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Volume 43, Issue 9
Displaying 1-17 of 17 articles from this issue
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Yukiteru Asayama1979 Volume 43 Issue 9 Pages 777-785
Published: 1979
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe precipitation process of Fe-12Cr-7Ni-4Mo-0.7Ti steel has been studied to make clear the behavior of the embrittlement produced by aging on maraging stainless steels.
It was identified from the measuring the changes in electrical resistivity that the two types of metastable precipitations P1 and P2, tentatively named, were present at low aging temperatures.
From the results of derivatives of resistivity changes obtained by low temperature aging after high temperature aging, P1 seems to be precipitate contained predominantly the solute atoms other than Mo, and P2 to be Mo rich precipitate.
The embrittlement occurred after some incubation time when aged at low aging temperatures, regardless of the heat treatment condition before the low temperature aging.
The activation energy for precipitation reaction determined from resistivity measurements was about 180 kJ/mol for the P1 precipitation and 250 kJ/mol for the P2. The activation energies conformed to the values determined from the embrittlement behavior.
It is inferred from the activation energies that the embrittlement is rate controlled by P2 precipitation, although P1 precipitation takes place in an earlier stage than P2 precipitation when the low temperature aging is performed immediately after solution treatment. However, the embrittlement is rate controlled by P1 precipitation when the low temperature aging is performed after the high temperature aging.
It has become clear that the precipitation of P1 is essential for the embrittlement, while the notch toughness depends strongly on hardness and Mo content in matrix before or after P1 precipitation. This may be the reason that the rate controlling process of the embrittlement differs with heat treatment before low temperature aging.View full abstractDownload PDF (720K) -
Takashi Yasunaka1979 Volume 43 Issue 9 Pages 786-792
Published: 1979
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe relationship between fracture behavior and microstructure in an Fe-21Cr-14Mn alloy, aged at a little higher temperature than that of a decomposition into Cr-rich and Cr-depleted phases, has been studied by means of tensile testing, V-notch Charpy impact testing, acoustic emission technique, Auger electron spectroscopy and microscopy.
The ductile-brittle transition temperature was found to increase with increasing aging time. This is due to the precipitation of the carbide (M23C6) at the grain boundaries.
On tensile testing above 223 K, intergranular microcracks are formed in the aged specimens during unstable plastic deformation, resulting in a decrease in ductility. In the temperature range from 153 to 183 K, twin-induced and propagation controlled fracture occurs. When the yield stress increases with decreasing temperature over the initial twinning stress detected on stress-strain curves, microcracks along the twin interface or cleavage microcracks are initiated. The mode of final fracture is cleavage.
In this fracture process it can be interpreted that carbides at the grain boundaries make the size of microcrack larger by associating an intergranular crack with a cleavage microcrack and a decrease in fracture stress.
At 77 K the tensile fracture stress is not so much affected by the precipitates at the grain boundaries because in this case the fracture is nucleation controlled.
The relationship of the intergranular fracture behavior of the impact specimens with temperature, however, is different from that of the tensile specimens.View full abstractDownload PDF (1442K) -
Masaru Yokota, Ryoichi Harada, Hiroyasu Mitani1979 Volume 43 Issue 9 Pages 793-799
Published: 1979
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe interdiffusion coefficients, \ ildeD, in a Ni-Mn binary alloy system have been determined by the Boltzmann-Matano method in the temperature range from 1073 to 1323 K for various couples consisting of pure nickel and Ni-(10∼40 at%)Mn alloys. Logarithm of \ ildeD increased linearly with the manganese content up to 35 at%Mn which was the upper limit of this experiment, while the activation energies and the frequency factors for interdiffusion decreased monotonously with manganese content. On the other hand the intrinsic diffusion coefficients, DMn and DNi, have been determined mainly by using Darken’s relation, showing that the diffusion of manganese atoms was twice or three times as fast as that of nickel atoms at the composition of 19.7±0.4 at%Mn. Furthermore, the intrinsic diffusion coefficients of them have been determined for reference by using Dayananda’s thermodynamical analysis, showing that the results according to his method were a little smaller than those of the above mentioned Darken’s analysis.View full abstractDownload PDF (549K) -
Masaru Yokota, Ryoichi Harada, Hiroyasu Mitani1979 Volume 43 Issue 9 Pages 799-804
Published: 1979
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe interdiffusion coefficients in a Ni base-Mn-Cu ternary system have been determined by the method after A. Brunsch et al. at a constant temperature of 1173 K, and the atomic mobilities of these elements have been calculated using Dayananda’s method. The results obtained from this experiment are as follows:
(1) The direct interdiffusion coefficients (DMnNiNi, DMnCuCu) and the cross interdiffusion coefficients (DMnNiCu, DMnCuNi) have shown strong concentration dependency; particulaly the interdiffusion coefficients DMnNiNi which are extrapolated to CCu→0 are consistent with those obtained from the other experiment for a Ni-Mn binary alloy system.
