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4. Comparison of powder-bed fusion, directed-energy deposition and hybrid additive manufacturing of Ti6Al4V components: microstructure, corrosion and mechanical propertiesAleksandra Kocijan, Simon Malej, 2025, izvirni znanstveni članek Ključne besede: additive manufacturing, Ti6Al4V, microstructure, corrosion, mechanical properties
Objavljeno v DiRROS: 10.04.2025; Ogledov: 192; Prenosov: 100
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5. 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: 245; Prenosov: 113
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6. Magnetic performance and anticorrosion coating stability of thermally demagnetized Nd-Fe-B permanent magnets for reuse applicationsTomaž Tomše, Pierre Kubelka, Rosario Moreno López, Peter Fleissner, Laura Grau, Matej Zaplotnik, Carlo Burkhardt, 2024, izvirni znanstveni članek Povzetek: Nd-Fe-B-type permanent magnets, containing approximately 30% critical rare-earth elements by weight, are essential components in renewable energy systems (e.g., wind turbines, hydroelectric generators) and electric vehicles. They are also critical for consumer electronics and electric motors in products like energy-efficient air conditioners and home appliances. In light of advancing sustainability goals, the direct reuse of magnets from end-of-life devices offers a promising alternative to energy-intensive and costly recycling methods based on hydro- and pyrometallurgical processes, as well as modern short-loop recycling through hydrogen processing. However, Nd-Fe-B magnets must be demagnetized before they can be extracted from devices. This study explores the effects of thermal demagnetization, performed either in air or a vacuum, on the stability of anticorrosion coatings and the magnetic performance of remagnetized magnets. Corrosion tests were conducted to assess the compatibility of various coatings with thermal demagnetization, identifying those most suitable for future applications involving magnet reuse.
Ključne besede: thermal demagnetization, microstructure
Objavljeno v DiRROS: 28.03.2025; Ogledov: 296; Prenosov: 133
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7. Glass-ceramic engineering:tailoring the microstructure and propertiesChristian Rüssel, Wolfgang Wisniewski, 2025, izvirni znanstveni članek Povzetek: Traditionally, glass-ceramics are inorganic non-metallic materials obtained by the controlled crystallization of a glass. A modern definition has widened this class of materials to solid materials containing at least one glassy and one crystalline phase. The glass is usually obtained by quenching a melt. Re-heating it to a temperature slightly above the glass transition temperature allows nucleation while an often applied second annealing step at a higher temperature causes most of the crystal growth. As in most materials, the composition and the microstructure of glass-ceramics widely governs their properties. The morphology, i.e., size, and aspect ratio of the crystal phases is of special significance and depends on the crystal structure and the occurring growth mechanism. The morphology is also affected by the chemical composition and the temperature/time schedule of the crystallization process, here components of minor concentrations can have a great effect. This review addresses the effects of nucleating agents, phase separation, crystal orientation alignment and stress introduction as tools to tailor the properties of glass-ceramic materials. Future developments in the field of glass-ceramics are discussed.
Ključne besede: glass ceramics, controlled crystallization, microstructure, properties
Objavljeno v DiRROS: 12.02.2025; Ogledov: 229; Prenosov: 125
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8. Enhancing magnesium bioactivity for biomedical applications : effects of laser texturing and sandblasting on surface propertiesMarjetka Conradi, Aleksandra Kocijan, Bojan Podgornik, 2024, izvirni znanstveni članek Povzetek: Magnesium and its alloys, valued for their lightweight and durable characteristics, have garnered increasing attention for biomedical applications due to their exceptional biocompatibility and biodegradability. This work introduces a comparison of advanced and basic methods—laser texturing and sandblasting—on magnesium surfaces to enhance bioactivity for biomedical applications. Employing a comprehensive analysis spanning surface morphology, hardness, wettability, tribological performance, and corrosion behavior, this study elucidates the intricate relationship between varied surface treatments and magnesium’s performance. Findings reveal that both laser texturing and sandblasting induce grain refinement. Notably, sandblasting, particularly with a duration of 2 s, demonstrates superior wear resistance and reduced corrosion rates compared to untreated magnesium, thereby emerging as a promising approach for enhancing magnesium bioactivity in biomedical contexts. This investigation contributes to a deeper understanding of the nuanced interactions between diverse surface treatments and their implications for magnesium implants in chloride-rich environments, offering valuable insights for prospective biomedical applications.
Ključne besede: biomaterial, microstructure, hardness, friction/wear, corrosion
Objavljeno v DiRROS: 18.10.2024; Ogledov: 396; Prenosov: 12552
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9. Comparison of the mineralogy and microstructure of EAF stainless steel slags with reference to the cooling treatmentMojca Loncnar, Ana Mladenovič, Marija Zupančič, Peter Bukovec, 2017, izvirni znanstveni članek Povzetek: TIn the present study the differences in the mineralogical composition and microstructure of various types of EAF stainless steel (EAF S) slag with regard to the cooling treatment, the operation practice in an EAF (electric arc furnace) and environmental ageing reactions were evaluated. It was shown that the mineralogy of the investigated EAF S slags varied from one slag to another, depending on the quality of the produced stainless steel. The production process of the treated steel also has a strong influence on the mineralogy of the slags. The conditions during water cooling treatment were not sufficient to prevent the crystallization of primary mineral phases, which occurs predominantly in air-cooled EAF S slags, probably due to the high basicity of the investigated slags. However, the water cooling treatment of hot slag leads to the absence of γ-CaSiO 4 and the formation of secondary mineral phases predominantly calcite, portlandite, ettringite, calcium aluminate hydrate and calcium silicate hydrate. It has been shown that during the environmental ageing test (down-flow column test) secondary mineral phases were formed, which were the same as those formed during the water cooling treatment.
Ključne besede: electric arc furnace stainless steel slag, cooling path, microstructure, mineralogy
Objavljeno v DiRROS: 14.08.2024; Ogledov: 619; Prenosov: 350
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10. Characterization of bloom iron smelting site remains in Pržanj, SloveniaJaka Burja, Barbara Šetina, Daša Pavlovič, 2024, izvirni znanstveni članek Povzetek: This paper gives an overview of findings, connected with metallurgical activity, at the Pržanj archeological site near Ljubljana, Slovenia. More than 230 kg of slag and other remains connected with early medieval (from the 5th to the 12th century AD) metallurgical activities was found at the excavation site. The remains were grouped into four categories, i.e., furnace remains, ore, slag and a ferrous product, and analyzed in detail to obtain their chemical composition, microstructural characteristics, and mineral phase composition. The furnace wall remains, identified by their morphology and chemical composition, revealed an intensive iron processing activity at the site. The iron ore at the site was identified as goethite (FeO(OH)), a surprising find in Slovenia where limonite is typically used, and its presence suggests the potential exploitation of local bog iron ore, given the site’s geological context. Abundant slag remains at the site, identified by their shape, molten microstructure, and mineral components like wuestite, fayalite, and hercynite, indicated sophisticated smelting practices, including the use of CaO-rich materials to lower the melting temperature, a technique likely preserved from antiquity. Findings of ferrous products at ancient metallurgical sites are rare due to their value, but the discovery of a corroded iron bloom conglomerate at this site, initially mistaken for furnace remains, highlights the challenges in identifying small, corroded ferrous fragments that are often misidentified as ore. The results indicate extensive metallurgical activity at the excavation site, marking it as the first documented early medieval iron smelting production site in Slovenia.
Ključne besede: bloom iron, bloomery slag, archaeometallurgy, microstructure
Objavljeno v DiRROS: 29.07.2024; Ogledov: 666; Prenosov: 420
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