Amorphous specimens were prepared in the range of 10≤X≤35 at%B by a single roller method. The crystallization process and the B concentration dependence of the Curie temperature were examined by differential scanning calorimetry, X-ray diffraction, Mössbauer spectroscopy and magnetic measurement. Two step crystallization was observed in the specimens of X<17: Amor.→Amor.+B supersaturated bcc phase (α-Fe(B))→t-Fe3B+α-Fe. The single α-Fe(B) phase was not observed. The transition temperature from t-Fe3B to stable (α-Fe+t-Fe2B) sensitively depends on B content in the alloys. The crystallization temperature (TX) of the amorphous alloys was almost unchanged in 17≤X≤31, but increased remarkably in the high boron concentration of X≥33, where the decomposition products consisted of t-Fe2B and o-FeB. The Curie temperature (TC) of the amorphous phase is as low as 480 K at X=10, increased with increasing B content up to 820 K and then decreased in the high B concentration alloys of X>28. The single α-Fe(B) phase was not detected in the as quenched specimens of X=8 and 10. The phase coexisted with the o-Fe3B and amorphous phases. The lattice parameter of the phase was 0.28610 nm which was smaller than that of pure iron by 2/1000, indicating the substitutional occupation of boron atoms in the bcc lattice.
The effect of annealing and creep deformation on the internal friction of metallic glass wire Pd77.5Cu6Si16.5 was investigated by the inverted torsion pendulum method. It was found that after an extended period of annealing, the glass reaches an internal pseudo-equilibrium state with respect to the internal friction which is a function of the annealing temperature. Cold rolling of the metallic glass ribbon Fe32Ni36Cr14P12B6 gives no change in the internal friction. And the tensile creep along the wire axis also causes no change in the internal friction of the metallic glass. On the other hand, the torsional creep results in a remarkable increase in the strength of internal friction, and the increased value decreases to the initial level with the recovery of torsional strain by additional annealing. To explain the change in the internal friction with the annealing temperature and tortional creep, a model of anelastic structural defects in the metallic glass is proposed.
The composition, crystal structure and hardness of TiAl(γ) phase contained in Ti-48-54 at%Al-0-12 at%Zr alloys annealed for 1 week at 1273 K have been studied. Obtained results are as follows: Soluble Zr atoms enter only into the Ti-sites of sublattice and increase only the a value of the lattice parameters, while, an increase of Al content increases only the c value. These anisotropic effects of the elements on the lattice parameters are attributed to the fact that covalent-like bonds are formed between the Ti atom layer and the Al layer. A region of a high degree of order shifts from (Ti1−xZrx)Al to Ti-rich side on the high Zr side. This cause is considered to be that Ti atoms play the same role as Al in the high Zr phase. A region of a low degree of order is located on the high Zr and high Al side, which is attributed to the existence of a degenerated ternary compound. The hardness depends not on the axial ratio c⁄a but on the degree of order. The solution hardening by Zr is observed only when the amount of the addition is small.
Electrical resistivity measurements, X-ray diffractometry and transmission electron microscopy of Fe-Pd alloys have been carried out. The electrical resistivity of 50-80 at%Pd alloys increases rapidly with ordering below the order-disorder transition temperature (Tc), while it is nearly constant in the disordered phase above Tc. Below Tc these alloys have the FePd superlattice (L10 type) in the range of 50-58 at%Pd and the FePd3 superlattice (L12 type) in the range of 63-77.5 at%Pd. All of the alloys below Tc are formed with long-range order. Fe-Pd ordered alloys are the first to show an increase in electrical resistivity associated with the formation of long-range order. It is suggested that the formation of superlattice of Fe-Pd system can be explained by the Brillouin Zone effect.
Reaction diffusion between pure Cu and Hf was studied in the temperature range from 1023 to 1223 K. Formation of six intermetallic compounds, Cu5Hf, Cu4Hf, Cu7Hf2, Cu3Hf, Cu3Hf2 and CuHf2, was observed in the diffusion zone. The layer thickness of these intermetallic phases, except Cu7Hf2 above 1173 K, was found to increase obeying the parabolic law, showing that the growth of phase layers was controlled by diffusion process. The temperature dependence of the growth rate constants of the Cu5Hf, Cu4Hf, Cu3Hf and CuHf2 phase layers satisfied the Arrhenius relationships. However, above 1173 K that of the Cu7Hf2 and Cu3Hf2 phase layers deviated downward from the Arrhenius relationship; the deviation was attributed to the growth of Cu3Hf phase and the transition of the Cu7Hf2 phase to the Cu4Hf phase at higher temperatures.
