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Volume 65, Issue 11
Displaying 1-11 of 11 articles from this issue
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Masato Yamashita, Akira Maeda, Hitoshi Uchida, Takayuki Kamimura, Hide ...2001 Volume 65 Issue 11 Pages 967-971
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSCrystalline rust compositions and weathering properties of steels exposed in nation-wide atmospheres for 17 years have been investigated using X-ray diffraction spectroscopy, with considering the amount of air-borne salt particles. The corrosion loss of the steels, which reflects the corrosion processes during long-term exposure, was related to the rust compositions; especially the corrosion loss was almost proportional to the relative amount of β-FeOOH in the rust layer formed on steels. It can be said that increase in the amount of protective goethite, which is a rust constituent with α-FeOOH structure, and therefore decrease in that of β-FeOOH causes increase in the protective ability of the rust layer. It becomes possible to relate mass ratio between goethite and other active rust constituents including β-FeOOH to the protective performance of the rust layer.View full abstractDownload PDF (390K) -
Ken’ichi Miura, Itsuo Ishigami2001 Volume 65 Issue 11 Pages 972-980
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSResidual stress produced in titanium nitride films deposited onto substrates of high speed steel, SKH51, was studied by using sin2ψ method as a function of process parameters: deposition temperature, deposition time, electron beam current, substrate bias voltage, distance from an evaporation source to a substrate, tilt angle of a substrate axis, total gas pressure, and gas mixture ratio [N2]⁄[Ar+N2]. Measurements showed that compressive stress occurred in the films except one deposited without any applied bias voltage to a substrate. Applying a little bias voltage to a substrate brought about a rapid increase in the compressive stress. Higher deposition temperature and lower deposition rate reduced the compressive stress. A decrease in total gas pressure increased the compressive stress. These results suggest that kinetic energy of incident ions on a substrate affects the generation of the compressive stress. In-plane lattice parameter increased with an increase in compressive stress; this variation was in good agreement with the distance calculated on the basis of the Poisson ratio effect. Hardness of the films increased with an increase in the compressive stress. Grain size of the films was determined by the method based on “Williamson-Hall plot” which can exclude the contribution of micro strain from line broadening of X-ray diffraction. Hall-Petch relationship is established between the grain size and the hardness. It seems that mobility of adatoms is closely related to the magnitude of the residual compressive stress.View full abstractDownload PDF (487K) -
Ken’ichi Miura, Itsuo Ishigami2001 Volume 65 Issue 11 Pages 981-986
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSEffects of factors on residual compressive stress produced in titanium nitride films were investigated. The factors examined were impurity oxygen concentration, ion bombardment and substrate temperature. The films were deposited onto substrates of high speed steel, SKH51. Measurements by particle induced X-ray emission method confirmed the absence of argon in the films. An increase in oxygen concentration gave rise to higher compressive stress in the film. The compressive stress increased with decreasing substrate temperature. The compressive stress produced in the films deposited onto insulated substrate was much less than that onto non-insulated substrate, and the stress in the films onto insulated substrate also increased with decreasing substrate temperature. Attempts have been made to measure the variation in the stress toward the film-substrate interface by a succession of measurements of the stress and dissolution of the film in a boiling hydrogen peroxide solution. Result indicated that the stress in outer layer of the film was smaller than that in inner layer. This variation corresponds the rise of substrate temperature on depositing. An increase in oxygen concentration brought about the grain size reduction. The grain size decreased remarkably by applying a little bias voltage. The grain size in outer layer of the film was larger than that in inner layer owing to the rise of substrate temperature during deposition. These factors affect mobility of adatoms; the grain size is therefore a measure of the mobility. It seems that residual compressive stress is affected by the mobility.View full abstractDownload PDF (664K) -
Yasuhira Ohta, Akio Kagawa, Masayuki Mizumoto, Taketoshi Chifu2001 Volume 65 Issue 11 Pages 987-992
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSA modified coupled-diffusion method using iron intermediate layer has been investigated for the surface modification of steels. The process consists of two stage heat-treatments. On the first stage heat-treatment for the diffusion of carbide forming element, Nb, solute distribution profile showed bending points at the concentrations where intermetallic phases, FeNb and Fe2Nb, were formed. The distribution of carbide volume fraction after carbon diffusion on the second stage heat-treatment was dependent upon the concentration profile of niobium on the first stage heat-treatment. The specimen subjected to the two-stage heat-treatment had a modified surface layer consisting of NbC layer about 15 μm thick on the surface and the carbide volume fraction decreased toward the steel substrate. It was demonstrated that the specimen having such a microstructure showed a promising effect to suppress a crack formation in the carbide layer.View full abstractDownload PDF (890K) -
Shintaro Ishiyama, Yasushi Muto2001 Volume 65 Issue 11 Pages 993-1001
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSA turbine disk model has been trially fabricated and tested which uses C/C composite material to lighten the turbo machinery rotor for HTGR-GT system. In present study, the design and production of the most large-scale 1/5 reduction turbine disk model (the outside diameter×inside diameter×thickness=φ400 mm×φ300 mm×t30 mm) in the world which enforced three-dimensional structure to the hoop, radius and thickness directions using the high strength carbon fiber has been implemented. As a result of spin tests, following conclusions were obtained.
