar Interface in (Mo,Nb)Si2 duplex silicide: A phase-field study to bridge experimental and first-principles investigations
Intermetallics, 2014Co-Authors: Toshihiro Yamazaki, Yuichiro Koizumi, Akihiko Chiba, Koji Hagihara, Takayoshi Nakano, Koretaka Yuge, Kyosuke Kishida, Haruyuki InuiAbstract:Abstract Cr segregation at Lamellar Interfaces in the MoSi 2 /NbSi 2 duplex silicide was examined using a newly developed phase-field model to elucidate the mechanism of interfacial segregation, which is believed to improve the thermal stability of Lamellar structures as well as creep resistance. This is because Lamellar structures can improve the high-temperature strength, and the stabilization of the Lamellar structures improves creep resistance. The model takes into account the segregation energy determined using first-principles calculations to reflect the chemical interaction between the solute atoms and the Interface, in addition to the elastic interaction. Cr segregation occurs at the Interface when the segregation energy is considered, whereas no segregation occurs in the case where only the elastic interaction is considered. However, the extent of segregation was much smaller than that observed experimentally when the segregation energy was evaluated using first-principles calculations without considering lattice vibrations (i.e., the calculations were performed for 0 K). A simulation that took into consideration the segregation energy with the lattice vibrations at 1673 K resulted in segregation similar to that observed experimentally, where the Cr-added MoSi 2 /NbSi 2 duplex silicide was equilibrated at 1673 K, namely, the temperature at which the segregation energy was calculated. Thus, it was revealed that the solute-Interface chemical interaction and its temperature dependence are responsible for the interfacial segregation of Cr. These results suggest that the segregation energy needs to be taken into account in the search for more effective additive elements for improving the thermal stability of Lamellar structures as well as the creep resistance.
Takayoshi Nakano - One of the best experts on this subject based on the ideXlab platform.
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Outstanding compressive creep strength in Cr/Ir-codoped (Mo 0.85 Nb 0.15 )Si 2 crystals with the unique cross-Lamellar microstructure
Scientific reports, 2017Co-Authors: Koji Hagihara, Takaaki Ikenishi, Haruka Araki, Takayoshi NakanoAbstract:A (Mo0.85Nb0.15)Si2 crystal with an oriented, Lamellar, C40/C11b two-phase microstructure is a promising ultrahigh-temperature (UHT) structural material, but its low room-temperature fracture toughness and low high-temperature strength prevent its practical application. As a possibility to overcome these problems, we first found a development of unique “cross-Lamellar microstructure”, by the cooping of Cr and Ir. The cross-Lamellar microstructure consists of a rod-like C11b-phase grains that extend along a direction perpendicular to the Lamellar Interface in addition to the C40/C11b fine lamellae. In this study, the effectiveness of the cross-Lamellar microstructure for improving the high-temperature creep deformation property, being the most essential for UHT materials, was examined by using the oriented crystals. The creep rate significantly reduced along a loading orientation parallel to the Lamellar Interface. Furthermore, the degradation in creep strength for other loading orientation that is not parallel to the Lamellar Interface, which has been a serious problem up to now, was also suppressed. The results demonstrated that the simultaneous improvement of high-temperature creep strength and room temperature fracture toughness can be first accomplished by the development of unique cross-Lamellar microstructure, which opens a potential avenue for the development of novel UHT materials as alternatives to existing Ni-based superalloys.
