A new type yielding phenomenon was observed in Al-Mg and Al-Cu alloys which were pulled at high temperatures above about 350°C. In order to determine characteristics of this high temperature yielding phenomenon, several binary aluminium alloys were investigated by tensile tests at various temperatures from room temperature to 500°C and at various strain rates from 4×10⁻⁴ to 4×10⁻² sec⁻¹. The results were as follows: (1) This yielding was observed only in Al-Mg and Al-Cu alloys which were relatively large in the size difference between solute and solvent atoms, but it was not shown in pure aluminium and its alloys such as Al-Ag, Al-Li and Al-Zn which were relatively small in the atomic size difference. (2) This yielding was observed to occur from a lower temperature with the increase of the solute concentration and the decrease of the strain rate. (3) Work hardening after the yield drop was practically zero. (4) The stress drop in this high temperature yielding was not so rapid as those in usual yielding phenomena, but it proceeds relatively slowly. The pre-yield strain in this yielding was fairly large. (5) Under a condition where this type of yielding was observed,the flow stress was severely affected by the test temperature and the strain rate. The temperature and strain rate dependences of the flow stress can be expressed by the state equation
\dotε=Aσⁿexp(−U₀⁄kT).
In Al-5.5 at% Mg, n=2,8∼3.3 and U₀=1.4 eV. In Al-2.2 at% Cu, n=4.5 and U₀=1.5 eV. (6) This yielding reappeared by annealing at the test temperatures. (7) No heterogeneous deformation related to this yielding phenomenon took place, the flow stress was independent of grain size.
From these experimental results it may be concluded that under the condition where the high temperature yielding occurs, the plastic deformation is controlled by the viscous motion of dislocations which drag the solute atmosphere around them and thereby the increase in the mobile dislocation density during plastic deformation causes a remarkable yield drop, as proposed by Johnston.

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A new type yield point phenomenon observed in some binary aluminium alloys such as Al-Mg and Al-Cu which are deformed at high temperatures above about 350°C has been reported in a previous papar. The present paper is devoted to a detailed explanation of the mechanism which controls the high temperature yield point phenomenon. The proposed theory in this work concerns the viscous motion of dislocations dragging the Cottrell atmosphere around them and the state equaton of deformation derived theoretically explains quite well the phenomenon observed at high temperatures. In the viscous motion of a dislocation, a fairly larger stress is needed to increase the dislocation velocity. This means that a remarkable yield drop must occur due to the dislocation multiplication during the deformation. This is the fundamental idea of the proposed theory to explain the high temperature yield point phenomenon. Comparing the state equations obtained experimentally and theoretically, it is deduced that the apparent relation between strain rate and stress, in which the strain rate increases in proportion to about the third power of the stress, occurs as a result of the proportional relationship of dislocation density to the second power of the stress and the proportional dependence of the dislocation velocity to the stress. The process of the increasing dislocation density calculated from the stress-strain curves shows that the density increases very rapidly in the initial deformation stage up to about 0.1% plastic strain and then gradually increases to an equilibrium density determined by the tensile conditon. For example, the equilibrium density is 2×10⁹ cm⁻² and 7×10⁸ cm⁻², respectively, when strained at 400°C at strain rates of 3×10⁻³ sec⁻¹ and 4×10⁻⁴ sec⁻¹, and 2×10⁷ cm⁻² at 500°C when the strain rate is 4×10⁻⁴ sec⁻¹. The density saturation to an equilibrium value is attained more rapidly at a higher temperature.
The stress-strain curves obtained by rapidly changing the tensile speed agree with the theoretical predictions from the strain rate dependence of the dislocation density. Further the theoretical prediction of the critical temperature, above which the viscous motion of dislocations dragging solute atmospheres controls the deformation, agrees well with the critical temperature for the yield point phenomenon determined experimentally. This shows that of the theory serves fairly well to explain the observation.

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Rods of Co-W (0∼25%) alloys were made by sintering and hot swaging. Dilatation behaviors through the α\ ightleftarrowsβ transformation and X-ray diffraction analyses of quenched or tempered specimens were examined for these alloys. The temper hardening and the T.T.T. diagram of the β-to-α transformation were measured in detail for Co-25% W alloys. The results obtained are concluded as follows: (1) The crystal structure of Co-25% W alloy quenched from 1100°C has the f.c.c. lattice of β phase. (2) Upon tempering of the quenched specimen at 600∼675°C, the retained β-phase transforms slowly into the h.c.p. lattice of α-phase accompanied by an increase in hardness. The rate of transformation is apparently controlled by diffusion. The maximum Vicker’s hardness value, 750, is attainable by optimum conditions of the tempering. (3) The T.T.T. diagram of the β-to-α transformation was determined in Co-25% W alloy by a metallographic method. The nose of the T.T.T. diagram is placed at about 750°C, where the beginning and the ending times of the transformation are about 700 sec and 10,000 sec respectively.

