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Povzetek: The influence of grain boundaries on deuterium (D) retention and transport was investigated in nanocrystalline tungsten (W) by exposing the samples to sub eV D atoms. Thin tungsten films with nanometer-sized grains were produced by pulsed laser deposition on tungsten substrates. Their grain size was increased up to one micrometer by thermal annealing in vacuum up to 1223 K. Irradiation damage was created by 20 MeV W ions at 290 K. The transmission electron microscopy analysis showed one order of magnitude larger dislocation density in nanometer-grained samples compared with the larger-grained samples. The samples were after W irradiation exposed to 0.3 eV D atoms at 600 K. D retention and D depth profiles were measured by nuclear reaction analysis. In the as-deposited nanometer-grained samples, D populated the damaged region more than three times faster than in the samples with larger grains, indicating that grain-boundaries increase D transport through the material. The concentration of defects was assessed by the final D concentration in the samples. The sample with a smallest grain size showed slightly larger D concentration in the irradiated area, but the difference in the D concentration is not substantial between different-grained samples. A large D concentration in the non-irradiated nanometer-grained sample was measured which is an indication for a high defect density in the initial material. From our observations, it can be postulated that the nanocrystalline microstructure did not substantially influence the generation of irradiation-induced defects by defect annihilation at grain boundaries.
Ključne besede: deuterium, tungsten, grain boundaries, transport, displacement damage, retention
Objavljeno v DiRROS: 12.12.2025; Ogledov: 730; Prenosov: 530
Celotno besedilo (7,06 MB)
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Povzetek: We investigated the microstructural evolution of W(111) single crystals under high-energy self-ion irradiation at 290 K and 800 K, using complementary characterization techniques, including Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Rutherford backscattering spectrometry in channelling regime (RBS-C), Positron annihilation spectroscopy (PAS), and Nuclear reaction analysis (NRA). Irradiation with MeV W ions allowed for controlled defect formation, with dose and temperature significantly affecting defect type and distribution. At 290 K, interstitial defects evolved from dislocation loops at low doses (0.02 dpa) to dislocation networks at higher doses (0.2 dpa). In contrast, at 800 K, lower dislocation densities were observed, with nm-sized dots and isolated lines forming at 0.02 dpa and developing into longer dislocation lines (~30 nm) at 0.2 dpa. RBS-C spectra support these findings, showing a trend of increasing dislocation density with dose but decreasing with temperature. PAS analyses revealed mono-vacancies and small vacancy clusters (V2–V4) at 290 K, coalescing into larger clusters (V25–V50) at 800 K. NRA measurements indicated greater deuterium retention at 290 K than at 800 K, consistent with lower vacancy mobility at the lower temperature. Combined TEM, RBS-C, PAS, and NRA observations highlight increased vacancy mobility and defect recombination with temperature, forming larger vacancy clusters at 800 K. This comprehensive study provides quantitative insights into defect formation and evolution in W single crystals, presenting a comparative analysis of defect distributions across multiple techniques and revealing temperature-dependent mechanisms of microstructural change.
Ključne besede: heavy-ion irradiation, structural defects
Objavljeno v DiRROS: 11.12.2025; Ogledov: 822; Prenosov: 484
Celotno besedilo (9,96 MB)
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Povzetek: The selection of the most suitable material for the EU DEMO divertor is still underway. Current research focuses on the development of tungsten-based materials for plasma-facing applications. In addition to other requirements, the candidate material must also exhibit low intrinsic hydrogen isotope retention. To verify the suitability of the tungsten carbide-containing materials, we examined the effect of carbon in the form of carbide or free carbon on deuterium (D) retention. The samples were consolidated by Field Assisted Sintering (FAST) and examined in terms of phase composition and microstructure before the d-retention studies. The Nuclear Reaction Analysis (NRA) technique was used to determine the depth distribution of D after the exposure to D plasma (fluence of 1.3 × 1024 D/m2 and 1.3 × 1025 D/m2 and an exposure temperature of 370 K and 523 K, respectively). Thermal Desorption Spectroscopy (TDS) was used to measure the D desorption spectra. The surfaces of samples exposed to D plasma were also examined in terms of microstructure by scanning electron microscopy. The study has shown that apart from the d-fluence and exposure temperature, the materials’ composition plays a vital role in d-retention, accompanied by blisters and pillar formation. The lowest d-retention was observed for tungsten and the highest in the W-W2C composite. The blisters and pillars were formed in these two materials but not in the WC, which also contains free carbon. At higher D fluence, approximately 15 to 20-times more blisters and pillars were formed in the W-W2C composite than in the tungsten prepared by the same method. The results suggest that the number of defects causing higher d-retention is the highest in W-W2C. On the other hand, the absence of surface irregularities in the WC-C sample after D retention studies indicates that the cause for higher D retention does not lie in the carbides, but, presumably, the microstructural and crystal lattice defects govern the D retention in tungsten-tungsten carbide systems.
Ključne besede: tungsten, (di)tungsten carbide, deuterium, nuclear reaction analysis, thermal desorption spectroscopy
Objavljeno v DiRROS: 03.09.2025; Ogledov: 930; Prenosov: 526
Celotno besedilo (5,58 MB)
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