(2) The Kirkendall effect is observed in this ternary alloy system; the marker interface always moves towards the lower nickel concentration side, and the diffusion fluxes at the marker interface containing Ni-(4.9∼20.5 at%)Mn-(5.3∼20.3 at%)Cu are related to JMn+JCu>JNi. The atomic mobilities of these elements calculated from Dayananda’s method at the above-mentioned marker position increase in the order of Cu, Ni and Mn, where it is assumed that Henry’s law is maintained in this ternary alloy system.View full abstractDownload PDF (530K) -
Masaru Yokota, Naoki Moto-oka, Akira Hara, Hiroyasu Mitani1979 Volume 43 Issue 9 Pages 804-809
Published: 1979
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSAn elaborate interpretation of the mechanism of penetration of liquids into capillary tubes has been given in this paper. Up to date many theoretical studies on the problem of the rate of penetration of liquids into capillary tubes have been carried out. In this case they have made an assumption that the contact angle between the capillary tube wall and the liquid surface is constant during the rising of liquids to reach the upper limit height (or equilibrium height).
However, this contact angle should not be virtually constant and must be an important factor which governs the rate of penetration of liquids into capillary tubes. In fact the previous investigators could not obtain any satisfactory results for explaining their experimental data. Therefore, we tried to modify the usual equation of motion of liquids into capillary tubes in due consideration of the time dependent contact angle.
The equation of motion of liquids into capillary tubes was introduced from Newton’s 2nd law of motion including the time dependent contact angle; that is cosθt=cosθ∞{1−αexp(−βt)}, where θt and θ∞ are time dependent and equilibrium contact angles, and α and β are constants characteristic of the system, respectively.
The final equation is given as a differential equation:
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\ oindentwhere R, η, ρ and g are the radius of capillary tubes, the viscosity and density of liquid and a gravitational constant, respectively. Unfortunately this equation has no general solution of an elementary form. Therefore direct calculations of the rising of water in the glass capillary tube and of molten copper in the iron capillary tube was attempted with a computer in accordance with the Runge-Kutta method.
The calculated relation between the rising height (h) and time (t) was in good agreement with the measured one. Thus the importance of the time dependent contact angle to the rate of rising of liquids in the capillary tubes has been confirmed.View full abstractDownload PDF (652K) -
Muneyuki Amano, Yasuo Sasaki, Takehiko Matsumoto1979 Volume 43 Issue 9 Pages 809-814
Published: 1979
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSEffects of annealing, hydriding-dehydriding cycles and particle size on hydrogen storage properties of FeTi have been studied by measuring the pressure-composition-temperature relations. The equilibrium pressure for the formation of the γ hydride phase in the as-cast specimen was lower than that in the annealed specimen. It can be explained in terms of the heterogeniety of composition due to imcompleteness of the peritectic reaction. The equilibrium pressure for the formation of the γ phase increased with increasing hydriding-dehydriding cycles. This is considered to be due to hardening caused by the high density of dislocations which are generated during the cycles. The activation for hydriding became difficult and the dissociation pressure of the β and γ phases increased with increasing particle size.View full abstractDownload PDF (535K) -
Akito Yoshida1979 Volume 43 Issue 9 Pages 815-820
Published: 1979
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSAn investigation of surface tension has been done on the basis of the following assumptions: (i) There is an analogy between surface formation and vaporization. (ii) The surface tension as a function of temperature is given by the equation, γ∝(1−T⁄Tc)B where Tc is the critical temperature and B is the exponent.