Specimens of Nb and Nb-40V having grain sizes 21 and 17 μm, respectively, were irradiated in JMTR (Japan Materials Testing Reactor) to a total neutron fluence 1.0×1023 m−2 (E>1 MeV). Tensile test was conducted for the unirradiated and irradiated specimens at a temperature range 293 to 77 K. The deformation structure was observed by optical and transmission electron microscopy. From the surface observation of the fractured specimens, deformation twins were found to be more extensively distributed in the irradiated Nb-40V than in the unirradiated Nb-40V specimen. No deformation twins were observed in unirradiated and irradiated Nb. The irradiated Nb showed a representative behavior in the mechanical properties, as general bcc metals, that is, the radiation hardness and radiation embrittlement occurred. On the other hand, the irradiated Nb-40V showed an anomalous behavior in the mechanical properties. The radiation softening occurred in Nb-40V, that is, the yield stress decreased by the irradiation, and moreover, it was constant over a whole range of tested temperature. The elongation of irradiated Nb-40V was almost the same as that of the unirradiated at 293 K and also maintained a constant value in the whole temperature range. For the unirradiated Nb-40V, the relation between the grain size and the mechanical properties was investigated. The specimen having a large grain size (45 μm) showed the mechanical properties similar to the irradiated specimen with a smaller grain size (17 μm), that is to say, neutron irradiation had the same effect as the increase in grain size on the mechanical properties as well as the occurrence of deformation twins for Nb-40V.
(1) In order to develop a new gamma prime precipitation hardened nickel base alloy which satisfies the specified strength of Alloy X-750 and has a stress corrosion cracking resitance in high temperature pure water superior to the Alloy X-750, we have studied on the effect of alloying elements as C, Cr, Ti, Nb and Al and heat treatment on the tensile properties, the precipitation behaviour and the stress corrosion cracking resistance of the gamma prime precipitation hardened nickel base alloys at 360°C in simulated primary water, based on our previous studies on the correlation between the stress corrosion cracking resistance and the type, morphology and coherency of precipitates at the grain boundaries of the Alloy X-750. As a result of the present study, it has been revealed that the gamma prime precipitation hardened nickel base alloy with C content higher than 0.02%, Cr content higher than 20% and similar contents of Ti, Nb and Al to those of the Alloy X-750 has an excellent stress corrosion cracking resistance. (2) In order to develop a new gamma double prime precipitation hardened nickel base alloy which satisfies the specified strength of Alloy 718 and has a superior stress corrosion cracking resistance in high temperature pure water to the Alloy 718, we have studied on the effect of alloying elements as C, Cr, Mo and heat treatment on the tensile properties, the precipitation behaviour and the stress corrosion cracking resistance of the gamma double prime precipitation hardened nickel base alloys at 360°C in simulated primary water. As a result of this study, it has been revealed that the gamma double prime precipitation hardened nickel base alloy with C content less than 0.07%, Cr content higher than 22%, Mo content higher than about 2.0%, higher Nb content and lower Ti and Al contents than those of Alloy 718 has an excellent stress corrosion cracking resistance.
Experiments have been made on the reduction of NiO pellets containing MgO with H2 or CO-CO2 mixtures bearing gaseous sulphur in the temperature range from 773 to 1273 K using a thermobalance; the sulphur activity in the reducing gas ranged from the value in the coexistence of Ni and Ni sulphide to 10−2 of it. Except the reduction of pure NiO with H2 or 99%CO-1%CO2 mixtures, a macroscopic reduction pattern of a pellet in the absence of sulphur is a homogeneous type with the formation of a dense Ni shell on the entire surface of NiO particles, and the pattern in the presence of sulphur is a topochemical type with the formation of a fine porous Ni layer. The reduction in the former pattern is retarded following the rate equation of oxygen diffusion control through a dense metallic nickel layer, while in the latter one it proceeds without the retardation and conforms with the mixed control equation. These facts are also observed in the reduction of pure NiO with 50%CO-50%CO2 mixtures. The phenomena mentioned above can be interpreted by a mechanism that adatoms of sulphur on the surface of metallic Ni suppress the development of the bonding between Ni and NiO. The gas diffusion through a porous Ni layer and the mass transfer in NiO solid were discussed using some diffusion data available.
