81. Relevance of inter-particle interaction in directed energy deposition powder streamTijan Mede, Matjaž Godec, 2024, original scientific article Abstract: Blown powder dynamics is one of the aspects of Directed Energy Deposition (DED) with a major influence on deposition quality and potential for improvement in simulation. Most currently employed computational models discard powder grain collisions as negligible, although little explicit evidence for that claim exists. A Discrete Element Method approach is thus employed in the present work to simulate the actual number of grain collisions in a powder stream of a commercial discrete coaxial nozzle and how that number varies with the key processing parameters. While the number of powder grain collisions is found to in fact be negligible at one side of the usable parameter spectrum, the opposite side results in as many as 84% of all the powder grains being involved in inter-granular collisions with an average rebound angle of 14◦, challenging the established hypothesis of the negligibility of this phenomena.
Keywords: DED, powder stream, grain collisions, DEM
Published in DiRROS: 31.01.2024; Views: 112; Downloads: 65
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82. High-temperature oxidation of boiler steels at 650 °CJaka Burja, Barbara Šetina, Borut Žužek, Tilen Balaško, 2023, original scientific article Abstract: This study presents a comprehensive investigation of the formation, composition and
behaviour of oxide layers during the high-temperature oxidation of four different steel alloys (16Mo3,
13Cr, T24 and P91) at a uniform temperature of 650 °C. The study is aimed at assessing the oxidation
damage due to short-term overheating. The research combines CALPHAD (CALculation of PHAse
Diagrams) calculations, thermogravimetric analysis (TGA) and advanced microscopy techniques, in-
cluding scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD), to elucidate
the complex mechanisms controlling oxidation kinetics and oxide layer development. CALPHAD
calculations were used to determine the thermodynamically stable phases for each steel type at 650
◦C and different oxygen activities. The results showed different phase compositions, highlighting
the importance of the chromium content in steel for the formation of oxide layers. The different
oxidation kinetics and oxide layer compositions are presented and associated with the increased risk
of material degradation due to overheating. These results have significant implications for industrial
applications, mainly the susceptibility to oxidation of low-alloyed steels like 16Mo3 and 13 Cr and
contribute to a deeper understanding of oxidation processes in steels.
Keywords: high-temperature oxidation, thermogravimetric analysis, kinetics, CALPHAD, boiler steels, SEM, EBSD
Published in DiRROS: 26.01.2024; Views: 235; Downloads: 113
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83. Morphological characteristics of young and old murine hematopoietic stem cell niches, as modeled in vitroMojca Justin, Ema Rogac Randl, Veno Kononenko, Matej Hočevar, Damjana Drobne, Primož Rožman, 2023, original scientific article Abstract: The hematopoietic stem cell (HSC) niche undergoes detrimental changes with age. The molecular differences between young and
old niches are well studied and understood; however, young and old niches have not yet been extensively characterized in terms of
morphology. In the present work, a 2D stromal model of young and old HSC niches isolated from bone marrow was investigated
using light and scanning electron microscopy (SEM) to characterize cell density after one, two, or three weeks of culturing, cell
shape, and cell surface morphological features. Our work is aimed at identifying morphological differences between young and
old niche cells that could be used to discriminate between their respective murine HSC niches. The results show several age-
specific morphological characteristics. The old niches differ from the young ones in terms of lower cell proliferating capacity,
increased cell size with a flattened appearance, increased number of adipocytes, and the presence of tunneling nanotubes. In
addition, proliferating cell clusters are present in the young niches but not in the old niches. Together, these characteristics
could be used as a relatively simple and reliable tool to discriminate between young and old murine HSC niches and as a
complementary approach to imaging with specific cellular markers.
