The Experts below are selected from a list of 303 Experts worldwide ranked by ideXlab platform
Kazuhiro Otsuka - One of the best experts on this subject based on the ideXlab platform.
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experimental study of Elastic Constant softening prior to stress induced martensitic transformation
Physical Review B, 2008Co-Authors: Xiangdong Ding, Kazuhiro Otsuka, T Suzuki, Jun Sun, Jian Zhang, Yu Wang, Yumei Zhou, Xiaobing RenAbstract:There has been a large body of experimental evidence for the existence of precursor lattice softening prior to temperature-induced martensitic transformation, but little is known about whether such softening effect also exists prior to stress-induced martensitic transformation. Recent molecular dynamics simulations suggested such a possibility, but direct experimental evidence remains unclear. In the present study, we established a simple experimental method that can measure Elastic Constant C from zero stress up to the critical stress prior to stress-induced martensitic transformation. By applying this method to a Cu-Al-Ni single crystal, we found C of 1011 ¯ 01 shear mode does soften with increasing applied stress along the 001 direction, until a stress-induced martensitic transformation occurs at a critical stress. This is direct evidence for the existence of lattice softening prior to a stress-induced martensitic transformation. Our result completes an important conclusion that the softening of Elastic Constant C is a common feature prior to both temperature- and stressinduced martensitic transformations. Furthermore, we also analyzed the dependence of C on uniaxial tensile stress through a theoretical model and obtained similar result as that of our experiment.
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study on Elastic Constant softening in stress induced martensitic transformation by molecular dynamics simulation
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2006Co-Authors: Xiangdong Ding, Kazuhiro Otsuka, T Suzuki, Jun Sun, Xiangyi RenAbstract:Abstract Precursor phenomena are critical issues for martensitic transformation, as they provide important clues for understanding the origin of the transformation and the structure of transformation products. Prior to temperature-induced martensitic transformation, it has been widely recognized for a long time that the basal plane shear modulus C′ (=(C11 − C12)/2) of the parent phase decreases with approaching transformation temperature. On the other hand, martensitic transformation can also be induced by stress. But little is known about whether similar precursor phenomenon also exists prior to such a stress-induced martensitic transformation (SIM). In the present study, we used molecular dynamics method to simulate the precursory stage of a stress-induced martensitic transformation. A new method for calculating the Elastic Constants C′ prior to SIM was proposed. The relationship between C′ and applied stress at different temperatures was calculated. Our results showed that the softening of Elastic Constant C′ is a common feature for both temperature and stress-induced martensitic transformation. For stress-induced martensitic transformation, the critical stress to induce the transformation increases with increasing temperature and obey Clausius–Clapyeyron relationship; at a given temperature, C′ decreases with the applied stress approaching the critical stress.
Masahiko Hirao - One of the best experts on this subject based on the ideXlab platform.
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resonant ultrasound spectroscopy for studying annealing effect on Elastic Constant of thin film
Ultrasonics, 2010Co-Authors: Nobutomo Nakamura, Hirotsugu Ogi, Takeo Nakashima, S Oura, Masahiko HiraoAbstract:In this paper, we study the Elastic property of thin films using resonant-ultrasound spectroscopy (RUS). RUS determines the Elastic Constants of a solid from its resonance frequencies of free vibration. There were two problems to be solved for applying RUS to thin films: accurate measurement of the resonance frequencies and mode identification of each resonance frequency. We solve these problems using the tripod needle transducers and the laser-Doppler interferometry (LDI). In this paper, we describe the RUS/LDI measurement setup we developed, and show the relationship between the Elastic Constant and annealing temperature for Cu thin films. Then, we discuss the effects of recrystallization and recovery on the Elastic Constant referring the X-ray diffraction measurement.
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recovery of Elastic Constant of ultrathin cu films by low temperature annealing
Applied Physics Letters, 2008Co-Authors: Nobutomo Nakamura, Hirotsugu Ogi, Tomohiro Shagawa, Masahiko HiraoAbstract:Annealing effect on the Elastic Constant of Cu thin films was investigated by acoustic-phonon resonance spectroscopy. Annealing treatment was performed after the deposition in vacuum condition for 30min at various temperatures up to 200°C. It did not cause obvious changes in the x-ray diffraction spectra, but it significantly increased the Elastic Constant. The Elastic Constant of the as-deposited Cu film was smaller than that of bulk Cu by 20%, and it recovered to the bulk value by the postannealing at 200°C.
