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Volume 63, Issue 5
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Yukio Inokuti1999 Volume 63 Issue 5 Pages 553-556
Published: 1999
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSIn order to clarify the crack morphology in 180° bend-forming of Ti films deposited on (011) [100] single crystal of silicon steel and ferritic stainless steel sheets, Ti coating by the hollow cathode discharge (HCD) method was done on polished single crystal and stainless steel sheets, and then the Ti-coated samples were 180° bend-formed and observed by the scanning electron microscope.
Ti-coated silicon steel of (011) [100] single crystal sample showed no distictive crack in Ti films on steel sheet, on which slip lines at intervals of 1∼5 μm to the [1\bar210]Ti direction could be observed in a rectangular-like morphology 10∼25 μm in width and 20∼60 μm in length. Moreover, many fine slip lines at intervals of 50∼200 nm to the [0001]Ti direction could be observed.
In contrast, Ti-coated stainless sheel sheet sample showed many highly-curved cracks of 10∼50 μm length in a slightly elongated state.
It should be noted that the crack of Ti films differed remarkably depending on the kind of steel sheet, whether the steel substrate was a single crystal and polycrystal. In particular, the Ti films deposited on (011) [100] single crystal of silicon steel showed epitaxial growth with a good coherency relationship between Ti films and the silicon steel matrix.View full abstractDownload PDF (707K) -
Yoshihiro Takahara, Nobutaka Narita1999 Volume 63 Issue 5 Pages 557-560
Published: 1999
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSLocal atomic structures of an amorphous Fe79B16Si5 alloy before and after structural relaxation have been studied by EXAFS (extended X-ray absorption fine structure) and Mössbauer measurements.
The structural analyses indicate that the interatomic distance of Fe-Si is larger than that of Fe-B and is close to the Fe-Fe distance. Such geometry becomes more obvious by structural relaxation. Discussions based on the medium range order model of capped trigonal prisms suggest that Si atoms do not occupy the center of the capped trigonal prisms as metalloid atoms. It is likely to locate the substitutional sites of Fe atoms. During structural relaxation, the distance of Fe-B decreases and that of Fe-Fe is slightly shortened, while the Fe-Si distance remains unchanged. The coordination number of B atoms around Fe decreases but that of Fe atoms increases a little. The coordination number of Si around Fe is almost constant. The coordination number increase of Fe around Fe during the structural relaxation is also confirmed in the Mössbauer spectra.View full abstractDownload PDF (366K) -
Hideo Numata, Tokuzou Tsujimoto1999 Volume 63 Issue 5 Pages 561-564
Published: 1999
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSFormation of metal-hydride (MH) on the Ti3Al surface by charging hydrogen (H) electrochemically in sulfuric acid with 0.5 g/m3 Sb2O3 as a hydrogen recombination poison has been studied by X-ray diffractometry (XRD) and thermal desorption spectrometry (TDS) combined with quadrupole mass spectrometry (QMS).
The two types of hexagonal phase were found in the XRD diagram after the cathodic charging (CP) for 1 h. The one is the α2 phase and the other is a MH phase which has lattice parameters of a=0.588 nm and c=0.794 nm.
Two peaks at 600°C and 700°C in the curves of TDS and QMS corresponded to desorption of hydrogen. The measurement of XRD after heating at various temperatures showed that the MH phase with a hexagonal structure decompose at 600°C and that the hydrogen in α2 phase discharges at 700°C.
The MH phase formed in Ti3Al is not considered to be the same substance with the hexagonal type of a MH phase formed on TiAl which was previously reported.View full abstractDownload PDF (332K) -
Hisaaki Takao, Hideo Hasegawa1999 Volume 63 Issue 5 Pages 565-568
Published: 1999
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe influence of thin coating of Au (70 nm) on the wettability of the Cu substrate by Sn-Ag eutectic solder (Sn-3.5Ag) was investigated, using a meniscograph testing machine equipped with a contact angle measuring system. Wettability of Cu by liquid Sn-3.5Ag was improved by Au coating, especially in contact angles. Namely, the contact angle was reduced to 29°∼30° on the Au-coated Cu from 42°∼45° on the uncoated Cu. On the Au-coated Cu, Au layers remained on unwetted areas, while it dissolved into solder on wetted areas, followed by the formation of a Cu-Sn intermetallic compound as seen on the uncoated Cu. The improvement in the wettability by Au coating on the Cu substrate would be caused by the difference of substrate-flux interfacial tensions (γsf).
