Ichihito Narita

To improve high-velocity oxy-fuel (HVOF) sprays and reduce CO2 emission, an iron-based metallic glass coating produced using HVOF apparatus with hydrogen gas without a fusing process was investigated. Crystallization phenomena of the metallic glass were also evaluated at elevated temperatures. The Fe-Cr-Mo-based alloy was sprayed on a mild steel substrate using a specific gun with hydrogen gas, and metallographic observation revealed that the alloy was successfully coated on the substrate even when using the hydrogen gas. In addition, the corrosion resistance was investigated by performing a combined cyclic corrosion test. Significant corrosion was prevented until 1578 h by a sealing treatment even without a fusing process. The metallic glass coating was heat-treated at 500 to 800 degrees C, and then X-ray diffraction analysis was performed. In the X-ray diffraction profile, the intensity of the observed broad peak from the metallic glass decreased with increasing temperature and holding time, while sharp peaks from the crystal phase appeared. The crystallization process was successfully predicted from the Johnson-Mehl-Avrami equation regarding nucleation and growth of crystal grains from the glass phase. Although the Vickers hardness of the as-sprayed specimen was 778 HV, it was improved to 1029 HV at approximately 80% crystallinity; thus, the nanoscale crystals enhanced the hardness of the metallic glass.

The effect of nitrogen addition on the microstructure formation and hardness during solidification and heat treatment was investigated and the possibility of nitrogen as an alloying element was discussed in terms of alloy chemistry for high-carbon high-speed tool steel type cast alloys. Nitrogen with a concentration from 48 ppm to 1542 ppm was successfully introduced by mixing Cr2N into a molten alloy. Analysis of the diffraction pattern revealed that the primary V2CN carbonitride crystallized upon the addition of nitrogen, whereas eutectic carbides mainly formed in N-free specimens. The chemical composition of the carbonitride is also affected by the addition of nitrogen. With increasing quenching temperature, the Vickers hardness gradually increased to a peak and then decreased. Nitrogen addition helps to increase the hardness similarly to carbon. A N-containing specimen also exhibited superior secondary hardening after tempering. It is known that a large amount of residual austenite finally transforms to a hard martensite phase after tempering. According to the results of XRD analysis, nitrogen addition increases the volume fraction of retained austenite in the matrix at a higher holding temperature. Furthermore, the precipitation of nanosize carbonitride was observed around the primary V2CN carbonitride in addition to the standard precipitation. Therefore, this carbonitride precipitation may induce the superior secondary hardening and ultimately increase the macrohardness of N-containing specimens.

Plastic deformation under fracture surface in non-combustible magnesium alloy was investigated using electron backscatter diffraction analysis after tensile tests of specimens having a fatigue pre-crack or shrinkage porosity, so that it revealed that the fracture mode of shrinkage porosity of the magnesium alloy can be treated as a crack. (C) 2015 Elsevier B.V. All rights reserved.

Influence of nitrogen addition as one of the alloying element on the formation of solidification structure and the improvement of hardness after thermal treatments was investigated for high-speed steel type alloys (Fe-1.7 similar to 2.3%C-5%Cr-5%Mo-5%V). Nitrogen content was successively varied from 48 ppm to 1542 ppm by the mixing of Cr2N into the molten alloy. Analysis of diffraction pattern reveals the formation of M2CN carbonitride at N-containing specimen, whereas the eutectic MC carbides containing mainly V solidifies at N-free specimen. The macrohardness of the quenched specimens gradually increases with increasing quenching temperature. Nitrogen addition helps to improve the hardness as carbon does. Macrohardness of the quenched specimen depends on both the amount and hardness of martensite matrix. The specimen, which contains high volume fraction of retained austenite, shows the superior secondary hardening after the optimized twice tempering. Furthermore, the hardening of specimens is enhanced by nitrogen addition. The precipitation of nano-size carbonitride is observed around primary micro-size carbonitride, which indicated that M2CN carbonitride diffuses nitrogen, causes carbonitride precipitation, and finally develops macrohardness at N-containing specimen.

The wear resistance without lubrication were studied experimentally for iron nitrides compound layer and high nitrogen martensite phase formed in the material surface by using industrial pure iron treated by nitriding and quenching followed by aging process. As a result both the compound layer where the generation of pores was suppressed by lowering the nitriding temperature and the high nitrogen martensite phase showed the same trend of high wear resistance. However, the pores in the compound layer decreased the wear resistance due to the acceleration of crack propagation.

