The present study was undertaken to evaluate the activities of both components in binary molten alloys and also to investigate the relations existing between the activities.
It was made clear that the activities of both components can be approximately calculated from the known thermodynamic values of the intermetallic compounds on the assumption of partial molar free energies neglecting the Gibbs-Duhem relationship.
A modified Gibbs-Duhem equation was then presented, which can be applied to the activities of both components measured by the TIE method.
The modified equation can be represented by the form
lna₁=k[−∫₁^N₁N₂⁄N₁dlnγ₂+lnN₁],
where a₁ and γ₂ are the activity of component 1 and the activity coefficient of component 2, N₁ and N₂ are the mole fractions of components 1 and 2, respectively, and k is a factor which varies with composition.

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Prolonged ageing behaviors of an Al-5.06 wt% Zn-0.94 wt% Mg alloy over 10000 hr at 100°C have been investigated by means of the specific heat measurements and the tensile test. It has been shown that the G. P. zones and the intermediate and the equilibrium phases are formed on ageing at 100°C. The intermediate phase precipitates only in the early stages of ageing, while the G. P. zones continue to exist over a long ageing period. Changes in the internal energy of the specimen during ageing and respective contributions of the G. P. zones and the precipitates to it have been determined as functions of the ageing time, from which the ageing characteristics of them have been deduced. It has been suggested that the precipitates grow at the sacrifice of the G. P. zones in the later stages of ageing.
Remarkable age-hardening has been observed. The maximum strength (0.2% proof stress) of about 24 kg/mm² has been obtained after ageing for about 500 hr. In the whole ageing intervals studied, the strength changes almost parallel to the variations in the internal energy due to the G. P. zones, suggesting that the zones make a predominant contribution to age-hardening of this alloy at 100°C. The strength decreases to the as-quenched level when the alloy is reversion heat-treated at 250°C for 30 sec even after ageing to the maximum of the strength.
The serrated stress-strain curve has been obtained on the alloy aged for a short period. Proposed mechanisms of the serrations have been discussed and it has been shown that the serrations should be explained by a mechanism based on the change in dislocation mobility due to the formation of the G. P. zones.

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A series of experiments has been carried out by the present authors by means of the Berg-Barrett method, the etch-pit technique, and transmission electron microscopy to make clear the substructure developed in copper single crystals during high temperature creep. In this paper the results obtained on the dislocation structures by transmission electron microscopy are reported. The dislocation motion and the creep rate in steady-state creep is also discussed on the basis of the experimental results. The main conclusions obtained are as follows:
(1) The subgrains surrounded by “large angle sub-boundaries” observed by the Berg-Barrett method and the etch-pit technique are further divided into smaller ones by “small angle sub-boundaries” which can be detected only by transmission electron microscopy.
(2) In steady-state creep mobile dislocations are emitted mainly from the small angle sub-boundaries. After gliding through subgrains, the mobile dislocations are absorbed into the neighbouring small angle sub-boundaries to become immobile. The mean free path of the mobile dislocations is thus limited by the small angle sub-boundaries, being a few μ to 10 μ and 10 μ to a few tens of microns for the primary edge and the primary screw dislocations, respectively.
(3) Steady-state creep rates can be explained quantitatively from the results by transmission electron microscopy, on the assumption that the glide motion of screw dislocations having super jogs is the rate-controlling process. The heights of the super jogs are ∼20 b and ∼6 b and their spacings are ∼0.4 μ and ∼0.2 μ at 745°C and 610°C, respectively.

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The effect of vanadium additions on the miscibility gap in the iron-chromium binary system has been investigated by means of differential thermal analysis and Moessbauer effect measurements. The miscibility gap obtained experimentally in the iron-chromium-vanadium ternary system are qualitatively in agreement with that predicted from thermodynamical data on three binary systems of iron-chromium, iron-vanadium and chromium-vanadium. The ternary miscibility gap in the iron-chromium-vanadium system is considered to take the form of a mountain with the peak.
The ternary tie-lines have been determined by means of the Moessbauer measurements of the binary and ternary alloys aged at 480°C. In the aged ternary alloys the greater part of the vanadium content is dissolved in the iron-rich matrix.

