1. The role of carbon presence on the strontium hexaferrite phase decomposition during pressureless spark plasma sintering (pSPS)Aleksander Učakar, Andraž Kocjan, Blaž Belec, Janez Košir, Tanja Kallio, Marjeta Maček, Bor Arah, Petra Jenuš, 2025, izvirni znanstveni članek 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: 544; Prenosov: 241
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2. Towards increased strength and retained ductility of Zn-Mg-(Ag) materials for medical devices by adopting powder metallurgy processing routesJiří Kubásek, David Nečas, Vojtěch Hybášek, Eva Jablonská, Črtomir Donik, Irena Paulin, Peter Gogola, Martin Kusý, Jaroslav Fojt, Miroslav Čavojský, Jan Duchoň, Jaroslav Čapek, 2025, izvirni znanstveni članek Povzetek: The development of bioabsorbable zinc-based alloys with tailored mechanical properties and biocompatibility holds great promise for advancing medical implant technology. In this study, Zn-Mg and Zn-Mg-Ag alloys were synthesized using mechanical alloying (MA) followed by extrusion to achieve a combination of enhanced strength, ductility, and corrosion resistance. MA for 4 hours produced ultrafine-grained powders incorporating Mg₂Zn₁₁ intermetallic phases and oxide particles, which contributed to microstructure stabilization during subsequent processing. Extrusion consolidated these powders into dense materials with a uniform grain size of ~700 nm, exhibiting ultimate tensile strengths up to 435 MPa and elongation to fracture of ~12%, representing a significant improvement over conventional processing methods. The addition of silver further enhanced the antibacterial properties, demonstrating notable efficacy against Staphylococcus epidermidis, while maintaining non-cytotoxic behavior in vitro. Corrosion rates remained low, with uniform surface degradation and the formation of protective corrosion layers. This work highlights the efficacy of combining powder metallurgy techniques to bioabsorbable zinc-based alloys with exceptional mechanical performance, corrosion behavior and in vitro cytocompatibility, providing a pathway for next-generation biodegradable medical devices.
Ključne besede: zinc, bioabsorbable materials, mechanical alloying, spark plasma sintering, microstructure
Objavljeno v DiRROS: 05.08.2025; Ogledov: 565; Prenosov: 309
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3. Microstructure refinement of Nd-Fe-B permanent magnets prepared via spark-plasma sinteringTomaž Tomše, 2024, izvirni znanstveni članek Povzetek: Sintered Nd-Fe-B-type permanent magnets are normally manufactured using a conventional powder-metallurgy approach. The limitations of such high-temperature, pressureless sintering methods include restricted control over the microstructure due to grain growth and constraints on the magnet’s geometry. The modern spark-plasma sintering (SPS) technique employs Joule heating and external pressure to offer lower consolidation temperatures and faster heating cycles compared to conventional approaches. As a result, the SPS has the potential for the rapid, low-temperature, net-shape manufacture of magnets. However, the nonequilibrium conditions associated with the SPS can lead to poor grain-boundary wetting and the formation of the soft-magnetic α-iron phase in samples prepared from anisotropic, microcrystalline Nd-Fe-B powders produced by standard procedures, i.e., strip casting, hydrogen decrepitation, and jet-milling. This study revealed that the absence of the Nd-rich grain-boundary film is related to the presence of hydrogen. Degassing the Nd-Fe-B powder before applying the SPS improved the distribution of the grain-boundary phase. Moreover, reducing the electrical currents in the sample during the SPS prevented the decomposition of the RE2Fe14B matrix, ensuring a favorable phase composition. Compared to magnets conventionally sintered at 1070 °C, the mean grain diameter of the SPS samples prepared at ≈880 °C was reduced by ≈33%. This reduction decreased the temperature coefficient of coercivity from -0.65 to -0.58%/°C. The coercivity increase measured for the SPS samples amounted to more than 15%, which was attributed to the combined effect of smaller grain size and reduced texture.
Ključne besede: spark-plasma sintering, microstructure refinement
Objavljeno v DiRROS: 28.03.2025; Ogledov: 974; Prenosov: 428
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4. Exploring the microstructure, mechanical properties, and corrosion resistance of innovative bioabsorbable Zn-Mg-(Si) alloys fabricated via powder metallurgy techniquesDavid Nečas, Vojtěch Hybášek, Jan Pinc, Andrea Školáková, Ilona Voňavková, Klára Hosová, Martin Zlámal, Anna Boukalová, Jan Pokorný, Drahomír Dvorský, Črtomir Donik, Dalibor Vojtěch, Jiří Kubásek, 2024, izvirni znanstveni članek Povzetek: Zinc alloys belong to the widely studied materials for applications like medical devices, however, they often
encounter an inappropriate combination of mechanical/corrosion/biological properties. In this respect, we
produced the Zn–1Mg and Zn–1Mg–1Si containing biologically friendly elements with potential strengthening
effects on zinc matrix by powder metallurgy methods including mechanical alloying, spark plasma sintering, and
extrusion further enabling the formation of materials with unique extremely fine-grained microstructures. The
systematic study of these materials showed the possibility of reaching homogeneous nano-grain microstructure
and high strength values exceeding 450 MPa in tension. Selected chemical composition and processing methods
led also to slightly decreased wear and corrosion rates and rather uniform corrosion.
Ključne besede: zinc, mechanical alloying, biodegradable metals, composite, spark plasma sintering, extrusion, powder metallurgy
Objavljeno v DiRROS: 23.07.2024; Ogledov: 1242; Prenosov: 977
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