The fracture strength of high-temperature materials is discussed in connection with grain boundary structure, taking up Mo, Si₃N₄ and SiC. For molybdenum, in which the fracture strength strongly depends on the grain boundary character, the effects of impurities C, O and N, and TiC addition on the strength of the weakest boundary which may control the fracture strength of polycrystalline material are described. For the non-oxide ceramics, Si₃N₄ and SiC, the high-temperature strength of sintered materials is described in relation to the grain boundary structure. Further, the effect of covalent bond strength and polarity on the grain boundary structure is discussed referring to the boundary structure observed in SiC and Si bicrystals and AlN-polytype Sialon.

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Diffusion coefficient of ⁵¹Cr in single crystal α-titanium has been measured over the temperature range from 875 to 1123 K. The diffusion coefficient of ⁵¹Cr in α-Ti is about two orders of magnitude larger than the self-diffusion coefficient in α-Ti. The temperature dependence of diffusion coefficient of ⁵¹Cr in α-Ti parallel and perpendicular to the c-axis is, respectively, expressed as
D_⁄⁄=(2.2_−1.4^+0.8)×10⁻⁶exp(−165.5±4.1kJ·mol⁻¹⁄RT)m²s⁻¹,
D_⊥=(2.2_−0.5^+0.4)×10⁻⁶exp(−169.4±2.1kJ·mol⁻¹⁄RT)m²s⁻¹.
The diffusivity of Cr in α-Ti parallel to the c-axis is larger than that perpendicular to the axis. Diffusion of Cr in polycrystalline α-Ti alloys: Ti-4.4Al, Ti-2.4Sn and Ti-3.7Al-2.5Sn (mass%), has also been investigated. The addition of Al suppresses the diffusion of Cr, while Sn hardly affects the diffusion.

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Tracer diffusion coefficient of ⁵¹Cr in α-iron has been determined by a serial radio-frequency sputter-microsectioning method in the temperature range 885 to 1174 K. In α-iron of the paramagnetic state from the Curie temperature to the α-γ transformation temperature the diffusion coefficient of chromium shows a linear Arrhenius relationship with negligible influence of the short range magnetic spin ordering. Below the Curie temperature, temperature dependence of the diffusion coefficient deviates from the linear Arrhenius relationship owing to the magnetic spin ordering. Taking into account the influence of the magnetic transformation, the temperature dependence of the diffusion coefficient, D, in the whole temperature range of α-iron across the Curie temperature can be expressed by
(Remark: Graphics omitted.)
m² s⁻¹, where s is the ratio of the spontaneous magnetization at TK to that at 0 K. The factor (0.133) in the above equation is smaller than 0.156 in the case of the self-diffusion in α-iron, indicating that the influence of the magnetic transformation on the diffusion of chromium in α-iron is smaller than that on the self-diffusion, as expected from the negative magnetic moment of chromium atom in the lattice of ferromagnetic iron.

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The B2\ ightleftarrowsB19 and B19\ ightleftarrowsB19′ transformations in a ternary 50Ti-40Ni-10Cu (at.%) alloy were investigated by means of electrical resistivity measurements, differential scanning calorimetry and constant load thermal cycling tests, and they were compared with the B2\ ightleftarrowsR and B2\ ightleftarrowsB19′ transformations in a thermo-mechanically treated binary 49.8Ti–50.2Ni alloy. The B2\ ightleftarrowsB19 transformation in the ternary alloy under load took place within a narrow temperature range (2 to 5 K), whereas the B19\ ightleftarrowsB19′ transformation took place over a wide temperature range (>80 K). The transformation start temperature of B2→19 transformation increased with increasing applied stress, but that of B19→B19′ remained unchanged with stress when the stress was below 30 MPa. The stress dependence of the transformation start temperature, transformation elongation and hysteresis of the B2\ ightleftarrowsB19 transformations in the ternary alloy were 8.4 MPa/K in the reciprocal form (dσ⁄dT) where σ is the critical stress for inducing the transformation, 3.2% and 11 K, respectively. They were in-between those of the B2\ ightleftarrowsR and B2\ ightleftarrowsB19′ transformations in the binary alloy.