(1) To establish an enforced structure to endure the amount of hoop tensile stress which occurs in spin test in case of design of the 1/5 disk model, 40 vol% carbon fiber containing quantity to the hoop direction in the preform was chosen. Moreover, to endured a compressive force to the thickness direction and prevent the delamination in the aspect of the carbon fiber product layer during spin test, the carbon fibers of 10 vol% and 4 vol% has been added to the thickness and radial directions.
Moreover, this preform was experimentally fabricated using the large-scaled carbon fiber weave equipment (the maximum manufacturing possible shape, the diameter×thickness, 1.5 m of φ2 m) and the experimental production of the 1/5 disk model was successfully implemented which is made from the C/C composite which was strengthened in the three dimensions, then graphitized and densified.
It is possible to manufacture the full size gas turbine disk of the HTGR-GT system by the application of this manufacturing technology.
(2) The ordinary circumferantial speed (∼350 m/s) of the small disk experimental production body has been achieved which is made form two or three dimensional reinforcement C/C composite in the past in case of spin test of the 1/5 reduction disk model.
(3) Moreover, in case of the solid disk created in the identical manufacturing condition, it was considered that the specimen can achieve the high rotational speed performance condition of the HTGR-GT system.View full abstractDownload PDF (1442K) -
Young Jo Park, Manabu Enoki2001 Volume 65 Issue 11 Pages 1002-1007
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSIn order to obtain the materials design ensuring the best performance for the ductile/brittle layered materials, the factors controlling fracture mode, single or multiple cracking, were investigated by numerical analysis. A new method, which can deal with dynamic behavior of crack propagation, was developed to predict crack nucleation toughness (KN) and crack propagation resistance (R-curve). An in-situ cracking phenomenon was demonstrated successfully by constructing finite elements containing cracking element in the brittle layer, in such a way that the elastic modulus of cracking element goes to zero when it reaches the fracture stress of brittle layer. Calculated critical thickness ratio, (tm⁄tc)cri, for the transition from single cracking to multiple cracking showed good agreement with the reported experimental values. Work-hardening of ductile layer is effective for multiple cracking, and residual compressive stress in brittle layer contributes to enhanced resistance for crack propagation. The proposed method was also expected to apply other fracture problems of crack propagation including the effect of loading configuration (plane stress or plane strain), work-hardening and residual stress.View full abstractDownload PDF (966K) -
Daisuke Isobe, Toshiyuki Ishii, Satoshi Shimizu, Hiromitsu Ino, Katsur ...2001 Volume 65 Issue 11 Pages 1008-1013
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe aim of this study is to examine the effect of Zr addition and quenching conditions on magnetic properties of Fe-Nd-B alloys. The cooling rate is varied by changing the wheel velocity of a single roller apparatus. Suppression of crystallization of soft magnetic phases (α-Fe and Fe3B) by adding Zr is confirmed by comparing the X-ray diffraction patterns of Fe85−xNd10ZrxB5 and Fe80−xNd10ZrxB10 alloys with and without Zr atoms. In the former alloys with x=0∼11, the amorphous formation ability is the highest at x=5 and 7. X-ray diffraction patterns and TEM observation show that hyperfine grains of 2-14-1 compounds, several nano-meters in diameter, are formed at a critical wheel velocity. It is confirmed by the measurements of Curie temperature and magnetic hyperfine field that considerable amount of Zr is present in the Nd2Fe14B phase. In a high boron alloy (Fe70Nd10Zr5B15), high coercive force of 1.2 MA/m is observed. The present work suggests the possibility of further improvement of the magnetic properties by the addition of Zr atoms.View full abstractDownload PDF (675K) -
Makoto Hasegawa, Hiroshi Fukutomi2001 Volume 65 Issue 11 Pages 1014-1022
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSNucleation mechanism from initial grain boundaries and the process of texture formation during dynamic recrystallization in pure nickel were studied in uniaxial compression tests at temperatures of 293 K, 873 K and 905 K and true strain rates of 1.0×10−3 s−1 and 1.0×10−4 s−1. Microstructures were observed by optical microscopy and SEM. Orientation measurements of individual grains were carried out by EBSP technique. Misorientation between neighboring points along grain boundaries in the specimen deformed at high temperature having wavy grain boundaries were greater than that in the specimen deformed at room temperature having smooth grain boundaries. Further, the misorientation was larger when the degree of grain boundary curvature was more severe. These indicate that vicinity of wavy grain boundaries is the region of inhomogeneous deformation. These regions have various orientations locally because of lattice rotation to various directions. New grains nucleated from these regions had almost random orientation. At high Zener-Hollomon parameter conditions, area of high pole density was distributed about 10 degrees away from (011) to (001). The reason is as follows; at fully dynamically recrystallized material, new grains nucleate with random orientation, followed by the orientation change towards (011) by the deformation. Before some grains reach to (011), however, new grains nucleate again with random orientation and grains with (011) orientation disappears.View full abstractDownload PDF (1250K) -
Kiyoshi Itoh, Feng Wang, Tohru Watanabe2001 Volume 65 Issue 11 Pages 1023-1028
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSElectrodeposited Ni-W alloy films were obtained from Nickel Sulfate baths containing Na2WO4. The crystallographic structure and morphology of electrodeposited Ni-W films were studied by XRD, HRTEM, SEM and heat-treatment technique. The crystallographic structures of electrodeposited Ni-W alloy films were also compared with the Ni-W thermal equilibrium diagram.