Based on the above assumptions the relations among the quantities participating in surface formation are considered. Then the following expressions for the relations are determined by statistical analysis of experimental data: (1) The surface entropy is given by the equation, s=0.1S where S is the specific vaporization entropy in J/(m2·K), defined as the vaporization entropy per unit area of the mono-atomic layer in bulk. (2) The surface tension is given by the equation, r=1.536×104S1.62 where γ is the surface tension in N/m. (3) The surface tension is given by the equation, γ=0.152+4.61×10−4EV⁄V2⁄3 where EV is the formation energy of a vacancy in eV and V is the atomic volume in m3.View full abstractDownload PDF (334K) -
Yoshinori Murata, Toru Miyazaki, Hirotaro Mori1979 Volume 43 Issue 9 Pages 821-825
Published: 1979
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe morphological changes in a modulated structure in Ni-38 at%Cu-5 at%Si alloy during aging were investigated by means of electron microscopy and electrical resistivity measurement.
The satellites associated with the main reflection spots in the electron diffraction were found to be useful for determining the wavelengths of composition modulation produced in the early stage of spinodal decomposition. In the early stage of aging the wavelength of the modulated structure retained a constant value depending on the aging temperature, and then it increased gradually with aging time. It was found that the resistivity of the alloy initially decreased slightly but steadily with aging and turned to a marked increase with further aging.
The spinodal temperature of the alloy was determined to be 645°C from a theoretically predicted linear relationship between a square of the wavenumber of composition modulation and aging temperature. The temperature was in good agreement with the results of electron micrography and resistivity measurement.View full abstractDownload PDF (421K) -
Toru Miyazaki, Shigenori Takagishi, Hirotaro Mori, Takao Kozakai1979 Volume 43 Issue 9 Pages 826-833
Published: 1979
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSStructural changes during ageing of Fe-13-15 and 20 at%Mo alloys were investigated by means of transmission electron microscopy and X-ray diffraction. The results obtained are as follows:
\ oindentIn an early stage of ageing, a typical ⟨100⟩ modulated structure, which had not been reported for the Fe-Mo alloy system in the liferature, was found in a Fe-20 at%Mo alloy aged at temperatures below 823 K. These modulated structures were theoretically proved to be produced through a mechanism of coherent spinodal-decomposition, and the critical temperature (spinodal temperature) was estimated at 860 K. With further ageing, coherency between the Mo rich and poor regions was broken down when the wavelength reached about 25 unit cells. Finally, a stable λ phase (Fe2Mo) was nucleated independently of the periodic structure formed spinodally. On the other hand, in a case where the alloys were held at temperatures over the spinodal line, plate-like precipitates were initially nucleated on the {100} plane instead of the modulated structure, and then the λ phase was produced. The latter structural changes is considered to be identical with the previously reported one for the Fe-Mo alloy system.View full abstractDownload PDF (781K) -
Youichi Tokunaga, Mitsuyuki Morishige1979 Volume 43 Issue 9 Pages 834-840
Published: 1979
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSRelations between the evolution peaks and the age-hardening in 18%Ni-Co-Mo maraging steels have been investigated by means of calorimetric analysis and hardness testing. The specific heat versus temperature curve of the quenched specimen is characterized by the appearance of three evolution peaks at 350, 470 and 530°C, respectively, and also an absorption peak at about 500°C. The 470°C peak which seems to be caused by the formation of Mo zones, is clearly observed in alloys containing the critical amount of coexisting Co and Mo. After various age-hardening treatments, the behavior of heat evolution during reheating have been compared with those of the hardness tests. The results are useful in providing information on the aging reaction of the 470°C peak and its relation to that of the 530°C peak. In 475°C isothermal aging, for example, Mo zones are formed in the early stage of hardening, and then these zones are considered to be replaced by the intermetallic compounds in the later stage which corresponds to the aging reaction of the 530°C peak.View full abstractDownload PDF (595K) -
