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Volume 48, Issue 7
Displaying 1-14 of 14 articles from this issue
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Minoru Kawasaki, Naoya Inoyama, Yutaka Kawano1984 Volume 48 Issue 7 Pages 669-674
Published: 1984
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe kinetic of first stage graphitization in white cast iron has been studied by Burke and Owen using the Johnson-Mehl equation, ξ=1−exp{−(kt)n}, and they have discussed the theoretical knowledge of the nucleation and growth of temper carbon. Then, most of the kinetic analyses have been based on their premises. But after wards, other authors put forward a question about estimation of the value of n of this method. It is considered that these disagreements are caused by the value of n varying with a starting point of graphitization. Therefore, this study was undertaken to determine accurately the value of n by modifying Johnson-Mehl equation as dξ⁄dt=nk{−ln(1−ξ)}(n−1)⁄n(1−ξ), and also the activation energies were measured.
The results are as follows:
(1) An accurate value of n was not obtained by a double logarithmic plot of the Johnson-Mehl equation, log·log(1⁄1−ξ)=nlogt+const.
(2) According to the analysis by the modified method, the value of n gradually decreases during the graphitization and finaly becomes about 1.
(3) The activation energy gradually decreases until approximately 50% graphitization and thereafter remains nearly unchanged at 2.6×105 J/mol.
(4) These results suggest that the latter half of reaction is controlled by the dissolution process of cementite.
(5) The meaning of the n value of time exponent proposed by Burke may have to be reexamined.View full abstractDownload PDF (861K) -
Yoshitaka Mori, Ishi Miura1984 Volume 48 Issue 7 Pages 675-681
Published: 1984
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSMorphological changes in two-dimensional grain structures have been studied by computer simulation on the basis of assumption of random nucleation sites and randomly oriented ellipsoidal growth. Wide ranges of grain growth anisotropy are given by limiting the growth rate of minor axis on the ellipsoidal growth. Coefficients of variation of the distributions of grain area, grain size and sides per grain increase with increasing growth anisotropy and growth rate. Morphological characteristic values of 4πA⁄P2, LD⁄BR and CP⁄P are calculated for each case, where A, P, LD, BR and CP represent the grain area, perimeter, longest dimension, breadth and convex perimeter, respectively. With increasing growth anisotropy, the values of 4πA⁄P2 and CP⁄P decrease and the value of LD⁄BR increases. The formation process of the dendrite structure of Al-4.3 mass%Cu is estimated by comparison with the result of computer similation study that the growth rate along the major axis is 0.25 at the growth anisotropy of 2.0.View full abstractDownload PDF (1380K) -
Shinichiro Omori, Koichiro Koyama, Yasuhiko Hashimoto, Masaru Yamashit ...1984 Volume 48 Issue 7 Pages 682-687
Published: 1984
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe phase relationships in the Ni-Mo-B and Ni-W-B systems at 1223 K have been determined over the whole ranges of composition by chemical and X-ray diffraction analyses and optical microscopy. In the Ni-Mo-B system, five ternary phases of two known compounds, NiMo2B2 and NiMo3B3, and three new compounds, Ni10Mo3B11, Ni20MoB17 and Ni23Mo4B29 appeared. The lattice parameters are a=0.6197, b=1.0737, c=0.3021 nm for Ni10Mo3B11; a=0.7553, b=1.3088, c=0.2985 nm for Ni20MoB17; a=0.8750, b=0.9393, c=0.3074 nm for Ni23Mo4B29. MoB12 is orthorhombic with a=0.6341, b=0.9083 and c=0.5203 nm. In the Ni-W-B system, two phases of a known compound, NiW2B2, and a new compound, Ni20WB17 appeared. Another known compound, NiW3B3 decomposed below about 1600 K. The lattice parameters of Ni20WB17 are a=0.7567, b=1.3099 and c=0.2983 nm.View full abstractDownload PDF (824K) -
Masahisa Otsuka, Ryo Horiuchi1984 Volume 48 Issue 7 Pages 688-693
Published: 1984
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe dependence of the hot ductility of Al-Mg solid solution on temperature, strain rate, grain size and solute content has been examined in detail by use of tensile test. At a constant strain rate, a ductility (reduction of area) versus temperature curve showed a remarkable trough. With increase in the strain rate, the ductility trough appeared at higher temperatures, while its depth remained almost constant. The temperature at which ductility becomes minimum (Tmin) can be correlated with the strain rate (\dotε) by \dotε∝exp(−Qφ⁄RTmin), where Qφ (137 kJ/mol) agrees well with the activation energy for volume diffusion. The ductility is determined uniquely by a parameter Z=\dotεexp(Qφ⁄RT), where R is the gas constant and T the absolute temperature. The effect of the grain size on the minimum ductility (φmin) at a constant strain rate, can be empirically expressed as φmin=1⁄(1+d⁄D0), where D0 is a materials constant and increases with increasing solute content. The ductility loss was associated with the intergranular fracture, and a number of small dimples were observed on the fracture surface, suggesting the growth and interlinkage of cavities. The results are compared with those for other metallic materials.View full abstractDownload PDF (1308K) -
