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The nature and magnitude of Ag diffusion in SiC has been a topic of interest in connection with the performance of tristructural isotropic (TRISO) coated particle fuel for high temperature nuclear reactors. Ion implantation diffusion couples have been revisited to continue developing a more complete understanding of Ag fission product diffusion in SiC. Ion implantation diffusion couples fabricated from single crystal 4H-SiC and polycrystalline 3C-SiC substrates and exposed to 1500-1625°C, were investigated by transmission electron microscopy and secondary ion mass spectrometry (SIMS). The high dynamic range of SIMS allowed for multiple diffusion régimes to be investigated, including enhanced diffusion by implantation-induced defects and grain boundary (GB) diffusion in undamaged SiC. Estimated diffusion coefficients suggest GB diffusion in bulk SiC does not accurately reflect the release observed from TRISO fuel.

The present paper investigated the grain and texture characteristics in a nanostructured oxide dispersion strengthened ferritic steel subjected to friction stir welding. The 'onion rings' structure obviously exhibited in the macrostructure overview of the welds. The electron backscatter diffraction (EBSD) work revealed that the 'onion rings' comprised alternate layers made by coarse and fine grains, while no strong texture was exhibited in the alternate layers of the 'onion rings'. Image quality maps of EBSD indicated that layers of fine grains were deformed under high strain conditions. Textures within the stir zone and thermomechanically affected zone were weak and exhibited some characteristics of bcc simple shear textures. Results of grain boundary revealed that the mechanical action in welding process promoted the transformation of low angle to high angle boundaries and contributed to the grain refinement.

The goal of this study is to characterize the hardness distribution and texture evolution in a friction stir welded oxide dispersion strengthened (ODS) ferritic steel. Hardness profiles were plotted by collecting data on the transverse cross section of the joint. The texture evolution and microstructure characteristics were studied by electron backscattering diffraction (EBSD). Results showed that regions near the bottom of the stir zone were the weak points in hardness, as those regions comprise coarser grains compared with the adjacent regions. EBSD results showed that the grain characterization (size, shape, and aspect ratio) varied within different regions and provided important insight into the material flow within the stir zone. EBSD results also revealed that textures within different regions presented some features of rotating coincidence. By suitable rotations of the poles figures, textures within different regions could superpose with each other almost exactly.

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