Setsuo Takaki, Youichi Tokunaga1979 Volume 43 Issue 9 Pages 840-845
Published: 1979
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe Strengthening behavior by the repeated strain againg and the low temperature aging process in maraging steels containing 18%Ni, 8%Co and 5%Mo have been investigated by specific heat and electric resistance measurements and also by the tensile test. The effect of cold working in the solution treated condition on the tensile strength and on the low temperature aging reaction is not significant. On the specimen aged at 475°C for a few minutes, cold working, however, greatly increases the tensile strength and also promotes the low temperature aging reaction in the following aging. During the first aging, Mo rich zones are formed on dislocation lines and pin down them, and the subsequent cold working increases the dislocation density by multiplication. The newly introduced dislocations supply sites for Mo zone formation, resulting the promotion for the reaction of low temperature aging in the following aging. Therefore, the repetition of aging and cold working results in a remarkable increase of the tensile strength. For example, the tensile strength of specimens treated 10 cycles repeated strain aging (5% reduction in area and 475°C-2 min aging) reaches 1700 MPa, which exceeds the highest tensile strength 1530 MPa attained by the static aging at 475°C for 20 h.View full abstractDownload PDF (548K) -
Yoshiro Ibaraki, Toshimi Sasaki1979 Volume 43 Issue 9 Pages 845-850
Published: 1979
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe micro-structure of as-cast Ti-6Al-4V alloy is the acicular alpha or the Widmanstätten structure, and it is believed that this structure cannot be changed to other structures by the conventional heat treatment. As forging or rolling cannot be amployed after casting, it is desirable to obtain a pre-heat-treated structure that can be conventionally heat-treated.
The cyclic heating has been developed, by which the acicular alpha or Widmanstätten structure is decomposed to give a two-phase structure (alpha+beta) capable of being conventionally heat-treated.
Two to 50 cycles of heating from 500 to 850∼950°C at a heating rate of 5.8 to 225°C/min have been applied to the castings and the micro-structual changes and the diffusion of the alloying elements were examined by means of a microscope and an X-ray microanalyser.
The following conclusions are obtained.
(1) The cast microstructure is improved by the cyclic heating and became nearly equiaxed alpha grains similar as in the forgings.
(2) It is possible to heat-treat this microstructure by the conventional heating method, and the two-phase structure (alpha+beta) is obtained.
(3) The diffusion of Al and V atoms is observed to stabilize the alpha and beta phase.View full abstractDownload PDF (837K) -
Nobuyuki Mori, Keisaku \={O}gi, Kimio Matsuda1979 Volume 43 Issue 9 Pages 851-858
Published: 1979
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSTo clarify the growth process of string ghosts in ingots, Al-3.5%, 5.5%, 15%Cu, Al-6%, 14%Mg, and Al-6%Mg-1.2%Cu alloys were holizontally, unidirectionally solidified, and quenched during solidification.
At low solidification rates (R), many string ghosts appeared in Al-Cu and Al-Mg alloys, in which the density of the interdendritic liquid (ρLS) changes remarkably with an increase in fraction of solid. On the other hand, few string ghosts appeared in Al-6%Mg-1.2%Cu alloy, in which ρLS is almost unchanged during solidification. In the holizontal cross-section of the specimens, the area occupied by string ghosts increased linearly with an increase in 1⁄R. The effect of R was larger in Al-Cu alloys than in Al-Mg alloys.
Tiny string ghosts arising from the neighborhood of the solidification front grow up to large ones with the progress of solidification. Since their growth is accompanied by the fluid flow in themselves, they cannot grow in the region with the fraction of solid exceeding 0.8±0.05 for Al-5.5%Cu alloy, or 0.7±0.1 for Al-14%Mg alloy, in which interdendritic liquid scarcely flow.View full abstractDownload PDF (1417K) -
Nobuyuki Mori, Keisaku \={O}gi, Kimio Matsuda1979 Volume 43 Issue 9 Pages 858-865
Published: 1979
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSMacrosegregation in holizontally solidified Al-5.5%Cu and 14%Mg alloys resulted mainly from fluid flow in the mushy zone which is composed of a number of dendrite arms and some string ghosts. The main driving force for the flow is gravity acting on liquid during solidification.
