This paper describes the development of the “Thermoseed,” a thermally self-regulating implant for induction thermocoagulation of brain lesions. The thermoseed should have a low Curie temperature and a high saturation magnetization that will cease heating at a predetermined temperature, i.e., 343–373 K.
In contrast to many nickel base alloys, the saturation magnetization of nickel increases or remains constant with the addition of manganese and/or palladium, in spite of the decrease in the Curie temperature. The Ni–Pd–Mn ternary system introduced by Köster and Sallam has been re-examined, and the composition dependence of both the Curie temperature and the saturation magnetization has been determined in the ternary fcc solid solution range. The desired composition for a thermoseed is selected as the intersection of the saturation magnetization ridge and the desired Curie temperature contour.

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The transformation of δ-ferrite to a eutectoid structure composed of austenite and alloy carbide during carburization was studied in binary iron alloys. The eutectoid composition was determined at the temperature range between 1100 and 1600 K. It was found that lamellar- or rod-eutectoid structure termed δ-pearlite was formed by the transformation. The growth velocity of δ-pearlite is controlled by the diffusion of carbon in austenite from the surface to the reaction front. The relationship between the growth velocity v and the inter-lamellar or inter-rod spacing S is expressed by the equation: vS²=kD_M^δ,
where D_M^δ is the diffusion coefficient of M atoms in δ-ferrite and k is the parameter depending on the alloying element concentration in δ- and γ-phases at the reaction front. A quantitative estimation of k was made on the thermodynamic basis. The experimental values of kD_M^δ agreed well with the theoretical ones. The results indicate that the inter-lamellar or inter-rod spacing is determined by volume diffusion of the alloying element in δ-ferrite.

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Eutectoid composition and microstructure of δ-pearlite were studied in the carburized Fe–Cr–M and Fe–W–M ternary alloys, where M is the third element. The chromium or tungsten content in the eutectoid alloy decreases with addition of a ferrite-stabilizing element and increases with addition of an austenite-stabilizing element.
The alloying element causes the change in shape of δ-ferrite/δ-pearlite interface from planar to cellular. Measurements of solute distribution in front of the cellular interface have revealed that a spike of substitutional solute concentration ahead of the tip of the cell is produced and solute segregation occurs at the cell boundary. The formation of the cellular structure is caused by the generation of the carbon-supersaturated region in δ-ferrite due to the presence of the spike.

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Transmission electron microscopy and selected area electron diffraction have been used to investigate the microstructures of the directionally solidified eutectic composite of a Ni-12.7 at%Al-21.6 at%Mo alloy. The as-grown composite consists of Mo fibers of square or rectangular cross-sections surrounded by an ordered γ′ phase. Between the γ′ phase regions a multi-phase region is formed. A selected area electron diffraction analysis of the multi-phase region suggested that the region consists of Ni₃Mo(tetragonal D0₂₂), Ni₂Mo(body-centered orthorhombic) and γ(face-centered cubic) matrix phases. Heating the composite above 1490 K followed by quenching results in the structure consisting of Mo fibers surrounded by the γ matrix dispersed with the ordered γ′ phase. The characteristic microstructure of the as-grown composite is ascribed to the eutectic solidification, subsequent peritectoid reaction and precipitation of coherent phases in the γ matrix during cooling from the eutectic temperature.

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The influence of ageing treatments on the hardness and microstructure of directionally solidified eutectic composite of a Ni-12.7 at%Al-21.6 at%Mo alloy has been investigated. On ageing at temperatures between 873 and 1373 K after quenching from 1533 K two kinds of precipitates are formed in the γ phase depending upon the ageing temperature and the ageing time. At ageing temperature below 1100 K, a fine coherent metastable phase of orthorhombic Ni₂Mo is formed. By ageing above 1100 K, Mo platelets precipitate in the γ matrix at the expense of the metastable Ni₂Mo. The hardness of the material changes appreciably by the ageing treatments.

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The time-variations of magnetostriction and magnetization of rod-shaped single crystals of Ni-25%Co alloy have been observed in an external magnetic field of 6.4 kA/m at high temperatures. The magnetostriction and magnetization at room temperature were also measured in an external field of 82 kA/m when the specimens were slowly cooled in the furnace without magnetic field after their time-variations had been terminated.
The absolute value of magnetostriction decreased with time showing a relaxation phenomenon in a temperature range from 350 to 500°C. At the same time, the magnetization increased with decreasing magnetostriction and finally both values became gradually constant. These variations in the direction of easy magnetization at high temperatures were very remarkable and most of the values remained unchanged when cooled down to room temperature. But in the direction of hard magnetization, their variations were small and the values at room temperature after magnetic annealing returned to those prior to magnetic annealing. However, activation energies calculated from the relaxation curves of magnetostriction and magnetization in both directions showed a same value of about 2.7 eV . In this case, the activation energy was a similar kind of energy required for the diffusion of atoms in a solid.
It seems most probable that the magnetic annealing effect arises from the rearrangement and fixing of domains due to the relaxation of internal stress caused by magnetostriction at high temperatures. In this process, it is supposed that the constituent atoms of the crystals and impurities, and structural defects such as dislocations, vacancies, etc. are moving and diffusing.

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The effect of a slight amount of dissolved oxygen below 0.02 at% on the surface tension of liquid copper has been carefully measured by the sessile drop method at 1373, 1473, 1573 and 1673 K. The surface tension of liquid copper over the region of dilute oxygen concentrations decreased with increasing partial pressure of oxygen in the atmosphere, and this tendency was remarkable at lower temperatures. The temperature coefficient of surface tension of liquid copper changed from negative to positive with increasing oxygen content. It can therefore be presumed that the results reported by Krause and by Pugachevich et al., in which the surface tension of liquid copper increases with increasing temperature, may be caused by the presence of a slight amount of oxygen in the atmosphere or specimen.

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An Al–2.4 mass%Si alloy specimen was kept in the solid-liquid coexisting zone having different fractions of solid and a vertical cylindrical hole was made artificially in its center. The flow rate of the interdendritic liquid flowing into the hole was obtained in relation to the fraction of solid.
The result obtained was examined by the application of a hydrodynamic theory for the seepage of water into a hole in the soil and the effective permeability which consists of the permeability, the liquid density and the liquid viscosity has been proposed to evaluate the fluidity of the interdendritic liquid.
The experimental method employed to obtain the effective permeability in the present work is suitable for studying the effects of the alloying element and the cooling rate on the effective permeability. Accordingly this method will be an effective means for the study on the formation mechanism of the macrosegregation in ingots.

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