Hiroshi Seki, Shigeru Asano1984 Volume 48 Issue 7 Pages 694-699
Published: 1984
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSInternal friction was measured at about 500 Hz from 160 K to 370 K in FCC Fe-Ni alloys subjected to electrolytic hydrogen charging. A relaxation peak of internal friction caused by hydrogen was found at 260 K in an Fe-54.0%Ni alloy and at 240 K in an Fe-72.8%Ni alloy, together with two small sub-peaks around 225 K and 265 K. The main hydrogen peak was always larger in the Fe-54.0%Ni alloy than in the Fe-72.8%Ni alloy. Their heights increased with the current density of electrolytic hydrogen charging and decreased with the hydrogen outgassing during repeated measurements. The activation energy of the hydrogen peak was estimated by the peak-shift method to be E=43.2 kJ/mol in the Fe-54.0%Ni alloy and E=42.3 kJ/mol in the Fe-72.8%Ni alloy. These values of the activation energy are comparable to recent data on hydrogen diffusion in the corresponding Fe-Ni alloys. Plastic deformation did not change the height and the shape of the hydrogen peak but affected considerably the higher-temperature sub-peak. Therefore, the hydrogen peak is independent of the presence of dislocations and might be a Snoek-type relaxation of dissolved hydrogen atoms, presumably being caused by the stress-induced ordering of hydrogen atom-pairs or clusters in the FCC lattice of Fe-Ni alloys. On the other hand, the higher-temperature sub-peak is a kind of the hydrogen cold work peak and might be caused by dislocation motion with hydrogen atmosphere.View full abstractDownload PDF (887K) -
Norikatsu Yokota, Shigehiro Shimoyashiki1984 Volume 48 Issue 7 Pages 699-704
Published: 1984
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSSpecimens of 2\ frac14Cr-1Mo steel, previously rusted in the air, were immersed in stagnant sodium at temperatures from 423 to 673 K for 3.6×103 to 3.6×106 s. The reduction of rust in liquid sodium was investigated as a function of the immersion temperature and immersion time. The rust studied contained γ-FeOOH and Fe3O4.
In the temperature range of 423 to 573 K, wetting of rust with sodium required 3.6×105 s and this process was the rate-determining step for reduction in sodium. At temperatures above 573 K, wetting occurred within 3.6×103 s, followed by reaction with sodium. Rust was reduced in sodium by the processes in which γ-FeOOH was converted into Fe2O3 by dehydration, and Fe2O3 was changed into Fe3O4 and finally Fe. These were surface reactions, controlled by diffusion of oxygen through sodium. The activation energy of diffusion of oxygen was measured as 8.8 kJ/mol.View full abstractDownload PDF (1555K) -
Atsushi Nishikata, Yasuhiko Shimatani, Shiro Haruyama1984 Volume 48 Issue 7 Pages 705-712
Published: 1984
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSElectrochemical studies of corrosion of Ni, Fe and their alloys have been made in molten chloride at 973 K by using potentiodynamic polarization, rotating disk electrode and polarization resistance methods. From the polarization experiments it was concluded that metallic corrosion in molten chloride occurs only in the presence of water, oxygen or other oxidants. The cathodic reduction of oxygen proceeds via a two-step reaction (O2+2e→O22− and O22−+2e→2O2−), exhibiting two current waves. In the presence of water, however, oxygen is reduced as O2+2H2O+4e→4OH−. Although metallic corrosion in molten chloride is generally caused by dissolved oxygen, it is greatly accelerated by the presence of water. Anodic dissolution current of Ni in molten chloride decreased with increasing concentration of carbonate (oxide) up to 0.5 mol%, whereas it incresed with increasing carbonate over 1 mol%. This complicated effect of carbonate was well explained by the acidic and basic fluxing model for the dissolution of NiO. The results of the polarization experiment correspond well to those obtained from mass loss measurements. The instantaneous rate of corrosion of Ni, Fe and their alloys in molten chloride was estimated by the electrochemical polarization resistance method. The results indicated that the corrosion resistance of Ni and Fe was somewhat improved by alloying with Cr or Mo.View full abstractDownload PDF (1080K) -
Atsushi Nishikata, Shiro Haruyama1984 Volume 48 Issue 7 Pages 713-720
Published: 1984
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSElectrochemical studies of corrosion of Ni, Fe and their alloys have been made in molten chloride containing sulfate and molten sulfate at 973 K by using potentiodynamic polarization and polarization resistance methods. It was concluded that metallic corrosion in these melts was well explained by the mixed potential theory. The oxidant for metallic corrosion in these melts was found to be SO3 and SO2 generated by the dissociation of sulfate ion. In contract to the corrosion in molten chloride or carbonate, the corrosion in sulfate was accelerated not by oxygen but by water. The acceleration of corrosion by water is attributable to SO3 and SO2 generated by the reaction of water with sulfate.
