Ultrahigh-purity aluminum with a residual resistivity ratio (RRR) of 60000-65000 was obtained by the ultrahigh-vacuum melting method. However, it was necessary to reduce the concentration of the elements with distribution coefficient k > 1 to further improve the purity of aluminum. Therefore, we prepared a sample with reduced concentrations of k > 1 elements from an ultrahigh-purity (99.9999.) aluminum material by the zone-refining method, and evaluated its purity by electrical resistance measurement and glow discharge mass spectrometry (GDMS). In addition, the zone-refining process was simulated, and the distribution of the solute atoms after approximately 10 passes of zone. refining was predicted. Moreover, the refining conditions were investigated with the aim of achieving higher purity. In experiments, when the zone width was increased from 60 mm to 80 mm at a zone speed of 60 mm/h, the concentrations of the elements with k > 1 in the second half of the material decreased and RRR improved. When the zone speed was decreased to 30 mm/h, a marked effect was observed and RRR increased to about 85000. The distribution of the solute atoms determined from the simulation was in good agreement with the results of GDMS analysis, thus confirming the usefulness of the simulation.
Ti-6Al-4V alloy plates with thickness of 5 and 12 mm were respectively welded using hybrid welding process of 10 kW class fiber laser and pulsed metal inert gas (MIG) arc, and their hybrid weldability was investigated in the present study. For the plate with thickness of 5 mm, sound welded joints can be acquired by single-pass welding, and the joint strength is the same as that of base metal. For the plate with thickness of 12 mm, welded joints with good bead appearance can be obtained by single pass welding from both sides, and the joint strength is almost the same as that of base metal. The hardness of both weld metal and heat affected zone of these welded joints is higher than that of base metal because of the formation of martensite.
The objective of the present study was to find the orientation relationship between a recrystallized grain at its initial stage and a deformation microstructure in a non-uniformly deformed copper single crystal.A tensile strain of 25% was applied to a < 110 > copper single crystal sample in which shallow grooves were made at both side faces before the tensile test to promote non-uniform deformation. A thin disc specimen prepared from the deformed sample was annealed in a high vacuum. A scanning electron microscope (SEM)/electron backscatter diffraction (EBSD) method was used to analyze the orientations of deformed and annealed states.There are two primary slip planes of the largest Schmid factor in a face-centered-cubic metal single crystal deformed along a < 110 > direction. In the present copper single crystal sample, both right-up and right-down band-like regions are formed in which either of the primary slips was activated. The arrangement of band-like regions on the overall sample surface was almost symmetrical. Between band-like regions, there were regions of patchy slip appearance, consisting of double-slip and single-slip areas. The band-like regions were rotated so that the slip directions moved towards the tensile axis. On the other hand, the rotation of patchy regions was relatively small.In the disc specimen annealed at 833 K, a recrystallized region was formed at the boundary between band-like and patchy regions. The recrystallized region consisted of two types of recrystallized grains having a twin relationship each other. Both types of recrystallized grains had an < 111 >-rotated orientation relationship with the band-like region.
A porous Ni electrode material for electric double layer capacitors was prepared from a commercially available Ni-Al alloy through an alkali-leaching process. The mesoporosity and metallic character of porous Ni have found to contribute to the development of higher capacitance per surface areas and superior rate performance, compared with the conventional microporous activated carbons. In an ionic-liquid electrolyte, furthermore, porous Ni has showed higher capacitance than that of microporous activated carbon, despite the specific surface area of the porous Ni was two orders of magnitude lower than that of activated carbon.
Metal suicides are potential materials because of their excellent properties such as corrosion resistance, oxidation resistance and wear resistance. In this study, the authors propose a new surface treatment process to form metal silicides on metallic materials by using an atmospheric controlled IH-FPP. Atmospheric controlled IH-FPP in which Si particles are bombarded to the substrate with an elevated temperature of 1173 K can form the iron silicide. Elevated temperature of the substrate enhances transfer of Si particles on the substrate, followed by mixing and/or diffusion into the substrate. This results in the formation of iron silicides. Atmospheric controlled IH-FPP with Si-Cr mixed particles also forms the iron silicide. Atmospheric controlled IH-FPP with the mixed particles followed by annealing of 873 K for 3600 s forms chromium silicide in accordance with Fe-Cr-Si ternary phase diagram. Carbon steel materials covered with the silicide layer exhibit better corrosion resistance since SiO2 is formed on the silicide.