Compared to conventional thermal spray coating, cold spray processing typically employs finer, smaller-diameter metal powders. Furthermore, cold-sprayed particles exhibit fewer surface oxides than thermally sprayed particles due to the absence of particle melting during spraying. For these reasons, it is important to consider the potential for dust explosions or fires during cold spray processing, for both industrial and R&D applications. This work examined the dust explosion characteristics of metal powders typically used in cold spray coating, for the purpose of preventing dust explosions and fires and thus protecting the health and safety of workers and guarding against property damage. In order to safely make use of the new cold spray technology in industrial settings, it is necessary to manage the risks based on an appropriate assessment of the hazards. However, there have been few research reports focused on such risk management. Therefore, in this study, the dust explosion characteristics of aluminum, titanium, zinc, carbonyl iron, and eutectoid steel containing chromium at 4 wt.% (4 wt.% Cr-eutectoid steel) powders were evaluated according to the standard protocols JIS Z 8818, IEC61241-2-3(1994-09) section 3, and JIS Z 8817. This paper reports our results concerning the dust explosion properties of the above-mentioned metal powders.

<p>  The formation prcess of cast structure and ferritization prcess was investigated in spheroidal graphite cast iron containing 1.7～1.9%C, 1.4/2.0%si, and 0.2～0.3%Mn. Thermal analysis and quenching experiment revealed that the primary γ started crystallization at around 1364℃ and developed dendritically to about 88% of the specimen. Eutectic graphite crystallized in the residual liquid among dendrites and the area fraction of graphite (F_g) was about 0.4% just after eutectic solidification. F_g increased to 3.5% by the precipitation of secondary graphite during cooling to eutectoid temperature. The behaviors of Si and Mn during solidification were also clarified based on the partition coefficients of these elements to primary γ. Ferritization heat treatment was carried out on as-cast specimens with pearlite matrix by heating them at 740℃, 720℃, and 700℃ for 1h to 10h. The changes in fraction of ferrite during ferritization were examined using a series of specimens quenched during heat treatment. The higher the heating temperature, the higher was the ferritization rate. When heated at 740℃ and 720℃ for 10h, the fraction of ferrite exceeded 90%. Ferritization was retarded in the Mn-rich pearlite area where the melt finally solidified. F_g increased to 7.4% after full ferritization. The number and size of graphite nodules also increased with the precipitation of secondary graphite and ferritization treatment.</p>

Cu nanoparticles doped with small amounts of noble metals were synthesized by ultrasonication. The noble metals selected were Pd, Pt, Ru, Rh and Ir. Mean particle size was most reduced for Cu nanoparticles doped with Pd, with Cu-Pd nanoparticles of approximately 50 urn in diameter being obtained. X-ray absorption, near-edge spectroscopy and extended X-ray absorption were used to conduct fine structure analysis, and these techniques confirmed that Cu-Pd nanoparticles possessed Cu-Pd bonds. High-angle annular dark-field scanning transmission electron microscopy and energy dispersive X-ray spectrometer mapping were used to show that Cu-Pd nanoparticles were dispersed as Pd clusters inside Cu nanoparticles. It was supposed that the surfaces of Cu-Pd nanoparticles were Cu-rich, and Pd clusters were dispersed inside these particles. It is proposed that heterogeneous nucleation of Cu onto Pd nuclei resulted when nucleation of Pd occurred.

The fractal dimension analysis was applied to the evaluation of primary dendrite and several eutectic structure morphologies in the high speed steel type cast iron for rolls which have been produced by the centrifugal cast technique. Initially, the affine parameter of the dendrite morphology of transparent organic alloy was evaluated based on the self-affine fractal theory. Primary gamma dendrite and several eutectic structures crystallize in the high carbon high alloying element roll specimen. The microstructural morphology of sliced gamma dendrite was analyzed by the self-similar fractal technique. The fractal dimension of each part of two-dimensionally-sliced dendrite varies from 1.05 to 1.13, and that of aggregation of dendrite's parts increases to 1.30. The fractal dimension of the primary dendrite among eutectic phases varies depending on the analysis area, and decreases with in decreasing of volume fraction of primary dendrite. In the specimen contained relatively high alloying elements, the round shape of sliced dendrite and the reduction of area fraction of primary dendrite cause to the difficulty of analyses using secondary dendrite arm spacing and fractal dimension of primary dendrite. Therefore, the fractal dimension of primary y and gamma+MC eutectic structure were evaluated. The fractal dimension analysis reveals that the morphology of dendrite and eutectic structure in segregated region slightly increases in comparison with the normal microstructure, and decreasing with the cooling velocity. Lower equilibrium partition coefficient of alloying elements and centrifugal force could cause the micro segregation of outer dendrites in roll specimen and complicated primary dendrite and gamma+MC eutectic structure.

