Stable structures of Fe-Si-Al ternary alloys and Fe-Si and Fe-Al binary alloys containing Al+Si up to about 40 at% were investigated by means of transmission electron microscopy. Results obtained are as follows: Two types of phase separation, B2+DO3 and α+DO3, are observed in the alloys whose compositions lie in a narrow band connecting Fe-10-14 at%Si with Fe-20-25 at%Al and also in the neighborhood of a Fe-30 at%Al-3 at%Si alloy. Such compositions of the alloys are located in the phase boundary of B2 and DO3 single phases or α and DO3 single phases. The phase separation in the Fe-Si-Al and Fe-Si alloys produces the 〈100〉 modulated structure which differs from the morphology formed by the phase separation of the Fe-Al system.
Fracture toughness testing in a Ti-6Al-4V alloy with acicular micro-structure was carried out using 20 mm thickness compact tension specimens, hot-rolled in β-phase temperature range. During the test, the amplitude distribution of Acoustic Emission signals were monitored, and these detected signals were classified into small and large amplitude distributions. With the aid of light micro-photography and electron fractography, it was revealed that small amplitude emissions result from micro-cracking due to inclusions and α-β phase boundary, and large emissions from the coalescence of these micro-crackings, that is, micro pop-in, in the unit of blocking prior β grain. The onset of stable crack growth, therefore, can be defined by the appearence of large amplitude emissions, and it can be concluded that the dynamic fracture process can be understood by the measurement of AE amplitude distribution.
Polycrystalline specimens with a modulated structure of a Cu-4 mass%Ti alloy were stretched in the temperature range from 4 to 70 K and at 293 K, and resulting microstructure were observed. Relationships between deformation twinning and serrated stress-strain curves were studied. Results obtained were summarized as follows: (1) Serrated deformation or sharp load drops on the load-elongation curves were observed during stretching at temperatures below about 40 K. They occurred at stress levels lower than that corresponding to the proportional limit. The number of load drops increased with increasing stress level or strain and also increased with decreasing deformation temperature. No indications of serrated deformation were observed in stretching at 68 K and 293 K. (2) Deformation twins were observed in specimens stretched up to certain stress levels at all the test temperatures. Volume fraction of deformation twins increased with increasing stress level or strain. It increased with decreasing deformation temperature for the same amount of strain. (3) Sharp load drops detected at stress levels below the proportional limit are due not to “discontinuous slip” not to “thermal instability” but to the deformation twinning. The twinning stress can be given by detecting the first small load drop. The observed twinning stress has a tendency to increase with decreasing deformation temperature at the cryogenic temperature range. This temperature dependence of the twinning stress is explainable in terms of temperature dependence of the stacking-fault energy, which can be estimated from the electron concentration of this alloy.
A laser flash apparatus has been modified to make thermal conductivity and specific heat measurements possible for slag melts at elevated temperatures. Particular emphasis has been placed to work out a two layer composite cell to avoid convective heat transfer and stably contain the melts during the measurements. Further, a numerical method has been elaborated to derive the thermal conductivity by comparing observed temperature decay of Pt-plate on the melts in the cell with theoretical prediction of heat transfer equation that involves conductive and radiative component. Separation of the conductive component from radiative one has been shown satisfactory for CaO-SiO2 and CaO-SiO2-Al2O3 melts for which the thermal conductivities, λ, have been determined at 1273 through 1723 K to be λ=0.51(±0.03)−2.5(±0.2)×10−5T for CaO-45 wt%SiO2 λ=0.60(±0.03)−6.0(±0.2)×10−5T for CaO-35%SiO2-15%Al2O3 \
oindentand λ=0.89(±0.06)−7.6(±0.4)×10−5T for CaO-45%SiO2-20%Al2O3, where λ and T are in unit of J/m·s·K and K, respectively.
The present study is concerned with the kinetics of carbon reduction of MnO and the identification of Mn carbide formed in this reduction process by the effluent gas analysis method. The results are as follows: (1) At the earlier stage of reduction, Mn carbide (Mn7C3) was formed, and the activation energy of 217 kJ/mol which is nearly equal to that for the Boudouard’s reaction was obtained. (2) When carbon was consumed entirely, the reaction between MnO and Mn7C3 to yield metallic manganese occurred, and the activation energy of 259 kJ/mol which corresponds to the reaction of CO2 with Mn7C3 was obtained. (3) Mn carbide formed in the reduction process of MnO was identified to be Mn7C3 phase, by the effluent gas analysis method using the He-O2 mixture. In addition, EPMA and X-ray diffraction examinations showed the presence of Mn7C3 phase in this reduction product.
