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Volume 49, Issue 2
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Hiroshi Arai1985 Volume 49 Issue 2 Pages 97-103
Published: 1985
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSOstwald ripening in solid matrices is studied theoretically considering the stress around dispersed particles induced by the volume gap.
Under the condition where the diffusion in matrix compensates the volume gap, a ripening rate equation is derived as follows:
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\ oindentThe equation is a generalized one for multi-components system and covers all conventional formulas.
Under the condition where the creep deformation takes place to compensate the volume gap, the equation is given as follows:
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The calculated results have revealed that the creep deformation is more dominant than the iron diffusion to compensate the volume gap for cementite coarsening in ferrite below 973 K.View full abstractDownload PDF (898K) -
Yutaka Hiraoka, Tadayuki Fujii, Masatoshi Okada, Ryoji Watanabe1985 Volume 49 Issue 2 Pages 104-111
Published: 1985
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSTensile tests at 77 K, 173 K and 293 K were performed on molybdenum single crystals having axial-orientations near ⟨011⟩-direction, which had been prepared by the secondary recrystallization method. Effects of island grains at the specimen surface and/or in the bulk and test temperature on the crack initiation and propagation characteristics were investigated.
At 77 K and 173 K: Cracks were initiated from island grains for all of the annealed or polished specimens and for most of the carburized specimens. Cracks propagated initially on the {011}-plane and then were divided on the {112}-and/or {001}-planes, though there was a tendency that the {011}-plane component just around the crack initiation sites diminished or vanished for the polished or carburized specimens. Fracture strength of the annealed or polished specimens depended on the size of island grains from which the cracks were initiated. On the other hand, the strength of the carburized specimens was constant regardless of the size of island grains.
At 293 K: Non-propagating cracks were observed at the interfaces between island grains and the matrix in the annealed or polished specimens. However, any island grains were not responsible at all for the final failure of the specimens. All the specimens indicated considerably high ductility.View full abstractDownload PDF (3302K) -
Masazumi Okido, Koichi Kimura, Takeo Oki1985 Volume 49 Issue 2 Pages 112-119
Published: 1985
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSElectrode impedance changes of iron, chromium and SUS430 steel in potential domains of active dissolution, passivity and transpassivity were measured in 1 kmol/m3 Na2SO4 solution with the frequency range from 10−3 Hz to 104 Hz. The impedance changes of iron was also measured in 1 kmol/m3 Na2SO4 with chlorine ions.
On the impedance diagram of iron, a negative resistance loop appeared after the induction time in active-passive transition potentials, and capacitive loops obtained at passivity potentials tended to increase in size with increasing potential and with holding time. On the impedance diagram of chromium and SUS430 at passivity potentials, the size of capacitive loop was larger than that of iron. The impedance diagram of iron changed remarkably in comarison with those of SUS430 and chromium at corresponding passivity potentials. The impedance of chromium showed no change with time, since a passive film was formed on the surface quickly. The impedance responce of iron in a pitting corrosion condition was different from that in the active corrosion condition. It was considered that the impedance of pitting corrosion was related to the formation of chloride film on the inside surface of pit.View full abstractDownload PDF (936K) -
Tsutomu Yamamoto, Kazuyoshi Kamachi1985 Volume 49 Issue 2 Pages 120-124
Published: 1985
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe surface residual stress of cemented carbide coated with TiC or TiN by the chemical vapour deposition process and the physical vapour deposition process was measured by the X-ray stress measureing method. It was mainly discussed from a stand point of residual stress that the insert coated with TiC or TiN by the CVD method was inferior in the failure resistance compared with that by the PVD method and the uncoated insert.
The results are as follows:
(1) The stress generated in the WC phase at the surface of the ground substrate was compressive and that of the substrate coated by the PVD method was also compressive but lower than that of the former. The residual stress in the layer deposited by the PVD was also compressive.
(2) On the contrary, the residual stress in the WC phase at the surface of CVD coated substrate was tensile, having no connection with the existence of η phase under the deposited layer. The stress measured in the deposited layer was tensile.
\ oindentIt is concluded that the remarkable decrease of the failure resistance of the CVD coated insert is accounted for by the tensile stress in the WC phase produced by the CVD coating.View full abstractDownload PDF (782K) -
Kazuo Yamanaka, Takao Minami, Katsuyuki Tokimasa, Hiroo Nagano1985 Volume 49 Issue 2 Pages 125-133
Published: 1985
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSIntergranular corrosion test methods were studied for the purpose of evaluating the degree of sensitization caused by chromium carbide precipitation at the grain boundaries in high chromium-nickel based alloys such as Alloy 690.
The results obtained are as follows:
(1) The most recommendable intergranular corrosion tests for the evaluation of sensitization in Alloy 690 are the immersion tests in the boiling solution of 65%HNO3+0.1%HF or 65%HNO3+0.2 kg/m3 Cr(VI) ions.
(2) TTS diagram for Alloy 690 obtained from these corrosion test results is characterized by the C-curve in the temperature range between 773 and 1073 K. It is also confirmed that the C-curve of TTS diagram shows the same tendency as that of TTP (Time-Temperature-Precipitation of Carbide) diagram in Alloy 690.
(3) The average chromium concentration at the chromium depleted zone in the Alloy 690 containing 0.025%C calculated on the basis of the value of corrosion rates is not less than 10%Cr even in the severely sensitized condition. This is the reason why Alloy 690 has high resistance to intergranular corrosion.