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mechanisms of cr segregation to c11b c40 Lamellar Interface in mo nb si2 duplex silicide a phase field study to bridge experimental and first principles investigations
Intermetallics, 2014Co-Authors: Toshihiro Yamazaki, Yuichiro Koizumi, Akihiko Chiba, Koji Hagihara, Takayoshi Nakano, Koretaka Yuge, Kyosuke Kishida, Haruyuki InuiAbstract:Abstract Cr segregation at Lamellar Interfaces in the MoSi 2 /NbSi 2 duplex silicide was examined using a newly developed phase-field model to elucidate the mechanism of interfacial segregation, which is believed to improve the thermal stability of Lamellar structures as well as creep resistance. This is because Lamellar structures can improve the high-temperature strength, and the stabilization of the Lamellar structures improves creep resistance. The model takes into account the segregation energy determined using first-principles calculations to reflect the chemical interaction between the solute atoms and the Interface, in addition to the elastic interaction. Cr segregation occurs at the Interface when the segregation energy is considered, whereas no segregation occurs in the case where only the elastic interaction is considered. However, the extent of segregation was much smaller than that observed experimentally when the segregation energy was evaluated using first-principles calculations without considering lattice vibrations (i.e., the calculations were performed for 0 K). A simulation that took into consideration the segregation energy with the lattice vibrations at 1673 K resulted in segregation similar to that observed experimentally, where the Cr-added MoSi 2 /NbSi 2 duplex silicide was equilibrated at 1673 K, namely, the temperature at which the segregation energy was calculated. Thus, it was revealed that the solute-Interface chemical interaction and its temperature dependence are responsible for the interfacial segregation of Cr. These results suggest that the segregation energy needs to be taken into account in the search for more effective additive elements for improving the thermal stability of Lamellar structures as well as the creep resistance.
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Interface migration with segregation in mosi2 based Lamellar alloy simulated by phase field method
Advanced Materials Research, 2014Co-Authors: Toshihiro Yamazaki, Yuichiro Koizumi, Akihiko Chiba, Koji Hagihara, Takayoshi Nakano, Koretaka Yuge, Kyosuke Kishida, Haruyuki InuiAbstract:MoSi2–based alloys are attracting attention as ultra-high temperature structural material for super-high efficiency gas turbine power generation systems. In this study, the effects of Cr-and Zr-addition on Interface migration in MoSi2/NbSi2 Lamellar silicide were examined by phase field simulations employing the segregation energies evaluated by the first principles calculation in addition to thermodynamic free energy in order to take into account the chemically-driven interfacial segregation. The simulation results indicate that both Cr and Zr can segregate at the Lamellar Interface to suppress its migration, and the Zr-addition is more effective to lower the Interface migration rate than the Cr-addition owing to its higher segregation energy.
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Mechanisms of Cr segregation to C11b/C40 Lamellar Interface in (Mo,Nb)Si2 duplex silicide: A phase-field study to bridge experimental and first-principles investigations
Intermetallics, 2014Co-Authors: Toshihiro Yamazaki, Yuichiro Koizumi, Akihiko Chiba, Koji Hagihara, Takayoshi Nakano, Koretaka Yuge, Kyosuke Kishida, Haruyuki InuiAbstract:Abstract Cr segregation at Lamellar Interfaces in the MoSi 2 /NbSi 2 duplex silicide was examined using a newly developed phase-field model to elucidate the mechanism of interfacial segregation, which is believed to improve the thermal stability of Lamellar structures as well as creep resistance. This is because Lamellar structures can improve the high-temperature strength, and the stabilization of the Lamellar structures improves creep resistance. The model takes into account the segregation energy determined using first-principles calculations to reflect the chemical interaction between the solute atoms and the Interface, in addition to the elastic interaction. Cr segregation occurs at the Interface when the segregation energy is considered, whereas no segregation occurs in the case where only the elastic interaction is considered. However, the extent of segregation was much smaller than that observed experimentally when the segregation energy was evaluated using first-principles calculations without considering lattice vibrations (i.e., the calculations were performed for 0 K). A simulation that took into consideration the segregation energy with the lattice vibrations at 1673 K resulted in segregation similar to that observed experimentally, where the Cr-added MoSi 2 /NbSi 2 duplex silicide was equilibrated at 1673 K, namely, the temperature at which the segregation energy was calculated. Thus, it was revealed that the solute-Interface chemical interaction and its temperature dependence are responsible for the interfacial segregation of Cr. These results suggest that the segregation energy needs to be taken into account in the search for more effective additive elements for improving the thermal stability of Lamellar structures as well as the creep resistance.
