足立 大樹

© 2016 The Author(s). Finding a physical approach for increasing the superconducting transition temperature (T c) is a challenge in the field of material science. Shear strain effects on the superconductivity of rhenium were investigated using magnetic measurements, X-ray diffraction, transmission electron microscopy, and first-principles calculations. A large shear strain reduces the grain size and simultaneously expands the unit cells, resulting in an increase in T c. Here we show that this shear strain approach is a new method for enhancing T c and differs from that using hydrostatic strain. The enhancement of T c is explained by an increase in net electron-electron coupling rather than a change in the density of states near the Fermi level. The shear strain effect in rhenium could be a successful example of manipulating Bardeen-Cooper-Schrieffer-type Cooper pairing, in which the unit cell volumes are indeed a key parameter.

© 2016 Informa UK Limited, trading as Taylor & Francis Group. At the synchrotron facility, Super Photon Ring – 8 GeV, in-situ X-ray diffraction during tensile deformation was conducted on ultrafine-grained Cu with a grain size of about 300 nm fabricated by equal-channel angular pressing. The diffraction profile was observed with the time resolution of about 1 s using multiple MYTHEN detectors, and the diffraction angle and the full-width at half-maximum of some Bragg peaks were determined using the pseudo-Voigt function. From the analysis of Bragg peaks, it was found out that there are microscopically three regions; elastic, plastic and transition regions. The 0.2% proof stress obtained from the stress–strain curve locates within the microscopic transition region. Microstrain was evaluated using the Williamson–Hall method and the dislocation density was also obtained from the microstrain. The dislocation density starts increasing before 0.2% proof stress, which is associated with dislocation bow-out and emission from grain boundaries. The Taylor relationship seems to be still satisfied after 0.2% proof stress.

The microstructure and texture evolution of an accumulative roll bonding (ARB) processed 4N-Cu with and without lubrication were compared in addition to the mechanical properties, in order to understand the effect of additional shear strain caused by the friction between the rolls and a sheet. Furthermore, subsequent annealing at 423 K, 448 K and 473 K was applied for 4N-Cu ARB processed with and without lubrication, and, softening was observed for all temperatures. The texture change due to the ARB process and subsequent annealing were discussed using {111} pole figures and ODF maps. As a result, a 45° rotated Cube texture around ND was formed by additional shear strain, whereas the typical fcc rolling texture was formed by ARB with lubrication. At higher ARB cycles of 4N-Cu, discontinuous recrystallization occurs due to its medium stacking fault energy. Cube orientation appeared in annealed-ARB processed 4N-Cu with lubrication, whereas no specific texture appeared in annealed-ARB processed 4N-Cu without lubrication.

In situ XRD measurements were conducted during the tensile deformation of both submicron-grained Ni specimens fabricated by accumulative roll bonding (having a grain size of 270 nm) and nanocrystalline Ni fabricated by electrodeposition (having a grain size of 52 nm). Variations in the dislocation density and the extent of elastic deformation could be determined with a time resolution of 1.0 s based on changes in the full width at half maximum of ten Bragg peaks and in the Bragg peak shifts, respectively. The dislocation density was found to vary in four different stages. Regions I and III were the elastic and plastic deformation regions, respectively, while Region II was the transition region. Here, the dislocation density rapidly increased to a value, ρII, necessary for plastic deformation. Since the increase in ρII was inversely proportional to grain size, it is evident that nanocrystalline materials require extremely high dislocation densities for deformation to progress solely by plastic deformation. In Region IV, the multiple dislocations were rapidly annihilated by unloading associated with fracture. In the case of the nanocrystalline Ni, there was little difference in the stress distribution in the grains depending on the crystal direction during plastic deformation and, accordingly, there was only minimal variation in the residual stress in the grain with different crystal directions after unloading.

© 2016 by American Scientific Publishers All rights reserved. In this study, the correlation between mechanical properties and microstructure was investigated in Ni-W alloys as a function of W content. In particular, we focus on the intrinsic ductility of Ni-W alloys fabricated by using a brushing technique. Ni-W alloys with varying W content were electrodeposited by the change in temperature of the plating bath. High-resolution transmission electron microscopy and XRD measurements revealed that Ni-W alloys with a W content of less than 14 at.% consisted of a nanocrystalline single phase, while those with W contents between 14.5 and 17.0 at.% consisted of a nanocrystalline-amorphous dual phase. In the Ni-W dual-phase alloys, the average grain size was about 6 nm, regardless of the W content. Thus, the volume fraction of the nanocrystalline phase decreased monotonically with increasing W content. The nanocrystalline Ni-W alloys exhibited a tensile strength of about 2400 MPa and low ductility. Ni-W dual-phase alloys consisting of a nanocrystalline and an amorphous phase exhibited a large plastic strain of about 6.5% with a maximum tensile strength as high as ~2500 MPa. Through synchrotron radiation X-ray diffraction measurements, the emergence of deformation-induced grain growth was confirmed in the Ni-W dual-phase alloy. This grain growth leads to an increase in strength. Thus, Ni-W dual-phase alloys possess work-hardening ability and can improve the tensile ductility.

