岡井 大祐

Type-B serrations were observed during room-temperature tensile deformation of Al-2.17 mass%Mg alloy with an average grain size of 12 µm. Digital image correlation was used to visualize Portevin-Le Chatelier (PLC) bands, and microstructural changes in these bands were observed by in-situ X-ray diffraction measurements using synchrotron radiation at SPring-8. The results indicated that the overall density of dislocations, including both mobile and pinned dislocations inside the PLC bands, increased substantially as the bands formed. This suggests that serration occurs due to an increase in the mobile dislocation density resulting from the formation of new dislocations from sources inside the PLC bands.

Abstract Adhesive layers were prepared using photoreactive polymer liquid crystals, and their application as dismantled adhesives based on the change in thermal properties associated with photoisomerization was investigated. Anisotropy in adhesive strength was successfully achieved by controlling the alignment of the liquid crystal using a polyimide alignment film. Furthermore, anisotropy in the adhesive strength due to photoalignment was investigated using the axis-selective photoreactivity of polymer liquid crystals to linearly polarized light.

Al-Zn-Mg alloys with different precipitate sizes were investigated to determine the influence of the precipitate size on the flow stress and dislocation density change during tensile deformation. The dislocation density was measured using in-situ X-ray diffraction at the SPring-8 synchrotron radiation facility with a time resolution of about 2 s. In region II with rapid dislocation multiplication, from under-aging to peak aging, the dislocation density increased with increasing aging time. Under over-aging conditions, the amount of dislocation multiplication in region II decreased with increasing aging time. Even in region III, the increase in dislocation density with plastic deformation was the largest for the peak aging conditions. However, the amount of work hardening was small and the contribution of dislocation hardening to the strength of the material was minimal. For over-aging conditions, the increase in dislocation density in region III was smaller than for the other regions, but the amount of work hardening was relatively large. It is considered that the influence of the dislocation density on work hardening is determined by the effectiveness of precipitates as obstacles to dislocation motion.

The liquid crystalline N-benzylideneaniline (NBA) polymer acts as an adhesive, and its bonded pieces detach upon exposure to UV light due to the trans-cis photoisomerization of the NBA moieties and subsequent phase transition of NBA from a liquid crystal polymer to an isotropic polymer. We improved the photoresponsive durability of the polymer and explored the effect of light irradiation on its thermal properties and adhesion stress. We observed that the transition points of the polymer's thermophysical properties (glass transition, liquid crystal-isotropic transition, G" slope, tan δ) shifted to lower temperatures under light irradiation.

The work hardening of aluminum alloys depends on the dislocation substructure in addition to the dislocation density. In this study, in-situ XRD measurements during tensile deformation were conducted on cold-rolled 1200 aluminum and change in the dislocation substructure was evaluated by analysis using Convolutional Multiple Whole Profile method. As a result, the dislocation cell structure was formed before tensile test and when the stress exceeded 32 MPa, the dislocation cell structure decomposed and the dislocation dispersion approached uniformly. It is considered that 32 MPa is a micro-yield stress at which the initial dislocations start to move. As the plastic deformation progressed, dislocation arrangements parameter decreased and finally became 0.5, it is considered that the dislocation cell structure was formed again.

A pure iron tape with cube orientation was fabricated by cold rolling and annealing. The orientation characteristics of the pure iron tape were evaluated using electron back-scattering diffraction (EBSD) analysis. The secondary recrystallized grains with cube orientation was formed on the tape surface for the pure iron tape. The coarse grains with a grain size of ca. 1mm were observed on the tape surface. The areal fraction of cube orientations with an angular deviation ≤ 20 ̊ amounts to ca. 81%.

© 2020 The Japan Institute of Light Metals. By conducting in-situ XRD measurement during tensile deformation while oscillating the tensile tester, it was possible to measure the change in dislocation density of a pure aluminum alloy having coarse grains with the grain size of 20 µm. In the coarse-grained material, the dislocation density during tensile deformation changed through four regions, as in the case of the fine-grained material. Since the dislocation multiplication start stress was very low at 22 MPa, the elastic deformation region was very short. Thereafter, the dislocations multiplied rapidly, but when the stress and dislocation density reached 33 MPa and 1.57 © 1014 m12, respectively, the dislocation multiplication rate was greatly reduced. This is considered to be due to the low dislocation density required to progress the deformation by plastic deformation in coarse-grained aluminum.