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Effects of 20 MeV proton pulse-irradiation and light pulse-exposure on the fatigue properties of solution treated 316 stainless steel were investigated using the large amplitude internal friction technique with about 200 Hz at 333 and 573 K. The light pulse-exposure caused a thermal-pulse in specimens. In situ thermal-pulse during the total strain (ε_t) controlled tests with ε_t\fallingdotseq10⁻⁴∼10⁻³ caused a step-like increase in the plastic strain ε_p at first, followed by a decrease in the fatigue hardening rate. The step-like increase in ε_p was reversible and therefore was surmised to be associated with an enhancement of dislocation motion surmounting obstacles. On the other hand, the decrease in the fatigue hardening rate did not recover after a stop of the light exposure; therefore it was surmised to be associated with a decrease in the number density of fatigue induced precipitates. The proton pulse-irradiation had two effects; one caused a step-like increase in ε_p, which was found to be due to thermal-pulse caused by beam heating. Another was an intrinsic effect of irradiation which was revealed by a subtraction of the effects of thermal-pulse. This intrinsic effect of irradiation or radiation damage-pulse was an enhancement of the fatigue hardening rate, which was much larger than that observed for continuous-irradiation. This increase in hardening rate due to radiation damage-pulse was found to largely cancel out the decrease in hardening rate due to thermal-pulse. The present results demonstrate that dynamic irradiation and thermal-pulse could cause significant changes in the fatigue properties of the potential fusion reactor materials.

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In order to clarify the yielding mechanism and the character of threshold stress for high temperature deformation of dispersion strengthened alloys, three kinds of Al–Mg–Mn alloys with different dispersion parameters were prepared. Their deformation behavior and threshold stresses were analysed by means of tensile and stress relaxation tests during the steady state deformation at strain rates from 3×10⁻⁵ s⁻¹ to 3×10⁻³ s⁻¹ at 673 K.
Their threshold stresses were very close to the calculated Orowan stresses. The dependence of the threshold stress on the interparticle spacing was quite similar to the dependence of the Orowan stress. However, from the analysis of their deformation behavior and microstructure after deformation, it is found that the threshold stress is not determined by the Orowan mechanism but determined by the attractive interaction of dislocations with dispersed particles.

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High temperature creep of dispersion-strengthened Al-1.5 vol%Be alloy has been studied over a stress range 3.1×10⁻⁵∼5.9×10⁻⁴E (E: the Young’s modulus of Al matrix), which corresponds to 0.40∼5.1σ_or (σ_or: the Orowan stress), at temperatures from 473 to 723 K. It is found that there occurs a threshold stress for creep deformation, σ_th, and the value of σ_th is approximately equal to that of σ_or and their ratio, σ_th⁄σ_or, is almost independent of the particle size and test temperature. At stresses below σ_th, plastic deformation of very slow rates takes place which may be associated with grain-boundary sliding and diffusional creep. In-situ HVEM observation reveals that the interaction between dislocation and particles is of attractive type and no dislocation line is visible at the particle/matrix interface, indicating that the stress field of a dislocation is almost completely relaxed at the interface. The observed threshold stress is discussed from the viewpoint of the attractive interaction.

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The plasma-arc melting process has reacently been noted for the refining and degassing of several metals, by applying hydrogen to the plasma-generating gas.
In this work, deoxidation and decarburization of crude tantalum, prepared by carbon-reduction smelting of Ta₂O₅ with Ar plasma-arc heating, has been investigated by using H₂–Ar plasma-arc melting under 0.1 MPa. Also, the possibilities and conditions for winning high purity and ductile tantalum metal has been examined.
The oxygen and carbon contents in tantalum by carbon-reduction smelting were dependent on the carbon mixing-mole ratio to Ta₂O₅, the product of (%O) and (%C) being nearly constant. Therefore, the ratio of carbon/oxygen in tantalum is able to be adjusted by the selection of a suitable C/Ta₂O₅ ratio, for the following refining process.
At the subsequent stage of H₂–Ar plasma-arc melting, oxygen in tantalum was quickly liberated but carbon was scarcely removed. As a result, ductile tantalum whose sum of oxygen and carbon was less than 100 mass ppm could be produced by the excellent deoxidation effect of H₂–Ar plasma-arc melting for a high oxygen- and low carbon-bearing tantalum. Since the deoxidation rate increased in proportion to the about 1/2th power of hydrogen composition of the plasma gas, deoxidation may be caused by dissociated and activated hydrogen atoms. Consequently. the evaporation of tantalum suboxide and tantalum, known in high vacuum melting, was so small in this stage that it was made possible to considerably reduce the loss of tantalum.