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The present authors have studied the structures and chemical compositions of oxide films produced on surfaces of 18–8 and 18 Cr stainless steels in 300°C water and vapor. Effects of the oxidation duration, polishing conditions, and the dryness of the vapor on the structures and chemical compositions of the oxides were investigated through electron microscopy, transmission electron diffraction and X-ray microanalysis.
Main results obtained are as follows :
(1) A corundum type oxide produced on a mechanically polished surface of 18–8 stainless steel at the early stage of oxidation in high temperature water (300°C, 1 hr) is identified to be (Cr, Fe)₂O₃ alone or its coexistence with α-Fe₂O₃. The corundum type oxide has been changed to a spinel type oxide containing Ni after a prolonged heating time (24 hr).
(2) After heating in high temperature vapor (dryness : 0.18) of 18–8 stainless steel, the corundum and spinel type oxides are found on both mechanically and chemically (or electrolytically) polished surfaces. In the case of the higher dryness (1.0), however, the corundum type oxides are detected on the three differently polished surfaces.
(3) On heating 18 Cr stainless steel in high temperature water and vapor under the same conditions, the oxide films are of the corundum type containing Fe and Cr. This evidence throws a light on the contribution of Ni to the formation of the spine1 type oxides detected in the initial oxide films of 18–8 stainless steel.

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The formation of annealing twins has been examined by observing 96% rolled and electrolytically thinned high-purity nickel foils in a heating stage of a 500 kV electron microscope.
The thickness dependence of the recrystallization temperature is found to be large; 500°C in specimens 0.2 μ thick, 350°C in those 0.7 μ thick as compared to 250°C in bulk ones. In specimens 0.2 μ thick which are transparent for 100 kV electrons, no annealing twins ars formed, whereas specimens 0.7 μ thick can generate many twins similar to those in bulk-annealed specimens.
The nucleation sites of the annealing twins are always high-angle boundaries in motion, and the twins are divided into two classes from a morphorogical point of view ; parallel-sided twins and thin twins, respectively. The parallel-sided twins result if the twinning plane is nearly parallel to the recrystallized grain boundary. These twins can grow to an extensive size through the migration of the high-angle boundaries, as in the case of usual recrystallized grain growth. On the other hand, the twinning planes of the thin twins are almost perpendicular to the boundary. The thin twins grow through a successive pile-up of stacking faults, probably by the pole mechanism, during dragging by the migrating boundary. The formation of twins is largely dependent on the local deformation texture at the site of twin nucleation.
A mechanism which conforms to the ‘stimulation theory’ proposed by Burgers has been considered to be the most plausible explanation of forming the parallel-sided twins.

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It was proposed that the zone formation due to a miscibility gap is a hardening mechanism in the age-hardening of Fe–Ni–Mn martensitic alloys, and the propriety of this mechanism was confirmed by thermodynamic considerations. The results obtained may be summarized as follows :
(1) The nose temperature of the hardening rate on the reciprocal temperature-time diagram (C-curve), was raised as the Ni and Mn contents were increased. This result showed the existence of a solubility limit surface in the bcc phase of the ternary Fe–Ni–Mn system.
(2) Possible combinations of the energy parameters of Fe–Ni, Fe–Mn and Ni–Mn binary systems were deduced from the extent of the miscibility gap island by application of Meijering’s treatment. This explained result (1).
(3) From the equilibrium phase diagrams of Fe–Ni, Fe–Mn and Ni–Nn systems, energy parameters for interaction between different atoms in bcc phase were estimated. The energy parameters of Fe–Ni and Fe–Mn systems were nearly equal, and that of Ni–Mn system was shown to have larger value of negative number than either of them. This result satisfies the condition of (2).
(4) Because the energy parameter of Ni–Mn system had a large negative value, the zone rich in Ni and Mn should be ordered. It was pointed out that both shearing of the ordered zone by dislocations and the strain caused by the zone formation contributed to the hardening of the alloy.
(5) The intense hardening response observed in the 10∼12% Ni, 5∼6% Mn alloy was interpreted in terms of the relation between the solubility line and the martensitic region.

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The inter-relation between the microstructural factor and hardness has been investigated on the quenched-and-tempered structure of 0.1∼0.6% C low-alloy steels under various tempering conditions above 550°C. The radius of carbide and ferrite grain size were determined by electron-microscopy and the multi-regression analysis was conducted on the relation of these factors to hardness. The following empirical formula was obtained.
Hv=0.8893λ^−1⁄2+0.6884l^−1⁄2+8.02w_c+41
where Hv, λ, l and w_c are the Vickers hardness, the intercarbide distance(cm), the mean free-ferrite-path from grain boundary to grain boundary (cm) and the amount of carbide (wt %), respectively. It was shown that the response of a low-alloy steel to softening on tempering is understood by the effect of the alloying element on λ and l.