Keywords: bone marrow, hematoopetic stem cell niche, aging, adipocytes, scanning electron microscopy
Published in DiRROS: 26.01.2024; Views: 212; Downloads: 105
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84. High temperature friction and galling properties of nanolayered (Cr,V)N coatings and effect of V contentBojan Podgornik, Marko Sedlaček, Barbara Šetina, Miha Čekada, 2023, original scientific article Keywords: (Cr, V)N coating, galling, high-temperature tribology, hot forming, self-lubrication
Published in DiRROS: 26.01.2024; Views: 208; Downloads: 129
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85. Autologous platelet and extracellular vesicle-rich plasma as therapeutic fluid : a reviewKaja Troha, Domen Vozel, Matevž Arko, Apolonija Bedina Zavec, Drago Dolinar, Matej Hočevar, Zala Jan, Matic Kisovec, Boštjan Kocjančič, Ljubiša Pađen, Manca Pajnič, Samo Penič, Anna Romolo, Neža Repar, Vesna Spasovski, Nejc Steiner, Vid Šuštar, Aleš Iglič, Damjana Drobne, Ksenija Kogej, Saba Battelino, Veronika Kralj-Iglič, 2023, review article Keywords: platelet-rich plasma, platelets, centrifugation, extracellular vesicles, small cellular particles, wound healing, regeneration, fresh-frozen plasma, intercellular signaling peptides and proteins
Published in DiRROS: 26.01.2024; Views: 232; Downloads: 121
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86. Evaluation and metrological performance of a novel ionisation vacuum gauge suitable as reference standardKarl Jousten, Sylke Bechstein, Matthias Bernien, Frédéric Boineau, N. Bundaleski, Claus Illgen, Berthold Jenninger, Janez Šetina, Ricardo A. S. Silva, Anke Stöltzel, O. M. N. D. Teodoro, Martin Wüest, 2023, original scientific article Keywords: ionisation vacuum gauge, hot cathode, sensitivity, secondary electrons, ion induced secondary electron yield
Published in DiRROS: 26.01.2024; Views: 206; Downloads: 94
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87. High sensitivity measurements of gas transport through films for food packaging and the ▫$O_2$▫ adsorption issueMarine Schott, Janez Šetina, Espedito Vassallo, Matteo Pedroni, Roberta Campardelli, Patrizia Perego, Luca Repetto, Giuseppe Firpo, 2023, original scientific article Keywords: oxygen transmission rate, food packaging, gas permeability, O2adsorption
Published in DiRROS: 26.01.2024; Views: 177; Downloads: 90
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88. Optimizing hot-work tool steel microstructure for enhanced toughnessAnže Bajželj, Tilen Balaško, Barbara Šetina, Jaka Burja, 2024, original scientific article Keywords: hot-work tool steel, austempering, bainitic transformation, lower bainite, impact toughness
Published in DiRROS: 24.01.2024; Views: 215; Downloads: 93
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89. Differences between 3-D printed and traditionally milled CoCr dental alloy from casted block in oral environmentMirjam Bajt Leban, Matej Kurnik, Igor Kopač, Matic Klug Jovičević, Bojan Podgornik, Tadeja Kosec, 2023, original scientific article Abstract: The aim of this study was to compare corrosion resistance and ion release in CoCr dental alloys with identical chemical compositions produced using different technologies (SLM – selective laser melting and milling from cast blocks) and heat treatment (SLM parts only). The corrosion properties were tested in artificial saliva, artificial saliva with fluoride ions, and artificial saliva with added lactic acid to simulate inflammations. The study included electrochemical tests, microstructural investigation and ion release tests in the three different environments for a total of 42 days. The best performance of CoCr as a result of potentiodynamic polarization was observed in the artificial saliva with added lactic acid, which is in contradiction with the highest ion release measured from all the materials tested and electrochemical impedance spectroscopy that showed a deterioration of the passive layer in an acidic environment. Microstructural investigation revealed that different phases precipitated by heat treatment trigger increased release of Mo and W ions. The printing method does not raise critically ion release from CoCr alloy, while the state of the surface greatly impacts the extent of the ion release. This study demonstrates the importance of an interdisciplinary approach to the study of corrosion and biocompatibility in dental alloys.
Keywords: CoCr dental alloy, selective laser melting, corrosion, ion release, artificial saliva
Published in DiRROS: 29.05.2023; Views: 340; Downloads: 288
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