Following a brief introduction of historical development of nuclear techniques used today for the study of metals and alloys, principles and metallurgical applications of Mössbauer spectroscopy, positron-electron annihilation method, and NMR method are described. All of the examples of their applications are from the results obtained in the author’s laboratory, and emphases are placed on the usefulness, the comprehensible principles, and well controllable characters and practices of the above techniques.

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The influences of environment in solute heat treatment and aging, and pre-aging at room temperature on the age-hardening behavior of Ti-14 and 20 mass% Mo alloys at 623 K were studied by Vickers hardness measurements. The solution heat treatments were performed in vacuums of 1.3 mPa and 8 Pa. The atmosphere, a pure argon current and a vacuum were used as the environments during aging. The periods of pre-aging were 1.6×10⁵ s for the short pre-aging and 1.0×10⁶–3.7×10⁷ s for the long one. The specimens which were solution heat treated in each vacuum and pre-aged for 1.6×10⁵ s showed a two-stage hardening. The first stage seemed to be due to a product formed by the reaction of quenched-in vacancies, interstitial atoms and metallic atoms, and the second stage was due to the formation of aged omega phase as reported previously. The age-hardening behavior of the specimen pre-aged for a short period was more active than that of the specimen pre-aged for a long period in spite of the solution heat treatments in either vacuum. The role of quenched-in vacancies in the age-hardening behavior was very important in Ti-20 mass% Mo alloys in connection with the pre-aging at room temperature. The higher the oxygen content in the environments during aging, the greater became the hardness values of the surface layer and the interior of Ti-14 mass% Mo alloys.

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Morphology, crystal structure and composition of bainite plates in a Cu-29.1at% Zn-6.7at% Al alloy have been studied by using a high resolution analytical electron microscope. The bainite plates at an early stage of growth were separated from the matrix by parallel straight interfaces and contained a lot of stacking faults. The bainite plates had a monoclinic ordered 9R structure like the martensites formed in the alloy at lower temperatures. High relosution electron microscopy of the straight interfaces revealed that the bainite lattice was coherent with the adjacent matrix. Energy dispersive X-ray spectroscopy demonstrated that the composition in bainite plates was different from that in the adjacent matrix even at the early stage of formation while the bainite plates had an ordered 9R structure. As heat treatment was prolonged, the bainite plates became thicker and the straightness of their interfaces was lost gradually, and the crystal structure changed from the ordered 9R structure into a disordered one and finally into a disordered fcc structure of the equilibrium α phase. The composition in the bainite plates was constant and nearly equal to that of the α phase within experimental error through the changes in morphology and crystal structure. The above results were accounted for by an idea that bainite plates were martensitically formed after some composition change had taken place at local areas in the matrix, and that the morphology and crystal structure changed during the growth of the plates.

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The bainitic transformation in a Ag-45 at% Cd alloy at 433 K has been examined by means of optical microscopy, high resolution analytical electron microscopy and electron diffraction. As a result, the following were clarified: Crystal structure and morphology of the bainitic product (α_B) in an early stage of growth were an internally faulted (orthorhombic) N9R type long period stacking order structure and a plate shape with parallel straight interfaces, respectively. They were very similar to those of (monoclinic) M9R or M18R type martensite plates in other noble metal base β phase alloys. However, they were different from an internally twinned 2H type stacking order structure and a spear shape, respectively, of the normal martensites produced in the sub-zero cooled Ag–Cd alloy, and moreover no ordered structure was recognized in the N9R α_B plates even in the very early stage of growth. The α_B plates approached the equilibrium α phase with the progress of growth, changing the faulted N9R to a non-faulted fcc structure and the straight interfaces to the swollen ones. Composition of the (α_B plates was almost the same as that of the equilibrium α phase from the very early stage of growth (more than 30 nm width). From these observations, it was concluded that diffusion of Cd atoms first occurred in the β₂ matrix, approaching the composition of the equilibrium α phase, and then martensitic transformation occurred due to a rise of M_s in the regions reduced in Cd content. This conclusion was consistent with the formation of 9R α_B plates which were different from the normal 2H martensites in the Ag–Cd alloy.