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Alnico 8-type magnet alloys containing more than 5% Ti have been well-known to have very high coercive forces, particularly when the isothermal field treatment is applied. As a primary approach in this research to explore its cause, the transformations, microstructures and magnet characteristics were investigated in a series of Alnico 8-type alloys with various titanium contents. The critical temperatures of the transformations including magnetic transition were determined as a function of titanium content. It may be reasonably concluded that the mechanism of magnetic hardening in these alloys is similar to that in Alnico 5-type alloys containing no titanium.
It was shown that when the alloys were subjected to isothermal field treatment, the coercive fore obtained depended largely upon the temperature of the treatment, and slightly upon the treating time. In each of the specimens, the optimum temperature of the treatment was found to exist about 50°C below the critical temperature of the two-phase separation reaction and to raise as the titanium content was increased. In addition, the magnetic anisotropy induced by the heat treatments in a magnetic field seems rather to decrease in magnitude with increasing titanium content. Furthermore, the electron microscopic observation has revealed that the precipitate particles developed by the optimal treatment are likely to increase in both size and dimension ratio with increasing titanium content.

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The deformation of 78 wt% Zn-22 wt% Al was surveyed in a deformation velocity range of ca. 3 to ca. 75 m/sec for various modes of heat treatment and deformation temperatures. In this range of deformation velocities and at a decomposition anneal temperature of 250°C, the alloy was only moderately ductile ; it was markedly more ductile at 0°C, becoming even more so as the aging time at 0°C was prolonged or the deformation velocity increased.
The basic mode of deformation was the formation-and-propagation of necks, two of which almost invariably developed at either end of the specimen. The plastic deformation was concentrated in those necks, i. e., the intervening portion was left nil deformed, or, as the deformation velocity increased or 0°C aging prolonged, deformed homogeneously though very little.
Analyzing the energy lost in the deformation into tensile stress, the strain rate sensitivity factor m in the σ=α·\dotε^m relationship was estimated to be ca. 0. 9.
The fundamental mechanism of deformation, which is characterized by easy and very fast propagation of necks and the high strain rate sensitivity of flow stress, was thought to be grain boundary sliding of the hydrodynamic boundary-layer type flow.

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The temperature dependence of the tensile deformation of α-brass (70 : 30 brass) shows some discontinuous remarkable phenomena, among which the repeated yielding (serration) and the abnormal work hardening were investigated.
In the temperature range below about 250°C, serrations of upward jerk appear at a certain level of strain until fracture and the strain to induce serrations moves toward the low strain side with rising temperature. In the range above about 250°C, the strain to initiate serrations contralily moves toward the high strain side as temperature rises, with serrations of downward jerk appearing only in a limited region of strain. Furthermore, immediately after disappearance of the serrations, abnormal work hardening phenomenon is observed.
These phenomena are discussed from the point of view of the interaction between solute atoms and dislocations and of the grain boundary behaviors at elevated temperatures.

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α-brass shows the decrease in ductility when deformed over a certain region of elevated temperatures. The phenomenon, so-called “Hot-shortness”, was investigated metallographically on the 70:30 brass specimen tensile-deformed at room temperature∼650°C. As described in the preceding report, the interaction between mobile dislocation and solute atmosphere results in such phenomena as repeated yielding and abnormal work-hardening at about 250°∼550°C. In order to release the stress concentration at grain boundary due to piled up dislocations, local migration of grain boundary occurs, revealing corrugated shape of grain boundary. The abnormal hardening of grain-inside will promote the grain boundary sliding, by which W-type cracks or voids are formed along the corrugated boundary or at the triple point of boundaries. The interlinking of those cracks forms a grain boundary fracture showing hot-shortness. At high temperatures above 550°C, the easy deformability of grain structure and the extensive migration of grain boundaries may dissipate the stress concentration and the crack growth along grain boundaries, leading to the recovery of ductility. Those behaviors are confirmed by the present metallographic study through optical micrography and electron fractography.

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