The Hall coefficient RH and the magneto-resistance Δρ⁄ρ0 were measured near 4.2 K on HgTe single crystals annealed at 553-723 K in the Hg vapour of 300 Pa-500 kPa. RH and Δρ⁄ρ0 showed the dependence upon the magnetic field in the range between 0 and 960 kA/m. Analyzing these results by the two carrier model, the carrier concentrations, Ne and Nh, and the carrier mobilities, μe and μh, were obtained. The subscripts e and h refer to electron and hole, respectively. Ne was in proportion to Hg vapour pressure PHg, while Nh was in reverse proportion to that in the experimental range of PHg. μe and μh had the maximum μe∗ and μh∗ at almost the same PHg∗, respectively. Both varied in proportion to PHg1⁄2 in the case of PHg<PHg∗, but to PHg−1⁄2 in the reverse case. The concentration product Ne·Nh was calculated at different temperatures and found to be constant independent of temperature, even though the crystals were annealed at different temperatures and pressures. The value of Ne·Nh⁄T3 was plotted against 1⁄T, and then thermal energy gap Eg=−0.32 meV was obtained from the slope of the curve. The negative value suggested that HgTe behaved as semimetallic.
Ribbon-shaped thin samples of the enforced solid solution of Al-Cu alloys (10-33 mass%Cu) were obtained by the rapid solidification using a rotating single roller technique, and the decomposition process of the enforced solid solution and the formation behavior of the periodic structures were investigated with a high resolution electron microscope (HREM). The solid solutions of Al-10, 15 and 20 mass%Cu alloys decompose rapidly by the aging heat treatment, and the characteristic periodic structure in which the Cu concentration changes periodically in the 〈100〉 direction with the spacing of about 0.8 nm was formed over a wide region of the alloys. The periodic structure grows gradually with aging time in the longitudinal direction keeping the spacing constant, and is replaced by the intermediate θ′ phase at the later stage of aging. With increasing aging temperature, the fine periodic structure changes into a more coarsened one, and above a critical temperature no periodic structure is formed. In Al-25 and 33 mass%Cu alloys, finer periodic structures are formed rapidly during solidification. Through the continuous HREM observation of the same regions in specimens, the aging condition as well as the formation process in which the periodic structure is formed is clarified.
In order to clarify the origin of considerable discrepancies among the reports on the work-hardening rate without dynamic restoring effect, h, and the softening rate without work-hardening effect, r, the two parameters have been measured by three different techniques; stress change, strain rate change and stress relaxation tests. These techniques have been applied to high-temperature steady-state deformation of pure aluminum with the same deformation and heat-treatment history, and it has been examined whether the discrepancies come from the difference in production history or the difference in experimental technique. It has been found that h values for the same deformation state agree with one another within less than 30 per cent and r within less than 20 per cent. The differences are much smaller than those found among the reports. It is concluded that the disagreements found in the previous reports are caused not by the difference in test technique but by the difference in production history of specimens.
Grain boundary sliding in five kinds of symmetric tilt coincidence systems was investigated for five types of orientation controlled bicrystal specimens of aluminium. The sliding behaviors were analyzed by the DSC dislocation mechanism. The grain boundary migration/sliding ratio was fixed for all the observed grain boundaries. Both the direction of the grain boundary migration and the magnitude of the migration/sliding ratio of one of the five grain boundaries were explained by the DSC dislocation mechanism previously proposed by Smith et al. Behaviors of the other four grain boundaries could not be explained by their model. It was found that not the step height minimum principle but the step vector in coincidence with a low index plane of one of the component crystals governed the selection of the grain boundary dislocations.
The influence of the notch shape on the elongation has been investigated for a Sn-38.1 mass%Pb superplastic alloy, using specimens with a couple of various V-type notches or a small hole-type notch. It seemed that the elongation of the notched specimens had a correspondence with the ratio of the cross-sectional area of the specimen, An⁄As, where An: the minimum area appearing at the bottom of notch and As: the original area in smooth part. However, since the concept based on the ratio itself had no consideration on any significant difference due to the shape of notch, the analysis could not explain the variation in the elongation of specimens with the different shape of notch. Therefore, according to a simple model proporsed for superplastic deformation, which was taking acount for distributions of both the strain rate and the m-value over the gage length on the specimen, a comparison between the experimental elongations and the calculated values through the present model was carried out systematically. Finally, it has been shown clearly that the both are in a fairly good agreement. It has been also considered that the flow stress during superplastic deformation up to before the fracture is almost directly related to the true strain rate.
