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Iskalni niz: "avtor" (Benjamin Podmiljšak) .

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1.
Anisotropy limitations in additive manufacturing with material extrusion
Benjamin Podmiljšak, Matej Komelj, Anubhav Vishwakarma, Petra Jenuš, Sašo Šturm, Kristina Žužek Rožman, 2026, izvirni znanstveni članek

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: 809; Prenosov: 472
.pdf Celotno besedilo (8,61 MB)
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2.
Unravelling the intricacies of micro-nonuniform heating in field-assisted sintering of multiphase metallic microstructures
Tomaž Tomše, Benjamin Podmiljšak, Lavinia Scherf, Reto Kessler, Spomenka Kobe, Andraž Kocjan, Sašo Šturm, Kristina Žužek Rožman, 2024, izvirni znanstveni članek

Povzetek: Micro-nonuniform heating in the field-assisted sintering (FAST) of electrically conductive powders has been a topic of discussion in the materials science community. Microstructural specifics, such as neck formation at low consolidation temperatures and density variations, have previously been ascribed to local overheating at the particle-particle contacts due to the Joule effect. However, recent theoretical modelling studies suggest that the very fast diffusion of heat within the micron-sized particles prevents the overheating, thereby challenging the conventional understanding of FAST-related heating effects. To provide a new experimental perspective on the local overheating and underscore its pivotal role in controlling the microstructure formation, we have studied the phase transformations in a Nd-Fe-B-type multiphase metallic powder during FAST. The formation of the α-Fe phase, following the peritectic decomposition of the Nd2Fe14B matrix phase expected at ≈1180 ◦C (TPER), was observed for FAST temperatures (TFAST) below TPER. A correlation between the electric current and the final phase composition, which can only be explained by considering the local overheating effect, was established. We showed that the formation of the α-Fe phase at TFAST < TPER can be mitigated by (i) decreasing the electric current through the sample, which is achieved by lowering the heating rate from 100 to 10 ◦C/min or by using electrically highly conductive pressing tools (WC) and a non-conductive coating (BN), or by (ii) interparticle necking achieved through a thermal pre-treatment of the powder compact that decreases the overall resistance. Our findings emphasize the criticality of the electric current modulation to minimize any undesired phase transformation, paving the way for future developments in rapid, FAST-based strategies aimed at refining the microstructures and tailoring the properties of multiphase metallic materials
Objavljeno v DiRROS: 28.03.2025; Ogledov: 1130; Prenosov: 408
.pdf Celotno besedilo (4,68 MB)
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