The influence of high hydrostatic pressure on the flow stress of zone-refined pure iron, carbon-deoxydized iron and molybdenum polycrystals has been studied at room temperature. Pressurizing tests to a pressure of 12000 kg/cm², tensile tests using the differential pressure method between atmospheric pressure and 12000 kg/cm² and tensile tests under a constant pressure of 12000 kg/cm² have been carried out. The results obtained are as follows : (1) For zone-refined iron and molybdenum, no effect of pressurizing is found on the stress-strain behaviour at atmospheric pressure while a decrease of about 2.4% in flow stress is observed for carbon-deoxydized iron in the region of Lüders deformation after pressurizing. This effect seems to be similar to the previous result which was explained by the generation of free dislocations around inclusions of FeO under hydrostatic pressure. (2) According to the results of tensile tests using the differential pressure method, the change of low stress is about 2.1% for zone-refined iron, 2.8% for carbon-deoxydized iron and 0.7% for molybdenum in the region of uniform deformation . These amounts of change coincide well with those of shear moduli of steel and molybdenum under hydrostatic pressure. (3) In the stage of Lüders deformation for iron, the change in the flow stress is much greater (5.6 to 5.9%) than that of the shear modulus of steel under the same pressure. Assuming that the difference is due to the activation volume for the thermally activated process which controls the deformation, an activation volume of about 0.2 atomic volume is obtained. (4) The increase in work-hardening rate under hydrostatic pressure is 1 to 2% for iron in the region of uniform deformation. For molybdenum it increases with strain and becomes constant (about 3%) at about 20% strain.

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The influence of high hydrostatic pressure on the flow stress of zinc and zirconium polycrystals has been investigated at room temperature. Pressurizing under a pressure of 12000 kg/cm², tensile tests using the differential pressure method between atmospheric pressure and 12000 kg/cm², and tensile tests under a constant hydrostatic pressure of 12000 kg/cm² have been carried out. The tensile load has been measured by a magnetostrictive load cell in the high pressure chamber. The results obtained are as follows : (1) Both materials belong to the hexagonal close-packed system and are anisotropic in their elastic constants. Therefore, it is expected that shear stresses are generated at grain boundaries when they are subjected to high hydrostatic pressure and cause the pressurizing effect. The effect of pressurizing, however, is very small and is within the error of measurement for both materials at atmospheric pressure. The reason seems to be that for zinc the most part of work-hardening caused by pressurizing disappears rapidly due to recovery before tensile test is carried out while for zirconium the shear strain caused by pressurizing is within the elastic region. But it is presumed that a pressurizing effect would remain latently under high hydrostatic pressure if the annealed material is not returned to atmospheric pressure. (2) In the differential pressure method, the change of flow stress with ambient pressure includes the latent pressurizing effect. At large strains where the latent pressurizing effect decreases and becomes negligibly small, the change of flow stress between 12000 kg/cm² and atmospheric pressure is shown to be about 8% for zinc and about 3% for zirconium. These values coincide with the variation in shear modulus of the materials with hydrostatic pressure which is estimated theoretically. (3) The work-hardening is enhanced for these materials under hydrostatic pressure. In the case of zirconium, the tendency of enhancement is similar to that observed with cubic metals. That is, at first it increases and then becomes saturated. For zinc, the enhancement continues to increase with increasing strain in the strain range tested. This seems to be due to the fact that recovery is suppressed under hydrostatic pressure, while it takes place actively at atmospheric pressure.

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Effects of 0.1at% Cr, Zr, Fe, V, Ag, Be, Cd, In, Si, Ge, Sn and 0.01∼0.5 at% Cu on aging characteristics of Al-9at% Mg alloy have been studied by measurements of electrical resistivity and hardness and electron microscope observations.
The rate of clustering in Al-9at% Mg alloy is remarkably decreased by the addition of more than 0.03 at% Cu. In the Cu-bearing alloys two kinds of clusters exist : one is composed of Mg and Al atoms and the other includes Cu atoms. The latter exists even above 100°C, at which the former is easily dissolved.
Transition elements such as Cr, Zr, Fe and V retard slightly the clustering, but accelerate precipitation at higher temperatures.
The effects of Ag, Be, Cd and In on aging kinetics are also similar to the case of those transition elements, except that these elements prevent the formation of precipitate-free zones and produce a finer dispersion of precipitates.
It seems that Si, Ge and Sn have no trace-element effect on the clustering and the precipitation in Al-9at% Mg alloy.

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In order to investigate the effect of grain size on Portevin-LeChatelier yielding, tensile tests were performed on Al–0.55 and 1 at% Mg alloys having various grain sizes. In a temperature range of −20°∼+40°C and a strain rate range of 3.3×10⁻⁵∼1.7×10⁻³/sec, the value of activation energy for the P–L effect was found to be 0.60±0.02 eV independent of grain size. The relation between strain rate \dotε and strain ε₀ required for the onset of the P–L effect at 0°C was expressed as \dotε∝ε^2.0±0.1 μ^0.53±0.02 where μ is grain size. It was found that the value of ε₀ was decreased and the stress at the onset of the P–L effect was increased with the decrease of grain size. The above fact is explained by the effect of grain size on the average velocity of moving dislocations.

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The variation of elastic wave velocities with composition has been measured for four eutectic binary systems, namely, Pb–Sn, Cu–Ag, Pb–Sb and Sn–Zn alloys, using the ultrasonic wedge-method. The variation of the calculated moduli is illustrated graphically. The moduli are found to vary continuously with a change in rate of variation at the eutectic composition. Hence the course of the moduli (Young’s and rigidity moduli) curves can be taken as a helpful guide in corroborating metallurgical data on the composition at which eutectic formation occurs. A qualitative explanation of the change in rate of variation at the eutectic composition is offered by considering the behaviour of alloy at the eutectic composition as a composite metal.