The X-ray diffraction patterns of Ni-W electrodeposited films with various W contents gradually changed from sharp peaks to broad peaks with increasing W contents in electrodeposited films. HRTEM observation revealed that the crystallographic structure of electrodeposited Ni-W film with 19.7 at%W content was crystalline and its crystal size was about 10 nm. Moreover, the crystalline structure was observed and the crystal size was about 5 nm in the electrodeposited Ni-W alloy film with 24.4 at%W content. However, when the film with 24.4 at%W content was heat treated, the crystalline phase did not grow and an unknown phase (Ni4W?) existed alone under 600°C heat-treatment. From this result, it was clear that the crystallographic structure of Ni-W film with 24.4 at%W content was amorphous.
Therefore, it can be concluded that the microcrystalline phase existed up to 22 at%W in electrodeposited Ni-W alloy film and the amorphous phase existed from 22 at% to 35 at%W.View full abstractDownload PDF (1126K) -
Katsuhiko Nonaka, Takeshi Kawabata, Hideo Nakajima, Kazuo Tanosaki, Ju ...2001 Volume 65 Issue 11 Pages 1029-1037
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSDeformation behavior and cracking of heat-treated Ti-46 mol%Al alloy with a coarsely spaced lamellar structure has been investigated by a discontinuous compression test and electron probe microanalysis.
Cracking of specimens with a coarsely spaced lamellar structure occurs at a compression plastic strain of 2.1% and a stress of 650 MPa. Crack initiation sites were clarified as \ding172 on a colony and a grain boundary of the lamellar structure, \ding173 within the α2 phase of the lamellar structure with the compression axis perpendicular to the lamellar planes, \ding174 on a near lamellar interface, and \ding175 within massively transformed α2 phase or on its interface. Fracture behavior of the specimens is explained as follows. A number of cracks mentioned above increased with increasing compression strain, and then the cracks propagate while growing and combining with each other, and making shear ligaments and deflections. The main crack propagates in a shear direction resulting in fracture.
Deformation behavior and dependence of angles between the compression axis and the lamellar planes were studied in polycrystals with a coarsely spaced lamellar structure on compression test. In the lamellae with the compression axis perpendicular to the lamellar planes, cracking within the α2 phase was observed without explicit deformation traces. On the other hand, in the lamellae with the compression axis parallel to the lamellar planes, a hard type of deformation across the lamellae occurred in the γ phase. However for the compression axis at intermediate angles, a hard type and an easy type of deformation traces were observed in the γ phase in addition to activation of a prism slip system in the α2 phase.View full abstractDownload PDF (2965K) -
Tatsuya Ohmi, Kazuhisa Takahashi, Masayuki Kudoh2001 Volume 65 Issue 11 Pages 1038-1044
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSEffects of surface modification by a laser remelting process on the structure and hardness of surface composite castings of hyperperitectic Al-Cr alloys have been investigated. These castings were produced by either Centrifugal Duplex Casting(CDC process) or conventional centrifugal casting. The CDC process is applicable to the production of a tubular casting with an in-situ composite layer containing fine intermetallic crystals. On the other hand, there are coarse intermetallic crystals in the composite layer of the tubular castings produced by the conventional centrifugal casting.
The intermetallic crystals in the laser-melted zone in each specimen were extremely refined regardless of their original size. However, many cracks were observed in the coarse intermetallic crystals near the melted zone on the specimen produced by the conventional centrifugal casting. On the contrary, no such defect were seen in the CDC specimens with finely dispersed intermetallic crystals. In these specimens, the hardness of the melted zone was about 50% higher than the substrate. Furthermore, addition of Cu was effective for the hardening of both of the substrate and the melted zone.View full abstractDownload PDF (1992K)
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