A new melting technique has been developed to measure the surface tension, γ, of levitated metal droplets oscillating about their spherical equilibrium shapes. Using this technique, surface tension is calculated from Rayleigh’s equation, after making an experimental determination of the droplet oscillation frequency. The applicability of Rayleigh’s equation to levitated metallic droplets is demonstrated, although it is shown that oscillation frequency, and hence the calculated value of surface tension, is a sensitive function of oscillation amplitude and that only low amplitude oscillations lead to reliable values of γ.
The surface tension of liquid copper was evaluated in an atmosphere of hydrogen over the temperature range of 1000 to 1330°C, including for the first time experimental data which make a substantial, 80°C incursion into the supercooled range. The surface tension of copper was found to vary linearly with temperature over the entire range investigated, with the results being represented by the equation:
γ=1390−0.43(t−1083)dyne/cm
where t is temperature in °C.

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Metallographical phenomena among many factors which control weldability on diffusion bonding has been investigated. Combinations of the base metals were classed into three types; the solid solution type, two-phase type and intermetallic compound type. Diffusion bonding was carried in hydrogen atmosphere using several bonding pairs such as Cu–Ni, Cu–Ag, Cu–Al, and Fe–Al.
The influence of the bonding temperature and time on the bonding strength was investigated and the microstructure at the interface was observed.
The minimum bonding temperature exists in the neighborhood of the softening temperature of one of two base metals. The increasing process of the initial bonding strength is considered as a transient phenomenon from recovery to recrystallization with stored energy and depends on the bonding temperature and time, satisfying Arrhenius’ equation. The bonding strength depends on the softening of base metals and alloying at the interface above the recrystallization temperature of the base metals. In the case of the solid solution type, the bonding strength increases with the rise of the bonding temperature and time. In the case of Cu–Ag joints, the effect of the bonding condition is not very large, but the bonding strength increases rapidly after 30 min heating at 700°C. In the case of the intermetallic compound type, the alloy layer increases in thickness and the bonding strength deteriorates in Fe–Al joints rapidly above the recrystallization temperature. The bonding interface tends to disappear with time above the recrystallization temperature of both base metals of the solid solution type, but it is retained as an interfacial boundary in the case of the two-phase type and the intermetallic compound type.

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An investigation of hydrogen diffusion in a martensitic Type 403 stainless steel subjected to heat treatment was carried out in an attempt to establish the effect of heat treated microstructure on diffusivity and solubility of hydrogen. The diffusivity and solubility vary with the microstructure and the diffusion coefficient increases in the following order; the structure tempered around 500°C, as-quenched martensitic structure, tempered martensite around 300°C, and coarse spheroidal pearlite tempered between 700 and 800°C. While the solubility of hydrogen has an opposite relation to the diffusion coefficient. The variation in solubility and diffusion coefficient can be explained in terms of a hydrogen trapping process involving the lattice imperfections such as dislocations, lattice vacancies, etc., produced by martensitic transformation and or by the precipitation of Cr-carbides.

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Fe–Cr alloys containing 5∼40 wt%Cr were oxidized in a stream of O₂ and wet H₂ at 1000 and 750°C. In O₂ at 1000°C the oxidation rate decreased with increasing Cr concentration, particularly from 10 to 20%.
The oxide scale on these alloys is generally cracked during oxidation because of the stress generated in the scale, which leads to severe oxidation. In the high Cr alloys having a bcc structure, however, sufficient Cr is supplied from the interior to the surface region owing to the high Cr diffusivity and the large Cr content. Consequently a healing layer will be readily formed when cracks are generated. In the low Cr alloys having a fcc structure, on the other hand, the Cr supply is insufficient because of the low Cr diffusivity and the small Cr content. Consequently these alloys will generally fail to form a protective layer. Thus the observed large difference in oxidation rate between high and low Cr alloys can be attributed to the difference in healing ability of both alloys. The Cr concentration profile in oxidized alloys supports the above consideration. The results in H₂ at 750°C are also reasonably explained in terms of crack generation and healing.
The comparison of oxidation behavior between Fe–Cr and Ni–Cr alloys leads to the conclusion that the oxidation resistance of Ni–Cr is afforded by less cracked Cr₂O₃ while that of Fe–Cr is, though the scale is often cracked, due to the rapid healing.

