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Povzetek: Achieving anisotropy in additively manufactured composites is essential for high-performance functional materials but remains challenging in fused filament fabrication (FFF). This study investigates a field-assisted FFF approach using strontium hexaferrite (SrFe12O19)–polyphenylene sulfide (PPS) composites, in which particle alignment is induced by processing on top of a high-strength neodymium–iron–boron (Nd–Fe–B) magnet. Two configurations were compared: (i) a continuous setup, where the growing printed material remains in direct contact with the magnet and can act as a flux-guiding core, and (ii) a spacer-based setup, where non-magnetic spacers separate the print from the field source. Structural, functional (magnetic) measurements and finite element simulations (FEMM) were used to quantify the evolution of anisotropy as a function of build height. In the continuous configuration, particle alignment—and thus macroscopic anisotropy—remains high up to about 20 mm, with 0.90, and then gradually declines while still being detectable at 57.5 mm. Spacer-printed samples lose anisotropy much earlier, with approaching isotropic values (∼0.5) beyond 20–25 mm. Simulations reproduce these trends and show that previously deposited material acts as a flux-guiding path, sustaining a predominantly uniaxial field with height. The results define practical limits for static-field alignment in material-extrusion processing and provide geometry-dependent design rules for scalable fabrication of anisotropic ceramic–polymer composites. The findings are relevant for materials and process design in applications where controlled anisotropy is required over centimetre-scale dimensions.
Objavljeno v DiRROS: 11.02.2026; Ogledov: 569; Prenosov: 275
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Povzetek: The phase composition and microstructure of Sr-hexaferrite (SFO) ceramics govern the hard magnetic properties. Here, pressureless spark plasma sintering (pSPS) technique was employed for the rapid consolidation (500°C/min) of SFO in a radiating graphite crucible under vacuum and, thus, reductive conditions. A numerical model depicting the temperature profile within the heating crucible was constructed to understand the temperature evolution within the samples. The combination pSPS sintering environment (graphite heating crucible under vacuum) promoted phase decomposition to Sr-enriched and depleted phases of various morphological variations, leading to reduction of hard magnetic properties. Notably, certain newly formed phases exhibited lower melting points, inducing a shift in the sintering mechanism from solid-state sintering to a partial liquid-phase sintering mechanism.
Ključne besede: pressureless spark plasma sintering, electronic ceramics, numerical simulations
Objavljeno v DiRROS: 03.09.2025; Ogledov: 805; Prenosov: 795
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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: 781; Prenosov: 370
Celotno besedilo (5,58 MB)
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