The orientation characteristics of a pure iron tape fabricated by cold rolling and annealing were evaluated using electron backscatter diffraction (EBSD) analysis. The {1 7 1}<4 <(3)over bar> 17> orientation, which is a near-cube orientation, was strongly formed on the tape surface. For the oriented iron tape, the out-of-plane misorientation of (0 0 1) from the cube orientation is ca. 11 degrees. The areal fraction of cube orientations with an angular deviation <= 20 degrees amounts to 94.7%. The average grain size is approximately 370 mu m for the near-cube oriented iron tape.

Previously we have reported that dislocation cells which are formed by cold rolling grew into recrystallized grains with other dislocation cells formed via the recovery of microstructures. There are not any differences between these cells after deformation and similar microstructural changes would occur in both cell types at an early stage of annealing. Intermittent observations via SEM-EBSD were performed during annealing on the same areas in the specimens of 1050 aluminum cold rolled at 28, 45 and 73% and then annealed at 673 K. Dislocation cells were formed in all the specimens except in an area of the specimen cold rolled at 28% in which dislocation tangles were formed. These tangles did not migrate or anneal out. Changes in the microstructure did not occur in area of annealing, and recrystallized grains which were formed through the SIBM mechanism invaded the area. In the specimen cold rolled at 45%, dislocation cells with orientations that deviated from the circumference were observed, which shrank and disappeared at the early stage of annealing, resulting in formation of regions composed of sub-grains having a similar orientation. These sub-grains were surrounded with low angle boundaries and exhibited suppressed growth. In the case of the specimen cold rolled at 73%, the orientation of the original grains split into two due to cold rolling, and dislocation cells that had each orientation were formed via dispersion with each other. Dislocation cells grew into sub-grains, and sub-grain boundaries migrated with areas of low dislocation density forming. At this stage, the sub-grain was composed of areas with low and high dislocation densities. The latter was invaded by other sub-grains via subgrain boundary migration, and the remaining area that had a low dislocation density being surrounded by high angle boundaries formed a recrystallized grain. This effect was due to the neighboring sub-grains having other orientations. Growth of dislocation cells into recrystallized grains depends on misorientation between the neighboring grains.

Changes in microstructures due to cold-rolling and annealing were observed with SEM-EBSD system. The material used was a commercial 1050 aluminum with 10 mm thickness. After solution heat treatment, specimens were cold-rolled at 83 % followed by intermediate annealing at 773 K for 10 s. Specimens for secondary cold-rolling were cut from the primary cold-rolled sheet, and then cold-rolled again at 83 % followed by final annealing at 773 K. Surface texture was formed after both the primary and secondary cold-rolling. Microstructures after the intermediate annealing and after the final annealing resembled one another, which composed of the surface texture components. Orientation splitting into the texture components was caused in each grain by cold-rolling. The recrystallized grains were formed as a result of growth of dislocation cells having orientations of the texture components, which lead to form the recrystallized microstructure with the surface texture. (C) 2014 Published by Elsevier Ltd.

The fracture behavior and adhesion strength of CrN/Cr and CrN films on SKD61 substrates were investigated by a three-point bending test. The SKD61 substrates were coated with a film with multilayer of CrN/Cr and a single film of CrN by a physical vapor deposition (PVD). The fracture behaviors of CrN/Cr and CrN films at three-point bending test were observed by scanning electron microscopy (SEM). Adhesions of the CrN/Cr/SKD61 and the CrN/SKD61 were also evaluated using a scratch tester. The scratch test resulted in no great difference in the adhesion strength between the CrN/Cr/SKD61 and the CrN/SKD61. On the other hand, the three-point bending test showed a high adhesion of the CrN/Cr with the intermediate layer of Cr film compared to the CrN on the SKD61. © (2014) Trans Tech Publications, Switzerland.