On the other hand, the wettability of the Au substrate by liquid Sn-3.5Ag with the contact angle of 60°∼64° was inferior to that of the Au-coated Cu. At the solder-Au substrate interface, Au-Sn intermetallic compounds were formed, which were not formed on the Au-coated Cu substrate. Consequently, the difference of the wettability between Au and Au-coated Cu is attributed to the difference of substrate-liquid solder interfacial tensions (γsl).
These results suggest that it is necessary for the Au layer to be thin so as not to form Au-Sn intermetallic compound at the solder-substrate interface for the improvement in the wettability of the Cu substrate.View full abstractDownload PDF (381K) -
Jun Onagawa, Yoshiyuki Sato1999 Volume 63 Issue 5 Pages 569-572
Published: 1999
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe present study was conducted in order to analyze the effects of sintering temperature on the microstructure and corrosion resistance of Ti-M (M=Ru, Rh, Pd, Ir, Pt) alloys prepared from titanium and M powders using spark plasma sintering (SPS). In addition, the practicality of the Ti-Ru alloy as a low-cost Ti alloy was discussed. The specimens were prepared at SPS temperatures of 800, 1100 and 1500°C. The microstructure of specimens were investigated using scanning electron microscopy (SEM) and X-ray diffraction. The corrosion resistances of specimens were determined by potentiodynamic polarization measurement at a scanning speed of 0.124 V/min using a 5% HCl solution open to air at 25°C. Measurement was performed at a specimen potential of from −1.0 to 2.0 V and the potential approached noble.
At a low SPS temperature, SPS alloys show a particle dispersion microstructure, in which the added element phases and intermetallic compound phases are dispersed in the Ti matrix. These phases affect the corrosion resistance of the alloys. At a high SPS temperature, the added elements and compounds are diffused in the Ti matrix, causing the alloy to approach a solid solution microstructure and increasing the formation of metastable βTi. In particular, at a high SPS temperature, in the Ti-Pt alloy increases slightly the amount of βTi, whereas increases greatly the amount of Ti3Pt. High SPS temperatures reduce the added element phases that serve as the cathodic pole, thus diminishing the cathodic current. In the anodic area, the reduction or dispersion of compound phases reduces the compound active region, thus diminishing the anode current.
Furthermore, high SPS temperatures produce similar polarization curves among Ti-M alloys, and provide SPS alloys having the same corrosion resistance equivalent to that of arc-melted alloys. Therefore, no problem is associated with the replacement of Pd with Ru.View full abstractDownload PDF (428K) -
Shinji Ando, Takushi Goto, Kazuki Takashima, Hideki Tonda1999 Volume 63 Issue 5 Pages 573-576
Published: 1999
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe core structures of (c+a) dislocations in HCP metals have been investigated by molecular dynamics simulation using a Lennard-Jones type pair potential. The edge dislocation has two types of stable core structures at 0 K; one is a perfect dislocation (Type-A) and the other is two 1⁄2(c+a) partial dislocations (Type-B). While the Type-B core is stable at 30 K and 293 K, the Type-A core extends parallel to the basal plane at 30 K. The Type-A core at 0 K transforms to the Type-B core by increasing temperature from 0 K to 293 K. In contrast, the extended Type-A core at 30 K is still stable at 293 K. These results suggest that the (c+a) edge dislocation glides on the {11\bar22} plane as two 1⁄2(c+a) partial dislocations and becomes sessile due to changes of the core structure. The screw dislocation exhibits a stable core spread over two {10\bar11} type planes at 0 K. The core transforms to unsymmetrical structure at 293 K, which is spread over {11\bar22} and {10\bar11}, and to a core spread parallel to {11\bar22} at 1000 K. The dependence of the yield stress on the shear direction can be explained from these core structures of screw dislocation.View full abstractDownload PDF (428K) -