Two types of internal friction caused and controlled by diffusion along the interface between a second phase particle and a matrix were studied using a Cu-GeO2 alloy. A relaxation peak was observed at 700 K-800 K in single crystals at a frequency ∼1 Hz. The relaxation time was proportional to the third power of the radius of GeO2 particles, indicating that the relaxation was caused by diffusion at the GeO2 particle-Cu matrix interface. The activation energy for interfacial diffusion was 1.5 eV. In polycrystalline samples, an additional internal friction peak was observed besides a peak identical to that observed in the single crystals. The relaxation time was proportional to the fourth power of the GeO2 radius and the grain size and inverserly proportional to the square of the GeO2 particle spacing on the boundaries. From this observation together with the magnitude of the relaxation strength, this additional relaxation was identified as being caused by grain boundary sliding, the effective viscosity of which was controlled by the interfacial diffusion of Cu-GeO2. The activation energy determined for this relaxation was in agreement with that for interfacial diffusional relaxation in the single crystals.
The evolution rates of SiO from silicate melted in a graphite crucible as a reductant have been studied by means of thermogravimetry under an atmosphere of argon, particularly at high temperatures, in order to investigate the reaction mechanism of SiO evolution from coke ash and blast-furnace slag. The main volatile species in silicate melts are SiO and Mg, but the evaporation of Ca and Al2O also can not be neglected at high temperatures. The evolution of SiO from silica is greatly accelerated by the addition of CaO, MgO or Al2O3, but is retarded when the latter oxide is added in excess. The addition of MgO to blast-furnace-type slag significantly retards the generation of SiO. The temperature dependence of the evolution rate of SiO at higher temperatures is larger than that at lower temperatures. These results may be explained by the fact that the slag composition exerts an influence upon the activity of silica and the fluidity of the slag, and by the assumption that the interfacial area for the reaction is dependent upon the wetting of the slag to the graphite crucible and the foaming of the slag.
A dense plate of Ni3S2-10 mass%Co9S8 was oxidized in a mixed O2-N2 gas stream at 923, 973 and 1023 K. Oxygen partial pressure was maintained at 2.0×104 Pa. In the earlier stage of oxidation, the sample mass was increased in accordance with the parabolic rate law. The rate of mass increase was higher than the rate of oxidation of Ni3S2 which was previously reported. A very small amount of SO2 gas was evolved in the initial few hundred seconds of oxidation and no SO2 gas was evolved thereafter. Two layers of oxide were formed on the sample surface; the outer layer was Co3O4 in which a small amount of nickel was contained, and the inner layer consisted of mixed Ni-Co oxide, (Ni, Co)O. The thickness of (Ni, Co)O layer increased rapidly in the earlier stage of oxidation at 1023 K. After a period of about 2 ks had elapsed, the Co3O4 layer was started to be formed, and the growth rate of (Ni, Co)O layer was lowered. The increase of the thickness of these oxide layers was also in accordance with the parabolic rate law. The apparent activation energy for the formation of (Ni, Co)O layer was estimated at 240 kJ/mol. The concentration profiles of NiO and CoO in the (Ni, Co)O layer were measured by EPMA. They were calculated on the basis of diffusion of Ni and Co in the same oxide layer. It was revealed that good agreement was obtained between the observed and calculated profiles.
Photocurrent iph vs. potential E and quantum efficiency φ vs. photon energy hω curves were measured on passive films of Fe-Cr alloys, pure Fe and pure Cr in neutral Na2SO4 solutions. The same kinds of measurement were conducted on thin films of γ- and α-Fe2O3, Cr2O3, NiO, and composite oxides of Fe2O3-Cr2O3 formed on Pt using MO-CVD technique. Conduction types and bandgaps of the passive films were examined based on the characteristics of these curves, comparing them with the results from the thin films. It was found that the passive films on pure Fe and Fe-Cr alloys containing 5 to 20 mass%Cr had n-type conduction and those on the alloys containing 30 to 80 mass%Cr and pure Cr had p-type conduction. Bandgaps of the passive films formed at 0.4 V on the former group increased from 2.28 eV for pure Fe to 2.66 eV for Fe-19 mass%Cr alloy with increasing Cr content. The results on the thin films formed by MO-CVD showed that their thickness did not affect the feature of iph vs. E and φ vs. hω curves but the magnitude of iph. The conduction type and the bandgap of the composite oxide films changed with their cationic mass fractions of Cr3+ ions, XCr. That is, the films of XCr<0.5 had n-type conduction and their bandgaps increased from 2.25 eV for XCr0=(γ-Fe2O3) to 2.48 eV for XCr=0.42, whereas those of XCr>0.8 p-type conduction. The changes in conduction type and bandgap of the passive films on Fe-Cr alloys can be explained from these results of the composite oxide films.
