Two drawbacks of TiAl, deficiency of room temperature ductility and difficulty of hot working have been surmounted substantially by the authors, and at present active research work of light heat-resisting TiAl-base alloys has been performed over a wide range from academic to technical fields aiming at practical uses. In this overview it is described that room temperature ductility is improved by the addition of Mn and, in connection with this improvement, concepts of the authors for the nature of TiAl and the roles of third elements which are soluble in TiAl are discussed. Drastical changes in microstructure by heat treatment and thermomechanical treatment, and methods for hot working TiAl are described. It is also shown that superplasticity occurs in TiAl alloys with the fine equiaxed α+γ structure which is obtained by elaborate thermomechanical treatment.

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Reduction of radiation exposure is one of the most important subjects of light water reactor (LWR) plants as well as improvements of reliability and availability. Several methods, for suppressing corrosion and deposition of radioactive ions, have been proposed and applied to some actual plants. The following recent studies of the pre-filming technique for LWR materials were presented from a point of view of the surface film in this paper. (1) Zinc and Aluminum ion injection methods. (2) Oxidation treatment in high temperature dissolved oxygen controlled water. (3) Pre-oxidation treatment by the RCT method. (4) Palladium coating treatment. (5) Pre-oxidation treatment in air or steam atmosphere. (6) Pre-oxidation treatment in low-oxygen potential atmosphere. It may be concluded that the key factors controlling the metal dissolution in high temperature water are thickness and denseness together with chemical composition of the oxide films.

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An icosahedral (I) quasicrystal with ferrimagnetism at room temperature was found for rapidly solidified Al–Pd–Mn–B and Al–Cu–Mn–B alloys in the composition ranges from 5 to 20 at% Pd or Cu, 10 to 35 at% Mn and 0 to 30 at% B. The lattice parameter of the I-phase decreases linearly with increasing B content. These alloys exhibited significant magnetization when the structure consisted of the I-phase and the magnetization disappeared by the annealing-induced phase transition from I to crystalline phase. From the thermomagnetic data, the ferromagnetic Curie temperature (Θ_f) and the asymptotic Curie temperature (Θ_a) were determined to be 473 to 508 K and 130 to 420 K, respectively, for I–Al_32.5−57.5Pd_7.5−17.5Mn₁₅₋₃₀B₁₀₋₂₀ alloys. The difference between Θ_f and Θ_a decreases with an increase in Mn content, and this change was interpreted to result from the increase in the ferromagnetic interaction. The largest magnetization at 293 K in the I–Al–Pd–Mn–B alloys attained to 6.1×10⁻⁷ Hm²/kg for Al_42.5Pd_7.5Mn₃₀B₂₀ and the residual magnetization was 3.2×10⁻⁹ Hm²/kg. The appearance of the ferrimagnetism is presumed to be attributed to the enhancement of magnetic Mn–Mn interaction through the decrease in the atomic distance by the dissolution of B.

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A mean-field approach, considering the number of neighbor bonds at a grain boundary, alloy effects, a surface tension term and a size effect, is applied to the grain boundary segregation at FCC [001] twist boundaries in a Pt-1 at.%Au, a Pt-1 at.%Ni, a Ni-1 at.%Pt, a Ni-1 at.%Cu and a Cu-1 at.%Ni alloy at 1000 K. The validity of the present model was tested by comparing with the Monte Carlo simulations utilizing embedded atom method (EAM) potentials. The agreement between the results from the present model and the simulation is fairly good. In a Pt-1 at.%Au alloy, the strong tendency of clustering of Pt–Au systems is the origin of the segregation of Au. The size mismatch between solvent and solute atoms plays a significant role in the solute segregation in the case of Pt–Ni alloys. On the contrary, the surface tension term is important in Ni–Cu alloys. That is, in both a Ni-1 at.%Cu and a Cu-1 at.%Ni alloy, Cu atoms, which have lower surface tension than Ni atoms, are enriched in the boundary.

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The mechanism of isothermal martensitic transformation has been studied, using the most typical alloy, Fe–Ni–Mn, of this type of martensitic transformation. The martensitic nucleation rate was investigated by measuring effect of applied stress on the transformation rate. The volume fraction of the martensite transformed was measured in situ by a magnetic detector with the coil covering the specimen. The transformation at liquid nitrogen temperature was studied in detail. The most important feature of observed results is that there is a critical stress level above which the initial transformation rate is drastically increased. This stress level coincides with the yield stress of the austenitic specimen in the case of alloys where no isothermal martensitic transformation occurs unless an external stress is applied. This fact, along with other characteristic observations, is qualitatively explained by the basic concept proposed by the present author that the nucleation rate of isothermal martensite is controlled by thermally activated motion of dislocations which accommodate the shape strain of a nucleating martensite. Furthermore, in the quantitative analysis of this thermally activated process, it is found that the activation volumes determined by three different methods coincide with one another and the calculated activation energy for thermally activated motion of dislocations in austenite is in very good agreement with the measured activation energy of isothermal transformation. These results confirm that the above mentioned proposition by the present author is correct.