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In measuring the oxidation rate, a temperature change of specimens could be observed when a reactive gas was introduced into a system which was sealed in vacuum. A quantitative measurement was made of the temperature change, and its effect on the oxidation rate was investigated. The temperature of the specimens changed in the following ways.
(1) When the gas was introduced, the original temperature of the specimens increased (or decreased) initially, and then reached a constant value after a certain time.
(2) When the gas was introduced, the original temperature of the specimens increased (or decreased) initially and reached a maximum (or minimum) value at a certain time, Then the temperature began to decrease (or increase) and finally recovered approximately the original temperature. These temperature changes depended largely on geometrical arrangements of the reaction system, temperature measurement and control methods, and conditions for the gas introduction. The temperature change has no great effect on the oxidation rate directly, but there is a secondary effect which may have influence on the oxidation rate even if it is removed immediately. For a kinetic study of the oxidation, it is necessary, therefore, to consider the extent of the temperature change and its secondary effect.

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A Ti-10 wt% Cr alloy was quenched from a high temperature (β region) and then tempered at various temperatures from room temperature to 800°C. The changes in physical properties, viz., internal friction specific heat coefficient of thermal expansion and hardness, with tempering were measured. The experimental results are summarized as follows:
(1) Heat evolution and abnormal contraction were observed at 250°∼350°C. After tempering at 150°∼300°C, the internal friction decreased. It is suggested that these changes correspond to the ω formation from retained β.
(2) Heat absorption and abnormal expansion were observed at 400°∼450°C. After tempering at about 400°∼450°C, the internal friction increased. These changes may correspond to redissolution of ω to β phase.
(3) Heat evolution and contraction were observed at about 490°C. The change seems to correspond to the α formation.

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Three α Cu-Si alloys containing 0.01% Fe, 0.15% Fe and 0.30% Fe, respectively, were rolled at room temperature and annealed at various temperatures. Hardness tests, microstructure observations and X-ray diffraction experiments were carried out to investigate the effect of iron on the annealing behavior of cold rolled Cu-Si alloys. The results may be summarized as follows:
(1) There was no difference in the hardening behavior among the three alloys when rolled.
(2) The addition of a small amount of iron greatly affected the annealing behavior, and had an effect to rise the recrystallization temperature. Recrystallization softening of Cu-Si-Fe alloys was rather gradual, while that of Cu-Si binary alloy was very abrupt.
(3) The breadth at the half maximum intensity of the (311) X-ray diffraction line decreased by annealing after cold rolling. This behavior was greatly affected by a small amount of iron.

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In order to determine of the free Mg and MgO contained in nickel sleeves, a high-purity Ni-Mg alloy was prepared by a high vacuum levitation melting method, and 0.4φ wires of the specimens were heat treated at 1100°C in wet H₂ and the residual resistance was measured. The results obtained are as follows. (1) When the duration of the wet H₂ treatment is increased, even the residual resistance of pure Ni remains constant; but that of the Ni-Mg alloy decreases approaching the value of pure Ni. (2) The decrease in the residual resistance of the Ni-Mg alloy by the wet H₂ treatment is caused by the reaction of the free Mg contained in the Ni-Mg alloy reacts with the H₂O in the wet H₂, which produces MgO; the speed of this reaction rate is governed by the diffusion velocity of the Mg in Ni. (3) When all the Mg contained in the Ni-Mg alloy is free Mg, the residual resistance can be expressed as ρ_Ni-Mg(μΩ-cm)=0.035+4.7×(at % of Mg). Using this result, the free Mg and MgO in the Ni-Mg alloy are successfully determined. This method can also be applied to actual products.