The determination of oxygen in powder of aluminum and its alloy by the inert gas fusion method has been investigated. The apparatus was equipped with an impulse furnace using nitrogen as a carrier gas. Nickel foil was used as a metal bath, and the comparison study between a metal bath method and a graphite capsule method using together with a nickel foil metal bath was performed. In the analysis of aluminum powders, three times of the amount of nickel foil as many as that of a sample were used and a gas extraction temperature was 2173 K. This technique was compared with the graphite capsule method in which gas was extracted at 2273 K. The analytical values well agreed with each other. The recovery of oxygen was over 98% when analysing the synthetic samples in which aluminum oxide was added, and so it was confirmed to completely extract oxygen in samples. In the analysis of Al-Zn(5.6%)-Mg(2.6%) powder (Extra super duralumin), ten times of the amount of nickel foil as many as that of a sample were used and increasing temperature method (1873→2173 K) was applied. In the analysis of Al-Ti-Ta alloy powder (MA 6000 master alloy), ten times of the amount of nickel foil were also used and a constant temperature method (2173 K) was applied. The analytical values by the metal bath method well agreed with those by the graphite capsule method. A rapid and accurate method has been established.
An analytical method has been established for the determination of trace tellurium and gallium in nickel-base heat-resisting alloys by graphite-furnace atomic absorption specrrometry. The alloy was dissolved in hydrofluoric acid nitric acid. After the solution (20 mm3) was pipetted into a L’vov platform furnace, it was ashed (Te; 1073 K-40 s, argon 5 cm3/s. Ga; 873 K-40 s, hydrogen 5 cm3/s) and atomized (Te; 2373 K-5 s. Ga; 2873 K-5 s) by using argon as a purge gas. Synthetic calibration solutions were prepared by adding tellurium and gallium standard solutions to nickel matrix solutions which had the same acid concentrations as those of the sample solutions. Relative standard deviation of the proposed method was within 3% at 12 ppm of tellurium and 4% at 8 ppm of gallium in nickel-base heat-resisting alloys. The limit of detection was 0.1 ppm of tellurium and 0.15 ppm of gallium, when one gram of the specimen was used.
An investigation is reported on stirring conditions and grain refinement of Al-Cu alloys including 10, 24 and 30 mass% copper with high ductility at an elevated temperature in the vacuum rheocasting in which the alloy is violently agitated at very high rotation speeds of a stirrer inserted in the solid-liquid coexisting zone. The results are as follows. The average size of primary solid particles in these alloys is consistently decreased with the increase in rotation speed from 20 to 67 rev/s at a cooling rate of about 0.42 K/s. The primary solid particle sizes at 67 rev/s are 90±29 μm in Al-10%Cu, 61±32 μm in Al-24%Cu and 46±14 μm in Al-30%Cu. The primary solid particle is more refined into 41±12 μm in diameter at a stirrer speed of 67 s−1 by addition of grain refiners of 0.5%Ti and 0.1%B to Al-24%Cu. It also becomes smaller in the rheocasting of Al-10%Cu and Al-24%Cu alloys in a mold with ribs machined along the face of cylindrical wall. The values of elongation at 773 K are 91% in Al-24%Cu and 71% in Al-30%Cu at an initial strain rate of 1.19×10−3 s−1.