The effect of temperature on the stress-strain responses under cyclic plastic deformation on a rolled AZ31B sheet was investigated by performing in-plane cyclic tension-compression experiments at various temperatures ranging from room temperature to 200℃. The change in the crystallographic textures during the cyclic deformation was examined by XRD analysis. From room temperature to 137℃, three deformation modes, i.e., slip, twinning and detwinning, were active. In particular at room temperature, the three deformation modes sequentially occurred in compression- tension experiment, and as a result, an unusual cyclic stress-strain curve with tension-compression asymmetry was observed. At 200℃, the cyclic-stress-strain curve was symmetric and its stress level was much lower than that at R.T., since, at this elevated temperature, CRSSs of nonbasal slip systems were low because slip deformation occurs rather than twinning.

５Ｍｎマルテンサイト鋼の高強度と高延性を示す原因を明らかにするため，放射光を用いて加工硬化と転位密度変化の関係を調べた．Ｍｎ含有量の増加は，転位密度を増加させ，高い加工硬化率をもたらした．ＸＲＤ，ＴＥＭ観察で得た転位配置パラメータは，５％Ｍｎの添加により転位セルの形成を遅らせることを明らかにした．

© 2015 Elsevier B.V. All rights reserved. A novel agitation technique, referred to as the "brushing technique" is proposed to treat the surface of a Ni-W alloy film during electrodeposition. This technique was developed to directly remove hydrogen bubbles on the film surface and to apply Ni ions to the interfacial layer with the substrate. The intrinsic mechanical properties of the Ni-W electrodeposits are then evaluated with respect to application. High resolution transmission electron microscopy observations revealed that both treated and untreated films have nanocrystallites of approximately 5 nm in diameter and an amorphous phase. There was a compositional difference of about. 1.4 at% W between the face side and the reverse side of the film that was not subjected to the brushing technique, whereas this difference was absent in the film subjected to the brushing technique. In addition, the brushing technique reduced the surface roughness of the film and decreased the number of defects. As a result, a large plastic strain of about. 2.9% was observed with work hardening under tensile testing.

In Al–Mg–Si alloys, the negative effect for the artificial age-hardenability occurs by the cluster (1) formation during natural aging following solution treatment and the positive effect occurs by the cluster (2) formation. For the purpose of obtaining information on the constituent elements of these clusters, soft X-ray absorption fine structure (XAFS) measurements of Mg–K edge and Si–K edge were carried out with the liquid nitrogen cooling. From radial structure function calculated from the extended X-ray absorption fine structure (EXAFS) spectra, since average nearest neighbor distance from Mg atom or Si atom decreases by the formation of cluster (1), it is considered that cluster (1) contains both Mg and Si atoms. The absorption edge energy of Si–K shifted to higher energy by the formation of cluster (1). This indicates that the Si valence increased and ion binding property is high for the bonding with neighbor atoms of Si atom in cluster (1). Since the binding force of ionic bond is stronger than that of a metallic bond, cluster (1) is difficult to be decomposed in the artificial aging and the negative effect is shown.

© 2015 The Authors. In this study, the local stress in an SUS304 austenitic stainless steel was measured during tensile deformation by a technique called energy dispersive X-ray diffraction microscopy using synchrotron radiation X-ray diffraction in SPring-8. The local stress evolution of two positions in different grains, respectively, were shown in this paper. At one position, the tensile component of principal stress increased with increasing the tensile strain, but slightly deviated from the macroscopic tensile direction. On the other hand, at another position, the tensile component of principal stress was substantially different from the macroscopic tensile direction, and the drastic change in direction of local stress were observed due to martensitic transformation.

© 2015 The Japan Institute of Light Metals. Ultra-fine-grained (UFG) aluminum with a grain size of 260nm was fabricated by annealing a severely plastically deformed A1100 alloy. The resulting UFG aluminum exhibited a 0.2% proof stress (σ0.2) that was four times larger than that predicted by the conventional Hall-Petch relation. In this study, the UFG aluminum, the fine-grained aluminum with a grain size of 960nm and the coarse-grained aluminum with a grain size of 4.47μm were prepared. The change in the dislocation density, was investigated during tensile deformation using in-situ X-ray diffraction measurements at SPring-8. It was found that as the strain increased, the changed in four distinct stages. The first stage was characterized by elastic deformation, and little change in the occurred. For the coarse-grained aluminum, this stage was almost absent. In the second stage, the rapidly increased until the stress reaches σII in which the plastic deformation begins to occur at a constant strain rate. In the third stage, only a moderate change in the occurred. Finally, in the fourth stage, the rapidly decreased as the test pieces underwent fracture. Additionally, it was found that the σ<inf>0.2</inf>-σ<inf>I</inf> was followed by the conventional Hall-Petch relation in all grain size range.

© 2013 Springer-Verlag Berlin Heidelberg. High strength nanocrystalline and amorphous Ni-14-24 at. % W alloys with their tensile strengths of about 3 GPa have been prepared by electrodeposition. Nano-microscale Ni-W alloy mould inserts, consisting of line and space structures with the line-widths of 700 and 300 nm and the height of 200 nm, were fabricated. High compression stress moulding of some metal plates of pure-Al, SUS-316L stainless steel and Zr69Cu16Ni5Al10bulk metallic glass with the Ni-W alloy inserts was carried out at room temperature. In the case of the pure-Al under moulding stress of about 350 MPa, full moulding was achieved with the depths of about 200 nm approximately equal to the height of the inserts. Repeat moulding of 200 cycles did not cause any noticeable change or degradation of the Ni-W alloy inserts. In the case of the SUS-316L stainless steel under the moulding stress of about 1 GPa, however, the nano-microscale moulding was not achieved. This may be due to the high strain hardening ability of the SUS-316L stainless steel during plastic deformation. In the case of the Zr69Cu16Ni5Al10bulk metallic glass with a high yielding stress of about 1.5 GPa and no strain hardening ability, full moulding was almost achieved successfully under the high moulding stress of about 2 GPa.