Measurements of thermodynamic quantities for the molten Ag2S-Sb2S3 and Cu2S-Ni3S2 binary mixtures were carried out by quantitative thermal analysis of the heating process. A double adiabatic wall calorimeter was used as the experimental apparatus. A proper experimental condition to determine enthalpies of the sulfide mixtures was established. Considerably large negative deviations from Raoultian behaviors were observed in aAg2S and aSb2S3 of the Ag2S-Sb2S3 system at 1123 K, double sulfide compounds seriously affecting the activities. While, slight deviations were observed in aCu2S and aNi2S2 of the Cu2S-Ni3S2 system at 1423 K.
It is of common knowledge that the synthesis of Ni2SiO4 from NiO and SiO2 by means of solid state reaction is very difficult. In this paper, the solid state reaction between NiO and SiO2 was studied by means of X-ray analysis, and the reaction of 2NiO+SiO2→Ni2SiO4 was discussed kinetically. When NiO was coupled with SiO2 and heated at 1673 K for 270 ks, the reaction layer about 10 μm thick was formed at the interface between NiO and SiO2. EPMA line analysis indicated that the reaction layer was composed of Ni2SiO4. The mixture of 2NiO and SiO2 was heated at temperatures between 1573 and 1673 K for a fixed time up to 100 ks, and the rate of reaction in 2NiO+SiO2→Ni2SiO4 was determined by means of X-ray diffraction analysis. The results indicated that the above-mentioned reaction followed the next equation of interface controlled reaction. (This article is not displayable. Please see full text pdf.) \
oindent(R=rate of reaction, k=apparent reaction-rate constant, t=time) In this experimental condition, the apparent activation energy of the reaction was approximately 248 kJ/mol.
Electrochemical impedance diagrams of Alloy 600 at active-passive transition potentials have been measured in sulphuric acid media of pH 0.0, 1.0 and 2.0 at 323 K over a wide range of frequencies, 10−3 to 104 Hz. It was found that the diagram for a partly passivated electrode, which can be obtained at a potential slightly lower than the passivation potential in a solution with lower pH, is composed of four semicircles; two of them are capacitive, the others inductive. The capacitive semicircle, which appeared in the highest frequency range in the diagram, was ascribed to the double layer capacity and the charge transfer resistance, the inductive one at higher frequencies to a dissolution reaction, the capacitive one at lower frequencies to a passivation-film-forming reaction, and the inductive one in the lowest frequency range to a passivation-assisting reaction. The degree of proceeding of the passivation in the alloy with increasing potential or solution pH can be evaluated from the vicissitudes of these semicircles in the diagram.
In order to improve the susceptibility of ultrahigh strength maraging steel to hydrogen gas environment embrittlement, the effect of aluminum coating prepared by ion-plating on the susceptibility has been studied. When ion-plating was carried out at a lower specimen temperature, a diffused layer between the coated layer and the steel that could be detected by EPMA was not formed, and the notch tensile strength of the coated specimen in hydrogen gas was higher than that of the steel itself, and the coated layer suppressed the hydrogen embrittlement. When the specimen temperature was increased during ion-plating up to a high temperature at which the maraging steel was overaged, a thick diffused layer identified as intermetallic compounds of aluminum and the alloying elements of the steel was formed in the coated layer. This diffused layer was very brittle, so that many cracks were initiated at the coated layer in the early stage of loading both in hydrogen gas and in vacuum. The notch tensile strength in vacuum was not lowered by the existence of the cracks. However, that in hydrogen gas was extremely lower than that of the steel itself, and the existence of the coated layer promoted hydrogen embrittlement.
Plates of SUS 304 up to 4.8 mm in thickness were quenched in an oil after having been annealed at temperatures from 1173 to 1473 K for 1.8 ks in 5.33 Pa. Surface brightness was measured by an optical microscope equipped with a silicon photocell. The carburization occurred on the plate surface oil-quenched from temperatures above about 1300 K. The case depth increased with increasing quenching temperature and increasing thickness of plate. The carburization brought about deterioration in corrosion resistance (in boiling 65% nitric acid) and in brightness which was caused by the formation of carbides (M23C6, M7C3) and/or by sooting. The two-stage cooling, that is, oil-quenching subsequent to the gas-cooling to about 1200 K is proposed as a method to prevent the carburization. No carburization was observed on the two-stage cooled plates. This cooling method extremely improved the brightness and corrosion resistance of SUS 304 plates. A comparison in the calculated cooling rate between the oil-quenching and the two-stage cooling showed little difference. A practical application of the two-stage cooling method was made. All the results showed that it was possible to prevent the carburization during oil-quenching by the two-stage cooling.
