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Volume 60, Issue 6
Displaying 1-12 of 12 articles from this issue
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Yuichi Ikeda1996 Volume 60 Issue 6 Pages 537-546
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSA new alloy design method was developed by combining molecular dynamics simulation and genetic algorithm. For multi components superalloys, it was impossible to optimize alloy composition using a conventional molecular dynamics simulation because of its huge computational demands. An optimization of composition under a given design rule becomes possible using the proposed method. We designed a Ni-based heat resistant superalloy which consists of Ni, Al, Cr, Mo and Ta. The obtained alloy composition and atom fraction in sublattice of the γ′ phase are in good agreements with experiments for the TMS-63 alloy. Furthermore the obtained lattice misfit was 0.42% at 1273 K and was much smaller than the experimentally measured misfits for most superalloys.View full abstractDownload PDF (1101K) -
Hiroshi Sato1996 Volume 60 Issue 6 Pages 547-552
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe isothermal section at 973 K and the liquidus surfaces of the phase diagram of the pseudo-ternary BaO-Fe2O3-B2O3 system were determined in a composition range of less than 50 mol%B2O3 using the thermal analyses and X-ray diffraction. The liquidus surface which is in equilibrium with Fe3O4 spreads over a wide composition range, while that in equilibrium with BaO·6Fe2O3 is long and tapers to BaO·B2O3. The pseudo-ternary BaO-Fe2O3-B2O3 compound does not exist in the composition range investigated. The ternary eutectic reaction is L→BaO·6Fe2O3+BaO·B2O3+3BaO·B2O3, occurring at 1033 K at the composition 48 mol%BaO-19 mol%Fe2O3-33 mol%B2O3.View full abstractDownload PDF (496K) -
Toshiyuki Koyama, Toru Miyazaki, Minoru Doi1996 Volume 60 Issue 6 Pages 553-559
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe numerical analysis of the diffusion controlled phase transformation based on the non-liner diffusion equation is one of the main subjects in the field of computer materials science. In the present study, we propose a new analyzing method of the nonlinear diffusion equation (“discrete type diffusion equation”), where the composition dependencies of atomic interaction energy, elasticity and mobility of atoms are taken into account so as to be able to calculate the phase decomposition in the real alloy system. Furthermore, the information on the solute atom occupation probability in the atom site is also included in the proposed calculation theory. The proposed new method has a capability of predicting not only the phase decomposition in the disordered phases but also the other phase transformations such as the stress-induced precipitates coarsening, order/disorder phase transitions, phase decompositions in ordering alloys and the formation process of tweed structures.View full abstractDownload PDF (744K) -
Toshiyuki Koyama, Toru Miyazaki, Minoru Doi, Abd El-Azeam Mohamed Mebe ...1996 Volume 60 Issue 6 Pages 560-568
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe two-dimensional computer simulations are performed for the phase decomposition in the Fe-Mo binary alloy system on the basis of a new method proposed by us. The thermodynamic data on the Fe-Mo phase diagram is used in the simulation. The microstructures theoretically obtained are well coincident with experimental facts of this alloy system. Furthermore, the typical features in the strain-induced microstructure changes calculated are as follows: (1) The competitive growth, which is just like a dislocation climbing mechanism, between the precipitate particles is observed in the coarsening process of the modulated structure. (2) The microstructure with the precipitate particles in same size aligned to the ⟨10⟩ direction appears in the later stage of coarsening. This phenomenon is caused by the effect of elastic interaction energy between the particles. (3) The elastically hard phase (Mo-rich phase) is covered by a elasically soft thin phase (Fe-rich phase). This microstructural morphology results from the stress field due to the elastic inhomogeneity, i.e. the effect of the inhomogeneous elastic stiffness which changes with the local composition in the microstructure.View full abstractDownload PDF (2586K) -
Sung-Kil Hong, Jung-Chul Choi, De-Zhung Lin, Hiroyasu Tezuka, Tatuo Sa ...1996 Volume 60 Issue 6 Pages 569-576
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSPrecipitation sequences of the age hardenable aluminum alloy composites are strongly affected by the dislocations generated during quenching from the solution treatment temperature. In this study, age hardening behavior of Al-4 mass%Cu and Al-4 mass%Cu-1.5 mass%Mg base composites reinforced with SiC whisker (SiCw) was investigated with micro-Vickers hardness measurement, differential scanning calorimetry and transmission electron microscopy. SiCw/Al-Cu and SiCw/Al-Cu-Mg composites indicate a remarkable age hardening in spite of the suppression of the G.P. zone or G.P.B. zone formation rate, and the age hardening rate is accelerated. In particular, age hardening of the SiCw/Al-Cu-Mg composite is larger than that of the unreinforced alloy. The precipitation process of the SiCw/Al-Cu composite is different from that of the unreinforced alloy. Many metastable θ′ phases (Al2Cu) precipitate preferentially on dislocations in the matrix prior to G.P. zone and contribute for the age hardening of the composite, but the posteriorly formed G.P. zone still plays the most important role in the hardness increase. In the case of the SiCw/Al-Cu-Mg composite, the age hardness steeply increases with the formation of the G.P.B. zone at the initial stage and decreases temporarily and then increases again due to the precipitation of a fine and high dense S′ (Al2CuMg) phase.View full abstractDownload PDF (1307K) -
Shinobu Matsushima, Han-Choel Choe, Shigeo Ohashi, Tadao Ishihara1996 Volume 60 Issue 6 Pages 577-581
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe effects of composition, heat treatment, test temperature and dissolved oxygen (DO) concentration on the stress corrosion cracking (SCC) behavior of Ni-Ti and Ni-Ti-Cu shape memory alloys in high temperature pure water were examined. The tests were conducted by using slow strain rate test machine.