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Phase-field study on the segregation mechanism of Cr to Lamellar Interface in C40-NbSi2/C11b-MoSi2 duplex silicide
arXiv: Materials Science, 2013Co-Authors: Toshihiro Yamazaki, Yuichiro Koizumi, Akihiko Chiba, Koji Hagihara, Takayoshi Nakano, Koretaka Yuge, Kyosuke Kishida, Haruyuki InuiAbstract:Cr-segregation to a Lamellar Interface in NbSi2/MoSi2 duplex silicide has been examined by a newly developed phase-field model. The model can take into account the segregation energy evaluated by a first principles calculation to reflect the chemical interaction between solute atoms and the Interface in addition to the elastic interaction. Cr segregation occurs at the Interface in the case with segregation energy whereas no segregation occurs in the case with only elastic interaction. However, the segregation is much smaller than that observed in the experiment when the segregation energy was evaluated by the first principles calculation without lattice vibration (i.e. for 0 K). Another simulations with the segregation energy with lattice vibration results in segregation comparable to that in the experiment. Thus, it has been revealed that the solute-Interface chemical interaction and its temperature dependence is responsible for the interfacial segregation of Cr.
Haruyuki Inui - One of the best experts on this subject based on the ideXlab platform.
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mechanisms of cr segregation to c11b c40 Lamellar Interface in mo nb si2 duplex silicide a phase field study to bridge experimental and first principles investigations
Intermetallics, 2014Co-Authors: Toshihiro Yamazaki, Yuichiro Koizumi, Akihiko Chiba, Koji Hagihara, Takayoshi Nakano, Koretaka Yuge, Kyosuke Kishida, Haruyuki InuiAbstract:Abstract Cr segregation at Lamellar Interfaces in the MoSi 2 /NbSi 2 duplex silicide was examined using a newly developed phase-field model to elucidate the mechanism of interfacial segregation, which is believed to improve the thermal stability of Lamellar structures as well as creep resistance. This is because Lamellar structures can improve the high-temperature strength, and the stabilization of the Lamellar structures improves creep resistance. The model takes into account the segregation energy determined using first-principles calculations to reflect the chemical interaction between the solute atoms and the Interface, in addition to the elastic interaction. Cr segregation occurs at the Interface when the segregation energy is considered, whereas no segregation occurs in the case where only the elastic interaction is considered. However, the extent of segregation was much smaller than that observed experimentally when the segregation energy was evaluated using first-principles calculations without considering lattice vibrations (i.e., the calculations were performed for 0 K). A simulation that took into consideration the segregation energy with the lattice vibrations at 1673 K resulted in segregation similar to that observed experimentally, where the Cr-added MoSi 2 /NbSi 2 duplex silicide was equilibrated at 1673 K, namely, the temperature at which the segregation energy was calculated. Thus, it was revealed that the solute-Interface chemical interaction and its temperature dependence are responsible for the interfacial segregation of Cr. These results suggest that the segregation energy needs to be taken into account in the search for more effective additive elements for improving the thermal stability of Lamellar structures as well as the creep resistance.
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Interface migration with segregation in mosi2 based Lamellar alloy simulated by phase field method
Advanced Materials Research, 2014Co-Authors: Toshihiro Yamazaki, Yuichiro Koizumi, Akihiko Chiba, Koji Hagihara, Takayoshi Nakano, Koretaka Yuge, Kyosuke Kishida, Haruyuki InuiAbstract:MoSi2–based alloys are attracting attention as ultra-high temperature structural material for super-high efficiency gas turbine power generation systems. In this study, the effects of Cr-and Zr-addition on Interface migration in MoSi2/NbSi2 Lamellar silicide were examined by phase field simulations employing the segregation energies evaluated by the first principles calculation in addition to thermodynamic free energy in order to take into account the chemically-driven interfacial segregation. The simulation results indicate that both Cr and Zr can segregate at the Lamellar Interface to suppress its migration, and the Zr-addition is more effective to lower the Interface migration rate than the Cr-addition owing to its higher segregation energy.
