A TiAl₃ crystal is a strong nucleant of α-aluminum solid-solution on solidification. To know the possibility of this nucleation by the addition within the solubility limit in the melt, the time required for the dissolution of TiAl₃ crystals into pure aluminum, was obtained experimentally and analyzed theoretically in the slowest condition to dissolve, that is, in the one-dimensional diffusion couple between pure aluminum and Al–Ti alloy. Both of them agreed well with each other. If the melt is held after the addition of TiAl₃ crystals for a longer time or at a higher temperature than the critical condition obtained here, the grain refinement by the nucleation of α-aluminum on dissolving TiAl₃ crystals will be impossible.
The grain structure of air cooled diffusion couple shows that TiAl₃ crystals are strong nucleants and reduced the grain size of aluminum extremely, and that in the region without the TiAl₃ crystals the aluminum grains were also reduced but moderately depended on the Ti concentration, which have been reported by many investigaters. The mechanism of this moderate grain refinement is not fully known only from this experiment.

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Molybdenum was neutron irradiated at reactor ambient temperature in the range from 6.3×10²¹ to 5.0×10²³ n/m² (E_n>1 MeV) and was tensile tested over a range of temperatures from 223 to 525 K and of strain rates from 2.8×10⁻⁶ to 2.8×10⁻²/s. The radiation softening was observed in the specimen irradiated to 6.3×10²¹ and 1.0×10²² n/m² in testing at room temperature with strain rates larger than 2.8×10⁻⁴/s. The softening is considered to be due to small defect clusters with strain field. The athermal component of the yield stress was increased by the neutron irradiation and further increased by post-irradiation annealing up to 780 K . The hardening is attributable to defect clusters without strain field.

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When ultrasonic oscillations are applied during static testing, the static flow stress decreases. The purpose of the present work is to elucidate to what extent ‘the stress superimposition effect’ can explain this phenomenon. On the basis of the stress superimposition, the decrements in static flow stress, Δτ, were calculated neglecting mean internal stress. From the measurements of specimen temperatures and the comparison between the measured and calculated decrements, the following conclusive remarks were drawn.
(1) The effect of the temperature rise on the decrements was negligible in the superimposed stress range investigated.
(2) The theory and experimental results both showed that the larger the dislocation velocity-effective stress exponent, the larger became the decrease in static flow stress.
(3) The measured decrements were larger than the calculated by a factor of about 1.5. They slightly decreased with increase in strain rates and slightly increased with increasing τ_A at which the superimpositions of stress were conducted.
(4) The results obtained above were qualitatively explained by the change in the fraction of mean internal stress to the flow stress.

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Recrystallization kinetics of an austenitic steel containing nominally 25%Cr and 20%Ni has been investigated mainly by optical and transmission electron microscopy. The activation energy for recrystallization was found to be 4.6×10⁵ J/mol which was excessively greater than the values previously observed in steel. It was surmised that a sigma phase formation accompanied the recrystallization phenomenon, and that this transformation acted as a barrier for growth of recrystallized grains. It is proposed that the sigma phase formation and recrystallization are concurrent and interacting phenomena and hence the activation energy described above is considered to be a sum of those for recrystallization, 2.3×10⁵ J/mol, and for diffusion of chromium atoms, 2.3×10⁵ J/mol, governing the sigma phase formation.

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Image characteristics of boundary dislocations, which have been deduced from theoretical computation in a previous paper, are compared with observed micrographs of dislocations lying in twin boundaries. Especially, a strong, light or dark contrast of an edge dislocation under the condition of g·b≈0 is confirmed. The use of the new method of dislocation identification which has been developed in the previous paper is demonstrated.
The dislocations which are identified in the twin boundaries are twinning partials (Remark: Graphics omitted.) and another kind of partials (Remark: Graphics omitted.). Twinning partials have been found in almost all the examined twin boundaries. It is likely that the latter dislocations have been formed by the reaction between a trapped lattice dislocation and a twinning partial. Dislocation nodes suggesting this reaction have been found.

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Isothermal holding of an Al-19%Si-0.02%P alloy has been carried out at 893 K to determine the rate of Ostwald ripening of primary silicon crystals in aluminum melt. The average radius of these crystals during isothermal holding is expressed by an equation; R³−R₀³=kt, where a constant k is determined as 1.6×10⁻¹² cm³/s. When a specimen is solidified at a constant cooling rate of ΔT⁄Δt, solidification growth and Ostwald ripening take place simultaneously. Such a solidification process can be approximated as repetitions of quenching by ΔT and isothermal holding for the period Δt. The change of the average radius of primary silicon crystals during solidification has been numerically analyzed by separating Ostwald ripening and solidification growth from each other. It is shown that the contribution of Ostwald ripening increases with decreasing cooling rate and with increasing number of primary silicon crystals formed at the onset of solidification. By comparing the analytical and experimental results, it is concluded that the number of primary silicon crystals after complete solidification is primarily dependent on their number at the onset of solidification and the effect of Ostwald ripening is negligibly small. Growth of primary silicon crystals during solidification is almost entirely due to solidification growth. These results on primary silicon crystals are also discussed in comparison with those reported on primary dendrites.

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Phase transitions centered around 25 at.%Bi in Tl–Bi system have been investigated by measurements of electrical resistivity, Hall coefficient and thermoelectric power. It has been clarified that the phase transition at about 390 K is an order-disorder one, though no superlattice lines in X-ray diffraction could be observed. It has been found that the quenched disordered phase with fcc structure transforms to a new fcc phase, which may very possibly be an ordered structure, above about 200 K when it is heated from the liquid nitrogen temperature. This phase is unstable above that temperature and makes subsequently transformation to another ordered phase of the hcp type.

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