The deformation behavior of the f phase in the Fe-Zn system has been investigated by micropillar compression tests at room temperature with the use of single crystals with 13 different crystal orientations prepared by the focused ion beam method. Two different slip systems, {110}〈112〉 and (100)[001], are observed to operate. The critical resolved shear stresses (CRSS) value for {110}〈112〉 slip is more than three times smaller than that for (100)[001] slip. From the anisotropy in CRSS for these two slip systems, {110}〈112〉 slip is predicted to operate for most crystal orientations, except for a narrow orientation region around [305] where (100)[001] slip operates. The CRSS for {110}〈112〉 slip shows an inverse power-law scaling against the specimen size with an exponent of -0.517. The bulk CRSS value for {110}〈112〉 slip is estimated to be 62-76 MPa by taking into account the specimen size effects of CRSS. The reasons why {110}〈112〉 slip with a rather long Burgers vector (0.7700 nm) is selected as the easiest slip system are discussed in terms of the nature of atomic bonding in the crystal structure, especially the rigid atomic bonding within an Fe-centered Zn12icosahedron (for slip plane selection), and the energetic barrier height along the slip direction and the resultant possible dissociation schemes (for slip direction selection). Some implications are made on how the deformability of the ς phase can be improved in the textured coating layer in galvannealed steels based on the results obtained. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

A study has been carried out into the formation of nanocrystalline grains during high-pressure torsion (HPT) deformation of Zr65Cu17Ni5Al10Au3 bulk alloys prepared using tilt casting. As a preliminary to this, X-ray diffraction (XRD) and differential scanning calorimetry (DSC) analyses were carried out on as-cast Zr65+xCu17-xNi(5)Al(10)Au(3) (x=0 similar to 5 at.%) and Zr65Cu20Ni5Al10 alloys, in order to determine the effect on the microstructure of the excess Zr content x and the presence of Au. From the XRD patterns, it was determined that all of the alloys had a metallic glassy nature. For Zr65Cu20Ni5Al10, the DSC results indicated the presence of a wide supercooled liquid region between the glass transition temperature (T-g) of 644 K and the crystallization temperature of 763 K, where the stable body-centered tetragonal Zr2Cu phase was formed. In contrast, for the Zr65+xCu17-xNi5Al10Au3 alloys, precipitation of an icosahedral quasicrystalline phase (I-phase) was observed in the supercooled liquid region at about 715 K. HPT deformation of the Zr65Cu17Ni5Al10Au3 alloys was carried out under a high pressure of 5 GPa. Both as-cast specimens and those annealed at T-g-50 K for go min were used. Following a single HPT rotation (N=1), transmission electron microscopy identified the presence of face-centered cubic Zr2Ni precipitates in the as-cast alloy, with a size of about 50 nm. For the annealed alloy, a high density of I-phase precipitates with sizes of less than 10 nm was observed following HPT with N=10, indicating that the combination of severe plastic deformation and annealing is effective at producing extremely small grains.

Accumulative roll bonding (ARB) was applied to three FCC metals, such as Al, Cu and Ni. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) were made to evaluate dislocation density rho of the ARB processed FCC metals. The values of rho of ARB processed Cu and Ni increased rapidly after the first ARB cycle, and then, tend to saturate after the following cycles. The evaluated values of rho of both ARB 8-cycled Cu and Ni using DSC were around 2x10(15) m(-2). Whereas, those using XRD were around 5x10(14)m(-2) (for Cu) and 3x10(14)m(-2) (for Ni). Although the rho values depend on the measurement methods, the trends that DSC values are about an order of magnitude higher than XRD values seem to be common. In the case of Al, dislocation density evaluated using XRD increased to about 1x10(13)m(-2) at the first ARB cycle, and then gradually decreased to about 1x10(12)m(-2) with increasing number of ARB cycles.

Magnesium alloy sheets have a potential to be widely used in many fields of industry due to their excellent lightweight property. Although magnesium alloys have low ductility at the room temperature due to their hexagonal close- packed structure, their formability can be improved at elevated temperatures. Therefore, warm press- forming of magnesium alloy sheets is an attractive technology. The objective of the present work is to investigate the cyclic plasticity behavior of an AZ31 sheet at elevated temperatures by performing cyclic tension- compression experiments. The cyclic deformation mechanism is examined by measuring the crystallographic orientation distributions by means of X- ray diffraction method at each stage of the cyclic deformation. The present findings are summarized as follows: ( 1) Stress- strain responses of an AZ31 sheet were investigated at various temperatures ( R. T, 100, 150 and 200 o C) at strain rates of 0.001, 0.01 and 0.05 s - 1. The flow stresses were insensitive to the strain rate at the room temperature, however the strain rate dependency of the flow stress becomes dominant at elevated temperatures of over 100 o C. ( 2) Cyclic plasticity behavior of the sheet at various elevated temperatures ( R. T, 100, 150 and 200 o C) at strain rates of 0.001, 0.01 and 0.05 s - 1 were investigated by performing warm in- plane cyclic compression- tension test. Similarly to the uniaxial tension test, apparent temperature and strain rate dependencies of the flow stress were observed at temperatures of over 100 o C. ( 3) At the room temperature an unusual cyclic stress- strain curve, which is very different from that of bcc and fcc metals, was observed. From the texture measurement it was found that such a specific stress- strain characteristic is due to its twinning and detwinning deformation mechanism. ( 4) In contrast, at an elevated temperature of 200 o C, the usual cyclic stress- strain response, which is similar to one appearing in most of metallic materials, was observed. This is because the major deformation mechanism at an elevated temperature is the slip, rather than twinning/ detwinning, since the CRSS decreases drastically with increasing temperature.