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Applicability of the stress relaxation test as a method of discerning frictional stress and internal stress is examined theoretically. It is found that the strain rate should change continuously on the onset of stress relaxation when an appreciable amount of frictional stress exists, while the strain rate should change discontinuously at the starting point of the stress relaxation when the frictional stress is negligibly small or the internal stress is the dominant component of the flow stress. Whether the contribution of the frictional stress to the flow stress is appreciable or not, can therefore be determined by comparing the strain rates immediately before and after the start of the stress relaxation.
By applying this method to the experiment of high-temperature deformation of metals and alloys, the following results are obtained: In pure aluminum and vanadium, the frictional stress is negligibly small, that is, the flow stress is almost equal to the internal stress. Meanwhile, in solution-hardened alloys, Al-5.7 at%Mg and V-5.0 at%Fe, the frictional stress appreciably contributes to the flow stress.
Merits and demerits of the proposed method are discussed comparing with the usual methods for measuring the internal stress.

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The morhpology of the ordered and disordered domains of the α+B2 phase field in Fe₃Al alloys has been investigated by means of electron microscopy, and the process is discussed with respect to the phase separation into two phases in combination with the results of our previous electron microscopy. The alloys of the composition within the α+B2 phase field are decomposed by isothermal annealing in this region after quenching from the disordered α or the ordered B2 single phase field. In the alloys in the vicinity of the phase boundaries leading to the transition α→α+B2 or B2→α+B2, phase separation is observed to take place by the nucleation and growth of the B2 domains in the α matrix or the α in B2. In the latter transition, the α-free zone is formed along the B2 type APB’s. In the central region within the α+B2 phase field we observed a microstructure which resembles the morphology of a spinodal decomposition in an isotropic system. This structure may be interpreted as the growth of fluctuations in the local composition and degree of order in the transition B2→α+B2, or as the diminution in the reverse case. In the case of nucleation and growth, the characteristic strain field contrast of coherent precipitates is observed due to the difference in the lattice parameter between α and B2 phases.

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The mechanism of the epitaxy has not completely been elucidated up to the present. A theory based on pseudomorphism, proposed by Frank and van der Merwe, is an ingenious idea and seems to be most promising, but it cannot be said that experimental evidence for it has so far been obtained. The present work proposes that alloying between deposit and substrate is possible to be an origin of the epitaxy in some cases, based on experimental results concerned with the growth of gold on palladium, aluminium on palladium and copper on gold. It is shown that in the first and last couples the alloying reasonably results in the parallel growth of deposit and necessarily generates misfit dislocations, just as the pseudomorphism does. It is thus emphasized that the effect of alloying on the epitaxy should not be underestimated.

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Phase boundaries and tie lines of the two-phase α+β field in the titanium-rich corner of the Ti–Mo–Al ternary system, which have previously been accurately obtained by using the electron probe X-ray microanalyser, are used for the determination of the interaction parameters in this system. It is shown that only when experimental tie line data are incorporated into the thermodynamical computer calculation, the evaluation of the parameters is feasible. It is found that the regular solution model can be used in this system only over a limited temperature range. Nevertheless, when the Ti–Mo parameters are allowed to change with temperature or composition so as to fit the experimental binary diagram, the Ti–Al and Mo–Al parameters that agree with the ternary data are fairly constant and determined to be −12000±1000 cal/mol for Mo–Al in both phases and −14000 and −13000 cal/mol for Ti–Al in the α and β phases, respectively. The Ti–Mo parameters in the α phase are positive and increase up to about +15000 cal/mol with decreasing Mo content.

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