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The wettability of solid Fe by liquid Bi has been determined by the sessile drop method at temperatures ranging from 573 to 1183 K. The effect of oxygen pressure on the wettability has been studied and discussed in relation to the surface energies of the solid phase (γ_s), liquid phase (γ₁) and the interfacial energy between the solid and liquid phases (γ_1s). From the analysis of the data we have reached the conclusion that oxygen pressure has a significant effect on the wettability in Fe–Bi system. The surface energy of the liquid phase decreases and the work of adhesion between the two phases increases with increasing P_O2.

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Magnetic properties of Fe–Cu–M–Si–B (M: Nb, Mo, Ta, W, etc.) alloys were investigated for development of new Fe-based soft magnetic alloys. The alloys were first formed into the amorphous ribbons, and then annealed above the crystallization temperature. The annealings gave rise to excellent soft magnetic properties which correspond to those of Co-based amorphous alloys. Especially, the alloys containing Cu and Nb were superior to the alloys containing other elements.
These new alloys were composed of ultrafine grain structure. The grains were about 10 nm in diameter and the main crystalline phase was presumed to be a bcc Fe solid solution which contains Si and B. This might be attributed to the nucleation process of the bcc Fe–Si–B solid solution influenced by Cu and the suppression of the grain growth by Nb.
The newly developed alloys are suitable for many kinds of magnetic components such as saturable reactors, choke coils and transformers, because of their excellent soft magnetic properties and high saturation flux density.

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The first-principles calculation is attempted for Au–Pd phase diagram in the vicinity of equi-atomic composition. The obtained transition temperature is about 350 K, for which experimental data scatter significantly. The transition seems to be of a second order below 40 at.% of Pd, which is most probably caused by a fairly big contribution of the multi-body interaction energy. Also a serious doubt is cast on the existing phase diagrams near the 1:3 and 3:1 composition.

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YBa₂Cu₃O_x superconductors prepared by the sinter method were heated for various times at temperatures from 1273 to 2241 K in alumina, platinum and iridium crucibles, and then their contents were press-quenched between two copper plates. Phases formed in the press-quenched samples were indentified by means of SEM, EPMA and X-ray diffractometry. YBa₂Cu₃O_x decomposed into Y₂BaCuO₅. BaCuO₂ and an unknown phase at 1293 K. BaCuO₂ was unstable at higher temperatures than 1373 K. Y₂BaCuO₅ decomposed into Y₂O₃ and a liquid phase at 1423 K and Y₂O₃ was stable in the temperature range from 1423 to 2241 K. Iridium crucible was most useful for the heat treatment of the Y–Ba–Cu–O system at the high temperatures.

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Iron-rare earth, Nd, Gd or Tb, alloy powders with the eutectic compositions were produced by using centrifugal atomization. The shapes, surface structures and cross sections of the powders were observed microscopically. Oxygen and nitrogen content were analysed at each sieved size. The obtained fine powder under 100 μm was almost spherical, while many worm-like-shaped particles were observed in the coarser powders with diameters of above 100 μm. The Fe–Nd powder had a smooth surface, and its oxygen content decreased with increase in powder size. The surface of Fe–Gd and Fe–Tb powders were covered with finely wrinkled surfaces. Many gooves were observed on the surfaces of the Fe–Gd powder and the coarser Fe–Tb powder. Fine microstructure without segregation was obtained in the powder having diameters of under 100 μm. The grain size decreased with decrease in particle size.

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