The microstructures of pure iron prepared by cold-rolling and annealing were observed with SEM-EBSD. The pure iron with 99.99% purity was used. The iron specimens were cold-rolled at reduction rates of 75~95%. The vacuum-annealing of the rolled specimens was performed above transformation temperature of 1185 K for the pure iron. The {100}-grains with millimeter-size appeared in the transformation textures after the annealing of the rolled iron sheets. The rolling at a high reduction rate led to the formation of strong {100} texture for the iron sheet after the rolling and annealing above the transformation temperature. The heavy deformation by the rolling resulted in a fine-microstructure for the iron sheet annealed above the transformation temperature after the rolling.

Crystal rotation due to cold rolling was investigated on commercial 1050 aluminum. A 3-mm-thick specimen was annealed at 803 K for 3.6 ks. The surface of the specimen was electro-polished and then observed using a scanning electron microscope (SEM)-electron backscatter diffraction (EBSD) system. Cold rolling to about 30% reduction in the same direction, electro-polishing and same-area SEM-EBSD observation were repeated until the accumulated reduction rate was 84%. In the present study, changes in grain orientation after the first pass in the cold-rolling process were analyzed in detail. Two types of grain orientation were observed before cold rolling. About 50% of the grains showed near-cube orientation, {001}< 100 >, and the rest showed orientations corresponding to the typical deformation texture for pure metals. Crystal rotations roughly in the rolling direction were observed for both the groups. When one < 011 > direction was close to the rolling direction, rotation occurred in the < 011 > direction. When two < 011 > directions were near the rolling direction, double slip would occur, causing grain rotation in the resultant direction. In the grains with near-cube orientations, rotations in two or three directions occurred in a single grain, leading to the formation of dislocation cells whose orientations differed from one another. Even in such a case, individual rotation of the cells could be interpreted in terms of the geometry in the < 011 > direction and the rolling direction.

The superconducting property of Zr55Cu(30-X)Al10Ni5NbX alloys prepared by arc melting and liquid quenching methods was investigated by magnetic susceptibility measurements. The crystalline alloys with X = 0 similar to 25 at.% prepared by arc melting method exhibited superconductivity with maximum T-c,T-on of 10.1 K. The alloys (X - 10 similar to 23 at.%) with crystalline particles embedded in an amorphous structure, which were fabricated by melt spinning method, showed superconductivity with Tc, on of less than 4.0 K. The superconducting property of the Zr-Cu-Al-Ni-Nb alloys was attributed to superconducting phases of Zr2Cu, Zr2Ni, Zr65Al10Nb25 and Zr-Nb contained in the Zr-Cu-Al-Ni-Nb alloys. The melt-spun Zr55Cu(30-X)Al10Ni5NbX (X = 10 similar to 20 at.%) alloys exhibited glass transition at 718 similar to 743 K and were found to be superconducting metallic glasses. (C) 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of ISS Program Committee.

The superconducting property of Zr(55)Co((30-x))Al(15)Nb(x) (x = 0-20 at.%) metallic glasses fabricated by rapid solidification was investigated. The Zr(55)Co((30-x))Al(15)Nb(x) (x = 5-20 at.%) metallic glasses with a mixture structure of amorphous and nanocrystal phases exhibited superconductivity of T(c,on) = 1.8-2.6 K. The maximum T(c,on) = 2.6 K was obtained for the Zr(55)Co(10)Al(15)Nb(20) metallic glass. This was attributable to the superconducting property of nanocrystalline particles contained in the Zr(55)Co(10)Al(15)Nb(20) alloy. The increase of Nb element in the Zr(55)Co((30-x))Al(15)Nb(x) alloy led to the increase of T(c,on) and the decrease of glass transition temperature. The glass transition temperature was between 704 and 749 K for the Zr(55)Co((30-x))Al(15)Nb(x) (x = 0-20 at.%) alloys. The temperature interval of supercooled liquid state was between 51 and 68 K for the Zr(55)Co((30-x))Al(15)Nb(x) (x = 0-20 at.%) alloys. (C) 2011 Published by Elsevier B.V.