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This paper reports the variation of elastic moduli with composition at room temperature in four binary systems, namely, Sn–Ag, Cu–Sb, Cu–Sn and Sn–Sb. The systems exhibit different phases at room temperature and the structure of some of the phases differ over certain ranges of composition. It is shown that the moduli curves exhibit brakes by way of maxima and minima whenever a phase change is accompanied by a structure change. It can be suggested the course of the moduli vs composition curves can be taken as a helpful guide in corroborating metallurgical information as to the composition at which structure changes occur.

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Self-diffusion of Co⁶⁰ in the bcc (α) and fcc (γ) phases of iron-cobalt alloys has been measured between 630° and 1310°C by the residual activity technique. Interesting changes in the diffusivity result from the α-γ phase change, the magnetic transitions in the α and γ phases, and the order-disorder transformation in the α phase. In both the phases, the activation energy for diffusion in the ferromagnetic state is larger than in the paramagnetic state. The diffusivity decreases discontinuously due to the α-γ transformation, and the order-disorder transformation causes a nonlinear relationship between logD and 1⁄T in the α phase.
The activation energies and frequency factors for the bcc and fcc phases vary with composition, showing minima at 25 and 75 at% Co and a maximum at about 50 at%. The effect of ferromagnetism is explained in terms of the changes in elastic properties.

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Anodic pit generation and pit growth of stainless steel at constant potential in a sulphuric acid solution containing chloride ion have been investigated by use of a rotating electrode. The electrode rotation makes the generation and growth of pits very stable and enables the pit generation frequency and the pitting current from a single pit to be measured potentiostatically. The pits break out at constant frequency and the rate of pit generation is a linear function of the potential, suggesting that the pit generation proceeds electromechanically rather than electrochemically. An incubation time, probably associated with the initial adsorption of chloride ion, is found before the linear pit generation commences, which differs from the induction time for opening an initial pit.
The pitting current is in proportion to the area of pit mouth with the current density (8 A/cm²) which is independent of the potential, indicating that the mass transfer is rate-limiting. The pit grows following a parabolic law and the rate constant is an exponential function of the potential, from which a pit model is proposed in which the transpassive film continuously forming and breaking down on the inner pit surface assumes a high electric field.

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Reversion characteristics due to the dissolution of G. P. zones in an Al-4wt% Cu alloy has been investigated by means of the electrical resistivity measurement and tensile tests. When the state of the aged alloy shows the electrical resistivity higher than that in the as-quenched state, the reversion heat treatment results in a decrease in electrical resistivity. On the other hand, when the state of the aged alloy shows the resistivity lower than that in the as-quenched state, the electrical resistivity increases in the initial stages of reversion and the electrical resistivity versus reversion time curve shows a peak. In all cases, the tensile strength decreases by the reversion treatment. It has been concluded that only the dissolution of the G. P. zones is responsible for the reversion.
A complete reversion can only be observed above the minimum temperature, T_GP, which depends sensitively upon the ageing temperature and the time corresponding with the stability of the G. P. zones formed during the ageing. Rather complicated reversion characteristics of this alloy reported in the literatures can be fully explained taking into account the stability of the G. P. zones as a function of ageing temperature and time. In Al-4wt% Cu alloy, the highest possible temperature for the formation of the G. P. zones is estimated to be 275°C.
The reversion kinetics shows that the reversion is rate-controlled by the diffusion of copper atoms in the matrix and the activation energy for the reversion is sensitively affected by the excess vacancies introduced in the alloy by quenching before ageing.

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The precipitation of χ-carbide and its transition to cementite during the tempering of high carbon martensite have been investigated by means of transmission electron microscopy.
The χ-carbide and the cementite were formed on the transformation twin interfaces and the orientation relationships among these two carbides and the twinned ferrites were determined. The carbide planes parallel to the twin plane were the (530)_χ for χ-carbide and the (101)_c for cementite. It was shown that these habits could theoretically be explained by the establishment of the low surface energy planes on the twin interfaces. These crystallographic results support the in situ transformation of χ-carbide to cementite.

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The deformation and fracture mechanisms of WC–Co cemented carbide subjected to compression forces were studied by determining stress-strain curves, and by measuring the changes in terms of microstructure and physical properties of the samples. It was found that the microfracturing of alloys occurred long before the sample itself fractured. Stress-strain curves deviated from the equation “σ=Aεⁿ” when the plastic strain exceeded about 0.2 percent, and a maximum stress occurred when the strain was equal to or greater than 1 percent. Stress decreased with increasing strain until the point of fracture. With the change in the microstructure, the density, hardness, coercive force, and Poisson’s ratio also changed. Changes in the structure of the cobalt phase was noted. The fracturing of the samples was caused by the boundary fracturing of WC grains and was not dependent on either the grain size or the cobalt content of the alloy.

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A quantitative metallographic analysis has been made on the microstructures of carbonyl iron powder compacts sintered in hydrogen at 850°C. Various parameters for grain, grain boundary and two types of voids, intersected with the grain boundary (void-A) and isolated in the interior of grains (void-B), were determined by the lineal and areal analyses made on the metallographic plane sections. Increase in grain size and decrease in grain boundary area as well as decrease in the number, volume fraction and the area of the free surface of void-A and the total area of free surfaces could be approximated by the simple power function of sintering time. On the other hand, the isothermal curves for the number, volume fraction and free surface of void-B had a maximum value at a certain period of sintering time. Spheroidization of the voids and the topological change in the sintering structure are also discussed.

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