A commercial purity aluminum was heavily deformed up to an equivalent strain of 4 at various temperatures and strain rates by torsion deformation to produce specimens with various ultrafine grained (UFG) microstructures. The microstructures were characterized by electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The microstructural observation revealed that the torsion deformed specimens had various mean grain sizes ranging from 0.38 to 8.6 μm. The grain size and dislocation density in the microstructures depended on the deformation conditions organized by ZenerHollomon parameter. The mechanical properties of the torsion deformed specimens were investigated by tensile test at room temperature. It was found that the ultrafine grained specimens showed high strength which reached a value almost three times higher than that of the starting material. The strength of the UFG aluminum was higher than the level expected from the HallPetch relationship for conventionally coarse grained aluminum. The strengthening mechanisms in the UFG aluminum were discussed in terms of substructures introduced during torsion deformation. © 2013 The Japan Institute of Metals and Materials.

The ultra-fine grained (UFG) aluminum with the grain size of 260 nm was fabricated by annealing for the severely plastic deformed A1100 alloy. This UFG aluminum showed the 0.2% proof stress (&sigma;_0.2) of four times the stress that the conventional Hall&ndash;Petch relation showed. In this study, for the UFG aluminum, the fine-grained (FG) aluminum with the grain size of 960 nm and the coarse-grained (CG) aluminum with the grain size of 4.47 &micro;m, dislocation density change during the tensile deformation was investigated by the In-situ XRD measurement using SPring-8. The dislocation density changed in four stages with increase in strain. The first stage was the elastic deformation region and the dislocation density hardly changed. Only in the CG aluminum, this stage was hardly observed and the stress in which the dislocation began to multiple (&sigma;_I) was almost 0 MPa. In the second stage, the dislocation density rapidly increased to &rho;_II in which plastic deformation became possible at constant strain rate. In the third stage, the change became moderately. In the fourth stage, the dislocation density rapidly decreased by the fracture of test pieces. Additionally, the &sigma;_0.2&ndash;&sigma;_I were followed the conventional Hall&ndash;Petch relation regardless of grain size.

In this work, we fabricated nanocrystalline austenite structures of Fe-Ni alloys by electrodeposition and subsequent heat treatment, and investigated the martensitic transformation behavior from the nanocrystalline austenite. The martensite transformation start temperature of the nanocrystalline austenite with a grain size of 224 nm was significantly lower than that of a coarse-grained austenite. The morphology of the martensite transformed from the nanocrystalline austenite was equiaxed and totally different from lenticular plate martensite and thin plate martensite that usually form from coarse-grained austenite. The martensite contained transformation twins with average twin width of 2.2 nm. The orientation analysis revealed that the martensitic transformation from the nanocrystalline austenite was accompanied with the formation of several martensite variants.

Commercial purity aluminum (1100Al) bars were severely plastic deformed by torsion deformation at room temperature. The specimens were deformed to ultrahigh equivalent strain of 5.85 in maximum. Microstructure evolution during the torsion deformation was characterized using electron back scatter diffraction analysis on two different sections: the longitudinal section parallel to the torsion axis and transverse section perpendicular to the torsion axis. The grain size decreased and the fraction of high angle grain boundary increased with increasing equivalent strain. Elongated ultrafine grained structure was obtained after an equivalent strain of 3.27. We have found that the microstructure evolution in the specimen deformed by torsion exhibited similar behavior to those in the same material heavily deformed by accumulative roll bonding. The average grain size of 0.32 mu m with the high angle boundary fraction of 0.76 was achieved in the specimen deformed to an equivalent strain of 5.27. Though the microstructure and hardness on the transverse section varied depending on the radial positions, they could be arranged as a simple function of equivalent strain. The present work confirmed that the torsion deformation worked as a kind of severe plastic deformation.