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The effect of hydrostatic pressures on martensitic transformations in Fe-24.0 at%Pt invar alloys with different degrees of order, S, (S≈0, S>0, S≈0.6, S≈0.8) has been examined by measuring electrical resistivity and magnetization under pressures up to 1.5 GPa. As a result, it was found that the transformation temperatures for the alloys with S≈0, S>0 and S≈0.6 were only decreased with increasing hydrostatic pressure, while those for the alloy with S≈0.8 were inversely increased under pressures lower than 0.25 GPa although they decreased under pressures higher than 0.25 GPa. The hydrostatic pressure dependences of equilibrium temperatures, which were obtained from the measured transformation temperatures, for the alloys with S≈0.6 and S≈0.8 have been calculated by putting the atomic volumes of austenite and martensite phases and the spontaneous volume magnetostrictions of austenite phase, ω_s, measured in the present study into a previously derived equation including a term of the ω_s related to the invar effect. Consequently, the calculated dependences for those alloys were all in good agreement with the measured ones in the applied hydrostatic pressure range, as in an Fe-29.9 at%Ni invar alloy previously examined. Thus, the previously proposed effect of spontaneous volume magnetostriction and the derived equation were further confirmed to be appropriate.

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The influence of temperature and strain rate on the type and nature of serrations observed during tensile tests in a 15Cr–15Ni–2.2Mo–Ti modified austenitic stainless steel was investigated. Tensile tests were conducted in the temperature range 300–1023 K and in the strain rate range 6.3×10⁻⁵ s⁻¹ to 1.26×10⁻² s⁻¹. Different types of serrations were found to occur in a systematic way within well-defined regimes of temperature and strain rate. A new arch type of serration and a pseudo-neck were observed and the possible mechanism responsible is discussed. A map in the reciprocal temperature-strain rate space which delineates the different regimes of serrated flow is presented.

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In the Au wire bond to Al pad on a monolithic IC, it is found that the bond degradation due to heat treatment after thermosonic ball bonding depends on the thickness of the Al film on the SiO₂/Si substrates. The bond degradation is lessened with thinning Al film. In the specimens with 0.2 μm and 0.5 μm Al films, the change in the bond resistance is small and the shear strength is almost invariable. In this case, the bond degradation is improved by reason of the fact that the volume of the diffused layer is reduced. It is also shown that the adhesion of the diffused layer to Au and SiO₂ is very strong and a little Kirkendall void is detected. In the specimens with Al films thicker than 0.5 μm, the bond resistance much increases and the bond shear strength decreases.

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As a fundamental study to investigate the mechanism of modification of Al–Si alloys, the change in silicon phase morphology at the solid/liquid interface due to the addition of strontium was observed using an improved unidirectional solidification method. A constant composition was required throughout the experiment, especially in the case of the unidirectional solidification method. In our research, a self sealing method was used to prevent the strontium from evaporating and oxidizing. We discovered that the Al–Si alloy was best aligned at a solidification speed of 2 mm/h and that strontium worsened the degree of alignment. As the solidification rate decreased, the degree of the interfacial smoothness also decreased in the Al–Si–Sr alloy, while it increased in the Al–Si alloy. The silicon phase protruded into the liquid phase in the Al–Si–Sr alloy whereas, the silicon phase was covered by α phase in the Al–Si alloy. This phenomenon was caused by the change in the balance between the α phase/liquid interfacial energy and the silicon phase/liquid interfacial energy. This was confirmed by observing the interface in equilibrium condition which was achieved by holding the furnace stationary for 5 h.

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Stircast Al–Pb Metal-Metal composites have been produced at a high rotational speed of 53 s⁻¹ with different lead contents and with the same lead content but different rotational speeds of 53, 37 and 25 s⁻¹ in a stircasting unit with facilities for bottom pouring and rapid solidification. Microstructure, particle size distribution and inter-particle distance have been determined by optical and scanning electron microscopy in order to see the effect of lead content and agitator speed. It has been observed that the microstructure of stircast composite is influenced significantly both by lead content and agitator speed during casting.

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Magnetic properties of Fe–Mn–Al alloys containing 1.0 mass% Al and 0.5–2.0 mass% Mn have been evaluated. The hot rolled alloys after annealing at 750–800°C have shown high induction, high remanence, low coercive force and reasonably high permeability. The annealed alloys have exhibited high tensile strength (335–345 MPa) and high elongation (30–40%). The d.c. electrical resistivity of the alloys have been found to be in the range 20−22×10⁻⁸Ω·m. Microstructural studies of the alloys have also been made and correlated with the magnetic properties.

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Grain boundary segregation in Fe-3 mass%Si alloys doped with tin was investigated by Auger electron spectroscopy (AES), in order to shed light on a fact that tin addition modifies secondary recrystallization of Si steels. It was found that in decarburized specimens tin was segregated at grain boundaries and its segregated amount increased with the bulk tin content. The effective grain boundary segregation energy of tin was estimated from the results, and the kinetics of the grain boundary segregation of tin was discussed.
As related to a phenomenon that the size of precipitates (inhibitors) in silicon steels becomes smaller by tin addition, interfaces between precipitates and matrix were also examined with AES. Significant segregation of tin was found at the interface between MnS and the matrix. This indicates that the tin segregation at the interface can affect morphology or size of the precipitates. The influence of tin on primary recrystallization and secondary recrystallization of Si steels was discussed from these results.

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