Changes in microstructures at recovery stage after cold-rolling at 50% reduction rate were observed in an Al-Mg-Si alloy by means of SEM-EBSD system. The same area in the specimen was observed before and after cold-rolling. Intermittent annealing at 673 K, Ar ion-polishing, and EBSD observation were repeated up to the annealing time of 3.6 ks. Dislocation cells formed by cold-rolling changed into subgrains with annealing. Low and high angle boundaries were formed with surrounding the subgrains depending on misorientations between the neighboring subgrains. The high angle boundaries migrated to form recovered microstructures. Original orientation of the dislocation cell was maintained in the recovered microstructure. Some of the recovered microstructures grew with invading others. Therefore, new discrete poles did not appear in a discrete pole figure during annealing but those in the invaded subgrains disappear, which made the pole figure of the annealed specimen different from that of the cold-rolled specimen. Secondary recovered microstructures were observed to be formed with invading primary formed recovered microstructures. The recovered microstructures were finally invaded by recrystallized grains to disappear. In a region where growth of recrystallized grains was delayed, coarse recovered microstructures composed of large subgrains were formed.

Microstructural changes in an Al-Mg-Si alloy during annealing at 673 K after cold-rolling with a 50% reduction rate were observed. An alloy specimen was repeatedly subjected to intermittent annealing using a salt bath, Ar ion-polishing, and observation with SEM (Scanning Electron Microscope)-EBSD (Electron BackScatter Diffraction) system. The observations were carried out in the same view field on a specimen. Large lattice rotation occurred due to cold-rolling, which lead to formation of dislocation cells having orientations with broad range of angles, and made existing grain boundaries unclear. Strain induced grain boundary migration was not observed in this case. After annealing, the dislocation cells changed into subgrains surrounded by high and low angle boundaries, and some of them grew into recrystallized grains without change in orientation. These recrystallized grains ("crystallites") originated from the dislocation cells in the deformed microstructure. The orientations of the crystallites were different from those of the surrounding subgrains.

Recrystallization phenomena in an Al-Mg-Si alloy cold-rolled at 30 and 50% reduction rates were observed on the same area in specimens during annealing at 673 K using SEM-EBSD method. After recovery in a narrow sense occurred, coarse subgrain microstructures were formed by migrating high angle boundaries at both reduction rates. The coarse subgrain microstructure contained low angle boundaries, and orientation gradients were observed in contrast to the recrystallized microstructure. Lattice rotation due to cold-rolling was recovered in the coarse subgrain microstructures for the case of 30% reduction. When the specimen was cold-rolled at 50%, lattice rotation occurred over a broad range of angles. As a result, prior grain boundaries became unclear, and the majority of the subgrains were surrounded by high angle boundaries. Some of the subgrains showed the coarse subgrain microstructure, and the others grew into recrystallized grains. [doi:10.2320/matertrans.L-MZ201122]

The superconducting property of Zr((1-x))Co(x) (x = 10-50 at.%) alloys and a Zr(55)Co(30)Al(15) bulk metallic glass fabricated using techniques of rapid solidification was investigated. The Zr(55)Co(30)Al(15) alloy crystallized by heat treatment in a vacuum atmosphere exhibited superconductivity of T(c,on) = 2.4 K. This was attributable to the superconducting property of a crystalline Zr-Co alloy precipitated in the Zr(55)Co(30)Al(15) alloy. The T(c,on) of the crystalline Zr((1-x))Co(x) alloy was sensitive to the Co content. The increase of Co content for the Zr((1-x))Co(x) alloy led to the decrease of T(c,on). The Zr((1-x))Co(x) alloy exhibited superconductivity of a maximum T(c,on) = 3.9 K for the Zr(80)Co(20) alloy with superconducting nanocrystal particles embedded in the amorphous matrix. (C) 2010 Published by Elsevier B.V.

The crystallization behavior of Ca50Mg22.5Cu27.5 metallic glass in supercooled liquid has been examined using a technique of differential thermal analysis. Crystallization mechanism of the alloys during isothermal annealing in supercooled liquid was analyzed using the Johnson-Mehl-Avrami (JMA) equation. The experimental data of the isothermal crystallization was interpreted by the JMA model. The Avrami exponents for the ribbon and bulk alloys are 2.5 +/- 0.5 and 2.3 +/- 0.3, respectively. Both values of the Avrami exponent suggested that the crystal growth is controlled by a long-range diffusion process. The scaling law for crystallization of the alloys was also examined. (C) 2010 Elsevier B.V. All rights reserved.