The 50∼50.9 at%Ni-Ti and 40∼41.5 at%Ni-Ti-10 at%Cu shape memory alloys were subjected to SCC in air saturated water of 561 K, except for the annealed 50 at%Ni-Ti alloy. The annealed 50 at%Ni-Ti was immune to SCC, but the SCC susceptibilities of the other Ni-Ti alloys were not affected by nickel concentration and heat treatment. In the case of Ni-Ti-Cu alloys both low nickel concentration and aging promoted SCC. SCC of Ni-Ti and Ni-Ti-Cu alloys initiated from the scratches and propagated transgranularly.
At 473 K, SCC occurred and the susceptibilities were not largely different from those at 561 K. In the case of a stainless steel shape memory alloy, the martensite phase specimens were susceptible to SCC in deaerated low temperature water. On the contrary, the martensitic Ni-Ti alloys did not crack in the deaerated water at 287 K.
The susceptibilities to SCC of Ni-Ti and Ni-Cu-Ti alloys in deaerated water of 561 K were the same as those in aerated water of the same temperature. Dissolved oxygen did not accelerate nor prevent SCC in high temperature water.View full abstractDownload PDF (1183K) -
Kouichi Kawahara, Sadahiro Tsurekawa, Hideharu Nakashima1996 Volume 60 Issue 6 Pages 582-588
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSIn order to clarify the activated slip systems of β-silicon nitride (Si3N4) during high temperature deformation, we have studied the dislocation structures in hot-pressed β-Si3N4 deformed at temperatures from 1820 to 2020 K with strain rates from 9×10−6 to 2×10−4 s−1.
Analysis of the dislocations by transmission electron microscopy revealed that the most of dislocations in β-Si3N4 plasticaly deformed at high temperatures were c dislocations which were mobile on the {10\bar10} as a primary slip plane. Moreover, a dislocations on the {10\bar10} slip plane were also found to be mobile. The density of a dislocations to that of c dislocations was roughly estimated to be the ratio of 1 : 10, irrespective of the deformation condition. In addition, (a+c) dislocations gliding on the {11\bar21} pyramidal plane were seen to be activated only under the limited deformation conditions at which β-Si3N4 showed a fairly good ductility without crack formation. The density of (a+c) dislocations was about two orders of magnitude lower than that of c dislocations.View full abstractDownload PDF (1808K) -
Manabu Noguchi, Toshio Narita1996 Volume 60 Issue 6 Pages 589-594
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSDeviation from stoichiometric composition of ferrous-sulfide Fe1−δS and solid solution sulfides (Fe, Cr)1−δS containing Cr up to 0.3 cation fraction was measured as functions of sulfide composition ξ, sulfur pressures (1∼10−5 Pa) and temperatures (973∼1173 K) using a thermogravimetric technique.
Nonstoichiometry δ increased with increasing Cr content in the (Fe, Cr)1−δS and sulfur pressures, while it decreased with increasing temperature at a constant composition and sulfur pressure. Cation vacancy is a predominant lattice defect in the (Fe, Cr)1−δS sulfide, and from the Libowitz model nonstichiometry δ and sulfur activity aS could be expressed by the following relation:
(This article is not displayable. Please see full text pdf.)