Gen Sasaki, Li Jun Yao, Makoto Yoshida, Jin Pan, Hideharu Fukunaga1999 Volume 63 Issue 5 Pages 577-580
Published: 1999
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSAl18B4O33 whisker reinforced Al, Mg alloy composites were prepared by a squeeze casting process. The interaction among the interface structure, heat stability and strength of the composites was analyzed. In the pure Al matrix composite, the interfacial reaction occurred only at a temperature higher than 750°C and its reaction products are γ-Al2O3. Interfaces between the whisker and reaction products have a preferred orientation with little mismatch. In the AC8A matrix composite, MgAl2O4 with a spinel structure was produced at the interface at a temperature higher than 500°C. These reaction products were shaped rectangularly. These reactions lead to the corrosion and shortening of the whiskers. It causes the degradation of the bending strength of the composites. In the AZ91D matrix composites, the reaction products are MgAl2O4 layers with a uniform thickness. This layer prevents the direct reaction between the whisker and the matrix. Consequently the whiskers are scarcely damaged and the composites have a good bending strength at high temperature.View full abstractDownload PDF (965K) -
Tadashi Fukuda1999 Volume 63 Issue 5 Pages 581-584
Published: 1999
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSEffects of morphology of carbide and nitride precipitates on the fatigue strength under pulsating tension of Fe-30 mass%Cr alloys containing 0.03 mass%C and 0.03 mass%N were investigated. Two kinds of heat treatments were adopted to obtain different types of morphology of grain boundary precipitates and that of precipitates within the grains.
The results obtained are summarized as follows:
(1) Fatigue strength of the specimens containing grain boundary carbide and nitride is lower than that of the specimens containing carbide and nitride within the grains. The difference of fatigue strength between above mentioned two different types of morphology of carbide and nitride precipitates increase with decreasing fatigue life.
(2) Fatigue strength of the specimen containing continuous, flat, and plate-like grain goundary nitride is lower than that of the specimen containing discontinuous grain boundary carbide around shorter fatigue life.
(3) Initiation of fatigue crack in the specimens containing grain boundary carbide and nitride precipitates is promoted by intergranular fracture of decohesion at the interfaces between the matrix and those precipitates.
(4) It is recommended to choose a heat treatment condition in which the formation of large, continuous, and flat grain boundary nitride is avoided.View full abstractDownload PDF (624K) -
Koji Tanoue, Hiroyuki Ogata1999 Volume 63 Issue 5 Pages 585-588
Published: 1999
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSIt is investigated how the morphological change of secondary recrystallized grains grown in powder metallurgy tungsten fine wires has an effect on creep at high temperatures after it is quantitatively estimated. The quantitative treatment of the grain morphology is possible by using f1 as the representative one of the grain shape parameters. The optimum interlocked grain structure is defined as the grain morphology in which the grain aspect ratio is minimized under the condition that the area of grain boundaries does not increase drastically. The high-temperature creep can then be characterized by the index ΔI(=f1−f10) which indicates the degree of deviation from the optimum interlocking of grains which is designated by f10. The region of power law creep in the deformation mechanism maps is minimized at ΔI=0 at which the grains are most favourably interlocked, being extended as ΔI deviates from ΔI=0. It is considered that the deformation in the region is strongly influenced by grain boundary sliding, being further done by grain boundary cavitation with an increase in ΔI at ΔI>0.View full abstractDownload PDF (551K) -
Byung-Nam Kim, Keijiro Hiraga, Yoshio Sakka, Byung-Wook Ahn1999 Volume 63 Issue 5 Pages 589-592
Published: 1999
