Showing papers by "Hirotsugu Ogi published in 2005"
TL;DR: In this paper, the authors studied the microstructure evolution of a nickel-based superalloy, Waspaloy, subjected to tensile creep at 1073 K through monitoring of shear-wave attenuation and velocity using electromagnetic acoustic resonance (EMAR).
27 citations
TL;DR: In this article, 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 was studied.
Abstract: 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 ...
26 citations
TL;DR: Using ultrasonic shear waves, this paper studied the kinetics of migration of vacancy to dislocations in aluminum, and attributed the 0.28-eV migration as fast diffusion of vacancy along dislocation.
20 citations
TL;DR: In this article, a piezoelectric tripod is used to measure the resonance frequencies of a layered specimen composed of a substrate and a deposited thin film to identify the vibration modes by measuring the displacement distributions on the specimen surface using laser-Doppler interferometry.
Abstract: Superlattice thin films are expected to show elastic anisotropy because of lattice misfits at interfaces among different elements. This study demonstrates that resonant-ultrasound spectroscopy and laser-Doppler interferometry can determine anisotropic elastic constants of superlattice thin films. Mechanical resonance frequencies of a layered specimen composed of a substrate and deposited thin film depend on the elastic constants, mass densities, and dimensions of the substrate and thin film. X-ray diffraction measurement determines accurately the total thiskness of a multilayer thin film. Therefore, the elastic constants of the multilayer thin film can be derived from measured resonance frequencies, provided that mode identification on observed resonance frequencies is achieved. We measure the resonance frequencies by a piezoelectric tripod and identify the vibration modes by measuring the displacement distributions on the specimen surface using laser-Doppler interferometry. We apply the present method to...
18 citations
TL;DR: In this article, an analysis of temperature dependence in the elastic moduli indicates that lattice anharmonicity in the longitudinal acoustic mode may play a dominant role in the martensitic phase transformations.
Abstract: Martensitic phase transformation from the β to the α'' phase (and vice versa) in a TiNbAl alloy system has been studied by ultrasound spectroscopy. Resonance frequencies and corresponding internal frictions are measured from ambient temperature to 12 K by electromagnetic acoustic resonance (EMAR) and resonant ultrasound spectroscopy (RUS) coupled with laser Doppler interferometry. Both in the cooling and heating processes, we observed a marked decrease in resonance frequency and an increase in internal friction approaching the transformation temperatures. The analysis of temperature dependence in the elastic moduli indicates that lattice anharmonicity in the longitudinal acoustic mode may play a dominant role in the martensitic phase transformations.
15 citations
TL;DR: In this article, a correlation between elastic constants and magnetic anisotropy of Co∕Pt superlattice thin films with various Co-Pt layer wavelengths were deposited on monocrystal silicon substrates by an ultrahigh-vacuum-evaporation method, keeping the volume fractions of the Co and Pt layers unchanged.
Abstract: This study is devoted to a correlation between elastic constants and magnetic anisotropy of Co∕Pt superlattice thin films. Co∕Pt superlattice thin films with various Co–Pt layer wavelengths were deposited on monocrystal silicon substrates by an ultrahigh-vacuum-evaporation method, keeping the volume fractions of the Co and Pt layers unchanged. Their perpendicular magnetic anisotropy ranged between −0.2 and 5.0MJ∕m3. Resonant-ultrasound spectroscopy coupled with laser-Doppler interferometry determined their hexagonal-symmetry elastic constants, which correlate with the magnetic anisotropy; higher perpendicular magnetic anisotropy causes larger in-plane elastic moduli and smaller out-of-plane moduli. The correlation is explained by internal elastic strain associated with lattice misfit at the Co–Pt interfaces.
12 citations
TL;DR: In this paper, the anisotropic elastic constants of Co/Pt thin films were determined using resonance ultrasound spectroscopy coupled with the laser/Doppler-interferometry method.
Abstract: The Co/Pt superlattice shows perpendicular magnetic anisotropy, which makes the magnetization direction of the Co layer perpendicular to the film surface when the Co layer is less than about 20 A thick. One possible cause of perpendicular magnetic anisotropy is large elastic strain at the interfaces between the Co and Pt layers. The elastic strain also changes the macroscopic elastic constants of the Co/Pt superlattice through lattice anharmonicity. In this study, we determined the anisotropic elastic constants of Co/Pt superlattice thin films using resonance ultrasound spectroscopy coupled with the laser/Doppler-interferometry method and studied the relationship between elastic and magnetic properties. We clearly observe a correlation between them, which is interpreted in terms of lattice anharmonicity.
11 citations
TL;DR: In this paper, the microstructural evolution of 2.25Cr-1Mo steels subjected to tensile creep at 923 K through monitoring of shear-wave attenuation and velocity, using electromagnetic acoustic resonance (EMAR).