\ oindentwhere μMeS is a free energy change for formation of a sulfide with stoichiometric composition as well as qVMe and σVMe are the formation and interaction energies of cation vacancies. It was observed that the values of σVMe were positive, ranging from 50 to 70 kJ/mol, independent of sulfide compositions, and the values of qVMe decreased from 56 to 17 kJ/mol with increasing sulfide composition.View full abstractDownload PDF (402K) -
Koichi Kotera, Hiroyoshi Tanaka, Masao Uchida, Takashi Hirao, Nobuya I ...1996 Volume 60 Issue 6 Pages 595-599
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSFluorinated carbon, which has low surface energy and better thermal stability, is applicable to water repellents, lubricants and battery cathods. In the present paper, we have examined the modification technology of CF4 electron cyclotron resonance (ECR) plasma treatment with rf-induced negative self bias voltage on graphite substrates in order to modify the surface of graphite to fluorinated structure. Especially with the purpose of preparating the durable fluorinated surface, we have investigated the treatment process factors, and compared the initial property of the modified surface and the property change with the elapse of time. The larger contact angle value of water than that of PTFE certified that the surface of graphite was modified. A further good result has been shown that there occurs only a slight change of the repelling property with the elapse of time. X-ray photoelectron spectroscopy (XPS) result indicated that the higher the rf-induced negative self bias voltage was, the larger the peak area ratios of CF2 and CF3 species to C1S spectrum became. It is considerd that the fluorinating reaction was accelerated by the ion bombardment due to rf-induced bias voltage, so that CF2 and CF3 species were formed in the deeper region from the surface. As mentioned above, it was found that applying the rf-induced negative self bias voltage on graphite substrates was an important factor to give the modified surface durability.View full abstractDownload PDF (493K) -
Hyunsoo Kim, Noboru Akao, Nobuyoshi Hara, Katsuhisa Sugimoto1996 Volume 60 Issue 6 Pages 600-606
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThin Fe2O3-TiO2 films were formed on Pt by a low pressure MOCVD technique and their corrosion resistance was examined in HCl and H2SO4 solutions by immersion tests, dynamic polarization tests, and in-situ ellipsometry under potentiostatic polarization. In the immersion tests, dissolution rate of the films was determined by ellipsometry.
The dissolution rate of the films in 5 kmol·m−3 HCl decreased with increasing cationic fraction of Ti4+ ions, XTi, in the films and formation temperatures of the films. When the value of XTi exceeded 0.32, the films formed at 673 K did not dissolve in 5 kmol·m−3 HCl and showed exellent corrosion resistance.
The films did not dissolve in 1 kmol·m−3 H2SO4 under anodic polarization, but dissolved owing to the cathodic reduction of Fe2O3 under cathodic polarization. The dissolution rate of the films under cathodic polarization decreased with an increase in potential and also in the cationic fraction of Ti4+ ions, XTi, in the films.View full abstractDownload PDF (877K) -
Masamichi Udaka, Kazuhiro Kawasaki, Takao Yamazaki, Minoru Umemoto1996 Volume 60 Issue 6 Pages 607-615
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSCu/AlN mixed ultrafine particles (UFP) were subjected to either pressurized or nonpressurized sintering to produce sintered compacts with ultrafine microstructure. Original Cu UFP 90 nm in mean surface diameter and AlN UFP 54 nm in mean surface diameter, produced by thermal plasma method respectively, were mixed by ultrasonic mixing in acceton. Their sintering behavior and characteristics were examined, and effects of AlN UFP as second phase particles on densification and on grain growth of the compacts were investigated.
The results obtained were as follows; (1) Grain size of Cu UFP compacts increased with increasing sintering time; however, that of Cu/AlN mixed UFP compacts became stationary by sintering in excess of 7.2 ks at 1273 K. (2) The stationary grain size of Cu/AlN mixed UFP compacts, were in inverse proportion to the volume fraction of AlN UFPs. It was consistent with the grain size predicted by the pinning effect. (3) In the case of Cu/AlN mixed UFP compacts, the densification was retarded as compared with the Cu UFP compacts, by decreasing the mobility and the driving force of sintering as decreasing the contact area of Cu UFPs by AlN UFPs. (4) Grain growth in the mixed UFP compacts were restrained by AlN UFPs and pores during sintering. Because of such effects of AlN UFPs, sintering of the mixed UFPs can be completed without grain growth, and a submicronsized microstructure in which the grain size were stationary, can be obtained.View full abstractDownload PDF (1238K) -
Kazuto Hamaishi, Hidekazu Sueyoshi, Shigeru Kadomatsu, Takayuki Shiomi ...1996 Volume 60 Issue 6 Pages 616-623
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSIn order to develop a method of gas nitriding of austenitic stainless steel SUS304 without chemical treatments, the steels were preheated in the atmosphere in a temperature range of 473 to 1273 K followed by nitriding in NH3 gas with a flow rate of 2.8 m3/h at 843 K for 20 h. The influence of atmospheric preheating on nitriding behavior was examined in connection with microstructures of the surface layers.
Atmospheric preheating in the temperature range of 673 to 1023 K results in the formation of a uniformly nitrided layer with the Vickers hardness of 1000 and the depth of 100 to 150 μm. X-ray photoelectron spectroscopy analysis suggests that the surface layer of the specimen preheated in the atmosphere in the temperature range of 673 to 1023 K is inferior in protective quality to that of the non-preheated specimen.
It is confirmed from the present results that gas nitriding of SUS304 is practicable without chemical treatments when atmospheric preheating is carried out in the temperature range of 673 to 1023 K.View full abstractDownload PDF (997K)
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