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Mechanisms of Cr segregation to C11b/C40 Lamellar Interface in (Mo,Nb)Si2 duplex silicide: A phase-field study to bridge experimental and first-principles investigations
Intermetallics, 2014Co-Authors: Toshihiro Yamazaki, Yuichiro Koizumi, Akihiko Chiba, Koji Hagihara, Takayoshi Nakano, Koretaka Yuge, Kyosuke Kishida, Haruyuki InuiAbstract:Abstract Cr segregation at Lamellar Interfaces in the MoSi 2 /NbSi 2 duplex silicide was examined using a newly developed phase-field model to elucidate the mechanism of interfacial segregation, which is believed to improve the thermal stability of Lamellar structures as well as creep resistance. This is because Lamellar structures can improve the high-temperature strength, and the stabilization of the Lamellar structures improves creep resistance. The model takes into account the segregation energy determined using first-principles calculations to reflect the chemical interaction between the solute atoms and the Interface, in addition to the elastic interaction. Cr segregation occurs at the Interface when the segregation energy is considered, whereas no segregation occurs in the case where only the elastic interaction is considered. However, the extent of segregation was much smaller than that observed experimentally when the segregation energy was evaluated using first-principles calculations without considering lattice vibrations (i.e., the calculations were performed for 0 K). A simulation that took into consideration the segregation energy with the lattice vibrations at 1673 K resulted in segregation similar to that observed experimentally, where the Cr-added MoSi 2 /NbSi 2 duplex silicide was equilibrated at 1673 K, namely, the temperature at which the segregation energy was calculated. Thus, it was revealed that the solute-Interface chemical interaction and its temperature dependence are responsible for the interfacial segregation of Cr. These results suggest that the segregation energy needs to be taken into account in the search for more effective additive elements for improving the thermal stability of Lamellar structures as well as the creep resistance.
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Phase-field study on the segregation mechanism of Cr to Lamellar Interface in C40-NbSi2/C11b-MoSi2 duplex silicide
arXiv: Materials Science, 2013Co-Authors: Toshihiro Yamazaki, Yuichiro Koizumi, Akihiko Chiba, Koji Hagihara, Takayoshi Nakano, Koretaka Yuge, Kyosuke Kishida, Haruyuki InuiAbstract:Cr-segregation to a Lamellar Interface in NbSi2/MoSi2 duplex silicide has been examined by a newly developed phase-field model. The model can take into account the segregation energy evaluated by a first principles calculation to reflect the chemical interaction between solute atoms and the Interface in addition to the elastic interaction. Cr segregation occurs at the Interface in the case with segregation energy whereas no segregation occurs in the case with only elastic interaction. However, the segregation is much smaller than that observed in the experiment when the segregation energy was evaluated by the first principles calculation without lattice vibration (i.e. for 0 K). Another simulations with the segregation energy with lattice vibration results in segregation comparable to that in the experiment. Thus, it has been revealed that the solute-Interface chemical interaction and its temperature dependence is responsible for the interfacial segregation of Cr.
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phase field study on the segregation mechanism of cr to Lamellar Interface in c40 nbsi2 c11b mosi2 duplex silicide
arXiv: Materials Science, 2013Co-Authors: Toshihiro Yamazaki, Yuichiro Koizumi, Akihiko Chiba, Koji Hagihara, Takayoshi Nakano, Koretaka Yuge, Kyosuke Kishida, Haruyuki InuiAbstract:Cr-segregation to a Lamellar Interface in NbSi2/MoSi2 duplex silicide has been examined by a newly developed phase-field model. The model can take into account the segregation energy evaluated by a first principles calculation to reflect the chemical interaction between solute atoms and the Interface in addition to the elastic interaction. Cr segregation occurs at the Interface in the case with segregation energy whereas no segregation occurs in the case with only elastic interaction. However, the segregation is much smaller than that observed in the experiment when the segregation energy was evaluated by the first principles calculation without lattice vibration (i.e. for 0 K). Another simulations with the segregation energy with lattice vibration results in segregation comparable to that in the experiment. Thus, it has been revealed that the solute-Interface chemical interaction and its temperature dependence is responsible for the interfacial segregation of Cr.
Steven E Wilson - One of the best experts on this subject based on the ideXlab platform.
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epithelial growth within the Lamellar Interface after laser in situ keratomileusis lasik
Cornea, 1997Co-Authors: Marco C Helena, David M Meisler, Steven E WilsonAbstract:Purpose To report the occurrence and follow-up of ec-topic, Interface, epithelial growth after laser in situ keratomileusis (LASIK) in four eyes (three patients) and provide suggestions for management. Methods Each eye was examined by slit-lamp biomicroscopy, and corneal topography was obtained with the Tomey TMS-1 instrument. Results Each eye with epithelium within the Interface after LASIK developed Interface opacities and surface irregularity. One eye had an early surgical intervention, and three eyes were observed. Each eye lost at least one line of best spectacle-corrected visual acuity and had visual disturbance at the last follow-up visit. Conclusions The presence of epithelium within the Lamellar Interface is a significant complication after LASIK. In some cases, Interface epithelium may be associated with early postoperative inflammation. When reoperation is required to treat this complication, we suggest scraping of both sides of the Interface with a metal blade. In some cases, light excimer laser treatment can be used to facilitate epithelial removal.