The influence of Ta addition on the solidification microstructure, solute distribution and hardness after quenching and tempering treatments was investigated for a high-carbon high-speed steel type cast alloy (Fe-1.9%C-0.5%Mn-4.9%Cr-5.0%Mo-5.0-7.2%V-0.4-1.4%Ta). The compositions of V and Ta were systematically changed to improve the distribution of hard MC carbides in the hypoeutectic range. Electron probe micro-analysis (EPMA) and X-ray diffraction (XRD) identified an oval microstructure as MC carbides containing mainly V and Ta, and a lamellar structure as M2C carbides containing mainly Fe and Mo among the austenite (gamma) dendrites. Redistribution of alloying elements during the solidification sequence of primary gamma, gamma + MC and M2C eutectic structure could be calculated from the Scheil-Gulliver equation and the initial composition. The macro-hardness of the quenched specimens gradually increased with increasing quenching temperature until a maximum was reached. This indicates that macro-hardness of the quenched specimens depends on both the amount and hardness of martensite matrix. All specimens which were tempered at 723-873 K showed secondary hardening. Furthermore, hardening of the specimens was most apparent when specimens containing large amounts of retained gamma were tempered at an optimum temperature. For example, the hardness of specimens with added Ta increased to around 900 HV after tempering at 823 K. These results suggest that the macro-hardness of tempered specimens is governed by the maximum amount of carbon in the gamma matrix at quenching temperature, the degree of transformation from retained gamma to martensite, and the precipitation and distribution of secondary carbides. [doi:10.2320/matertrans.F-M2011836]

The influence of V and Ta addition on solidification structure and hardness after quenching and tempering treatments was investigated for high speed steel type alloy (Fe- 1.9%C- 0.5%Mn- 4.9%Cr- 5.0%Mo- 5.0～7.2%V- 0.4～1.4%Ta). The compositions of V and Ta were systematically changed for the purpose of distributing hard MC carbides in the hypoeutectic range. EMPA and XRD analysis identified the lamellar structure as M₂C carbide containing mainly Fe and Mo, and the oval microstructure as MC carbide containing mainly V and Ta among austenite dendrite. The macrohardness of the quenched specimen gradually increased with solution treatment and increasing quenching temperature, and then decreased later. This indicates that the macrohardness of the quenched specimen depends on both the amount and hardness of the martensite matrix. All specimens which were tempered at 723K to 873K showed secondary hardening. Furthermore, hardening of the specimen was conspicuous when specimens containing large amounts of residual austenite were tempered at the optimum temperature, as seen with the increase in the hardening of Ta-contained specimen to around 900HV at the tempering temperature of 823K. These results suggest that the macrohardness of tempered specimens is governed by the amount of carbon in the austenite at quenching temperature, the degree of transformation from residual austenite to martensite, and the precipitation of secondary carbides.

Crystalline CoSe2, with the pyrite structure, supported on carbon powder has been synthesized by a wet chemical method. Samples were characterized by a range of techniques, including X-ray diffraction and transmission electron microscopy for structure, and X-ray photoelectron spectroscopy and scanning Auger microscopy (SAM) for surface composition. Electrochemical dynamic polarization measurements were carried out using the CoSe2-decorated carbon powder as part of a rotating disk electrode to assess its catalytic activity for the oxygen reduction reaction (ORR), and the surface analysis methods were used to identify changes in surface composition. Comparisons of ORR activities were made with CoSe and Pt powder catalysts prepared by comparable methods. Stationary cyclic voltammetry was used to assess the stability of the as-prepared CoSe2 powder catalyst in an acidic electrochemical environment. A preliminary investigation was also made of an electrochemical modification treatment for CoSe2. The surface formed was characterized by the rotating ring-disk electrode technique and by micro-Raman spectroscopy, backscattered-electron imaging and SAM. The latter combination of characterization techniques helped to relate an observed passivation to a thin layer of Se formed by the modification treatment. (C) 2010 Elsevier B.V. All rights reserved.

Co nanocrystallites were encapsulated in boron nitride closed shells using a one-step simple chemical method, the decomposition of amine complex in the presence of KBH4 and nitrogen atmosphere at 1000 degrees C. Magnetic measurements determined a value of the saturation magnetization of 72 emu/g and a weak ferromagnetic behavior, with a coercivity of 82 Oe. Synchrotron X-ray diffraction combined with Rietveld analysis demonstrated that type sigma(II), residual stresses of up to similar to 2 GPa were present in the encapsulated Co nanocrystallites. We observed an interesting decrease. in Bragg reflection half-width with increasing order of reflection, observed previously only in another fcc-metal nanosized material, a similar to 5 nm polycrystalline Ni. (C) 2009 Elsevier B.V. All rights reserved.