(4) Reactivation charge obtained by the EPR method in 0.5 kmol/m3 H2SO4+0.01 kmol/m3 KSCN solution at 303 K showed a good correlation with corrosion rate in the boiling solution of 65%HNO3+0.1%HF.View full abstractDownload PDF (1356K) -
Kyoko Wasai, Kusuhiro Mukai1985 Volume 49 Issue 2 Pages 134-143
Published: 1985
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSEquations (\ efe1) and (\ efe2) have been derived by applying an ideal associated solution model assuming associated compounds, MpO(a), for the analysis of the thermodynamics of oxygen dissolution into liquid metals, 1/2O2(g)→O(at%).
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\ oindentStandard free energies, ΔGMpO°(a), enthalpies, ΔHMpO°(a), and entropies, ΔSMpO°(a), of formation of the associated compounds, MpO(a), have been calculated from eq. (\ efe1) and (\ efe2) using the published values of ΔHsol° and ΔSsol° of the reaction, 1/2O2(g)→O(at%). Variations of the standard enthalpies and entropies of formation of MpO with the atomic number of constituent metal, M, are analogous in the solid, liquid (associated compounds), and gaseous states. Linear relations are found in the following combinations of the quantities; ΔHMpO°(s) vs ΔHMpO°(a), ΔHMpO°(a) vs ΔHMpO°(g), ΔHMpO°(s) vs ΔHMpO°(g), ΔSMpO°(s) vs ΔSMpO°(a), ΔSMpO°(a) vs ΔSMpO°(g), and ΔSMpO°(s) vs ΔSMpO°(g). Except for the relation of ΔSMpO°(s) and ΔSMpO°(a), this linear relation is sub-divided into two different lines; one of which consists of transition metal oxides and the other of non-transition metal oxides. Standard enthalpies, ΔHM° and ΔHB°, of MpO(a) of melting and boiling are proportional to the melting and boiling temperatures TM and TB, respectively, and the relation between ΔHB° and TB° agrees with Trouton’s rule. If the associated solution is not ideal, the following equations hold.
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\ oindentIn this case the thermodynamic values, ΔHMpO\invdiameter(a) and ΔSMpO\invdiameter(a), of the infinite dilute associated compounds MpO(a) in liquid metal, not pure MpO(a), are calculated from eqs. (\ efe3) and (\ efe4). It is to be noted that all the results based on eqs. (\ efe1) and (\ efe2) are also effective when ΔHMpO°(a) and ΔSMpO°(a) are replaced by ΔHMpO\invdiameter(a) and ΔSMpO\invdiameter(a).View full abstractDownload PDF (1607K) -
Takayoshi Yoshimori, Toshihiko Taniuchi, Koji Ishiwa, Yutaka Kamimura, ...1985 Volume 49 Issue 2 Pages 144-148
Published: 1985
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe wet decomposition-nonaqueous titrimetric method was used for the determination of microamounts of carbon in metals. The samples were decomposed with a mixture of chromic and sulfuric acids in purified oxygen stream. Various suitable mixtures were used to decompose samples completly. For example, steels should be decomposed with the mixture of 100 cm3 of concentrated sulfuric acid and 180 cm3 of water containing 0.016 kg of purified potassium dichromate. On the other hand, aluminum was dissolved with the mixture of the potassium dichromate (0.016 kg), 180 cm3 of cupper sulfate solution (0.1 kg·m−3) and 100 cm3 of concentrated sulfuric acid. Though most part of carbon in the sample may be oxidized to carbon dioxide, its some part may escape in the form of hydrocarbon and carbon monoxide. Therefore, generated gases were passed through heated (1073 K) platinum asbestos and oxidized to carbon dioxide. Then total carbon dioxide was absorbed with N,N-dimethylformamide containing 1% of 2-aminoethanol, 1% of water and thymolphthalain as an indicator. The carbon dioxide absorbed was titrated with tributyl methylammoniumhydroxide (TBMAH) standard solution in 2-methyl-2-propanol. The standard solution was standarized against pure benzoic acid. Microamounts of carbon (0.78-58.4 μ g) in sucrose were able to be accurately determined by this method with the relative standard deviation (calculated from range) of about 2.7%. Trace amounts of carbon (9-250 ppm) in iron, titanium, zirconium alloy and aluminum were able to be determined precisely and accurately. A blank value of each determination was able to be reduced to less than several μg.View full abstractDownload PDF (795K) -
Kazuo Isonishi, Masaharu Tokizane1985 Volume 49 Issue 2 Pages 149-155
Published: 1985
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSAn ultra high carbon steel powder prepared by N2-gas atomizing was hot pressed in a vacuum for 0.9-10.8 ks at 20-160 MPa at 973 K. Dense compacts having a relative density more than 99% of the theoretical value were obtained by hot pressing for 0.9 ks at 160 MPa and for 7.2 ks at 100 MPa. The analysis of the densification process by hot pressing theory indicated that sintering by a superplastic type flow mechanism occurred during the hot pressing.
The flow stress-strain rate relationship obtained flom the results of change-in-strain rate test of the hot pressed specimen (>99% relative density) at 973 K yielded the high strain rate sensitivity (m=0.44). At the same time, the hot pressed compacts showed an excellent formability by compressive creep tests at 973 K. It has been concluded that superplastic flow operats during the deformation process of the hot pressed compacts of the present material.View full abstractDownload PDF (2514K)
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