The viscosity of all kinds of the alkali fluoride melts has been measured over the temperature range from the respective melting temperature to about 1370 K by the use of a high temperature oscillating vessel viscometer. The viscometer has been modified so as to be able to measure the period and the logarithmic decrement from the observed intervals between the times when the oscillation passes two deflection angles, and to calculate the viscosity automatically. Discussion has been made on the sources of error accompanying the measurement. The results are summarized as follows: (1) The largest error in the measurement is considered to be the one in the determination of radius of crucible. The limit of error is estimated to be 1-2%. (2) Values of the viscosity of alkali fluorides at the melting temperatures lie in the range of 1.35-1.9 mPa·s. LiF and KF show the highest and lowest values, respectively, at their melting temperatures. Values of apparent activation energy for viscous flow of molten alkali fluorides are nearly identical with those of molten alkali chlorides. (3) Values of the viscosity obtained were analyzed on the basis of the corresponding state principle. By the use of Dymond’s equation, the relation among the reduced temprature, volume and viscosity has been calculated. The reduced volume is the ratio of volume at the experimental temperature to that at the melting temperature. Values of the viscosity of molten alkali fluorides calculated from the equation agreed well with the experimental ones within 10%.
Oxidation of Sm, Eu and Gd was investigated by conventional weight gain tests and SEM with small plates (1 mm×1 mm×0.2 mm) and by the measurement of resistivity of metal thin films in oxygen atmosphere at elevated temperatures. The temperature at which the oxidation of Sm thin film (thickness: 1 μm) began was 780 K and was close to that for the oxidation of Sm metal plate. Thin films of Eu and Gd (thickness: 1 μm) oxidized abruptly above about 400 K. However, the oxidation temperatures of the metal plates differed largely from one another. The reaction kinetics for Sm was parabolic and the others obeyed a linear oxidation law. The values of the activation energy of oxidation were compared with those reported in the literature. Further, the state of surface oxide was briefly discussed on the basis of the SEM photographs of cross sections of the oxidized Eu and Gd plates.
Corrosion of iron, nickel, chromium, stainless steels and Cr-Mo alloy in (Na, K)2SO4-Fe2(SO4)3 melt has been studied with the electrochemical polarization technique at 923 and 973 K under SO2-O2-CO2 atmosphere. The rate of corrosion estimated from polarization resistance was consistent with that obtained from mass loss. With the increase in chromium content of the alloys, the rate of corrosion decreases shifting the corrosion potential to anodic direction. This behavior was well explained by the superposition of the partial anodic and cathodic polarization curves. The partial cathodic reaction is the cathodic reduction of ferric ion in the melt, which was independent of the composition of the alloys. The anodic polarization curves exhibit a passive region. Both the currents at the peak and the passive state decrease with the increase in chromium content of the alloys. Therefore, high chromium alloys are highly corrosion resistant in molten sulfate. The result is well consistent with that obtained by Salt-coating test.