With increasing concentration of sulfate in molten chloride, the anodic dissolution current decreased, but the cathodic reduction current increased. The complicated corrosion behavior of metals in molten chloride containing sulfate is attributable to these opposite effects of sulfate on anodic and cathodic reactions, respectively.
The instantaneous rate of corrosion of Ni, Fe and the their alloys was well estimated by the electrochemical polarization resistance method. The corrosion resistance of alloys increased greatly, when the alloy contains chromium more than 20%. Alloying with molybdenum sometimes deteriorated the corrosion resistance. Electrochemical techniques are a very useful method for obtaining mechanistic data as well as for monitoring the rate of hot corrosion.View full abstractDownload PDF (1156K) -
Atsushi Nishikata, Shiro Haruyama1984 Volume 48 Issue 7 Pages 720-725
Published: 1984
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSElectrochemical studies of corrosion of Ni, Fe and their alloys have been made in molten carbonate at 973 K by using potentiodynamic polarization and polarization resistance methods. It was concluded that metallic corrosion in molten carbonate was well explained by the mixed potential theory. Partial cathodic reaction for metallic corrosion in molten carbonate was found to be the reduction of the peroxide ion (O22−) formed by the reaction of carbonate ion with dissolved oxygen. The anodic dissolution current of Ni in molten carbonate increased with increasing pressure of CO2 gas, namely, with decreasing oxide ion activity. The rate of metallic corrosion in molten carbonate was controlled by cathodic reaction rates at high PCO2, whereas, at low PCO2 it was controlled by anodic reaction rates.
The instantaneous rate of corrosion of Ni, Fe and their alloys in molten carbonate was estimated by the electrochemical polarization resistance method. The results of corrosion monitoring by this method indicated that Fe-base alloys with high Cr content (more than 25%) exhibited a little better corrosion resistance than Fe, but high Mo content alloys exhibited very poor corrosion resistance in molten carbonate. The results well correspond with those obtained from anodic polarization curves.View full abstractDownload PDF (829K) -
Kusuhiro Mukai, Tatsuhiko Masuda, Kouji Gouda, Tsutomu Harada, Jyouki ...1984 Volume 48 Issue 7 Pages 726-734
Published: 1984
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSLocal corrosion of solid oxides at the slag-metal interface has been investigated for the systems of Al2O3, SiO2-(PbO-SiO2) slag-Pb. Results obtained are as follows : (1) The major part of the local corrosion zone appears below the horizontal slag-metal interface, and slag film below 350 μm in thickness exists between the solidified metal and the oxide specimen in the local corrosion zone. (2) Direct observation of the local corrosion occurring in a transparent fused silica tube has revealed the modes of the slag film formation and its active motion in the local corrosion zone. Changes in SiO2 content in the solidified slag film are detected along and perpendicular to the inner surface of the tube in the local corrosion zone. (3) Shape and linear loss, Δds-m, of both the oxide specimens in the local corrosion zone show characteristic changes with dipping time and slag composition. For SiO2 specimen, they show marked changes with the initial diameter of the specimen and the thickness of the bulk slag phase. (4) These experimental evidences support that the local corrosion for the present system is mainly caused by the interfacial turbulence of the thin slag film between the metal and the oxide specimen in the local corrosion zone.View full abstractDownload PDF (2270K) -
Akira Ohkawa, Ryukiti R. Hasiguti, Hisami Yumoto1984 Volume 48 Issue 7 Pages 735-741
Published: 1984
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe bonding charactor between ceramic coating and metal substrate is important from the viewpoint of application to high temperature machine parts such as the first wall coating of nuclear fusion devices. Reaction zone structures of vacuum annealed 316L stainless steel coated with TiC by CVD process were investigated. The samples were annealed in vacuum of about 10−4 Pa at 1173-1473 K for 36-720 ks. The diffusion and reaction zones near the interface were investigated by XMA and SEM. (Ti, Mo)C solid solution and FeTi intermetallic compound in the TiC matrix and (Cr, Ti, Fe)7C3 carbide and precipitated TiC solid solution in stainless steel were identified.