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe enhanced grain growth behavior during superplastic deformation is analyzed on the basis of grain boundary diffusion mechanism. On the grain boundary where both static and dynamic potential differences exist, matter diffusing along the boundary is assumed to deposit on the grain surface locating opposite to the direction of grain boundary migration and to contribute to the dynamic grain growth. The amount of the diffusive matter is calculated for the deformation of a spherical grain and is converted to the increment in the mean boundary migration velocity. The obtained relationship between the strain rate and the dynamic grain growth rate is independent of the mechanism of superplastic deformation. The dynamic grain growth behavior predicted from the present model is consistent with the experimental results of ZrO2-dispersed Al2O3.View full abstractDownload PDF (494K) -
Goroh Itoh, Naoki Haramura, Tomoaki Ihara1999 Volume 63 Issue 5 Pages 593-596
Published: 1999
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSHydrogen microprint technique, which can visualize microscopic location in the surface where hydrogen atom has been evolved, was applied to an isothermally forged Ni-23.4 mol%Al alloy sheet to investigate the behavior of hydrogen in Ni3Al compounds. Considering that Ni3Al shows marked embrittlement in hydrogen gas atmosphere, the surface location on one side where hydrogen atoms had been evolved was observed by SEM, with the other side exposed to hydrogen gas of 0.1 MPa. The influence of tensile deformation by 3% on the behavior of hydrogen was also investigated. When the specimen was not deformed, largest number of hydrogen atoms penetrated into the specimen, although their distribution was not uniform. It was found that hydrogen evolution quantity was decreased by the deformation. When the specimen was not exposed to the hydrogen gas, a small amount of hydrogen was evolved at slip steps by the deformation, while no hydrogen was detected in the specimen which was not deformed. From the results obtained, it was concluded that hydrogen molecules in the environment were decomposed into atoms at Ni3Al surface and penetrated into the interior. It was deduced that hydrogen atoms were trapped by dislocations and moved with gliding dislocations in Ni3Al, in a way similar to other metallic materials.View full abstractDownload PDF (407K) -
Kyu Seop Park, Fujimitsu Masuyama, Takao Endo1999 Volume 63 Issue 5 Pages 597-600
Published: 1999
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSCreep behavior of a Mod.9Cr-1Mo steel statically aged under various conditions has been analyzed using the Omega method. The aging temperature and time are between 873 and 948 K, and between 100 and 10000 h, respectively. Tertiary creep was expressed by the following equation;
(This article is not displayable. Please see full text pdf.)
\ oindentwhere \dotε0 is the imaginary initial creep rate and Ω is the strain rate acceleration factor. The imaginary initial creep rate was expressed as a function of aging time, ta and aging temperature, Ta as follows;
(This article is not displayable. Please see full text pdf.)
\ oindentwhere the values of Aa, nta, Q0a, na and Qa are 1.02×103 s−1, 0.19, 52 kJ/mol, 13.0 and 623 kJ/mol in this order.
Behavior of primary creep was approximated by a logarithmic creep equation containing two parameters, which were correlated with the imaginary initial creep rate. Consequently, creep life was estimated from a knowledge of imaginary initial creep rate. It was found that the calculated creep life from the modified Omega method in which primary creep was taken into account, agreed well with the measured one.View full abstractDownload PDF (362K) -
Takanori Suda, Ryouichi Kobayashi, Seiichi Watanabe, Somei Ohnuki, Hei ...1999 Volume 63 Issue 5 Pages 601-604
Published: 1999
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSMost of hydrogen storage alloys show decrepitation during hydriding-dehydriding cycles. The decrepitation assists initial activity and reaction rate. However, it causes lowering of thermal conductivity, difficulties of handling, degradation and others. In this work, the decrepitation process was examined with regard to mechanical properties and microstructure.
