Speaker
Description
Tungsten (W) has attracted great attention as a target material in high-intensity proton accelerator and plasma facing materials/components in future fusion reactors due to its high melting point, low thermal expansion coefficient, high density, etc. In these environments, helium (He) is produced by (n, α) nuclear reaction or spallation in bulk W. He tends to accumulate and precipitates into He bubbles, which may lead to material degradation such as high temperature embrittlement, and blistering. Therefore, many studies have been carried out so far to clarify the effect of He bubbles by introducing He into bulk W samples mainly using high-energy He-ion implantation. In this method, irradiation induced defects such as dislocation loops are also generated via displacement damage. Therefore, it is difficult to know the independent effect of He bubbles. In addition, the irradiated samples become radioactive and difficult to handle in ordinary laboratory experiments.
In order to fabricate W materials containing He bubbles without irradiation inducement, a powder metallurgical route via mechanical alloying (MA) under a He atmosphere, spark plasma sintering (SPS), and grain-boundary-sliding based microstructural modification (GSMM) was employed for the fabrication of W-1.1%TiC. GSMM was compression of the SPSed compact utilizing superplastic deformation due to grain boundary sliding. Microstructure was observed by transmission electron microscopy (TEM) including weak beam dark field method, high-angle-annular-dark-field scanning transmission electron microscopy (HAADF-STEM), and energy dispersive X-ray spectroscopy (EDS). TEM observations revealed that the present fabrication process successfully achieved incorporation of He bubbles in W-1.1%TiC, which had diameters of approximately 6~10 nm or less in as-SPS sintered and GSMM-processed samples. This is the first report on the fabrication of materials such as W alloys that contain He bubbles not by resorting to He implantation or (n, α) reaction by neutron irradiation, hence without radioactivation and irradiation induced defects. The present fabrication of W-1.1%TiC containing He bubbles without irradiation defects can be expected to be useful in fundamental understanding of independent effect of He bubbles on physical and mechanical properties of various materials concerned.
| Themes for the contribution | 4 Target design, analysis, and validation of concepts: |
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