Papers by Keyword: TEM

Abstract: In order to elucidate the predominance of Goss grains after SIBM in electrical steel sheets, Goss, D-Cube and {111}<112> grains after temper rolling of 5 and 9% reduction were observed by TEM. In 5% strain the amount of dislocations in Goss grains was the smallest of the three orientations. In 9% strain dislocations in Goss grains were distributed more heterogeneously than the other two types of grains. It is considered that {111}<112> grains have large amounts of dislocations owing to high Taylor factors and the differences of microstructures between Goss and D-Cube grains are due to orientation stabilities. Goss grains are speculated to be easy to recover and therefore they are predominant after SIBM.

Abstract: Pure Cu, CuZr and an Al-alloy were processed by Equal Channel Angular Pressing (ECAP) at room temperature applying route Bc. Microstructure evolution during ECAP and subsequent annealing was investigated. The deformed and annealed states were characterized by EBSD, TEM and microhardness tests. The microstructure variation was recorded and compared to the behavior of conventional cold rolled material. The study revealed a very low thermal stability of ECAP deformed pure Cu samples compared to cold rolled material with same total strain. However, the thermal stability was significantly improved by alloying with Zr. In contrast, ECAP deformed Al-alloy showed higher thermal stability than cold rolled material.

Abstract: Precipitation phenomena in an austenitic stainless steel, SUS316L cold-rolled with various reduction rates were studied by transmission electron microscopy and synchrotron radiation diffractmetry. After the aging at 573 K for 15000 h, two of precipitates were observed, which were identified as M7C3 and M23C6 by SR diffraction and electro diffraction measurements. The precipitates M7C3 were formed at both innergranular and grain boundary, while the precipitate M23C6 was formed at innergranular. The precipitation was promoted with increasing cold rolling reduction. Also segregation of phosphorous was detected along grain boundaries. Besides, the residual stresses were measured with side inclination method using a synchrotron radiation facility, SPring-8. The residual stresses were increased with increasing the cold rolling reduction rate.

Abstract: A low impurity magnesium alloy has bean prepared. Deformation behavior in cold-rolling and corrosion behavior of the alloy were compared with those of a commercial alloy. The specimens were cold-rolled at room temperature with reduction rates of 0~80 %. Transmission electron microscopic observations on the cold-rolled specimens were carried out. In the case of the low impurity magnesium alloy, recrystallization easily occurred. Analyses of microstructures in the deformed specimens were carried out by means of EBSP, and the recrystallization phenomena have been discussed. Another effect of lowering the impurities is to improve a corrosion resistance with changing the corrosion morphology.

Abstract: The microstructure and strain characteristics of self-assembled InAs/GaAs quantum dots (QDs) were studied by using transmission electron microscopy. Compressive strain was induced to uncapped QDs from GaAs substrate and the misfit strain largely increased after the deposition of GaAs cap layer. Tensile strain outside QD was extended along the vertical growth direction; up to 15 nm above the wetting layer. Vertically nonaligned and aligned stacked QDs were grown by adjusting the thickness of GaAs spacer layers. The QDs with a lens-shaped morphology were formed in the early stage of growth, and their apex was flattened by the out-diffusion of In atoms upon GaAs capping. However, aligned QDs maintained their lens-shaped structure with round apex after capping. It is believed that their apex did not flatten because the chemical potential gradient of In was relatively low due to the adjacent InAs QD layers.

Abstract: La2O3 and/or Ga2O3 doped, and the double dopant γ-Al2O3 composite powder samples were prepared by the sol-gel method. Nanostructural characterizations of the powder samples were performed by high resolution transmission electron microscopy (HRTEM) in order to clarify the role of the metal oxide dopants for the improved hydrothermal stability of the La2O3-doped Ga2O3-Al2O3 composite material. The results of HRTEM study and selected area electron diffraction (SAED) analysis revealed the formation of the uniform solid solution of Ga2O3-Al2O3. In addition, the results of X-ray elemental mapping analysis revealed the existence of well-dispersed La2O3 on the grain surface of Ga2O3-Al2O3 solid solution. These structural features could act an important role for the improved hydrothermal stability of the La2O3-doped Ga2O3-Al2O3 composite material.

Abstract: “Environmental cell” microscopy was applied for surveying gas reaction of hydrides in magnesium base alloys, which are candidates for hydrogen storage materials in advanced hydrogen energy systems. In order to clarify the mechanism of hydrogenation process, in-situ experiment has been carried out by using a 200 kV transmission electron microscope (TEM) equipped with a newly developed environmental cell, which is capable to 0.1 MPa in the temperature range between R.T. and 200°C. When hydrogen gas reacted with magnesium powders, straightening of surface steps (60~70 nm in height) was observed, indicating that volume expansion occurred. In addition, the formation of MgH2 was indicated in selected-area-diffraction patterns (SADP). The precise study on this in-situ experiment, as well as its improvement, will be continued, with using transparent films.

Abstract: We indicated synthesization of LCMO by hydrothermal reaction. The results of transmission electron microscopy revealed that the LCMO particles had wide range in size and various in shapes. The LCMO particles had a perovskite-type crystal structure with some other phases. Magnetic property was measured by physical property measurement system. Their crystallinity and magnetization tended to increased with increasing reaction time.

Abstract: Manganese-alloyed Ru2Si3-based alloys with various alloy compositions have been prepared and the phase relationships of these alloys have been investigated as a function of the Mn concentration using X-ray powder diffraction, scanning electron microscopy and transmission electron microscopy. A series of Ru1-xMnxSiy chimney-ladder phases is confirmed to be formed over a wide compositional range (x ≥0.12). These chimney-ladder phases are considered to be formed to stabilize the HT-Ru2Si3 chimney-ladder phase through the substitution of Ru with Mn. The compositions of the chimney-ladder phases are, however, significantly deviated from the idealized composition satisfying the valence electron concentration rule: VEC=14.

Abstract: Effect of the ternary element of Mo on the crystal structure and thermoelectric properties of ReSi1.75 has been investigated. The crystal structure of Mo-containing ReSi1.75 has shear structure up to 1.5 at%, the structure changes into adaptive structure at larger Mo contents. The concentration of Si vacancies estimated from the crystal structures determined decreases with increasing Mo content. Thermoelectric properties of Mo-containing ReSi1.75 indicate that the character changes from p- to n-type semiconductor upon alloying with Mo, which is explained by the decrease in Si vacancy concentration.