Four types of alloys; LaNi5, TiMn1.5, TiFe0.8C0.1 and ZrNi are used for this work. Compression test, Vickers hardness measurement and high-resolution electron microscopy observation were carried out before and after hydrogenation. Ductile alloys did not show remarkable decrepitation. Brittle alloys showed typical decrepitation, in which the nano crystal grains were observed by use of high-resolution microscopy. These results emphasize that the decrepitation process is different each other’s, depending on the ductility or brittleness of the alloys.View full abstractDownload PDF (760K) -
Yi Tan, Hisao Tanaka, Chaoli Ma, Akio Kasama, Ryohei Tanaka, Yoshinao ...1999 Volume 63 Issue 5 Pages 605-608
Published: 1999
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSMechanical behavior of binary Nb-Ir alloys was investigated by compression tests at the temperatures ranging from room temperature to 1773 K. It was found that 0.2% flow stress increases with increasing Ir content within the single phase region of Nb solid solution, up to 6 mol%Ir and exhibits a distinct solid solution hardening. The 0.2% flow stress of the two-phase alloys consisting of Nb solid solution and an intermetallic compound Nb3Ir, in the alloys with 6 to 22 mol%Ir, also increases with increasing Ir content presumably by the precipitation hardening of the intermetallic phase. The strength of the single phase compounds seemed to be very high and the measurement of 0.2% flow stress by compression tests was unsuccessful due to premature failure below 1473 K. The Vickers hardness of the compound was about 11000 to 12000 MPa at room temperature.View full abstractDownload PDF (594K) -
Ikuo Ioka, Jyunji Mori, Chiaki Kato, Masatoshi Futakawa, Kaoru Onuki1999 Volume 63 Issue 5 Pages 609-612
Published: 1999
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe thermochemical hydrogen generation process has been developed at Japan Atomic Energy Research Institute. This process has a severely corrosive environment, such as sulfuric and hydriodic acids. A silicon-iron alloy with fractional gradient is one of the candidate materials in a boiling sulfuric environment. So, the corrosion resistance and the passive film of Fe-20 mass%Si alloy in boiling sulfuric acids were studied in this work.
The Fe-20 mass%Si alloy was prepared by arc melting of iron (99.9 mass%) and silicon (99.99 mass%). The specimens were ground to a 600 grit finish and rinsed with distilled water and acetone. The specimens were immersed in 50 vol% or 95 vol% sulfuric acids at the boiling temperature (140°C or 320°C) and then weighed to yield a corrosion rate. The passive films on the specimens were evaluated in terms of the appearance, Auger electron spectroscopy (AES) analysis and X-ray photoelectron spectroscopy (XPS) analysis.
The alloy showed good resistance in boiling 50 vol% and 95 vol% sulfuric acids. By AES, the passive film of the specimen exposed 50 vol% sulfuric acid consisted of O and Si. The passive film of the specimen exposed to 95 vol% sulfuric acid consisted of O, Si and S. It seems that S in the passive film of the specimen exposed to 95 vol% sulfuric acid is attributable to the cathodic reduction of sulfuric acid. The growth rate of the passive film of the specimen exposed to 95 vol% sulfuric acid is about 30 times as fast as that of the specimen exposed to 50 vol% sulfuric acid. It is considered that the faster growth rate is attributable to the low density of the film. From the result of XPS, the passive films on the specimens exposed to 50 vol% and 95 vol% sulfuric acids can be described as SiO2 and as a composite of SiO2 and SiO, respectively.View full abstractDownload PDF (370K) -
Toshihiko Fukui, Shunkichi Ueno, Ryohei Tanaka, Seiji Miura, Yoshinao ...1999 Volume 63 Issue 5 Pages 613-616
Published: 1999
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSEffects of Nb or V additions on microstructure and hardness of MoSi2/Mo5Si3 eutectic alloys are investigated for the improvement of room temperature toughness of multi-phase intermetallic alloys based on MoSi2. Alloys prepared by the argon arc melting process have compositions of 4-23 mol%Nb or 10-19 mol%V which substitutes Mo in MoSi2 and Mo5Si3 phases. Examinations are made on microstructural observation by back scattered electron image, X-ray diffraction for phase identification, the concentration of Nb or V in the constituent phases by EPMA, and Vickers hardness of the multi-phase alloys in both macro- and microscopic scales. The phase constitution changes from the two-phase, MoSi2(C11b) and (Mo, Nb)3Si5, to the three-phase, MoSi2(C11b)/(Mo, Nb)Si2(C40)/(Mo, Nb)5Si3, with increasing Nb additions. In the series of alloys with V additions, a similar shift from the two- to the three-phase is accompanied with increasing V addition. Macroscopic hardness of the multi-phase alloys with Nb addition exhibits a complex concentration dependence, in which with increasing Nb content, the hardness first decreases, exhibits a minimum and then increases back. The reason could be attributed to the fact that the hardnesses of the C40 and C11b phase have individual dependence on Nb concentration as revealed by micro-scale hardness measurement. For the improvement in toughness, Nb additions to the eutectic alloys may be preferred because the MoSi2/Mo5Si3 eutectic microstructure is fine as compared with that obtained by the V addition.View full abstractDownload PDF (791K) -