To obtain fundamental data on the compatibility of high-chromium ferritic steels in sodium, high-purity Fe-0.1C-1Mo-5, 9 or 13Cr ferritic steels were prepared by vacuum melting. Test specimens of these steels which were normalized and tempered and a reference type 316 stainless steel (316 ss) were exposed to two sodium-velocity regions for periods up to 10.8 Ms in a sodium loop system which had a direct resistance main heater and was made of SUS 316. The test temperature, the maximum temperature, of the loop system in this work was 873 K, the oxygen content of sodium was 1-2 ppm, and the sodium velocities were about 4.0 and 0.02 m/s. The specimens exposed to the high sodium-velocity region revealed that corrosion loss at a zero downstream position of the three kinds of ferritic steels was smaller than that of the reference 316 ss; about one fifth for the 5 and 9%Cr steels and one half for the 13%Cr steel. The surface analysis showed deposition of Ni that dissolved at upstream for all the ferritic steels, deposition of Cr for the 5%Cr steel, and selective dissolution of Cr for the 9 and 13%Cr steels. The ferritic steels without Ni and with less amounts of Cr than the reference 316 ss would result in their smaller corrosion loss than the 316 ss. Transfer of carbon, nitrogen and oxygen was not remarkable, except the carburization of the 5%Cr steel. The specimens of the three kinds of ferritic steels which were exposed to the low sodium-velocity region revealed much smaller corrosion loss than that in the high velocity region, deposition of both Ni and Cr, and no transfer of carbon, nitrogen and oxygen except for slight carburization of the 13%Cr steel.
The self-activation of passivated titanium was investigated in a sulfuric acid solution. The stability of the anodically formed film on a titanium surface was measured under several values of applied current densities ranging from cathodic to anodic. The reduction process of the film was affected additively by the applied current. Under various conditions two kinetic parameters, the amount of the charge accumulated in the film, Qo, and the rate of the self-activation process, io, were obtained with the linear relationship between density of the applied current and the inverse value of the activation time. The linear variation of Qo with the passivation potential (1.85×10 C·m−2·V−1) is attributed to the formation of a barrier-type film. The values of io depend on the conditions, by which the values of Qo are not affected, such as pH of the solution and passivation time. This result is explained in terms of the presence of defect in the films.
To refine the grain structure of aluminum ingots, a 99.6 mass%Al melt was oscillated in shell, graphite or chill molds using a rod-type oscillator. The variables which affected the ingot structure were the frequency, the amplitude, and the oscillator position. The frequency range was 10 s−1 to 50 s−1 and the amplitude range was 0.2 mm to 4 mm. Thermal analysis carried out at various positions in the melt showed that the first solidification occurred on the mold wall touching the molten surface. The authors have already demonstrated that at this position equiaxed crystals are repeatedly formed and separated. Consequently, in most experiments, the oscillator was set horizontally near the mold wall, just below the molten surface. Increase in the frequency and the amplitude of the oscillator enlarged the equiaxed crystal zone and decreased the grain size. The oscillator must be heated to a temperature over 973 K, in order to prevent the trapping of the oscillator in the solidifying shell when a chill mold is used.
The grain structure of continuously cast aluminum ingots was refined without addition of a grain refiner. A ring-type oscillator which had a heating coil insulated with alumina cement was set just below the molten surface of a mold 80 mm in inside diameter. Coarse crystals at the chill zone and columnar crystals inside the chill zone appeared, when no oscillator used. As the temperature of the oscillator was lower than the melting point of aluminum, the oscillator was trapped by a solidifying shell, and so continuous casting was not possible. Main variables which affected the equiaxed crystal zone were the frequency, the amplitude and the diameter of the oscillator. In this experiment, the frequency was 20 s−1 to 50 s−1, the amplitude was 0.5 mm to 4 mm, and the diameter of the oscillator was 56 mm, 64 mm and 72 mm, respectively. The largest oscillator gave the largest equiaxed crystal zone. A greater frequency and amplitude enlarged the equiaxed zone still further. Using an oscillator 72 mm in diameter, a fully equiaxed crystal zone was obtained, when the frequency and the amplitude exceeded 40 s−1 and 4 mm, respectively.
Deterioration of ductility inward the bloom of continuously cast S43C steel associated with small casting defects was studied by tensile test and observation of fractured surface using a scanning electron microscope. Area fraction of the defects in fractured surface Rs, increased with increasing distance from surface to interior of the bloom, and fracture strain εf decreased. Appearance of fracture changed from cup-cone to shear with increase in Rs, and εf decreased linealy with increasing square root of Rs. It was found that these deteriorations were mainly attributed to the increase of small casting defects named intredendritic separation defect resulting from restriction of feeding to compensate the volume contraction in liquid-solid transformation during solidification. This presented a significant effect of the feedability on the ductility of cast steel.