It is known that pure metals having ultrafine grains (UFGs) exhibit softening and grain coarsening at temperatures about one third of the melting temperatures. When such low-temperature annealing (LTA) of UFG copper is conducted under uniaxial tensile stress, the retardation of the softening is found to occur compared with that without stress. Observations of the microstructure and texture analysis indicate that the softening and the grain coarsening are attributed to recrystallization, and the presence of uniaxial tensile stress during LTA retards recrystallization. High voltage transmission electron microscopy revealed that the dislocation density of UFG copper annealed under uniaxial tensile stress is lower than that after LTA without stress. The retardation of recrystallization is associated with the reduction of the dislocation density of unrecrystallized UFG copper induced by dynamic recovery. [doi:10.2320/matertrans.MD201117]

Effect of pre-existing precipitates on microstructure evolution during severe plastic deformation was studied. An Al-0.2 mass%Sc alloy was aged at 300 and 400 degrees C for having different sizes of Al3Sc precipitates. The mean precipitate size of Al3Sc was 3.62 and 50 nm for 300 and 400 degrees C aging, respectively. In the as-aged specimens, Al3Sc had coherency with the Al matrix. The three kinds of specimens that were solution-treated (ST), aged at 300 degrees C or aged at 400 degrees C, were then heavily deformed by the accumulative roll bonding (ARB) process up to 10 cycles (corresponding to an equivalent strain of 8.0) at room temperature. After 10 cycles of the ARB process, the specimens showed a lamellar boundary structure having the mean lamellar interval of 0.37, 0.24 and 0.27 pm in the ST, 300 degrees C Aged and 400 degrees C Aged-specimens, respectively. Additionally, the fraction of high angle grain boundaries (HAGBs) and the average misorientation between boundaries in the Aged-specimens were both higher than those in the ST specimen ARB processed to the same strain. It indicated that grain refinement during the ARB process was accelerated by the pre-existing precipitates. The reasons for the acceleration in microstructural evolution are considered to be the introduction of shear bands, the enhancement of dislocation multiplication rate and the inhibition of grain boundary migration by the precipitates in the pre-aged specimens. [doi:10.2320/matertrans.MD201125]

To investigate the deformation behavior of a magnesium sheet, the finite element calculation was carried out under tension and in-plane cyclic tension-compression test. From the experimental data, the twin deformation was observed during the tensile deformation after uniaxial compression. For the accurate description of the above mentioned twin deformation, we have developed the constitutive equation of twining behavior. From the comparison, it is found that the developed constitutive equations can calculate stress-strain response accurately.

The effect of prior and subsequent precipitation on recrystallization behavior during the isothermal annealing of an Al-0.2%wt.Sc alloy heavily deformed by accumulative roll bonding (ARB) up to 10 cycles at ambient temperature was investigated. Three kind of different microstructures, i.e., solution treated one, 300 degrees C pre-aged one and 400 degrees C pre-aged one, were prepared as the starting structures for the ARB process. It is found that precipitation pinning effect of Al3Sc suppresses recrystallization and especially the 400 degrees C pre-aging was effective to stabilize the ultrafine grained structure of the matrix. Dissolution of pre-aging Al3Sc precipitates was suggested by re-precipitation during annealing of the ARB processed specimens at around 300 degrees C.

The plastic behaviour of Co-3(Al, W) polycrystals with the L1(2) structure has been investigated in compression from 77 to 1273 K. The yield stress exhibits a rapid decrease at low temperatures (up to room temperature) followed by a plateau (up to 950 K), then it increases anomalously with temperature in a narrow temperature range between 950 and 1100 K, followed again by a rapid decrease at high temperatures. Slip is observed to occur exclusively on {111} planes at all temperatures investigated. The rapid decrease in yield stress observed at low temperatures is ascribed to a thermal component of solid-solution hardening that occurs during the motion of APB-coupled dislocations whose core adopts a planar, glissile structure. The anomalous increase in yield stress is consistent with the thermally activated cross-slip of APB-coupled dislocations from (111) to (010), as for many other L1(2) compounds. Similarities and differences in the deformation behaviour and operating mechanisms among Co-3(Al, W) and other L1(2) compounds, such as Ni3Al and Co3Ti, are discussed.

The microstructure of the recently developed coated conductors was investigated by using electron back scatter diffraction pattern (EBSP). We prepared TFA (trifluoroacetates)-MOD (metal organic deposition) derived YBa2Cu3O7-delta (YBCO) films on CeO2/LaMnO3/IBAD-MgO/Gd2Zr2O7/Hastelloy C276 substrates of 1 cm-width. The EBSP observation showed that there was a difference of surface microstructure between the midsection and the end of TFA-MOD YBCO film layer in the direction of width. This is attributed not to the local difference of the biaxial texture of CeO2 top layer but to the local difference of growth condition during TFA-MOD process. (C) 2010 Elsevier B.V. All rights reserved.

The deformation behavior of Ti5Si3 single crystals with the hexagonal D8(8) structure has been investigated in compression as a function of crystal orientation in a temperature range from 1200 to 1500 degrees C. Three different types of deformation modes - {1 (1) over bar 0 0}[0 0 0 1] prismatic slip, {2 (1) over bar (1) over bar 2}1/3 &lt; 2 (1) over bar (1) over bar (3) over bar &gt; pyramidal slip and {2 (1) over bar (1) over bar 8}&lt; 8 (4) over bar (4) over bar (3) over bar &gt; twinning - were identified for the first time as being operative in Ti5Si3 at temperatures above 1300 degrees C, depending on the loading axis orientation. The critical resolved shear stresses (CRSSs) decrease steeply with increasing temperature for all deformation modes. The values of the CRSSs for {1 (1) over bar 0 0}[0 0 0 1] prismatic slip are considerably lower than those for {2 (1) over bar (1) over bar 2}1/3 &lt; 2 (1) over bar (1) over bar (3) over bar &gt; pyramidal slip, but are comparable to those for {2 (1) over bar (1) over bar 8}&lt; 8 (4) over bar (4) over bar (3) over bar &gt; twinning. The favored deformation modes are discussed on the basis of anisotropic elasticity theory of dislocations. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Directionally solidified alloys in the Ru-Mn-Si system exhibit a particular microstructure including columnar compositional variation due to the formation of many different chimney-ladder phases along the growth direction. Despite the existence of the compositional variation, the crystal orientations of the neighboring chimney-ladder phases are preserved. Over the compositional interfaces, the metal sublattice is considered to be continuous while the Si sublattice is not. Heat treatment of the directionally solidified alloy with the nominal composition of Ru0.10Mn0.90Si1.732 at 1100°C coarsens the compositional domains so as to reduce the density of the compositional interfaces. The values of the thermal conductivity increase with the decrease in the density of the compositional interfaces whereas those of the Seebeck coefficient and electrical resistivity are almost unchanged after the heat treatment. It is considered that the thermoelectric properties of the chimney-ladder compounds in the Ru-Mn-Si system can be enhanced by introducing a high density of the compositional interfaces. © 2010 Materials Research Society.