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stiffened ultrathin pt films confirmed by acoustic phonon resonances
Physical Review Letters, 2007Co-Authors: Hirotsugu Ogi, Nobutomo Nakamura, Takeshi Yasui, Makoto Fujii, Masahiko HiraoAbstract:Resonances of coherent acoustic phonons were excited and detected by femtosecond light pulses for determining the normal Elastic Constant of ultrathin platinum films. The Elastic Constant increases with the decrease of the film thickness, exceeds the bulk value at the thickness near 5 nm, and significantly increases at low temperatures. It shows a correlation with the normal lattice distance. Thus, this Letter provides evidence of the stiffness enhancement in ultrathin films caused by lattice anharmonicity.
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correlation between Elastic Constant and perpendicular magnetic anisotropy in cobalt platinum superlattice thin films studied by picosecond ultrasounds
Journal of the Acoustical Society of America, 2006Co-Authors: Nobutomo Nakamura, Hirotsugu Ogi, Takeshi Yasui, Masahiko HiraoAbstract:The easy magnetization direction of a Co monolayer thin film is always parallel to the film surface, but it can be perpendicular to the film surface for Co/Pt multilayer thin films when the Co layer consists of a few atomic layers. This property is called perpendicular magnetic anisotropy (PMA), achieving ultrahigh‐density magnetic recording media. PMA occurs because of the large lattice misfit (near 10%) at the Co‐Pt interfaces, and large Elastic strains must affect the Elastic Constants through lattice anharmonicity. Thus, Elastic Constants and magnetic properties of Co/Pt superlattice thin film should show a correlation, which was investigated by picosecond ultrasound. The pulse‐echo signals of the longitudinal wave traveling in the thickness direction were detected by the laser pump‐probe technique, which gave the Elastic Constant C33. The film thickness was determined by the X‐ray reflectivity measurement. Co/Pt superlattice thin films were prepared by the magnetron‐sputtering method, changing the Pt‐layer thickness between 0.2–2 nm and keeping the Co‐layer thickness to be 0.4 nm. Total film thickness was near 80 nm. C33 showed good correlation with the degree of PMA and it differed from the modulus predicted from the Elastic Constants of bulk materials.
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off diagonal Elastic Constant and sp2 bonded graphitic grain boundary in nanocrystalline diamond thin films
Applied Physics Letters, 2005Co-Authors: Hirotsugu Ogi, Nobutomo Nakamura, Masahiko Hirao, Hiroshi Tanei, Ryuji Ikeda, Mikio TakemotoAbstract:This letter studies the relationship between the off-diagonal Elastic Constant C12 and bond configuration in nanocrystalline-diamond (NCD) thin films deposited by the nitrogen-doped chemical vapor deposition method. The film thickness was varied between 2.4 and 11.3μm. The Elastic Constants were measured by resonant-ultrasound spectroscopy coupled with laser-Doppler interferometry. The diagonal Elastic Constants C11 and C44, and Young’s modulus in NCD films are smaller than those of the bulk polycrystalline diamond and microcrystalline-diamond (MCD) thin films, and they decrease as the film thickness decreases. However, the off-diagonal Elastic Constant of the NCD films is significantly larger than that of the bulk diamond, while that of the MCD films is smaller. Micromechanics calculations revealed that this exceptional enhancement of C12 occurs when the material includes randomly distributed thin graphitic plates in the isotropic diamond matrix. Thus, this result indicates that the NCD films consist of ...
T Suzuki - One of the best experts on this subject based on the ideXlab platform.
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experimental study of Elastic Constant softening prior to stress induced martensitic transformation
Physical Review B, 2008Co-Authors: Xiangdong Ding, Kazuhiro Otsuka, T Suzuki, Jun Sun, Jian Zhang, Yu Wang, Yumei Zhou, Xiaobing RenAbstract:There has been a large body of experimental evidence for the existence of precursor lattice softening prior to temperature-induced martensitic transformation, but little is known about whether such softening effect also exists prior to stress-induced martensitic transformation. Recent molecular dynamics simulations suggested such a possibility, but direct experimental evidence remains unclear. In the present study, we established a simple experimental method that can measure Elastic Constant C from zero stress up to the critical stress prior to stress-induced martensitic transformation. By applying this method to a Cu-Al-Ni single crystal, we found C of 1011 ¯ 01 shear mode does soften with increasing applied stress along the 001 direction, until a stress-induced martensitic transformation occurs at a critical stress. This is direct evidence for the existence of lattice softening prior to a stress-induced martensitic transformation. Our result completes an important conclusion that the softening of Elastic Constant C is a common feature prior to both temperature- and stressinduced martensitic transformations. Furthermore, we also analyzed the dependence of C on uniaxial tensile stress through a theoretical model and obtained similar result as that of our experiment.