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Epithelial growth within the Lamellar Interface after laser in situ keratomileusis (LASIK)
Cornea, 1997Co-Authors: Marco C Helena, David M Meisler, Steven E WilsonAbstract:Purpose To report the occurrence and follow-up of ec-topic, Interface, epithelial growth after laser in situ keratomileusis (LASIK) in four eyes (three patients) and provide suggestions for management. Methods Each eye was examined by slit-lamp biomicroscopy, and corneal topography was obtained with the Tomey TMS-1 instrument. Results Each eye with epithelium within the Interface after LASIK developed Interface opacities and surface irregularity. One eye had an early surgical intervention, and three eyes were observed. Each eye lost at least one line of best spectacle-corrected visual acuity and had visual disturbance at the last follow-up visit. Conclusions The presence of epithelium within the Lamellar Interface is a significant complication after LASIK. In some cases, Interface epithelium may be associated with early postoperative inflammation. When reoperation is required to treat this complication, we suggest scraping of both sides of the Interface with a metal blade. In some cases, light excimer laser treatment can be used to facilitate epithelial removal.
Toshihiro Yamazaki - One of the best experts on this subject based on the ideXlab platform.
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mechanisms of cr segregation to c11b c40 Lamellar Interface in mo nb si2 duplex silicide a phase field study to bridge experimental and first principles investigations
Intermetallics, 2014Co-Authors: Toshihiro Yamazaki, Yuichiro Koizumi, Akihiko Chiba, Koji Hagihara, Takayoshi Nakano, Koretaka Yuge, Kyosuke Kishida, Haruyuki InuiAbstract:Abstract Cr segregation at Lamellar Interfaces in the MoSi 2 /NbSi 2 duplex silicide was examined using a newly developed phase-field model to elucidate the mechanism of interfacial segregation, which is believed to improve the thermal stability of Lamellar structures as well as creep resistance. This is because Lamellar structures can improve the high-temperature strength, and the stabilization of the Lamellar structures improves creep resistance. The model takes into account the segregation energy determined using first-principles calculations to reflect the chemical interaction between the solute atoms and the Interface, in addition to the elastic interaction. Cr segregation occurs at the Interface when the segregation energy is considered, whereas no segregation occurs in the case where only the elastic interaction is considered. However, the extent of segregation was much smaller than that observed experimentally when the segregation energy was evaluated using first-principles calculations without considering lattice vibrations (i.e., the calculations were performed for 0 K). A simulation that took into consideration the segregation energy with the lattice vibrations at 1673 K resulted in segregation similar to that observed experimentally, where the Cr-added MoSi 2 /NbSi 2 duplex silicide was equilibrated at 1673 K, namely, the temperature at which the segregation energy was calculated. Thus, it was revealed that the solute-Interface chemical interaction and its temperature dependence are responsible for the interfacial segregation of Cr. These results suggest that the segregation energy needs to be taken into account in the search for more effective additive elements for improving the thermal stability of Lamellar structures as well as the creep resistance.
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Interface migration with segregation in mosi2 based Lamellar alloy simulated by phase field method
Advanced Materials Research, 2014Co-Authors: Toshihiro Yamazaki, Yuichiro Koizumi, Akihiko Chiba, Koji Hagihara, Takayoshi Nakano, Koretaka Yuge, Kyosuke Kishida, Haruyuki InuiAbstract:MoSi2–based alloys are attracting attention as ultra-high temperature structural material for super-high efficiency gas turbine power generation systems. In this study, the effects of Cr-and Zr-addition on Interface migration in MoSi2/NbSi2 Lamellar silicide were examined by phase field simulations employing the segregation energies evaluated by the first principles calculation in addition to thermodynamic free energy in order to take into account the chemically-driven interfacial segregation. The simulation results indicate that both Cr and Zr can segregate at the Lamellar Interface to suppress its migration, and the Zr-addition is more effective to lower the Interface migration rate than the Cr-addition owing to its higher segregation energy.