\ oindentSmall pores were observed in the reaction zone, suggesting that they were caused by the Kirkendall effect. The diffusion of Mo and Fe in TiC was found to proceed by grain boundary diffusion followed by bulk diffusion.View full abstractDownload PDF (2363K) -
Hideo Takei, Takaaki Oshita, Tomei Hatayama1984 Volume 48 Issue 7 Pages 742-747
Published: 1984
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSClosed die forging of the water quenched superplastic and the furnace cooled non-superplastic Zn-22Al alloys was made in the axi-symmetric conditions to investigate the effects of superplasticity on the working force and material flow behaviours. The results are as follows.
(1) Working force of the quenched material was 1/3-1/5 of that of the furnace cooled materials, but there was no remarkable difference in the material flow behaviours between both the materials. Surfaces of worked pieces were smoother in the quenched materials than in the furnace cooled materials.
(2) In the axial flow type forging, working force for the movable container type die was 1/3 of that for the fixed type die in both the materials.
(3) Working force in the centrifugal flow type forging was the lowest in both the materials, when a forging type was adopted by which nearly perfect centrifugal flows of materials were produced.View full abstractDownload PDF (1057K) -
Tatsuo Sato, Than Trong Long, Hiroyasu Tezuka, Akihiko Kamio, Tsuneo T ...1984 Volume 48 Issue 7 Pages 748-754
Published: 1984
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSRibbon-shaped thin samples of Al-Cu alloys (4-33 mass%Cu) were obtained by the rapid solidification using a rotating single roller technique, and the decomposition structures were investigated with a high resolution electron microscope.
In the electron transparent regions, homogeneously supersaturated solid solution was found to be formed in Al-4-15 mass%Cu alloys, on the other hand, the combination of lamellar and cellular structures, and banded and randomly distributed structure of θ′ and θ phases were formed in addition to solid solution in Al-20-33 mass%Cu alloys.
It was also clarified that the characteristic fine periodic structure, in which the Cu concentration changed periodically in the ⟨100⟩ direction with the spacing of about 0.8 nm, was formed over a wide region in Al-20-33 mass%Cu alloys. The fine periodic structure, which is quite different from that of the well-known phase in the Al-Cu system, is considered to be a new metastable phase.View full abstractDownload PDF (4239K) -
Takeshi Takeyama, Yoshinobu Sato1984 Volume 48 Issue 7 Pages 754-760
Published: 1984
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe effective permeability μe, and its stress-sensitivity in high frequency fields (H=0.4 A/m, f=1-100 kHz) were investigated for Ni-Fe-V alloys containing 80-84%Ni, 3.5-6.5%V, 0.4%Mn and bal.Fe, severely cold rolled to 0.025 mm in thickness, annealed at 873-1473 K in a pure hydrogen atmosphere and then subjected to the low temperature heat treatment of either controlled cooling or baking. The d.c. magnetic properties, saturation magnetostriction, Curie point and electrical resistivity were also measured.
The optimum annealing temperature to get the maximum value of μe shifts to lower temperature with increasing frequency. The optimum baking temperature lowers and the time becomes longer with increasing V content. For example, the temperature and the time for the maximum values of μe at 100 kHz in the cases of representative alloy specimens with 5.76 and 6.38%V are about 20 ks at 733 K and 140 ks at 713 K, respectively. The alloys in the region of 82.5±0.2%Ni, 6.0±0.5%V, 0.4%Mn and bal.Fe have the values of high electrical resistivity such as 0.80±0.05 μΩ·m and low magnetostriction, therefore these alloys are excellent in both μe and its insensitivity to stress. However, the Ni content of the composition for a maximum μe at a higher frequency such as 100 kHz becomes slightly lower than the alloy region mentioned above, while that for a minimum stress-sensitivity factor does not change.View full abstractDownload PDF (965K)
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