It is well known that Al₃Zr and Al₃(Sc, Zr) particles precipitate in the matrix by adding Zr and Sc to aluminum alloys and these particles inhibit a static recrystallization by pinning the grain boundary. In this study, 1.33%Zr, 0.4%Sc&ndash;0.8%Zr and 0.8%Sc&ndash;0.4%Zr (in mass%) were added to 7000 series aluminum alloys in supersaturation by using powder metallurgy. By applying rapidly solidified powders of these alloys to a heat treatment at 773 K, Al₃Zr and Al₃(Sc, Zr) particles were precipitated in high density. Subsequently, hot extrusion was carried out at 773 K. During extrusion, continuous dynamic recrystallization (DRX) occurred and fine DRX grains with a diameter of 1 &mu;m were formed. Continuous DRX is generated since the particles pin the grain boundaries and the mobility of the grain boundary lowers. So, the number of DRX grains are strongly related to the pinning force calculated by the average diameter of Al₃Zr and Al₃(Sc_0.5, Zr_0.5) particles precipitated in 1.33%Zr added alloy and 0.4%Sc&ndash;0.8%Zr alloy, respectively. Though, in 0.8%Sc&ndash;0.4%Zr added alloy, since Al₃(Sc_0.5, Zr_0.5) and Al₃(Sc_0.86, Zr_0.14) particles were precipitated concurrently, the diameter of particles exhibits a bimodal distribution and shows a widely dispersed distribution. As a result, the pinning force can't be accurately calculated by using the average diameter of particles and the number of DRX grains are weakly related to the calculated pinning force in 0.8%Sc&ndash;0.4%Zr added alloy.

The DI (dynamically innovative)-BSCCO-Bi2223 tapes achieved high critical current as well as high modulus of elasticity. Further the reversible strain limit and the corresponding stress for critical current have been remarkably increased by means of lamination technique. During the course of development, their optimized architecture has been designed based on the principle of the rule of mixture for maximizing the force free strain exerted on the superconducting component. The reversible strain/stress limit (A(rev)/R(rev)) was defined as a strain, at which the critical current recovers to the level of 99% I(co). Selecting several kinds of laminating materials and changing condition of the fabrication, the excellent Cu alloy-3ply tape with I(co) of 311 A/cm was realized of which A(rev) and R(rev) reached 0.42% and 300 MPa, respectively. Further during the theoretical analysis, the increase of reversible strain limit were made clear to be attributed to the increase of thermally induced residual strain as well as the compensation effect of laminated layers against a local fracture mode.

The deformation behavior of the surrounded Cu stabilized YBCO coated conductor based on the Hastelloy substrate and its influence on the critical current were precisely investigated. The mechanical properties were assessed at room temperature and 77 K. The greatest contribution was brought by two metallic components of the Hastelloy substrate and Cu stabilized layers. The internal strain exerted on the superconducting YBCO layer was determined directly by using synchrotron radiation facilities. The thermally induced residual strain with compressive component decreased during the tensile loading and changed to a tensile component at the force free strain (Lambda(ff)), at which the internal stress becomes zero in the YBCO layer. Beyond Aff, the increasing rate of internal strain slowed down, suggesting brittle behavior, that is, the formation of micro-cracks. The applied strain dependence of the critical current could be divided into two regions. In the reversible region, the strain dependence obeyed the intrinsic strain effect and was well expressed by the Ekin formula. Beyond the reversible limit, the critical current decreased rapidly with strain. The degradation is suggested to be attributed to the formation of cracks in the YBCO layer. The force free strain evaluated from the mechanical properties was 0.26%. On the other hand, the strain at the critical current maximum was observed to be 0.035-0.012%. These facts suggest re-examining the hypothesis supposing that the critical current maximum appears at the force free strain in YBCO coated conductors.

Mesoalite series alloys were formed using rapid solidification powder metallurgy (RS-P/M) by hot extrusion. The addition of Mn and Zr to the basic Mesoalite alloy (Meso10) in excess led to continuous dynamic recrystallization (DRX) in the alloy during hot extrusion through a different mechanism. In order to achieve a synergistic effect, Mn and Zr additives were used simultaneously. It was found that the DRX mechanism was governed by the addition of Mn, while the Zr addition was effective in coarsening control.

