Papers by Keyword: TEM

Abstract: The formation of hydrides in zirconium alloy has been one of the essential matters of discussion to maintain mechanical strength of nuclear fuel cladding tubes. In this work, we examined the precipitation process of zirconium hydride by transmission electron microscopy under hydrogen ion irradiation. Zircaloy-4, which has been used extensively as nuclear fuel cladding, was irradiated with hydrogen ion at room temperature to achieve enough hydrogen concentration for precipitation. The growth of hydrides accompanied with dislocations around hydrides was observed under hydrogen implantation. The observed hydride was the γ-hydride phase with fct structure and the orientation relationship was <110>γ ||<1120>α as reported previously. As the hydride grew, the dislocations were generated gradually. This process can be explained using a ratchet mechanism suggested by Carpenter. The growth rate became lower according to the approach of other hydrides. This behavior is considered to be influenced by the strain field caused by other hydrides.

Abstract: SrTiO3 crystals were implanted with 100 keV xenon (Xe+) ions at 673 or 1073 K up to 2.0 × 1020 ions m−2. Defect clusters formed in the ion-implanted samples were investigated with conventional and high-resolution transmission electron microscopy. Nanometer-sized clusters were formed in the samples. The clusters grew large in size after post-implantation annealing and with increasing the implantation dose. The clusters were faceted with {100}, or {110} of SrTiO3. Though the nano-sized clusters were expected to contain Xe atoms, they were not in crystalline state. The results suggest that even if the clusters contain Xe atoms, they also contain other point defects such as vacancies.

Abstract: TEM is one of the most powerful experimental tools for the study of nanometer-sized particles. In the present work, the finite size effect on both the stability of two-phase microstructure and the solid solubility has been examined by in situ TEM using particles in the Au-Ge system. The size effect on the two-phase microstructure is rather small when the size of particles is larger than approximately 10 nm in diameter. However, the effect becomes strong in particles smaller than about 10 nm in diameter and an amorphous structure appears instead of the crystalline two-phase microstructure. The solid solubility in each solid solution in nanometer-sized alloy particles with a two-phase microstructure gradually increased as the particle size decreased. The enhancement of solid solubility was large in gold solid solution as compared with the in germanium solid solution.

Abstract: Isolated and oriented hard magnetic FePtCu ternary alloy nanoparticles with the L10-type ordered structure have been directly fabricated by rf-magnetron sputtering onto NaCl substrate kept at 613K without any post-deposition annealing. Structure and morphology of those particles were studied by TEM. When the sputtering duration decreases, the particle size decreases and the particle areal number density increases. These nanoparticles have <100> orientation on the NaCl substrate. Alloy composition distribution from particle to particle examined by nano-beam elemental x-ray analysis was found to be quite small, which can be attributed to the homogeneous structure formed by co-deposition of Fe, Pt and Cu by sputtering. Thermal fluctuation of the magnetization becomes prominent in the specimen with the particle size smaller than about 10nm in diameter.

Abstract: We report the damage-free planarization of 4H-SiC (0001) wafers using a new planarization technique we named CAtalyst-Referred Etching (CARE). The CARE setup equipped with a polishing pad made of a catalyst is almost the same as a lapping setup. Since the catalyst generates reactive species that activate only when they are next to the catalyst surface, SiC can be chemically removed in contact with the catalyst surface with a pressure noticeably lower than that in a conventional polishing process. The processed surfaces were observed by optical interferometry and AFM. These observations presented a marked reduction in surface roughness. A step-terrace structure was observed with a step height of approximately 3み, corresponding to one-bilayer thickness of Si and C, in the AFM images. To estimate the crystallographic properties of the CARE-processed surface, the surfaces were observed by cross-sectional TEM. The TEM images showed that a more crystallographically well-ordered surface was realized in comparison with the conventional CMP-processed surface.

Abstract: QuaSiC TM substrates can be obtained by transferring a single crystal SiC layer onto a poly SiC substrate using the Smart Cut TM technology. In order to overcome the difficulty of limited thickness, an important improvement has been demonstrated, which consists in obtaining thick SiC structure by growing epitaxial SiC layers on top of transferred layers. The aim of this work is a structural analysis of such layers by Transmission Electron Microscopy and Photoluminescence.

Abstract: Inconel 690 alloy is a Ni-Cr-Fe austenite solid solution alloy with a wide range of applications such as steam generator tubes in nuclear power plant due to its good mechanical properties and corrosion resistance. In this study, the effects of heat treatment on the microstructural properties of Inconel 690 alloy were investigated. Inconel 690 alloy was annealed at solid solution temperature of 1150°C for 20 min, and cooled down to 800°C with different cooling rates, and then aged at 800°C for 100 min in vacuum, and then cooled down to room temperature by water quenching. The optical microscopy, scanning electron microscopy, and transmission electron microscopy results indicated that in case of the cooling rate of 0.5°C/min, discontinuous carbides along the grain boundaries were formed and when the cooling rate was 10°C/min, continuous carbides were formed. In both cases, many annealing twins were also formed. These results can help to improve the understanding of microstructural properties of Inconel 690 alloy.

Abstract: In the present study, a new approach is conducted to evaluate dislocation structure induced by cyclic plasticity. First, cyclic plastic loading tests are carried out up to 100 cycles with three different small strain amplitudes on SUS316L stainless steel at room temperature. The test result presents the dependence of the strain amplitude on cyclic hardening and softening behaviors. Specifically, it is found that the cyclic loading test with strain amplitude of 0.25% shows both cyclic hardening and cyclic softening, while the cyclic loading tests with strain amplitudes of 0.75% and 1.0% show no cyclic softening. Secondly, the dislocation structures of the specimens after cyclic loading are observed by using a transmission electron microscope (TEM), and this observation reveals that the dislocation structure after cyclic loading test depends on the strain amplitude. Finally, a quantitative evaluation method of the dislocation structure is also proposed. The TEM images are converted into binary images and the resolution dependence of the generated binary image is used to visualize the characteristics of the dislocation structure. The relationship between strain amplitudes of cyclic plasticity and dislocation structure organization is clarified by the evaluation method. Finally, the heterogeneity of the dislocation structure is discussed.

Abstract: The intergranular microstructure in a liquid phase sintered silicon nitride based ceramic may be viewed as an oxynitride glass-ceramic. This work is concerned with the incorporation of yttrium B-phase, which is a five-component phase, into the intergranular regions of silicon nitride ceramics. The silicon nitride materials were fabricated with the addition of a powdered B-phase parent glass with composition (e/o) 35Y:45Si:20Al:83O:17N, or the addition of a mixture of Y2O3, SiO2 and Al2O3 with cation composition (e/o) 35Y:45Si:20Al. The starting powder mixtures contained 10 wt% of sintering additives. Sintering for 2 h at 1800°C was followed by a two-step post-densification heat treatment in order to promote nucleation and growth of yttrium B-phase. Detailed imaging and elemental analysis of the intergranular regions was carried out by EDX in a FEGTEM.

Abstract: Ductility of Mg – alloys is linked to a shortage of independent slip systems. Basaltextured samples of Mg-Al-Zn alloy are examined for presence of dislocations of different types after hot compression tests of cast samples and cold compression tests of hot-rolled samples. The JEM-1000, electron transmission microscope with an accelerating voltage of 750 kV using a dark field–weak beam method of observation and the g·b=0 invisibility criterion as a basic method of the analysis of Burgers vectors, is used to analyse the samples. Dislocations with Burgers vectors , [c] and are found. The results are used to evaluate the dislocation density and determine the possible dislocation reactions.