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The phase transition of Fe1-xCrx alloys after thermal aging at 748 K has been investigated by means of positron annihilation spectroscopy. It was observed that the implanted positrons preferentially annihilate with Fe electrons. The Cr concentration dependence of the W-parameter before thermal aging is quantitatively described by a preferential positron annihilation model within the first two coordination shells. After thermal aging, the W-parameter increased for all alloys, probably on account of an enhanced preferential positron annihilation of Fe atoms according to the growth of Cr-rich phases by thermal aging. Simultaneously, Fe-rich phases were formed and the interface condition between the Fe- and Cr-rich phases changed, providing another mechanism by which positrons are preferentially annihilated with Fe electrons in the Fe-rich phases. [ABSTRACT FROM AUTHOR]

Abstract: The mechanical strength of oxide dispersion strengthened (ODS) ferritic steels depends on the dispersion and microstructural stability of the oxide particles. Yttria is normally selected as dispersion particles to strengthen ODS ferritic steels, and other additional elements such as titanium and aluminum are added to obtain finer dispersion particles for the improvement of the mechanical properties of the ODS steels. Kyoto University is involved with the development of new ODS ferritic steels. 16Cr–0.1Ti–0.35Y2O3 ODS steel is a fusion structural material. In this research, the irradiation resistance of 16Cr–0.1Ti–0.35Y2O3 (16Cr0.1Ti) ODS steel was investigated by high-resolution TEM and by performing an ion irradiation experiment. The ODS steel was consolidated by hot extrusion at 1150°C and annealed at 1050°C for 1h for recrystallization. Oxides in 16Cr0.1Ti ODS steel were characterized by HRTEM and STEM-EDX and specified as (Y, Ti) complex oxides with an atomic ratio of Y:Ti=2:1. A 1.7MeV tandem accelerator for heavy-ion irradiation at the dual-beam material irradiation facility for energy technology (DuET), Kyoto University, was used to introduce irradiation damages in materials. The comparison of the dispersion, shape, and chemical composition of the oxides between the pre- and post-irradiated materials revealed that (Y, Ti) complex oxides were stable under the ion irradiation up to 60dpa at 650°C. [Copyright &y& Elsevier]

Abstract: SiCf/SiC composites are candidate structural and functional materials for fusion blankets, attractive for their potential application for higher temperature liquid metal blankets compared to the range possible for metallic materials. However, the experimental data on the long term compatibility of SiCf/SiC composites with high temperature liquid metal is inadequate. To acquire parametric data on the compatibility of NITE SiCf/SiC composites with a high temperature liquid metal stream, the corrosion behavior was examined in liquid Pb–Li using a rotating disk apparatus. The materials used in this study were exposed to relative flow velocity of ∼10–37cm/s at 900°C for 1000h. Oxidation layers were detected on the matrix and fiber near the surface exposed to liquid Pb–Li at 900°C for 1000h. Additional results for shorter exposure times and relationship to flow velocity are discussed. [Copyright &y& Elsevier]

Abstract: Breeding blankets are the most important components in DEMO. The DEMO blanket has to withstand high neutron flux typically 15–30 dpa/year under continuous operation. Therefore integrated and effective development of blanket structural materials and breeding/multiplying materials is essential in the blanket development for DEMO. In parallel to the ITER program, broader approach (BA) activities are initiated by EU and Japan. Based on the common interest of each party towards DEMO, R&D on reduced activation ferritic martensitic (RAFM) steels as a DEMO blanket structural material, SiCf/SiC composites which have potential for use in DEMO blankets, advanced tritium breeders and neutron multiplier for DEMO blankets, and tritium technologies including tritium behavior studies in advanced materials for DEMO blanket applications will be carried out as a part of the BA activities. [Copyright &y& Elsevier]

Abstract: The effects of He on the fracture behavior of reduced-activation ferritic/martensitic steels, including oxide dispersion-strengthened (ODS) steels and F82H, was determined by characterizing the microstructural evolution in and fracture behavior of these steels after He implantation up to 1000appm at around 550°C. He implantation was carried out by a cyclotron with a beam of 50MeV α-particles. In the case of F82H, the ductile-to-brittle transition temperature (DBTT) increase induced by He implantation was about 70°C and the grain boundary fracture surface was only observed in the He-implanted area of all the ruptured specimens in brittle manner. By contrast, no DBTT shift or fracture mode change was observed in He-implanted 9Cr-ODS and 14Cr-ODS steels. Microstructural characterization suggested that the difference in the bubble formation behavior of F82H and ODS steels might be attributed to the grain boundary rupture of He-implanted F82H. [Copyright &y& Elsevier]

The zero-point of indentation depth in nanoindentation or depth-sensing instrumented indentation tests should be precisely set to evaluate the indentation hardness and indentation elastic modulus of materials to be tested, especially at shallow depths. A critical contact stiffness value has been widely used to determine the zero-point in nanoindentation tests with a Berkovich tip using the continuous stiffness measurement (CSM) method. However, this criterion occasionally gives an inadequate zero-point owing to the surface roughness of materials, the vibration of the testing system, and the flaws of the CSM method at shallow depth. This study proposes a practical method to determine the effective zero-point of indentation depth, which was obtained linearly at the zero-point of contact stiffness and extrapolated from the depth-dependent contact stiffness values, except for those at initially unstable contact depths. The proposed method enables nanoindentation tests to obtain a constant indentation elastic modulus and low deviation of nanoindentation hardness of homogenously fused silica and metallic materials, which provides an efficient way to obtain more accurate test data., (© 2022. The Author(s).)