Mitigation of embrittlement caused by recrystallization and radiation is the key issue of tungsten (W) based materials for use in the advanced nuclear system such as fusion reactor applications. In this paper, our nanostructured W materials development performed so far to solve the key issue is reviewed, including new original data. Firstly, the basic concept of mitigation of the embrittlement is shown. The approach to the concept has yielded ultra-fine grained, recrystallized (UFGR) W(0.251.5) mass%TiC compacts containing fine TiC dispersoids (precipitates). The UFGR W(0.251.5)%TiC exhibits favorable as well as unfavorable features from the viewpoints of microstructures and various thermo-mechanical properties including the response to neutron and ion irradiations. Most of the unfavorable features stem from insufficient strengthening of weak random grain boundaries (GBs) in the recrystallized state. The focal point on this study is, therefore, to develop a new microstructural modification method to significantly strengthen the random GBs. The method is designated as GSMM (GB Sliding-based Microstructural Modification) and has lead to the birth of toughened, fine-grained W1.1%TiC in the recrystallized state (TFGR W1.1TiC). The TFGR W1.1TiC exhibits much improved thermo-mechanical properties. The applicability of TFGR W1.1TiC to the divertor in ITER is discussed.
Magnetic field-induced strain (MFIS) along the [001]P (the symbol “P” represents parent phase) direction due to the conversion of martensite variants has been investigated for a disordered Fe–31.2Pd(at. %) single crystal and an ordered Fe3Pt single crystal exhibiting martensitic transformations from cubic phases to tetragonal phases at 85 and 230 K, respectively. The tetragonality c/a of Fe–31.2Pd at 77 K is 0.940 and that of Fe3Pt at 14 K is 0.945. When magnetic field is applied to the martensite phase along the [001]P direction, the specimen expands along the field direction for Fe–31.2Pd and contracts for Fe3Pt, suggesting that the c axis is the hard axis of magnetizaion for Fe–31.2Pd and is the easy axis for Fe3Pt. The conversion of variants by magnetic field is almost perfect for Fe–31.2Pd and is not perfect for Fe3Pt. The recoverable strain in the field removing process is small for Fe–31.2Pd and is about 0.6% for Fe3Pt. In the cooling process under magnetic field of 3.2 MA/m, the fraction of preferable variants reaches 100% in a narrow temperature range for Fe–31.2Pd, but it does not reach 100% for Fe3Pt (the maximum fraction is about 80%), although the fraction increases with decreasing temperature.
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