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study on Elastic Constant softening in stress induced martensitic transformation by molecular dynamics simulation
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2006Co-Authors: Xiangdong Ding, Kazuhiro Otsuka, T Suzuki, Jun Sun, Xiangyi RenAbstract:Abstract Precursor phenomena are critical issues for martensitic transformation, as they provide important clues for understanding the origin of the transformation and the structure of transformation products. Prior to temperature-induced martensitic transformation, it has been widely recognized for a long time that the basal plane shear modulus C′ (=(C11 − C12)/2) of the parent phase decreases with approaching transformation temperature. On the other hand, martensitic transformation can also be induced by stress. But little is known about whether similar precursor phenomenon also exists prior to such a stress-induced martensitic transformation (SIM). In the present study, we used molecular dynamics method to simulate the precursory stage of a stress-induced martensitic transformation. A new method for calculating the Elastic Constants C′ prior to SIM was proposed. The relationship between C′ and applied stress at different temperatures was calculated. Our results showed that the softening of Elastic Constant C′ is a common feature for both temperature and stress-induced martensitic transformation. For stress-induced martensitic transformation, the critical stress to induce the transformation increases with increasing temperature and obey Clausius–Clapyeyron relationship; at a given temperature, C′ decreases with the applied stress approaching the critical stress.
Xiangdong Ding - One of the best experts on this subject based on the ideXlab platform.
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experimental study of Elastic Constant softening prior to stress induced martensitic transformation
Physical Review B, 2008Co-Authors: Xiangdong Ding, Kazuhiro Otsuka, T Suzuki, Jun Sun, Jian Zhang, Yu Wang, Yumei Zhou, Xiaobing RenAbstract:There has been a large body of experimental evidence for the existence of precursor lattice softening prior to temperature-induced martensitic transformation, but little is known about whether such softening effect also exists prior to stress-induced martensitic transformation. Recent molecular dynamics simulations suggested such a possibility, but direct experimental evidence remains unclear. In the present study, we established a simple experimental method that can measure Elastic Constant C from zero stress up to the critical stress prior to stress-induced martensitic transformation. By applying this method to a Cu-Al-Ni single crystal, we found C of 1011 ¯ 01 shear mode does soften with increasing applied stress along the 001 direction, until a stress-induced martensitic transformation occurs at a critical stress. This is direct evidence for the existence of lattice softening prior to a stress-induced martensitic transformation. Our result completes an important conclusion that the softening of Elastic Constant C is a common feature prior to both temperature- and stressinduced martensitic transformations. Furthermore, we also analyzed the dependence of C on uniaxial tensile stress through a theoretical model and obtained similar result as that of our experiment.
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study on Elastic Constant softening in stress induced martensitic transformation by molecular dynamics simulation
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2006Co-Authors: Xiangdong Ding, Kazuhiro Otsuka, T Suzuki, Jun Sun, Xiangyi RenAbstract:Abstract Precursor phenomena are critical issues for martensitic transformation, as they provide important clues for understanding the origin of the transformation and the structure of transformation products. Prior to temperature-induced martensitic transformation, it has been widely recognized for a long time that the basal plane shear modulus C′ (=(C11 − C12)/2) of the parent phase decreases with approaching transformation temperature. On the other hand, martensitic transformation can also be induced by stress. But little is known about whether similar precursor phenomenon also exists prior to such a stress-induced martensitic transformation (SIM). In the present study, we used molecular dynamics method to simulate the precursory stage of a stress-induced martensitic transformation. A new method for calculating the Elastic Constants C′ prior to SIM was proposed. The relationship between C′ and applied stress at different temperatures was calculated. Our results showed that the softening of Elastic Constant C′ is a common feature for both temperature and stress-induced martensitic transformation. For stress-induced martensitic transformation, the critical stress to induce the transformation increases with increasing temperature and obey Clausius–Clapyeyron relationship; at a given temperature, C′ decreases with the applied stress approaching the critical stress.
Nobutomo Nakamura - One of the best experts on this subject based on the ideXlab platform.
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resonant ultrasound spectroscopy for studying annealing effect on Elastic Constant of thin film
Ultrasonics, 2010Co-Authors: Nobutomo Nakamura, Hirotsugu Ogi, Takeo Nakashima, S Oura, Masahiko HiraoAbstract:In this paper, we study the Elastic property of thin films using resonant-ultrasound spectroscopy (RUS). RUS determines the Elastic Constants of a solid from its resonance frequencies of free vibration. There were two problems to be solved for applying RUS to thin films: accurate measurement of the resonance frequencies and mode identification of each resonance frequency. We solve these problems using the tripod needle transducers and the laser-Doppler interferometry (LDI). In this paper, we describe the RUS/LDI measurement setup we developed, and show the relationship between the Elastic Constant and annealing temperature for Cu thin films. Then, we discuss the effects of recrystallization and recovery on the Elastic Constant referring the X-ray diffraction measurement.