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The dilute Cu–Si, Cu–Si–Ti and Cu–Si–Zr alloys were internally oxidized in the temperature range of 973–1323 K. The crystal structures of dispersed oxides in the internally oxidized alloys were identified by X-ray diffractometry. The measurements of mean particle sizes, analysis of dispersed particles and the observation of precipitate morphology were carried out with an analytical transmission electron microscope. The hardness measurements were performed using a micro-Vickers hardness tester.
The oxide particles in the internally oxidized Cu–Si binary alloys were initially dendritic and subse-quently transformed to spherical in process of time. By addition of Ti and Zr into the Cu–Si alloy, the dispersed oxide particles became remarkably finer. The oxide phase in the internally oxidized Cu–Si alloys in the temperature range of 973–1073 K was amorphous SiO₂, but at 1173–1323 K α-cristobalite was precipitated in addition to amorphous SiO₂. The amount ratio of α-cristobalite to amorphous SiO₂ was increased with increasing oxidation temperature. The dispersed oxide phases in the internally oxidized Cu–Si–Ti alloy were amorphous SiO₂ and rutile-type TiO₂, and in the Cu–Si–Zr alloy amorphous SiO₂, monoclinic ZrO₂, tetragonal ZrO₂ and ZrSiO₄ were precipitated. Pairs of SiO₂ and TiO₂, or SiO₂ and ZrO₂ were formed in the ternary alloys. The oxide particles precipitated in the ternary alloys were finer than those in the binary alloys. The effect of Zr on refining dispersed oxide particles was greater than that of Ti. The hardness values of internally oxidized ternary alloys were higher than those of binary alloys.

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As the wettability of solid oxides by liquid metals gives important information on the development of composite materials, metal- ceramics joinings, and the behaviour of deoxidation products in liquid metal, a large number of papers have been published. However, there are large discrepancies among the values reported.
In this work, the wettabilities of solid oxides (Al₂O₃, MgO, CaO, ZrO₂, and SiO₂) by liquid pure metals (Sn, Ag, Au, and Cu) have been measured over a wide temperature range by the sessile drop method.
Main results obtained are as follows:
(1) Surface tensions of pure liquid metals can be expressed by the following equations:
γ_Sn=551−0.09[T(K)−505],
γ_Ag=910−0.17[T(K)−1234]
γ_Au=1105−0.28[T(K)−1336]
γ_Cu=1320−0.28[T(K)−1356]
(2) Contact angles and work of adhesions between liquid pure metals and solid oxides were closely related to the standard free energy change of formation of oxides. Values of contact angle and work of adhesion changed linearly with temperature and in some systems refracted points were observed at the temperatures which corresponded to the refracted points in the free energy-temperature diagram.
(3) The wettability of solid oxides by liquid metals depended not only on the stability of solid oxides which can be expressed by the standard free energy change of oxide formation but also on ionic radii of metals which compose oxides.

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The main purpose of this work is to investigate the possibility of solid state amorphization of Pd–Si crystal powder. A Pd–Si alloy powder was obtained by mechanical alloying using conventional ball milling machine. X-ray diffraction patterns of mechanical alloyed samples were measured as a function of the milling time. A halo pattern, which can be taken as the confirmation for the formation of an amorphous structure, was obtained from the sample which was made by milling for 7.2×10⁵ s. This is the first report concerning complete amorphization of Pd–Si crystal powder by ball milling.

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New decagonal alloys in the Al–Ni–Fe and Al–Ni–Co systems have been produced by liquid quenching. Their formations extend in the ranges of 9 to 16 at% Ni and 9 to 21 at% Fe or Co. The whole replacement of Fe or Co in Al₇₅Ni₁₀(Fe or Co)₁₅ alloys by V, Cr, Mn or Ru gives a mixed structure consisting of decagonal, icosahedral and crystalline phases. The decagonal phase consists of large grains with a size above 1 μm and the magnitude of the phason strain frozen during liquid quenching is relatively small probably because of the two-dimensional quasicrystalline structure.

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