We investigated the crystal structure and spin conduction property of Co2FeAl0.5Si0.5 (CFAS) full-Heusler alloy thin films deposited on Si substrate. The multilayer films with different barrier layer were deposited by RF magnetron sputtering system to compare their spin conduction properties. Spin injection signals were observed only with Si sub.//Mg/MgO/CFAS structure. It is considered that the crystal structure near the interface changed by insertion of Mg layer affected the spin conduction property.
Characteristic cellular structure is formed on the ion implanted surface of GaSb, InSb and Ge, by the self-organizational behavior of point defects induced by ion irradiation. In this work, fabrication of the nano-cell structure is performed for Ge. Formation process of the cellular structure in Ge is somewhat different from those in GaSb and InSb. In Ge, the irradiated layer is amorphized prior to the cell formation while its amorphization occurs after the cell formation in GaSb and InSb. Two kinds of nano-cell fabrication were performed and the nano-cell developments in both fabrications were compared. One is initially to form the ordered void lattice and to develop it to the cell lattice. In the other method, initially the surface layer of Ge wafer was amorphized by ordinary ion irradiation and then, nano-cell structure was formed on it by the same process. These processes were performed using 30 keV Ga+ in a focused ion beam apparatus at room temperature. The results showed that secondary void formation was remarkable in the initially amorphized Ge. Probably the high mobility of the vacancy-type defects in amorphous Ge might have accelerated the formation of secondary voids between the initial voids.
Attempts have been made to clarify polarization behavior of aluminum alloy 1050 in 30 mass%nitric acid solution which is in deaerated and stagnant solution condition. It is shown that the dissolution of aluminum behaves in the fast and like a general dissolution manner when the 1050 specimen was dipped into the solution. It was found that the corrosion rate of 0.25 mA.cm(-2) obtained from the corrosion weight loss roughly corresponded to the current density of 0.29 mA.cm(-2) on the assumption that the dissolution of aluminum in the nitric solution is categorized to electrochemical reaction of the fast system.
GaSe crystal has been expected as one of the promising nonlinear optical crystals for highly efficient Terahertz (THz) wave generation. However there are several reasons why it is difficult to grow the bulk crystals with fewer defects. To overcome the obstacles, temperature difference method under controlled vapor pressure (TDM-CVP) is applied for crystal growth. According to this method, crystals with stoichiometric composition can be grown at the constant growth temperature under the application of controlled Se vapor pressure and lower temperature growth enables the reduction of point defect concentration. In this article, surface morphology is observed by optical microscope. To identify polytypes, backscattered Raman spectra were measured. X-ray diffraction confirmed the polytypes and single crystalline phase. Infrared (lambda = 1 mu m) and Terahertz wave (1 similar to 3 THz) transmittance measurements were performed to calculate the absorption coefficient in these wavelength regions. From these results, it is shown that the grown crystals have shown an epsilon-type single phase and the absorption coefficients of grown crystals have been improved according to the increase of applied Se vapor pressure during crystal growth.
An attempt is made to enhance the strength of a Cu-1.4 mass%Ni-0.25 mass%P-0.1 mass%Zr alloy by forming ultrafine grain structure with a high dislocation density using cryo-rolling. Previously the influence of accumulative roll-bonding (ARB) and aging on the tensile properties of the alloy has been examined. The grain sizes of the alloy pre-aged at 450 degrees C and ARB-processed in 7 cycles (P-ARB) and the alloy pre-aged at 450 degrees C and cryo-rolled to a 90% reduction (P-90CR) are refined to 0.4 mu m and 0.6 mu m, respectively. The P-90CR alloy aged at 350 degrees C that has a higher 0.2% proof stress of 790 MPa and a higher ultimate tensile strength of 840 MPa than the P-ARB alloy aged at 400 degrees C is successfully produced. The higher strength of the aged P-90CR alloy is caused by the higher dislocation density in the alloy.
