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Povzetek: Rapid radiation techniques, such as pressureless spark plasma sintering (pSPS) and ultra-fast high-temperature sintering (UHS), have proven effective in achieving rapid densification of ceramics, including additively manufactured components. However, sintered component sizes tend to be small, disk-shaped or having thin-strutted geometries. Here, fused filament fabrication (FFF) of a commercial filament was used for manufacturing complex-shaped and large-sized alumina tetrahedra with edge thickness of 5 mm, varying the edge size (15‒40 mm). The aim was to investigate the effect of heating rate (33‒300°C/min) and tetrahedron size on the pSPS outcome. The pSPS reductive environment discoloured the tetrahedra, but were all successfully rapidly sintered to full density irrespective of their size and heating rate employed. The evolved thermal gradient contributed to differential, anisotropic densification related shrinkage, microstructure and mechanical properties specific to tetrahedra` edge position, i.e., core versus shell and base versus lateral, also triggering cracking of the largest tetrahedra.
Ključne besede: additive manufacturing, fused filament fabrication, pressureless spark plasma sintering
Objavljeno v DiRROS: 15.06.2026; Ogledov: 106; Prenosov: 77
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Objavljeno v DiRROS: 19.12.2025; Ogledov: 531; Prenosov: 186
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Povzetek: Within the framework of the EUROfusion Consortium, the Characterization of armour, heat sinks materials and joints sub-project of the Work Package Material (WP-MAT) has been dedicated to the development of different tungsten (W) monoblock mock-ups equipped with advanced materials for divertor target applications in the EU-DEMO fusion reactor. Assessing the status of the relevant joining interfaces of these mock-ups, not only after fabrication but throughout the whole component lifetime, plays a key role in the qualification process. At the ENEA Special Technologies Laboratory (TES), a number of facilities have been built to perform non-destructive inspections of plasma-facing components for fusion applications by ultrasonic testing (UT). The present work reports on the results of the UT inspections assessing the structural integrity of the relevant joining interfaces of three small-scale mock-ups provided with advanced W armour materials, specifically W-matrix with W2C inclusions consolidated by Spark Plasma Sintering (SPS), K-doped rolled W and K-doped laminated W. The UT examinations are carried out after fabrication and after the high heat flux tests (HHFT) at the neutral beam facility GLADIS. All results confirm the high-quality joining achieved by HIP and HRP. During the HHF tests of mock-ups, after a few hundred HHFT cycles defects are detected at the joining interfaces, due to debonding, delamination and W material cracks mainly affecting the loaded zone. The ultrasonic pulse-echo technique provides not only the size and position of the defects in the plane orthogonal to the ultrasonic beam, but also their depth in the material. During the analysis, the probe is inserted inside the pipe and the mock-up is examined in a cylindrical configuration. The coupling medium (demineralized water) is poured only inside the pipe. The main inspection parameters and the piezoelectric probes are chosen to obtain the maximum resolution in accordance with the thickness and joining interfaces to be analyzed.
Ključne besede: DEMO, divertor, advanced tungsten, high heat flux test, non-destructive test, ultrasonic examination
Objavljeno v DiRROS: 03.09.2025; Ogledov: 604; Prenosov: 344
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Povzetek: Tungsten-copper (W-Cu) composites have a wide range of engineering applications, from arc-resistant electrodes and high-voltage electrical contacts to heat sinks for integrated circuits and plasma-facing components for fusion reactors. They combine high corrosion and erosion resistance, very good thermal and electrical conductivity, low thermal expansion, with good mechanical properties. However, the fabrication of such materials is limited in terms of shape complexity and the internal distribution of the individual phases. Furthermore, the dissimilar thermo-mechanical properties (melting temperature, thermal conductivity, coefficient of thermal expansion) of the constituent phases impose severe constraints on the fabrication and use of W-Cu composites. To overcome the challenges of component design and enable greater freedom in terms of composition, W-Cu composites were produced by a combination of additive manufacturing and liquid-melt infiltration (LMI). Porous W-lattice structures were manufactured by laser powder-bed fusion (LPBF) followed by infiltration with molten Cu. A series of composites was produced with Cu contents from 3 to 75 vol% and evaluated in terms of thermal, electrical, and mechanical properties. The LPBF-LMI W-Cu composites exhibited comparable thermo-mechanical properties to W-Cu materials manufactured using powder-metallurgical processing, but with an expanded composition range and shape complexity. Lower thermal expansion coefficients (4.5–5.8 × 10−6 K−1) and an improved thermal stability of the Young’s modulus, only a 27–33 GPa decline in the range 27–827 °C, were observed for all the compositions, which was ascribed to the W-phase connectivity in all the W-Cu composites, independent of the volume fraction of Cu.
Ključne besede: termomechanical properties, liquid-metal infiltration, laser powder-bed fusion, metal-matrix composites
Objavljeno v DiRROS: 07.02.2025; Ogledov: 1296; Prenosov: 251
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Povzetek: In the southernmost outcrops of the Slovenian Basin the Middle Jurassic coarse-grained limestone breccia (mega)beds are interstratified within a succession that is otherwise dominated by hemipelagites and distal turbidites. In this paper, these beds are described as the Ponikve Breccia Member of the Tolmin Formation. We provide descriptions of the studied sections with detailed geological maps and analysis of the breccia lithoclasts. From the latter, a non-outcropping margin of the Dinaric Carbonate Platform is reconstructed. In the Late Triassic the platform margin was characterized by a Dachstein-type marginal reef. After the end-Triassic extinction event, the platform architecture remained, but the reefs were replaced by sand shoals characterized by ooids. In the late Early Jurassic and/or early Middle Jurassic a slope area might have been dissected by normal faults and a step-like paleotopography was formed. In the Bajocian, during a period of major regional geodynamic perturbations, extensional or transtensional tectonic activity intensified and triggered the large-scale collapses of the Dinaric Carbonate Platform margin producing the limestone breccias described herein. This may in turn have caused a backstepping of the platform margin, as is evident from the occurrence of Late Jurassic marginal reefs that are installed directly above the Upper Triassic and Lower Jurassic inner platform successions.
Ključne besede: Slovenian Basin, Dinaric Carbonate Platform, Middle Jurassic, limestone breccia, debris-flow, stratigraphy, Ponikve breccia
Objavljeno v DiRROS: 18.01.2023; Ogledov: 2022; Prenosov: 1242
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