Heat-resistant aluminum alloys are generally developed by dispersing stable intermetallic compounds by adding transition metals (TM) whose diffusion coefficient in aluminum alloys is low even at high temperatures. Commonly used intermetallic compounds include Al-TM binary intermetallic compounds, for example, Al6Fe, Al3Ti and Al3Ni. By contrast, multicomponent intermetallic compounds are hardly used. The present study focuses on Al-Mn-Cu and Al-Mn-Ni ternary intermetallic compounds, and by finely dispersing these intermetallic compounds, attempts to develop heat-resistant alloys. Through the atomization method, Al-(4.96-5.96) Mn-(6.82-7.53) Cu-0.4Zr and Al-(5.48-8.76) Mn-(2.23-4.32) Ni-0.4Zr (in mass%) powders were fabricated, and by degassing these powders at 773 K, intermetallic compounds were precipitated. These powders were then solidified into extrudates by hot extrusion at 773 K. The microstructural characterization of powders and exrudates was carried out by XRD analysis, SEM/EDX and TEM. The mechanical properties of extrudates were determined at room temperature, 523 K and 573 K. In Al-Mn-Cu alloys, while a small amount of Al2Cu was crystallized, precipitated Al20Mn3Cu2 intermetallic compounds were mainly dispersed. In Al-Mn-Ni alloys, while a small amount of Al6Mn intermetallic compounds was precipitated, the precipitated A(60)Mn(11)Ni(4) intermetallic compounds were mainly dispersed. Both ternary intermetallic compounds were about 200 nm in size. The compounds were elliptical, and their longitudinal direction was oriented along the extrusion direction. In the Al-Mn-Cu alloys, since the work hardening at room temperature was high, the tensile strength became 569 MPa. At elevated temperatures, since hardly any work hardening was observed, the tensile strength decreased markedly. However, in Al-Mn-Ni alloys, since the work hardening is low even at room temperature, the room-temperature strength is not high. Thus, the decrease in tensile strength at elevated temperatures is relatively small and a high strength was obtained at 523 K and 573 K: 276 MPa and 207 MPa, respectively.

Al3Sc particles are well known to be a recrystallization inhibitor in Al alloys. In this study, 0.4, 0.8 and 1.5 mass% Sc were added to 7000 series Al alloys in supersaturation by using powder metallurgy. By subjecting rapidly solidified powders of these alloys to a heat treatment at 773 K, Al3Sc particles were precipitated in the matrix. Subsequently, hot extrusion was carried out at 773 K. During extrusion, continuous dynamic recrystallization (DRX) occurred and fine DRX grains with a diameter of 1 mm were formed. The number of DRX grains was the largest in the 1.5Sc alloy. Even though the amount of Sc added in this case was two times larger, the number of DRX grains in 0.4Sc was almost the same as that in 0.8Sc. Since continuous DRX occurs only under conditions where the grain boundary mobility is low, the number of DRX grains is strongly related to the pinning force on the initial grain boundary exerted by Al3Sc particles. The pinning force varied with the diameter and volume fraction of Al3Sc particles. When the pinning force was calculated from the diameter of Al3Sc particles, which was measured by TEM, it was proven that the number of DRX grains was proportional to the calculated pinning force. Except in the case of 0.4Sc, the Al3Sc particle diameter was twice that obtained at the maximum pinning force (d(max)). It is possible to promote continuous DRX by decreasing the Al3Sc particle diameter in 0.8 and 1.5Sc alloys. Lowering the heating rate before heat treatment for degassing reduced the critical nucleus size for precipitation of Al3Sc particles as well the diameter of Al3Sc particles. Thus, the pinning force increased in 0.8Sc and 1.5Sc alloys, and the number of DRX grains also increased, as expected.

Mesoalite series alloys were formed using rapid solidification powder metallurgy (RS-P/M) by hot extrusion. The addition of Mn and Zr to the basic Mesoalite alloy (Meso10) in excess led to continuous dynamic recrystallization (DRX) in the alloy during hot extrusion through a different mechanism. In order to achieve a synergistic effect, Mn and Zr additives were used simultaneously. It was found that the DRX mechanism was governed by the addition of Mn, while the Zr addition was effective in coarsening control. © 2009 TIIM, India.

The evolution of orientation distributions of γ and γ′ phases in crept Ni-base single crystal superalloys have been investigated by theoretical calculations with elastic-plastic models and by experiments. As creep deformation proceeds, the crystallographic orientation distributions for both phases are broadened as a result of the waving of the raft structure, which occurs to reduce the total mechanical energy. The broadening of the orientation distribution occurs in such a way that the 0 0 1 pole broadens isotropically while the h k 0 poles broaden preferentially along the 〈0 0 1〉 directions. Since the extent of the broadening increases almost linearly with the number of creep deformation, the measurement of the broadening by X-ray diffraction can be utilized in non-destructive methods to predict the lifetime of Ni-base superalloys. © 2008 Acta Materialia Inc.