A diffusion equation which describes carburizing of steels during oil-quenching has been developed on the assumption that the diffusion of carbon into the steels is a rate-controlling step as, (This article is not displayable. Please see full text pdf.) \
oindentwhere C is the concentration of carbon at a distance x below the surface, C0 the initial concentration within the steels, Cs the concentration at the surface, Tcs and Tcf are respectively the starting and the finishing temperatures of carburizing, D(T) the diffusion coefficient, which is assumed to be a function of temperature T only, and t=f−1(T) is an inverse function of the cooling curve T=f(t) at a vapor cooling stage. Measurements of the case depth have been made on iron specimens quenched from various temperatures in two kinds of oils. A comparison between the measured and the calculated depths has shown that the above equation expresses the dependence of the case depth upon quenching temperature fairly well. Effects of Tcs, Tcf, and T=F(t) on the case depth have been discussed based on this equation.
Grain boundary reaction under low and high frequency fatigue conditions was studied in Pb-Sn-Sb alloys containing a small amount of Sn and Sb. Under low frequency fatigue tests, the grain boundary reaction progresses with increasing number of cycles. Cracks on the surface of all alloy samples were found after almost the same number of cycles. Cracks in the inside of samples were, however, found only in the case of a high concentrated alloy at 6.94×10−5 Hz (6 cycles/d) and in the case of a low concentrated alloy at 1.389×10−4 Hz (12 cycles/d). Under high frequency fatigue tests at 50 Hz, slip lines appear in the localized reacted zones of aged samples with increasing number of cycles, but the boundary reaction is not developed. The crystallographic orientation of the matrix of a reacted zone is the same as that of the adjacent grain, and the habit plane of a precipitate in a nodule is (111)Pb matrix. The composition of a precipitate in a reacted zone is analyzed as SbSn by EPMA.
The present study was carried out to investigate the effects of Te and As addition on the microstructure and mechanical properties of a Pb-0.10%Sn alloy. The results are summarized as follows: (1) The tensile strength after extrusion and aging at room temperature and 373 K increases with increasing As content up to 0.05%As. (2) The increasing tendency of fatigue resistance at 50 Hz is more remarkable in the addition of As than of Te. (3) The hardness change during aging at 333-473 K for Pb-Sn-Te-As alloys is mainly dependent on the As content. (4) A characteristic cell structure due to constitutional undercooling during solidification at casting is caused by the addition of Te, and the structure is considerably stable under heating after casting.
Quenched and aged ferritic-austenitic two-phase stainless steel was cathodically charged with hydrogen, and tensile properties of the steel have been investigated at room temperature. Results obtained are as follows: (1) Tensile properties of the steel quenched at 1423 K, 1323 K and 1223 K decrease with increasing hydrogen charging time. In a shorter hydrogen charging time, hydrogen-induced cracking occurs from the ferritic phase near the surface or in the matrix, and the crack growth is suppressed by the austenitic phase. For the steel surfficiently charged with hydrogen, the hydrogen-induced transformation occurs in the austenitic phase, so that the transformed austenitic phase no longer suppresses the growth of crack initiated only in the ferritic phase on the surface. (2) The hydrogen susceptibility of the steel aged at 748 K and 1023 K increases with increasing aging time owing to the phase transformation, and the tensile properties greatly decrease with increasing charging time compared with those of the quenched steel. The aged steel surfficiently charged with hydrogen is observed to fracture without plastic deformation.
The monotectic solidification mechanism is considered for the non-directionally solidified Al-In alloys. For the monotectic and hypermonotectic alloys, the Al solid of a monotectic product spherically grows in volume. The L2 phase which separates simultaneously with formation of the Al solid from the melt arrays radiately from a center of the spherical Al solid. On the other hand, the monotectic solidification morphology depends on the primary Al dendrite for the hypomonotectic composition. That is, the deposition of Al solid of a monotectic product onto the primary Al dendrite results in a nearly random L2 phase distribution.