Hidenobu Ohta, Makoto Takagi, Toru Imura, Yoshihito Kawamura, Akihisa ...1999 Volume 63 Issue 5 Pages 617-620
Published: 1999
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSHigh strength P/M Al-Ti-Fe-TM(TM: Cr, Mo, V, Zr, Mn, Nb) based alloys were prepared by extrusion of rapidly solidified powders which were produced by the high-pressure He gas atomization technique. It was found that the wear resistance of all the P/M aluminum alloys thus prepared was better than that of the conventional aluminum alloys. The Al92.5Ti2.5Fe2.5Cr2.5 alloy showed the best wear resistance among the P/M aluminum alloys studied in this work. In order to understand the reason for the difference of the wear properties in those P/M aluminum alloys, their wear traces were analyzed using SEM and EPMA. The hard oxide layer was found to be formed on the surface of the wear trace of the Al92.5Ti2.5Fe2.5Cr2.5 alloy. The Al92.5Ti2.5Fe2.5Cr2.5 alloy was also found to be superior in the heat resistance property at elevated temperatures. Through the TEM observation, it was confirmed that the nanocrystalline structure of the Al92.5Ti2.5Fe2.5Cr2.5 alloy remained unchanged even after heat treatment at 673 K for 100 h.View full abstractDownload PDF (529K) -
Tsutomu Ishikawa, Masataka Masuda, Yasunori Hayashi1999 Volume 63 Issue 5 Pages 621-624
Published: 1999
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSRecently, compound semiconductor thin films have been studied very actively for applications to electrical and optical devices that could be the base of the information industry. But the study of metal nitride thin films has not proceeded faster than that of metal oxide thin films. And there are some nitrides that have not been studied on their fundamental properties. In this paper, copper nitride (Cu-N) thin films were prepared by reactive RF sputtering and the relation between electrical properties and sputtering conditions were investigated. As a result, it was clear that the properties of Cu-N thin films were connected with sputtering conditions, especially the content of nitrogen gas and deposition rate of Cu-N thin films. Various Cu-N thin films that were prepared under different conditions had a band gap in the range of 0.5-1.5 eV and their resistivity values were widely changed. Lower values of band gap energy and resistivity than reported values indicated that these Cu-N films are non-stoichiometry and they are supposed to have many defects. Hydrogen implantation treatment of the samples was done in order to improve their properies such as band gap energy, resistivity and carrier density. In result, electrical resistivity drastically decreased from 102 to 10−4 Ωm with increasing carrier density. And the structural peculiarity was not influenced by hydrogen implantation. This result shows that implanted hydrogen ions could produce electrons correlated to electrical conduction.View full abstractDownload PDF (370K) -
Shin Ishikawa, Mitsuyuki Fujisawa, Jun-ichi Shimomura, Kei-ichi Yoshio ...1999 Volume 63 Issue 5 Pages 625-633
Published: 1999
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESS18 mass%Cr steels containing small amount of C and N individually were water-quenched or air-cooled after solution treatment. Grain boundary precipitates and Cr-depleted zone in the steels were observed by FE-TEM/EDX.
In C-containing steels, M7C3-type carbides were formed densely at the grain boundaries. Both the size of the carbides and the degree of Cr depletion observed near the grain boundary carbides in the air-cooled sample were larger than those in the water-quenched samples. In N-containing steels, Cr2N-type nitrides were formed at the grain boundaries. The size and the density of the nitrides were very different in each grain boundary and smaller than those of the carbides in C-containing steels. A Cr-depleted zone was not detected clearly when the grain boundary nitrides were small. Near some grain boundaries, where the large nitrides are formed separately, the degree of Cr depletion at the grain boundary apart from the nitrides was larger than that at the interface between the nitride and matrix. From his fact it is deduced that the growth of the nitrides and the formation of the Cr-depleted zone are controlled by Cr diffusion from the matrix to the nitrides via grain boundaries. The difference in precipitation behavior between grain boundary carbides and nitrides may indicate that the nitrides hardly nucleate at grain boundaries and that the nucleation behavior of the nitrides depends on the grain boundary structure more sensitively than that of the carbides.