Abstract: We studied the microstructural evolution of 2.25Cr-1Mo steels subjected to tensile creep at 923 K through monitoring of shear-wave attenuation and velocity, using electromagnetic acoustic resonance (EMAR). Contactless transduction based on the magnetostrictive mechanism is the key to establishing a monitor for microstructural change in the bulk of the metals with a high sensitivity. In the short interval, 50 to 60 pct of the creep life, attenuation experiences a peak, being independent of the applied stress. This novel phenomenon is interpreted in terms of the drastic change in dislocation mobility and rearrangement, which is supported by transmission electron microscopy (TEM) observations for dislocation structure. At this particular period, the dense dislocation structure starts to transform to subgrain boundaries, which temporally accompanies long, free dislocation, absorbing much ultrasonic energy to produce the attenuation peak. The EMAR has the potential to assess the damage advance and to predict the remaining creep life of metals.
11 citations
TL;DR: In this paper, the influence of the elastic anisotropy of the tip and the specimen on the determination of the local elastic modulus in RUM by introducing the Hertziancontact stiffness for orthorhombic materials.
Abstract: The classical Hertzian-contact theory for an isotropic material has been adopted to simplify quantitative evaluation of local elastic modulus by resonance-ultrasound microscopy (RUM). However, the validity of this simplified model must be confirmed because most materials show elastic anisotropy in small regions. This study investigates the influence of the elastic anisotropy of the tip and the specimen on the determination of the local elastic modulus in RUM by introducing the Hertzian-contact stiffness for orthorhombic materials. Numerical results reveal that specimen anisotropy significantly affects the contact stiffness and the quantitative evaluation of local elastic modulus even for specimens with weak anisotropy when we consider the anisotropy of the oscillator tip in RUM.
9 citations
TL;DR: In this article, a resonant-ultrasound-microscopy method was developed for measuring the local Young's modulus of a material by measuring the resonance frequency of a langasite (La3Ga5SiO14) oscillator touching the material.
Abstract: A resonant-ultrasound-microscopy method has been developed for measuring the local Young's modulus of a material. This method detects the effective Young's modulus through the resonance frequency of a langasite (La3Ga5SiO14) oscillator touching the specimen. Because the vibration of the oscillator is induced and detected with a solenoid coil in noncontacting, wireless, and electrodeless way, it is affected only by its contact with the specimen, achieving an absolute measurement. Elastic-constant mapping was performed on cross sections of a duplex stainless steel and a NbTi/Cu superconducting wire. Analysis with the static contact stiffness predicts the frequency change smaller than that measured, and the necessity of considering the dynamic contact stiffness is discussed.
8 citations
TL;DR: In this article, an advanced resonant ultrasound spectroscopy (RUS) method was proposed to determine the elastic constants C ij of thin films using a piezoelectric tripod.
Abstract: This paper presents an advanced resonant ultrasound spectroscopy (RUS) method to determine the elastic constants C ij of thin films. Polycrystalline thin films often exhibit elastic anisotropy between the film growth direction and the in-plane direction, and they macroscopically show five independent elastic constants. Because all of the C ij of a deposited thin film affect the mechanical resonance frequencies of the film/substrate layer specimen, measuring resonance frequencies enables one to determine the C ij of the film with known density, dimensions and the C;j of the substrate. Resonance frequencies have to be measured accurately because of low sensitivity of the C ij of films to them. We achieved this by a piezoelectric tripod. Mode identification has to be made unambiguously. We made this measuring displacement-amplitude distributions on the resonated specimen surface by laser Doppler interferometry. We applied our technique to copper thin film and diamond thin film. They show elastic anisotropy and the C ij smaller than bulk values of C ij . Micromechanics calculations indicate the presence of incohesive bonded regions.
TL;DR: In this article, two advanced acoustic methods for the determination of anisotropic elastic constants of deposited thin films are presented, which are resonant-ultrasound spectroscopy with laser-Doppler interferometry (RUS/Laser method) and picosecond-laser ultrasound method.
Abstract: This paper presents two advanced acoustic methods for the determination of anisotropic elastic constants of deposited thin films. They are resonant-ultrasound spectroscopy with laser-Doppler interferometry (RUS/Laser method) and picosecond-laser ultrasound method. Deposited thin films usually exhibit elastic anisotropy between the film-growth direction and an in-plane direction, and they show five independent elastic constants denoted by C11,C33,C44,C66 and C13 when the x3 axis is set along the film-thickness direction. The former method determines four moduli except C44, the out-of-plane shear modulus, through free-vibration resonance frequencies of the film/substrate specimen. This method is applicable to thin films thicker than about 200 nm. The latter determines C33, the out-of-plane modulus, accurately bymeasuring the round-trip time of the longitudinal wave traveling along the film-thickness direction. This method is applicable to thin films thicker than about 20 nm. Thus, combination of these two methods allows us to discuss the elastic anisotropy of thin films. The results for Co/Pt superlattice thin film and copper thin film are presented.
TL;DR: In this article, the complete set of elastic moduli Cij of an Fe-Si-B amorphous-alloy thin film using thickness resonance with electromagnetic acoustic resonance (EMAR) and newly developed resonance ultrasound spectroscopy (RUS)/laser methods was measured.