The role of chromium contents on atmospheric corrosion of steel in the environment containing chloride ion was studied by exposure test and electrochemical experiments. It was found that corrosion resistance of 1% chromium steel was lower than that of the steel without chromium in the environment whose concentration of chloride ion was very high by the exposure test. On the other hand, containing chromium increases corrosion resistance in the environment with low chloride concentration. In neutral chloride solution corrosion rate of 1% chromium steel was lower than that of the steel without chromium, but was high in low pH chloride solution. The pH dependence of corrosion resistance of 1% chromium steel corresponded with the corrosion resistance by the exposure test.
Adhesion strengths and microstructures of TiN coatings on white layer composed of epsilon nitride (Fe2-3N) were examined. In the present study a hot work tool steel, SKD61, was used for a substrate. The substrates were coated with TiN by physical vapor deposition (PVD). Specimens were prepared with changing the conditions for polishing the surface of the substrate, and conditions for nitriding before PVD treatment. Peeling of the coated film occurred on un-polished specimen surface. Other specimens can be coated with TiN film without peeling. The microstructures, phase identifications and adhesion strengths were investigated by scanning electron microscopy (REM), X-ray diffraction (XRD), scratch tester and Rockwell adhesion tester, respectively. The black layer formed between the TiN film and white layer was observed by SEM, which generally deteriorates adhesion strength. However the scratch tests showed that the adhesion strengths of the specimens with black layer were higher than those on the specimen without the black layer. The black layer would not always decrease the adhesion strength.
Light couples with free electrons in metals on the nanometer scale, exhibiting a localization and enhancement effect known as Localized Surface Plasmon Resonance (LSPR). LSPR has been exploited in many scientific and industrial fields, such as sensors, optical waveguides, high-sensitivity optical detection, high-resolution microscopy, etc. In spite of the versatility of LSPR, the applicable wavelength range of LSPR has been limited to the visible and infrared because the host materials for conventional LSPR, mainly gold and silver, do not exhibit metallic behavior at ultraviolet (UV) wavelengths. We used aluminum as a new candidate LSPR material at UV wavelengths and optimized its structure for better coupling with light from UV to deep-UV. Aluminum nanostructures were fabricated by a nanoparticle lithography method. In this report, we especially focus on the relationship between the LSPR wavelength and the height of the nanostructures. By increasing the height of the nanostructures, blue shifts of the LSPR wavelength were observed. With finer tuning of the nanostructures, an LSPR wavelength of 244 nm was successfully achieved, which is the shortest reported LSPR wavelength.
In this report, the surface properties and microstructure of chromium-molybdenum steel samples prepared by two-stage gas nitriding with a short isothermal time in stage one are compared with those prepared by one-stage gas nitriding. Two-stage gas nitriding was performed with a short isothermal time in stage one followed by a second stage with lowered NH3 partial pressure. One-stage gas nitriding under conventional conditions was compared with it. The variation in microstructure, compound layer thickness (CL), nitrided case depth (d) and surface hardness (HVs) was clarified. In one-stage gas nitriding, the CL, d and HVs increase with increasing isothermal time. In contrast, in two-stage gas nitriding, the CL decreases with isothermal time in the second stage, and surface microstructure observations show partial dissipation of the compound layer. The d and HVs increase at a lower rate of increase than the values observed in one-stage gas nitriding. However, when the second stage temperature was increased in two-stage gas nitriding, the CL decreases and partially dissipates in a shorter time, and d increases at a faster rate than those observed for one-stage gas nitriding. The HVs exhibits a faster rate of increase in the second stage when a higher temperature was used, but the rate is lower than that observed in one-stage gas nitriding. These experimental results are briefly discussed in relation to the microstructure.
We successfully controlled thermal expansion of metal matrix composites (MMCs) containing antiperovskite manganese nitrides with giant negative thermal expansion (NTE). The NTE of the manganese nitrides is greater than -30 ppm/K in alpha (coefficient of linear thermal expansion), which is several or ten times as large as that of conventional NTE materials. Powder metallurgy using pulsed electric current sintering enables us to reduce temperatures and times for fabrication of MMCs. Consequently, chemical reactions between a metal matrix (Al, Ti, or Cu) and the nitride filler can be controlled and high-melting-point metals can be used as a matrix. Thermal expansion of these MMCs is adjustable across a wide range of a values, even negative ones, with high reproducibility.