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recovery of Elastic Constant of ultrathin cu films by low temperature annealing
Applied Physics Letters, 2008Co-Authors: Nobutomo Nakamura, Hirotsugu Ogi, Tomohiro Shagawa, Masahiko HiraoAbstract:Annealing effect on the Elastic Constant of Cu thin films was investigated by acoustic-phonon resonance spectroscopy. Annealing treatment was performed after the deposition in vacuum condition for 30min at various temperatures up to 200°C. It did not cause obvious changes in the x-ray diffraction spectra, but it significantly increased the Elastic Constant. The Elastic Constant of the as-deposited Cu film was smaller than that of bulk Cu by 20%, and it recovered to the bulk value by the postannealing at 200°C.
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stiffened ultrathin pt films confirmed by acoustic phonon resonances
Physical Review Letters, 2007Co-Authors: Hirotsugu Ogi, Nobutomo Nakamura, Takeshi Yasui, Makoto Fujii, Masahiko HiraoAbstract:Resonances of coherent acoustic phonons were excited and detected by femtosecond light pulses for determining the normal Elastic Constant of ultrathin platinum films. The Elastic Constant increases with the decrease of the film thickness, exceeds the bulk value at the thickness near 5 nm, and significantly increases at low temperatures. It shows a correlation with the normal lattice distance. Thus, this Letter provides evidence of the stiffness enhancement in ultrathin films caused by lattice anharmonicity.
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correlation between Elastic Constant and perpendicular magnetic anisotropy in cobalt platinum superlattice thin films studied by picosecond ultrasounds
Journal of the Acoustical Society of America, 2006Co-Authors: Nobutomo Nakamura, Hirotsugu Ogi, Takeshi Yasui, Masahiko HiraoAbstract:The easy magnetization direction of a Co monolayer thin film is always parallel to the film surface, but it can be perpendicular to the film surface for Co/Pt multilayer thin films when the Co layer consists of a few atomic layers. This property is called perpendicular magnetic anisotropy (PMA), achieving ultrahigh‐density magnetic recording media. PMA occurs because of the large lattice misfit (near 10%) at the Co‐Pt interfaces, and large Elastic strains must affect the Elastic Constants through lattice anharmonicity. Thus, Elastic Constants and magnetic properties of Co/Pt superlattice thin film should show a correlation, which was investigated by picosecond ultrasound. The pulse‐echo signals of the longitudinal wave traveling in the thickness direction were detected by the laser pump‐probe technique, which gave the Elastic Constant C33. The film thickness was determined by the X‐ray reflectivity measurement. Co/Pt superlattice thin films were prepared by the magnetron‐sputtering method, changing the Pt‐layer thickness between 0.2–2 nm and keeping the Co‐layer thickness to be 0.4 nm. Total film thickness was near 80 nm. C33 showed good correlation with the degree of PMA and it differed from the modulus predicted from the Elastic Constants of bulk materials.
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off diagonal Elastic Constant and sp2 bonded graphitic grain boundary in nanocrystalline diamond thin films
Applied Physics Letters, 2005Co-Authors: Hirotsugu Ogi, Nobutomo Nakamura, Masahiko Hirao, Hiroshi Tanei, Ryuji Ikeda, Mikio TakemotoAbstract:This letter studies the relationship between the off-diagonal Elastic Constant C12 and bond configuration in nanocrystalline-diamond (NCD) thin films deposited by the nitrogen-doped chemical vapor deposition method. The film thickness was varied between 2.4 and 11.3μm. The Elastic Constants were measured by resonant-ultrasound spectroscopy coupled with laser-Doppler interferometry. The diagonal Elastic Constants C11 and C44, and Young’s modulus in NCD films are smaller than those of the bulk polycrystalline diamond and microcrystalline-diamond (MCD) thin films, and they decrease as the film thickness decreases. However, the off-diagonal Elastic Constant of the NCD films is significantly larger than that of the bulk diamond, while that of the MCD films is smaller. Micromechanics calculations revealed that this exceptional enhancement of C12 occurs when the material includes randomly distributed thin graphitic plates in the isotropic diamond matrix. Thus, this result indicates that the NCD films consist of ...