Applications of various noble metal nanoparticles were investigated for newly, ecology and economy home electric appliances (microwave, ultrasonic) used system. Noble metal oxides have merit in metal particles fabrication, as one of these example example, there are decomposed by only heating in air. That is, noble metal oxide don't use strong reduction atmosphere. This reduction is ecologically clean, because many noble metal oxides are not toxic and during decomposition O-2 is evolved. We have reduced noble metal oxides by microwave and ultrasound, and tried to fabricate noble metal nanoparticles, and investigated various processing. These energy are widely used by home electric appliances. By choosing suitable process and conditions, it is reasonable to expect that home electric appliances ecology and economy fabrications can be extended to obtain simply various noble metal nanoparticles related materials.

Boron nitride (BN) nanotubes, nanohorns, nanocoils were synthesized by annealing Fe4N and B powders at 1000 degrees C in nitrogen gas atmosphere. Especially, Fe-filled BN nanotubes, bamboo-type and cup-stacked type BN nanotubes were produced. Formation mechanism and nanostructures were investigated by high-resolution electron microscopy, high-angle annular dark-field scanning transmission electron microscopy, electron diffraction, energy dispersive X-ray spectroscopy and molecular mechanics calculations.

Iron (Fe) nanoparticles coated with boron nitride (BN) nanomaterials were synthesized by using Fe4N and B powders as raw materials. The Fe4N was reduced to alpha-Fe during annealing at 1000 degrees C for several hours with flowing 100 sccm N-2 gas. The reaction was predicted by Ellingham diagram. The atomic structure and magnetic properties were investigated by high-resolution electron microscopy and vibrating sample magnetometer system.

Boron nitride (BN) nanocapsules encaging Fe or Co nanoparticles were synthesized by using Fe4N/B or Co(NH3)(6)CI3/KBH4 powders as raw materials, respectively. The Fe4N was reduced to alpha-Fe during annealing at 1000 degrees C for several hours with flowing 100 sccm N-2 gas, and the reaction was predicted by Ellingham diagram. Co nanoparticles with BN layers were also produced by annealing the powders at 1000 degrees C in nitrogen atmosphere. These BN nanocapsules with magnetic nanoparticles exhibited soft magnetic characteristics and good oxidation resistance. (c) 2006 Elsevier Ltd. All rights reserved.

Bamboo-type boron nitride (BN) nanotubes with cup-stacked structures were produced by annealing of Fe4N and boron particles at 1000 degrees C for 5 h in nitrogen atmosphere. The iron nitride particles were reduced to alpha-Fe. Atomic structure models and the formation mechanism were proposed from the results of high-resolution electron microscopy (HREM), image simulations and molecular mechanics calculations. The nanotube structures would be stabilized by stacking of BN cup-layers. (c) 2005 Elsevier Ltd. All rights reserved.

Various carbon nanocage fullerene materials (clusters, metallofullerenes, onions, nanotubes, nanohorns and nanocapsules) were synthesized by electron-beam irradiation, chemical reaction, hybrid arc discharge, and self-organization. Atomic structures and structural stability of these materials were investigated by high-resolution electron microscopy, molecular dynamics, and molecular orbital calculations. Photoluminescence as well as magnetic and electronic properties of these fullerene materials were also investigated. The present work indicates that the new carbon nanocage fullerene materials with various atomic structures and properties can be produced by various synthesis methods, and a guideline for designing the carbon fullerene materials is summarized.

Cobalt (Co) nanocapsules coated with boron nitride (BN) layers were synthesized by annealing of ammine complex. KBH4 and [Co(NH3)(6)]Cl-3 were used as starting materials, and annealed these powders at 500-1000 degrees C with flowing nitrogen gas. Formation of fcc-Co nanocapsules coated with BN layers was observed from X-ray diffraction patterns and high-resolution electron microscopy. Particle size of fcc-Co prepared at 1000 degrees C with flowing 100 sccm N-2 gas was approximately 40 nm, and the values of saturation magnetization and coercivity were 74.5 emu/g and 88 Oe, respectively. Good oxidation- and wear-resistances were obtained by encapsulating Co nanoparticles with BN layers. (c) 2006 Elsevier Ltd. All rights reserved.