In this paper, the mushy zone is simulated as porous medium with pipes. Applying D’Arcy’s and Poiseuille’s Laws to the fluid flow in the mushy zone, the flow velocities and the resulting macrosegregation are numerically analyzed. The diameter and distribution of the pipes are decided on the basis of the experimental results on the formation of string ghosts.
The analysis shows that solute-rich interdendritic liquid flows into the bulk liquid through the string ghosts, resulting in a distinctive macrosegregation in the slowly solidified specimens. The calculated effective segregation coefficient (Ke), which is a measure of macrosegregation, decreases with an increase in 1⁄R, thus showing good agreement with the experimental result.View full abstractDownload PDF (677K) -
Hiroh Numata, Shiro Haruyama1979 Volume 43 Issue 9 Pages 866-871
Published: 1979
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSImpedance measurement of Ni/Ni(II) electrode reaction has been made in the LiCl-KCl eutectic melt in the frequency range between 100 K∼0.01 Hz, with regard to the exchange current density, electrical double layer and transfer coefficient. The experiments were made at 500°C under argon atmosphere. The electrode potential of nickel in the molten salt containing NiCl2 (1×10−2∼9×10−1 mol%) revealed a reversible potential. The cathodic polarization curves exhibited a limiting current density controlled by diffusion of nickel (II) ion, whereas the anodic branch obeyed the Tafel relation. The Cole-Cole plot of the electrode impedance consisted of a semicircle at high frequencies and a straight line with a slope of 45° at low frequencies, which corresponded to the charge transfer and diffusion process respectively.
The exchange current density obtained from the radius of the semicircle increased with increasing Ni(II) concentration from 1.18 to 9.75×104 A·m−2 the transfer coefficient being 0.49. The double layer capacitance depended strongly on the electrode potential, exhibiting a diffuse-type character.View full abstractDownload PDF (493K) -
Kazumi Ogino, Hitoshi Taimatsu1979 Volume 43 Issue 9 Pages 871-876
Published: 1979
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe surface tension of liquid Ni-O alloys and the wettability of Al2O3 substrates by liquid Ni-O alloys were measured by a sessile drop method in an atmosphere of Ar+H2O+H2 gas mixtures at 1873 K. The adsorption of oxygen in a surface layer and the adhesion in the liquid Ni-O alloy/Al2O3 substrate interface were considered on the basis of experimental results. The following conclusions have been obtained.
(1) The surface tension of liquid Ni was remarkably lowered with the addition of a very small amount of oxygen.
(2) Excess surface concentration corresponding to monolayer coverage was 18×10−6 mol/m2, and this value agreed approximately with the reported values in the liquid Fe-O system.
(3) The wettability of Al2O3 by liquid Ni was strongly affected by the dissociation of Al2O3 in the region of very small content of oxygen (<0.003 wt%O) and the formation of NiAl2O4 layer at the interface in the region of higher oxygen contents (>0.005 wt%O).View full abstractDownload PDF (540K) -
Minoru Ichimura, Mamoru Imabayashi, Masahiro Hayakawa1979 Volume 43 Issue 9 Pages 876-883
Published: 1979
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe diffusion coefficient (D) and solubility (S) of hydrogen in solid aluminum (99.99%) were measured by the vacuum solid extraction method. The temperature dependence of D and S obtained for the specimens melted in vacuum and solidified unidirectionally are as follows:
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\ oindentThese values represent the behavior of atomic hydrogen in aluminum lattice. For the specimen melted in air and solidified in a metal mold, it was found to decrease the diffusivity and to increase the solubility as compared with the above values, and these discrepancies were more remarkable at lower temperatures. These changes in D and S can be explained simply by a void model based on the equilibrium between gaseous hydrogen in voids and atomic hydrogen dissolved in the lattice. The apparent diffusivity and solubility are a function of total volume of voids which are formed by hydrogen gas during the solidification process of specimens. The differences in the melting or casting condition of specimens will be one of the most probable reason for the large scatter in the data reported previously for the diffusivity of hydrogen in pure solid aluminum.View full abstractDownload PDF (698K)
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