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The crystal structure of electrodeposited nickel with a preferred orientation was investigated by electron microscopy and electron diffraction. A number of twins occurred frequently in all of the deposits having (100), (110), (210) and (211) preferred orientations, respectively. Particularly in those with the (211) orientation, twin pyramids of a two-fold symmetry with a twin plane perpendicular to the substrate surface were observed. An extra diffraction spot arising from deposits with the (211) orientation has been considered to be due to a hexagonal close-packed phase of nickel or cobalt coexisting with a face-centered cubic phase. However, since the extra spot arises from the effect of kinematical double diffraction at boundaries between matrix and twin, the previous interpretation of this extra spot in terms of the presence of a hexagonal close-packed metal is not justifiable. It was considered that in the above four preferred orientations the deposits would not be chemically stable and there is no great difference in chemical activity among the deposits with different preferred orientations.

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It has been reported in some literature that the magnesium-indium alloy is only the case in which the long-period superlattice of the CuAu II type has so far been found, except the copper-gold system itself. The present study was carried out in order to examine whether such an orthorhombic superlattice exists stably in the definite temperature and composition ranges. The alloys with the compositions from 36.8 to 56.3 at% In were investigated at room temperature and at temperatures up to 350°C by the X-ray powder diffraction method, and by the measurements of heat capacity using an adiabatic calorimeter on heating.
Contrary to the results of earlier investigators, the experimental results gave no evidence of the existence of the orthorhombic phase with the long-period superlattice. This conclusion was discussed from the theoretical point of view.
The lattice constants in the ordered phase β″ with the tetragonal superlattice (CuAu I type) were determined as a function of concentration at room temperature. The temperature of the order-disorder transformation from β″ to β (f.c.c. solid solution) was determined, and a revised partial phase diagram was proposed on the basis of the present investigation.

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In order to clarify the cause of the magnetism at the grain boundary and the slip plane of the work-hardened Hadfield steel, manganese steels of various compositions were examined mainly by the magnetic colloidal method after cold working, In every case, whenever an austenitic manganese steel is work-hardened by impact at room temperature, by static tension at room temperature, or by impact at the liquid nitrogen temperature, a small amount of ferromagnetic products is formed at the traces of slip planes and at grain boundaries. These ferromagnetic products are not formed at every slip plane and grain boundary observed in the etched surface, but formed very partially.
In unstable austenitic steels, both grain boundaries and slip planes become thicker layers in the magnetic colloid patterns, but with increase of the carbon or manganese content in steels, the magnetism at the slip planes is gradually diminished first, and next at the grain boundaries. Ferromagnetic products are not formed at grain boundaries in Fe-Mn alloys. The magnetism at the grain boundaries can be decreased or disappeared by annealing prior to cold working, but the magnetism at the traces of slip planes is not wholly affected.
The ε phase in manganese steels are considered a paramagnetic substance as in the γ phase, but has a slightly stronger magnetism than the γ phase at room temperature. Even when the ε phase coexists in large quantities with the γ phase, the magnetic colloid does not deposit at both phases. It is considered that ferromagnetic products at grain boundaries in the work-hardened Hadfield steels are caused by the segregation of carbon at their grain boundaries, which are accelerated by cold-working and grown up to a complex carbide. It is anticipated that a small amount of very thin martensitic layer is present along the traces of slip planes.

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Magnetic properties of ferromagnetic Co-Al alloys containing 4.32∼24.90% alminum have been measured. It has been found that the alloys containing more than about 10% aluminum shows high coercive forces when temperedat 500∼550°C after water-quenching from 1380°C (non-magnetic β′ phase): The 15.02% aluminum alloy showing the highest coercive force has a residual magnetic flux density of 4,200 G, a coercive force of 1200 Oe and a maximum energy product of 1.71×10⁶ G·Oe. Thus the present investigators have named these alloys “Malcolloy” which is an abbreviation of the magnetic Al-Co alloy. These alloys having high coercive forces consist of many ferromagnetic elongated particles about 300∼1000 Å in mean diameter dispersed in the matrix of the non-magnetic β′ phase and consequently it may be concluded that the high coercivity of the alloys is probably caused by the existence of these small particles, each of them being composed of a single magnetic domain.

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The magnetoresistance effect of 80-20 Ni-Fe thin films is studied. It is found that a difference in resistivity, when the magnetization parallel and perpendicular to the electric current, decreases with the decreasing thickness below about 200 Å. A similar decrease in saturation magnetization with the decreasing thickness was observed by F.B. Humphrey, using the films prepared by the same apparatus from the same melt as used in the present experiment. Comparing the both results, it is concluded that the resistivity difference is proportional to a square of the saturation magnetization.

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