Boron nitride (BN) cages were synthesized by annealing Fe4N and B powders at 1000 degrees C for 1 h in nitrogen gas atmosphere. To remove non-BN clusters such as metal catalyst particles, purification of BN cages was carried out by acid treatment and centrifugation. Large amounts of BN cages were observed by high-resolution electron microscopy and energy-dispersive X-ray spectroscopy, and the cages showed photoluminescence peak at similar to 3.8 eV. (c) 2004 Elsevier B.V. All rights reserved.

Boron nitride (BN) nanocage clusters of B12N12 were synthesized, and detected by laser desorption time-of-flight mass spectrometry. The B12N12 clusters consisted of 4- and 6-membered BN rings satisfying the isolated tetragonal rule, which was optimized by molecular orbital calculations. The electronic structure showed a bandgap energy of 5.1 eV, which is a little smaller than that of B36N36 cluster. (C) 2004 Elsevier Ltd. All rights reserved.

Boron nitride (BN) nanohorns were synthesized by an arc-melting method, and atomic structure models for BN nanohorns with tetragonal BN rings were proposed from high-resolution electron microscopy. Stability and electronic structures of the BN nanohorns were investigated by molecular orbital/mechanics calculations. The calculation showed that multiwalled BN nanohoms would be stabilized by stacking of BN nanohorns. The energy gap of BN nanohorn was calculated to be 0.8 eV, which is lower compared to those of BN clusters and nanotubes. (C) 2004 Elsevier Ltd. All rights reserved.

Boron nitride (BN) nanocage clusters (BnNn: n = 24-60) were synthesized by arc-melting method and detected by mass spectrometry and high-resolution electron microscopy. Endohedral boron nitride clusters Y@BnNn would also be formed. The BN clusters consist of 4-, 6- and 8-membered BN rings satisfying the isolated tetragonal rule, which was optimized by molecular orbital calculations. The electronic structure showed that bandgap energies increase with increase of cluster size. (C) 2004 Elsevier B.V. All rights reserved.

The carbon onion with a tetrahedral structure was produced by electron-beam irradiation on amorphous carbon synthesized from polyvinyl alcohol. Atomic structure analysis and structural optimization of the onion were carried out by high-resolution electron microscopy, image simulation, molecular mechanics and molecular orbital calculations. A structure model of C-84@C-276 was proposed at the center of the tetrahedral carbon onion. (C) 2003 Elsevier B.V. All rights reserved.

Boron nitride (BN) nanotubes with zigzag- and armchair-type structures were investigated by high-resolution electron microscopy, image processing, image simulation and molecular mechanics calculations. Chiralities of BN nanotubes were directly determined from high-resolution images, and structure models were proposed. Total energies of BN nanotubes with a zigzag-type structure were lower than those of armchair-type structure, and these results agreed well with the experimental data of disordered tube structure. (C) 2003 Elsevier B.V. All rights reserved.

Hexagonal networks of boron nitride (BN) nanotubes were investigated by high-resolution electron microscopy (HREM) and image simulation. From HREM images, lattice planes of {002} and hexagonal rings of a BN nanotube were confirmed. Asymmetrical layer arrangements were found, and a structure model for double-walled BN nanotube with an armchair-type structure has been proposed. (C) 2003 Elsevier Ltd. All rights reserved.

BN nanotubes, nanocages and nanocapsules were synthesized from LaB6 and Pd with boron powder by using an arc melting method. Thermogravimetry/differential thermogravimetric analysis of BN nanomaterials produced from LaB6 and Pd/boron powder showed possibility of hydrogen storage of 1-3 wt%. Conditions of H-2 gas storage in B36N36 cluster, which was considered as a cap structure of B99N99 nanotube, were predicted by first principle single point energy calculations. H-2 molecules would be introduced from hexagonal rings of the cage structure. BN fullerene materials would store H-2 molecule easier than carbon fullerene materials, and its stability for high temperature would be good. (C) 2003 Elsevier Ltd. All rights reserved.

Boron nitride (BN) nanotubes were investigated by high-resolution electron microscopy (HREM) and image processing. From the HREM image, a BN nanotube encapsulating yttrium nanowire was confirmed by comparing calculated diffraction and a nanostructure model. The present work indicated that yttrium elements could be confined in BN nanotube with large energy gap. (C) 2003 Elsevier Ltd. All rights reserved.

High-resolution electron microscopy, mass spectrometry and molecular mechanics/orbital calculations of the boron nitride-based clusters showed the formation of B36N36 and Y@B36N36. Image simulations of these clusters confirmed the proposed structure model. (C) 2003 Elsevier Ltd. All rights reserved.