The degree of corrosion at each grain boundary observed after EPR tests was strongly related to the degree of Cr depletion determined by TEM. This result suggests that the corrosion behavior of the whole specimen is presented by the average of the corrosion susceptibility of each grain boundary.View full abstractDownload PDF (1587K) -
Katsuhiko Takahashi, Minoru Asada, Masahiro Kawakami1999 Volume 63 Issue 5 Pages 634-640
Published: 1999
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe microstructure of Ni reduced from (Ni, Mg)O was observed, and then the effects of MgO content and temperature on sintering characteristics of the reduced Ni powder were investigated. The results were summarized as follows.
The fine MgO particles were uniformly dispersed in the reduced nickel. The diameters were 10-50 nm.
The porosity of sintered Ni was increased with an increase in MgO content at 1273-1573 K. The sintering temperature of more than 1473 K was required for Ni containing MgO to remarkably decrease the porosity. The porosity decreased linearly as a logarithmic function of time. The grain growth of Ni was expressed by a 1/3 power function of time.
Consequently, the smallest porosity of sintered Ni containing MgO was obtained at 1573 K, and then its hardness increased with increasing MgO content and sintering temperature.
It was obvious by observing the microstructure that the sintering behavior showed an intermediate stage. The sintering mechanism was discussed by assuming the vacancy volume diffusion.View full abstractDownload PDF (813K) -
Koji Kakehi1999 Volume 63 Issue 5 Pages 641-648
Published: 1999
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe yield strength of high strength nickel-base superalloys for gas turbine blades increases with increasing temperature up to a peak temperature (650∼800°C). The influence of crystallographic orientation on the high-temperature mechanical properties of single-crystal nickel-base superalloys was investigated by a systematic study of the deformation mechanism at a temperature above the peak temperature. Tensile and creep tests were carried out at 900°C. Initial tensile orientations were selected over a wide range on the standard stereographic triangle. In the tensile test, Schmid’s law, based on an assumption of {111}⟨\bar101⟩ slip system, broke down because of the cross slip of superlattice dislocation pairs from the unique slip plane. The effect of both cube slip in the γ′ phase and by-passing mechanism is to give a suppression of the yield strength in [\bar111] orientation. In the creep test, it was found that the orientations in which the operation of {111}⟨\bar101⟩ slip systems is unstable exhibited the planar slip fracture surfaces and low ductilities; on the contrary, the stable-slip orientations exhibited the large ductilities, and the specimen with [\bar111] orientation exhibited the longest rupture life as a result of a low Schmid factor for the {111}⟨\bar101⟩ slip systems. Therefore, creep deformation occurs primarily by viscous slip of the relaxed a⁄2⟨\bar101⟩ dislocation pairs controlled by climb of the anti phase boundary. Furthermore, the operation of cube slip in the γ′ phase, as well as octahedral slip which shears both γ′-γ phases, gave a good account of the orientation dependence of creep strength.View full abstractDownload PDF (1706K) -
Hiroshi Kimura, Kazuhiro Hongo1999 Volume 63 Issue 5 Pages 649-655
Published: 1999
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSFull density powder processing, which consists of reaction ball milling and the instrumented electric discharge consolidation method, is proposed for the development of bulky oxide ceramic materials with nanoscale grain. We find that mechanical alloying of the powder mixture, ZrO2-20 mass%Al2O3 can produce solid state amorphization, when the conditions for planetary reaction ball milling yield the optima. When electric discharge consolidation is combined with high-rate heating of the mechanically alloyed amorphous ceramic powder, we obtain fully dense ZrO2-20 mol%Al2O3 at 1347 K when a pressure of 100 MPa is applied. The densification in the supercooled liquid of ZrO2-20 mol%Al2O3 is fairly well expressed by an Arrhenius type equation of viscous flow: η=η0exp(H⁄kT). The process viscosity (η) is below 1012 Pa·s at the glass temperature and the activation energy (H) decreases from 337 to 184 kJ·mol−1 with increasing current applied to the graphite die. For cubic ZrO2-20 mol%Al2O3 with a monoclinic phase, synthesized via crystallization at 1366 K, the average grain size is estimated at 19.6 nm from X-ray line broadening. Vickers’ pyramidal hardness is 1051 DPN when the initiation of cracks at the corners of indentation is avoided.View full abstractDownload PDF (1308K) -