An annealing effect on elastic moduli of a Ca48Mg27Cu25 bulk metallic glass has been investigated. The elastic moduli of Ca48Mg27Cu25 bulk metallic glass were estimated using a technique of ultrasonic velocity measurements. The Young's modulus (E), Poisson's ratio (v), shear modulus (G) and bulk modulus (B) for the as-cast Ca48Mg27Cu25 alloy at room temperature were found out to be sensitive to the change of amorphous structure for the alloy. The crystallization of Ca48Mg27Cu25 bulk metallic glass led to the increases of E, G and B, and the decrease of v for the alloy. (C) 2010 Elsevier B.V. All rights reserved.

The static mechanical properties of a Ca48Mg27Cu25 bulk metallic glass were investigated using a technique of ultrasonic measurement and compressive test. The Young's modulus (E), Poisson's ratio (v), shear modulus (G) and bulk modulus (B) for the Ca48Mg27Cu25 alloy at room temperature are significantly smaller than those for Zr- and Pd-based bulk metallic glasses. The values of E, v, G and B for the Ca48Mg27Cu25 alloy are 29.8GPa, 0.230, 12.1GPa and 18AGPa, respectively. The results of compression test for the Ca48Mg27Cu25 alloy have been also described.

YBa(2)Cu(3)O(7-x) (YBCO) films have been prepared on piezoelectric (001) Pb(Mg(1/3)Nb(2/3))(0.72)Ti(0.28)O(3) (PMN-PT) substrates for dynamic investigations on the influence of strain on the superconducting transition temperature. The YBCO films deposited by off-axis pulsed laser deposition showed a perfect epitaxial growth on the piezocrystals but also significant surface roughness due to the miscut of the substrate. The in-plane lattice constant of the PMN- PT substrate was varied dynamically by the application of an electric field of <= 10 kV cm(-1). As a result, a reversible shift of the superconducting transition by about 0.1 K was found on an optimally doped YBCO film for an applied strain of 0.05%. The results show for the first time that this approach is suitable for studying the strain dependence of superconducting properties in detail.

Temperature dependence of the mechanical resonance frequency f(m) of ultrasonic wave in as-quenched and annealed Zr60Al10Cu40 metallic glasses was measured from room temperature to liquid nitrogen temperature. The mechanical resonance of longitudinal wave for the as-quenched sample disappeared in lower temperature below 200 K. The resonance was restored at about 240K with increasing temperature. A hysteresis was observed in temperature dependence of f(m). The qualitatively similar behaviors were observed also for transverse wave. The phenomena for the annealed samples are different from ones for the as-quenched one. The excess free volume may cause anomalous temperature dependence of f(m).

Temperature dependence of an adiabatic elastic stiffness constant c(11) for metallic glasses Zr55Al10Cu35-xNix (x = 0, 5) is estimated from that of ultrasonic velocity measured by a technique of mechanical resonance of continuous waves from room temperature to 90 K. Temperature dependence of the sample length is also measured. The value of c(11) at room temperature is between those of main constituent elements Zr and Cu, and is near to one of Zr. The temperature dependence of c(11) for the metallic glasses is weaker than that of any constituent element, Zr, Al, Cri and Ni. This weak dependence may come from a peculiar structure characterizing the metallic glasses. (c) 2007 Elsevier B.V. All rights reserved.

Crystal nucleation and time evolution during isothermal annealing in amorphous Zr2Ni at several temperatures just below a crystallization temperature T, and in supercooled liquid of metallic glass Zr2Cu are examined using a technique of differential thermal analysis. Time dependence of the fraction of crystallization at several temperatures is analyzed by the Johnson-Mehl-Avrami equation. The Avrami exponent is 3.0 +/- 0.2 for Zr2Ni and varies from about 3 to 7 for Zr2Cu with increasing temperature. It is Suggested for Zr2Ni that the crystal growth at temperatures just below T-x is Riled by a short range diffusion process of constituent elements. The time evolution of crystallized fraction was not well scaled by the half of complete time for full crystallization.