Thin films of Mn3CuN were prepared by a reactive sputtering method to evaluate the magnetic anisotropy. A stoichiometric Mn3CuN undergoes a ferromagnetic and a cubic-to-tetragonal structural transition simultaneously at 143 K, and displays large magnetostriction below this temperature. The origin of magnetostriction is believed to be ferromagnetic shape-memory effect, a phenomenon still not well understood as there are not many compounds known to belong to this class of materials. The magnetic anisotropy is one of the most important parameters for understanding ferromagnetic shape-memory effect. A (111) oriented thin film was obtained on an yttria-stabilized zirconia (YSZ) substrate with a T-C similar to bulk samples. On the other hand, (100) oriented thin films were obtained on MgO substrates, although T-C was higher than bulk samples, which may be attributed to nitrogen deficiency. Magnetic hysteresis measurements revealed a rather large magnetic anisotropy despite the small crystallographic anisotropy. This confirms that the magnetic shear stress is large, as expected for a ferromagnetic shape-memory material.
We investigated the structural property of MgO thin films on Si(001) substrates by molecular beam epitaxy in order to obtain (001)-oriented MgO barrier for high spin polarization on Si substrate. The MgO layer deposited at 200 degrees C and deposition rate of 0.30 nm/min grew with (001)-orientation on Si(001) substrate. The (001)-orientation and crystallization of the MgO layer were enhanced by insertion of Mg layer into interface between Si substrate and MgO layer. It is considered that the Mg layer prevented oxidation of Si at interface and functioned as buffer layer.
Recently, with increase of demand of flat panel displays, it is required to develop a transparent electroconductive film without using a rare metal. In this study, we carried out the formation of a transparent electroconductive film derived from fullerene. C-60 was evaporated on a quartz substrate, and then we irradiate ultraviolet light on the films for 72 or 120 h, respectively. After the irradiation, nickel thin film formed on the C-60 film, and then heat. treatment was carried out in an electric furnace with a vacuum of 10(-4) Pa. Raman spectra showed that C-60 films were polymerized by ultraviolet light irradiation. Although polymerized C-60 films tended to become amorphous structure by heat. treatment of 873 K for 10 min, the films covered with nickel as a catalyst tended to be graphitized by the same treatment. The obtained films indicated transparency, and the minimum electrical resistivity was 10(-3) Omega cm.
Hybrid welding process of 10 kW class fiber laser and pulsed metal inert gas (MIG) arc was applied to pure titanium plates with thickness of 12 mm, and the hybrid weldability of the pure titanium thick plates was investigated in the present study. It is found that sound welded joints with good bead appearance and high tensile strength are available by single pass welding from both sides using the optimized welding parameters. The hardness of both weld metal and heat affected zone is slightly higher than that of base metal. Laser focal position is an important parameter, and welding spatter and defects can be remarkably reduced or prevented by focusing laser beam on back side of titanium plate.
Anodizing of Ti specimens were performed in concentrated H3PO4 aqueous solutions with a purpose to incorporate a large amount of phosphate ion into anodized coatings, and their osteoconductivity was evaluated in in vivo test. Ti specimens were anodized in 0.1 similar to 11 M H3PO4 aqueous solutions up to 200 V at a rate of 0.1 V s(-1). Anodized coatings were evaluated with SEM, TEM, XRD, XPS, and laser microscope. Anodized specimens were implanted in rats' tibia for 14 d, and then extracted.When anodized in concentrated (>= 2 M) H3PO4 aqueous solutions under spark discharge, crystallized anatase transformed to amorphous anatase by containing a large amount of PO43- in crystal lattice of TiO2. The amorphous anatase coatings had better osteoconductivity than the crystallized anatase coatings. It is not exactly clear what was the intrinsic factor for the high osteoconductivity, but the crystallinity of anatase and/or PO43- in the film is considered to be responsible for the difference in bone-forming ability of TiO2 films.