The present study aims at the correspondence between theory and practice on the particle size distribution of actual powders. First, from the investigation into the particle size distributions of twenty eight kinds of metallic (iron and copper) powders, a comparison was made between the adaptabilities of two practical distribution laws, namely the log-normal and the Rosin-Rammler ones. Based on the results, a modified Rosin-Rammler distribution was deduced for the conformation to the reality of the powders. Then, another investigation was carried out to obtain interrelations between the mathematical parameters of mass and number bases in the modified distribution for the connection between the measurement and the theoretical analysis. The results are summarized as follows: (1) The modified Rosin-Rammler distribution law shows a good adaptability for the actual powders in the same way as the conventional Rosin-Rammler one. (2) There are certain well-ordered interrelations between the parameters of mass and number bases in the modified equation, which can be expressed by the simple eqs. (19) and (20). (3) The relative deviation estimated by the modified eq. (17) is only 0.051 at most according to the computation by the analytical eq. (16). That deviation can be further suppressed down to 0.010 at most by the application of the eq. (21). These are applicable not only to metallic powders but also to all the powders to which the (modified) Rosin-Rammler distribution is adaptable.
Monotectic Al-Bi, Al-Pb binary alloys and Al-Bi-Pb ternary alloys were solidified unidirectionally in various growth conditions. The alloys were quenched during growth to observe the monotectic growth front morphology. Attempts were made to produce the instability of the solid-liquid interface by adding 0.025 mass%Fe to Al-Bi alloys. Morphology of monotectic composite varies depending on the ratio of temperature gradient G/growth rate R. Random dispersion of L2 droplets forms at G⁄R below 109 Ks/m2, on the other hand, a regularly arrayed fibrous composite structure forms at G⁄R over 109 Ks/m2. Further increase of G⁄R results in the growth of aluminum single phase structure without L2 phase. The addition of Fe increases the critical value of G⁄R for the structural transitions. Morphological change in the monotectic structure of aluminum base alloys is explained by the interfacial energy balance between a solid and two liquids as well as the interaction between liquid L2 phase and monotectic growth front.
Magnetization, Young’s modulus and thermal expansion at 150-600 K and crystal structures at room temperature were investigated for Mn-Ge based ternary alloys containing Ti, V or Cr less than 14% which have various structures such as γ(14%Ge), γ+ε(16-20%Ge) and ε(22%Ge) phases. Magnetization value of the ternary alloys are at the most 0.4-0.5×10−6 Wb·m·kg−1 in the range of measured temperatures. Temperature dependence of magnetization of the ternary alloys shows a similar tendency to that of the basal binary alloys and distinct variations at Tt, TN(ε) and/or TN(γ) corresponding to the β\
ightleftarrowsγ or β\
ightleftarrowsε reversible phase transformation, antiferromagnetic Néel point of the ε phase and that of the γ phase, respectively. At each point of Tt, TN(ε) and TN(γ), both Young’s modulus and thermal expansion of the ternary alloys show distinct variations. Elinvar characteristic is observed in the temperature range between Tt and TN(ε) or in the range below TN(γ), and a small thermal expansion coefficient is obtained in the temperature range below TN(ε) for the alloys having an ε or ε-rich phase. A very small temperature coefficient of the Young’s modulus in the vicinity of room temperature is obtained in the wider composition range for the Mn-Ge-Ti system than that of the alloys containing V or Cr. Unlike the case of elasticity, Mn-Ge-Cr alloys show a small thermal expansion coefficient in the wider composition range than that of other alloys. In the Mn-Ge-V alloys, there are some composition ranges in which both a very small thermal expansion coefficient and a small temperature coefficient of Young’s modulus are observed in the vicinity of room temperature. Therefore, the temperature coefficient of the ultrasonic delay time shows a relatively small value.
Precipitation in nickel-rich Ni-Al-Mo ternary alloys in the temperature range from 873 to 1373 K has been investigated by transmission electron microscopy, selected area electron diffraction and hardness measurements. Various stable and metastable phases, γ′, NiMo(δ), Ni2Mo, Ni3Mo and Ni4Mo, and short range order (SRO) are formed during ageing of the alloys depending on the alloy composition and ageing temperature. Constitutional diagrams showing the fields in which each precipitate forms are presented. The γ+γ′ two phase region extends to the lower Al region at low temperatures. Ni2Mo, Ni3Mo and SRO form in the alloys with wide compositional ranges. Ellipsoidal or polyhedral Ni2Mo, plate-like Mo and cuboidal γ′ are considered to be important strengthening phases of the Ni-Al-Mo ternary alloys. Precipitation of grobular δ phase occurs at high temperatures only in the alloys with high Mo content.