Abstract: We have measured the complete set of elastic moduli Cij of an Fe-Si-B amorphous-alloy thin film using thickness resonance with electromagnetic acoustic resonance (EMAR) and newly developed resonance ultrasound spectroscopy (RUS)/laser methods. From the thickness-resonance measurements, out-of-plane shear moduli (C44 and C55) were found to be 73.2 and 71.0 (GPa). This indicates that the amorphous-alloy thin film shows transverse-isotropy elastic symmetry. RUS/laser measurements gave the remaining moduli : C11=193.6, C33=234.3, C23=72.1, C12=79.8 and C44=72.1 (GPa). From the ratios of the elastic modulus, (C33/C11=1.21 and C44/C66=1.26), the amorphous Fe-Si-B thin film shows elastic anisotropy between in-plane and the out-of-plane directions in the range of 20-30%. These results also indicate that this ultrasonic technique is also applicable for measuring all Cij of other thin films.
09 Apr 2005
TL;DR: In this paper, all independent elastic moduli of an Fe•Si•B amorphous alloy thin film using electromagnetic acoustic resonance (EMAR) and resonant ultrasound spectroscopy coupled with laser-doppler interferometry (RUS/Laser) have been determined using a thickness resonance EMAR technique.
Abstract: All independent elastic moduli of an Fe‐Si‐B amorphous alloy thin film using electromagnetic acoustic resonance (EMAR) and resonant ultrasound spectroscopy coupled with laser‐doppler interferometry (RUS/Laser) have been determined Using a thickness resonance EMAR technique, in‐plane shear moduli of c44 and c55 are determined to be 732 and 710 GPa indicating that the amorphous alloy thin film has a hexagonal‐type elastic symmetry The remaining moduli are obtained by RUS/Laser technique as follows: c11 = 1936, c33 = 2343, c23 = 721 and c12 = 798 GPa Using the complete set of elastic moduli, the acoustic Debye temperature, ΘD, is estimated to be 451 K which is close to that of pure α‐Fe (ΘD = 471 K) Compressional and shear anisotropies become c33/c11 = 121 and c66/c44 = 126 indicating remarkable elastic anisotropies between in‐plane and out‐of‐plane directions even though in the amorphous structure
TL;DR: In this article, the contribution of the magnetoelastic anisotropy effect on the magnetic anisotropic energy of Co/Pt superlattice thin films was investigated.
Abstract: In this paper, we study contribution of the magnetoelastic anisotropy effect on perpendicular magnetic anisotropy of Co/Pt superlattice thin films. The effective-magnetic anisotropy energy was measured for Co/Pt thin films with a constant Co-layer thickness (4 A) deposited on silicon substrate by the ultrahigh-vacuum deposition method. As the Pt-layer thickness increases, the effective-magnetic anisotropy energy increases and decreases after showing a maximum at the Pt-layer thickness of 12 A. This behavior can be explained only by the magnetoelastic anisotropy effect, that is, elastic-strain energy released through the magnetostriction effect with the strain-dependent elastic constants.
TL;DR: In this paper, the contribution of magnetoelastic-anisotropy effect on perpendicular-magnetic anisotropic of Co/Pt superlattice thin films is studied considering the strain-dependent elastic constants.
Abstract: In this paper, the contribution of magnetoelastic-anisotropy effect on perpendicular-magnetic anisotropy of Co/Pt superlattice thin films is studied considering the strain-dependent elastic constants. We measured the effective-magnetic-anisotropy energy changing the Pt-layer thickness (2 to 20 A) keeping the Co-layer thickness unchanged (4 A). The effective-magnetic-anisotropy energy changed depending on the Pt-layer thickness and showed a maximum near dPt=12 A. This result is explained by calculating the magnetoelastic-anisotropy energy considering the change of the elastic constants caused by the lattice misfit. We measured anisotropic elastic constants of Co/Pt superlattice thin films by resonance-ultrasound-spectroscopy method coupled with laser-Doppler interferometry and the picosecond laser-ultrasound method. The measured elastic constants showed elastic anisotropy between the in-plane and out-of-plane directions. They agreed with those predicted from the strain-dependent elastic-constant model. The elastic constants show correlations with the perpendicular-magnetic anisotropy.
TL;DR: Using resonant-ultrasound spectroscopy coupled with laser-Doppler interferometry, this paper determined the independent elastic constants of nanocrystalline CVD-diamond thin films with thickness between 2-12 μm.
Abstract: Using resonant-ultrasound spectroscopy coupled with laser-Doppler interferometry, we determine the independent elastic constants of nanocrystalline CVD-diamond thin films with thickness between 2-12 μm. They are deposited on oriented monocrystal silicon substrates by the hot-filament methane/nitrogen CVD method. The diagonal components of the elastic constants are smaller than those of microcrystalline CVD diamond films and bulk diamond. However, the off-diagonal component is larger. We attribute these observations to the presence of sp
2-bonded graphitic phase at grain boundaries. A micromechanics model assuming inclusions of thin graphitic plates consistently explains the observations.