An epitaxial Y(2)O(3)/ YSZ/ CeO(2) buffer architecture has been prepared using pulsed laser deposition on cube texture Ni - 3 at.% W/ Ni - 10 at.% Cr - 1.5 at.% Al and Ni - 5 at.% W/ Ni - 10 at.% W composite tapes. The buffer layer growth was studied in detail and revealed good texture transfer throughout the structure, similar to standard Ni - 5 at.% W substrates. YBCO layers were successfully deposited on the buffered tapes and compared to films grown on SrTiO3 single crystals. A superconducting transition temperature of about 90 K with a small transition width was observed on all metal substrates. A critical current density Jc of about 1 MA cm- 2 was measured at 77 K in a self- field. It was found that Jc is mainly limited by the grain boundary network in magnetic fields below 4 T, whereas similar values as on SrTiO(3) single crystals were measured at higher fields.

Viscosity of Zr55Cu30Al10Ni5 and Zr50Cu40-xAl10Pdx (x = 0, 3 and 7 at.%) supercooled liquid alloys having bulk metallic glass forming ability has been measured by using a penetration viscometer with a cylindrical probe under high speed heating conditions at heating rates between 20 and 400 K/min in the temperature range from the glass transition temperatures (T-g) up to above the crystallization temperatures. Effect of Pd addition on the viscosity of Zr-base supercooled liquid alloys has been also examined. The viscosity of these alloys decreased with increasing the heating rate and tended to saturate at the heating rate of 200 K/min and above. These viscosities can be well represented by the Arrhenius relation. The activation energy for viscous flow for Zr55Cu30Al10Ni5 Supercooled liquid alloys was about 350 kJ/mol. In the Zr50Cu40-xAl10Pdx (x = 0, 3 and 7 at.%) alloys, the viscosities increased with increasing the Pd-content, while the activation energy for viscous flow decreased from 337 to 276 kJ/mol. (c) 2006 Published by Elsevier B.V.

The temperature dependence of electrical resistivitiy of Zr(55)Cu(30-X)Al(10)Ni(5)Nb(X) (numbers indicate at.% X = 0, 1, 3 and 5) bulk metallic glasses was investigated below 300 K. For the Zr(55)Cu((30-X))Al(10)Ni(5)Nb(X) alloys with X = 1, 3 and 5 consisting of nanocrystals dispersed in the amorphous matrix, the electrical resistivities decreased abruptly below approximately 2.3-2.9 K. For the amorphous Zr(55)Cu(30)Al(10)Ni(5) alloy, the electrical resistivitiy increased with decreasing temperature from 300 K up to approximately 2.0 K. The significant decrease of electrical resistivities of nanocrystal-dispersed amorphous alloys was attributable to the zero-resistivity effect of superconducting phases contained in the alloys. The Nb addition to Zr(55)Cu(30)Al(10)Ni(5) metallic glass was found to precipitate superconducting phases within the amorphous matrix. (c) 2006 Elsevier B.V. All rights reserved.

Viscosity of a Zr55Cu30Al10Ni5 supercooled liquid alloy having bulk metallic glass forming ability has been measured by using a penetration viscometer with a cylindrical probe under high speed heating conditions at rates between 20°C/min and 400°C/min in the temperature range from the glass transition temperatures (Tg) up to above the crystallization temperatures (Tx). The viscosity of the alloy decreased with increasing the heating rate and tended to saturate at the heating rate of 200°C/min and above. Corresponding measurements of the differential thermal calorimetry (DSC) under the high-speed heating conditions have been also done.

A crystallization process in an amorphous state under isothermal condition is examined for binary alloys ZrNi and ZrNi2 by differential thermal analysis (DTA). Time dependence of DTA curves is measured at several constant temperatures just below crystallization temperature. The fraction of crystallized volume in amorphous state and its time evolution during isothermal annealing are measured. These data are analyzed by the Johnson-Mehl-Avrami formula. The Avrami exponent is 2.4 +/- 0.1 for ZrNi and 3 similar to 4 depending on the set temperature for ZrNi2. The activation energy for crystallization of amorphous ZrNi and ZrNi2 was estimated by plots of lnt(1/2) vs. 1/T.