Masahiko Kato, Hisaoki Sasano, Toshiyuki Suzuki1999 Volume 63 Issue 5 Pages 656-660
Published: 1999
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSInterdiffusion in single-phase Ti3Al has been investigated using a vapor-solid diffusion couple in the temperature range between 1086 and 1345 K. Aluminum was diffused by a chemical transportation technique in which aluminum chloride was used as the carrier gas. The results show that the interdiffusion coefficients at temperatures above 1209 K are almost the same at both sides of stoichiometry. However, the diffusion mode below 1132 K is completely different from that above 1209 K. Although the diffusion layer is formed uniformly in the surface of the base metal above 1209 K, the new crystal grains which are obviously different from the grains in the base metal are formed in the surface of the base metal below 1132 K. As the result, aluminum diffuses along the newly formed crystal grain boundary. This means that the interdiffusion below 1132 K must be controlled by a grain boundary diffusion mechanism instead of the lattice diffusion above 1209 K.View full abstractDownload PDF (1075K) -
Masayuki Kondo, Yuzuru Ogura, Tatsuo Morimoto1999 Volume 63 Issue 5 Pages 661-668
Published: 1999
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSAs an oxidation protection system for carbon/carbon composites beyond 1973 K, the authors have proposed a Y2SiO5 oxidation protection coating system, which is a multilayer coating system composed of a Y2SiO5 outer layer and a SiC inner layer. This work evaluated the Y2SiO5 coating in oxidation protection properties and emissivity properties. For oxidation protection properties, an erosion test was performed at 2073 K for 50 min in low oxygen pressure and high velocity gas flow (Mach 3, Ar-20 vol%O2) by an arc wind tunnel, and isothermal oxidation tests were performed in Ar-0.2 vol%O2 with an Iridium-heater electric furnace. In the erosion test, the Y2SiO5 coating protected a carbon substrate from oxidation, and the inner SiC layer was oxidized in active oxidation. The Y2SiO5 layer adhered to the SiC layer after the erosion test. In the isothermal oxidation tests, the Y2SiO5 coating performed oxidation protection at 1973 K for more than 10 h, but, the adhesion of the Y2SiO5/SiC interface was degraded by the isothermal oxidation tests. Total emissivities of the Y2SiO5 coating was estimated to be 0.54 at 1973 K by spectrum emissivities of the Y2SiO5 coating from 700 to 2500 nm. Therefore, this work showed that the Y2SiO5 coating performs oxidation protection above 1973 K at low oxygen pressure, and that an improvement of the emissivity properties was required for re-entry applications. For the improvement of the emissivity properties, it was proposed to coat the Y2SiO5 layer with high-emissivity oxides which had a high melting point.View full abstractDownload PDF (2014K) -
Genjiro Motoyasu, Hideki Kadowaki, Hiroshi Soda1999 Volume 63 Issue 5 Pages 669-674
Published: 1999
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSZinc wires of 2 mm diameter have been produced using the horizontal Ohno Continuous Casting(OCC) process at casting speeds of 0.5, 1.7, and 2.8 mm·s−1. The effects of casting speed on crystal orientation and the mechanical properties of the cast wires have been studied. It was found that the cast wires produced under the above three speeds were single crystals. At higher castling speeds (1.7 and 2.8 mm·s−1), the crystal orientation of the wires in the casting direction tended to be [0001]. With a slow casting speed of 0.5 mm·s−1, the orientation of the cast wires varied the most. Some of those single crystal wires were ductile and could be bent repeatedly before fracture occurred. The cast wires with an angle between the (0001) cleavage plane and wire axis of less than about 1 rad (wire axis near [1\bar211] direction) were significantly more bendable than those with an angle of over 1.3 rad (wire axis near [0001]) which fractured with only a single bending. It was also found that the cast wire with its wire axis close to the [1\bar210] direction (a cleavage angle of approximately 0.6 rad) exhibited tensile elongation as large as 350%.View full abstractDownload PDF (717K)
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