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Mechanisms of Cr segregation to C11b/C40 Lamellar Interface in (Mo,Nb)Si2 duplex silicide: A phase-field study to bridge experimental and first-principles investigations
Intermetallics, 2014Co-Authors: Toshihiro Yamazaki, Yuichiro Koizumi, Akihiko Chiba, Koji Hagihara, Takayoshi Nakano, Koretaka Yuge, Kyosuke Kishida, Haruyuki InuiAbstract:Abstract Cr segregation at Lamellar Interfaces in the MoSi 2 /NbSi 2 duplex silicide was examined using a newly developed phase-field model to elucidate the mechanism of interfacial segregation, which is believed to improve the thermal stability of Lamellar structures as well as creep resistance. This is because Lamellar structures can improve the high-temperature strength, and the stabilization of the Lamellar structures improves creep resistance. The model takes into account the segregation energy determined using first-principles calculations to reflect the chemical interaction between the solute atoms and the Interface, in addition to the elastic interaction. Cr segregation occurs at the Interface when the segregation energy is considered, whereas no segregation occurs in the case where only the elastic interaction is considered. However, the extent of segregation was much smaller than that observed experimentally when the segregation energy was evaluated using first-principles calculations without considering lattice vibrations (i.e., the calculations were performed for 0 K). A simulation that took into consideration the segregation energy with the lattice vibrations at 1673 K resulted in segregation similar to that observed experimentally, where the Cr-added MoSi 2 /NbSi 2 duplex silicide was equilibrated at 1673 K, namely, the temperature at which the segregation energy was calculated. Thus, it was revealed that the solute-Interface chemical interaction and its temperature dependence are responsible for the interfacial segregation of Cr. These results suggest that the segregation energy needs to be taken into account in the search for more effective additive elements for improving the thermal stability of Lamellar structures as well as the creep resistance.
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Phase-field study on the segregation mechanism of Cr to Lamellar Interface in C40-NbSi2/C11b-MoSi2 duplex silicide
arXiv: Materials Science, 2013Co-Authors: Toshihiro Yamazaki, Yuichiro Koizumi, Akihiko Chiba, Koji Hagihara, Takayoshi Nakano, Koretaka Yuge, Kyosuke Kishida, Haruyuki InuiAbstract:Cr-segregation to a Lamellar Interface in NbSi2/MoSi2 duplex silicide has been examined by a newly developed phase-field model. The model can take into account the segregation energy evaluated by a first principles calculation to reflect the chemical interaction between solute atoms and the Interface in addition to the elastic interaction. Cr segregation occurs at the Interface in the case with segregation energy whereas no segregation occurs in the case with only elastic interaction. However, the segregation is much smaller than that observed in the experiment when the segregation energy was evaluated by the first principles calculation without lattice vibration (i.e. for 0 K). Another simulations with the segregation energy with lattice vibration results in segregation comparable to that in the experiment. Thus, it has been revealed that the solute-Interface chemical interaction and its temperature dependence is responsible for the interfacial segregation of Cr.
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phase field study on the segregation mechanism of cr to Lamellar Interface in c40 nbsi2 c11b mosi2 duplex silicide
arXiv: Materials Science, 2013Co-Authors: Toshihiro Yamazaki, Yuichiro Koizumi, Akihiko Chiba, Koji Hagihara, Takayoshi Nakano, Koretaka Yuge, Kyosuke Kishida, Haruyuki InuiAbstract:Cr-segregation to a Lamellar Interface in NbSi2/MoSi2 duplex silicide has been examined by a newly developed phase-field model. The model can take into account the segregation energy evaluated by a first principles calculation to reflect the chemical interaction between solute atoms and the Interface in addition to the elastic interaction. Cr segregation occurs at the Interface in the case with segregation energy whereas no segregation occurs in the case with only elastic interaction. However, the segregation is much smaller than that observed in the experiment when the segregation energy was evaluated by the first principles calculation without lattice vibration (i.e. for 0 K). Another simulations with the segregation energy with lattice vibration results in segregation comparable to that in the experiment. Thus, it has been revealed that the solute-Interface chemical interaction and its temperature dependence is responsible for the interfacial segregation of Cr.