The internal strain state of the superconducting film in a coated conductor should be clarified to understand the strain effect on the critical current (I(c)). We have developed an in situ strain measurement technique using synchrotron radiation for YBa(2)Cu(3)O(7-delta) (YBCO) coated conductor, and the internal strain of the YBCO film was directly evaluated. YBCO powder obtained from the film in the coated conductor was used as a reference of the zero-strain state. Shifts of the Bragg peaks of the (020) plane of the YBCO film were measured under applied tensile strain, and the internal strain was calculated from the change in the interplanar spacing. The residual strain of the YBCO film in this coated conductor at room temperature (RT) was directly determined to be -0.061%. The fracture strain of the YBCO film was also evaluated from the relationship between the applied strain and the internal strain of YBCO. Surface observation of the coated conductor suggests that fracture initiates in the MgO buffer layer. The irreversible strain (epsilon(irr)) determined by I(c)-strain characteristics at 77 K was compared with the result from in situ strain measurement. The validity of our technique using synchrotron radiation is discussed.

In order to clarify the mechanical properties and their influence on the critical current of DI- BSCCO tapes with and without lamination, mechanical tests and critical current measurements were performed, and the corresponding residual strain exerted on the BSCCO component was measured by a neutron diffraction technique. Also the residual strain analysis was calculated using the rule of mixtures. The measured modulus of elasticity, the second slope, and the stress corresponding to the force free strain were self- consistently explained on the basis of this analytical model. The calculated residual strain in the BSCCO component was found to be nearly identical with that determined by neutron diffraction for all DI- BSCCO tapes except for the case of the low strength insert tape. The difference between the strain corresponding to 95% I(c) retention and the force free strain was explained by the fracture strain of BSCCO filaments. An approximate expression to evaluate the residual strain in the BSCCO filaments is also presented along with a procedure for estimating the initial temperature T(0) at which the residual strain starts to accumulate during cooling after the fabrication heat treatment.

Powder metallurgy was used to supersaturate a 7000 series of aluminum alloys with 0.4, 0.8 and 1.5 mass% Sc. Al₃Sc particles were precipitated in high density upon applied heat treatment at 773 K. During subsequent hot extrusion, continuous dynamic recrystallization (DRX) occurred and fine DRX grains with a diameter of 1 &mu;m formed. The 1.5 mass%Sc alloy achieved the greatest number of DRX grains. Interestingly, the number of DRX grains observed for the 0.8 mass% Sc alloy was almost the same as that observed for the 0.4 mass% Sc alloy, although the amount of Sc added was two times larger. Continuous DRX occurs only under conditions in which the grain boundary mobility is low; therefore, the number of DRX grains is strongly related to the pinning force on the initial grain boundary exerted by Al₃Sc particles. When the pinning force was calculated from the diameter of Al₃Sc particles (measured by TEM), the number of DRX grains was determined to be proportional to the calculated pinning force. However, in the case of 0.8 and 1.5 Sc alloys, the Al₃Sc particle diameter was twice that obtained at the maximum pinning force (d_max). Thus, it is possible to promote continuous DRX by decreasing the Al₃Sc particle diameter in 0.8 and 1.5 Sc alloys. Lowering the rate of heating prior to heat treatment for degassing was found to reduce the critical nucleus size for precipitation of Al₃Sc particles as well the diameter of Al₃Sc particles. Thus, the pinning force increased in 0.8 Sc and 1.5 Sc alloys, and the number of DRX grains also increased, as expected.

The deformation behaviour of a YBa2Cu3Ox (YBCO)-coated conductor based on Ni-W substrate and its influence on the critical current were precisely investigated. From a room temperature tensile test, the change of permanent strain as a whole of the coated conductor was divided into two regions of micro- and macroscopic yielding. The precise lattice constant measurement by synchrotron radiation at Spring8 revealed that the permanent strain in the YBCO layer was characterized by two regimes related just to the two regions of yielding mentioned above. In the micro- yielding region, the permanent strain in the YBCO layer was identical with that in the metallic components, suggesting that the YBCO layer behaves elastically and any damage-like cracks were not introduced. In the macroscopic yielding region, the smaller permanent strain in the YBCO layer compared with the metallic components suggested that damage-like cracks were introduced in the YBCO layer during loading and remains under zero external load. There the invariant of total length is accommodated by the existence of damage-like cracks. The reversibility of the critical current was evaluated by loading/unloading experiments. The permanent strain ensuring the reversible limit and the corresponding applied strain were found to be 0.17% and 0.52%, respectively. This reversible limit coincided with the limit of micro-yielding. Furthermore the irreversible degradation of the critical current as a function of strain is suggested to relate to the macroscopic yielding.

Two different types of lithium lanthanum titanate (LLT)/LiCoO2 assemblies were produced by depositing the LiCoO2 cathode on the cleaved or polished surfaces of polycrystalline LLT to investigate the effects of the LLT/LiCoO2 interface structure on the electrochemical properties of the assemblies. The microstructures and electrochemical properties of the assemblies were investigated as a function of charge/discharge cycle number. Cyclic voltammetry indicates that anodic and cathodic peaks shift to higher and lower potentials, respectively, with cycle number for the assembly produced with the cleaved LLT, whereas these potential changes are negligibly small for that produced with the mechanically polished LLT. LiCoO2 is formed epitaxially on LLT with the orientation relationships (110)(LLT)// (11 (2) over bar0)(LiCoO2) and [001](LLT)//[(4) over bar 401](LiCoO2) for both assemblies, but amorphous regions are formed at the interface for the assembly produced with polished LLT. The amorphous region is considered to play an important role in the cycle stability of the assembly upon charging/discharging. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.