11. Mechanisms of premature fracture in modular neck stems made of CoCrMo/Ti6Al4V and Ti6Al4V/Ti6Al4V alloyDrago Dolinar, Miro Gorenšek, Klemen Avsec, Barbara Šetina, Matej Hočevar, Matjaž Godec, Borut Žužek, Mojca Debeljak, Monika Jenko, John T. Grant, Boštjan Kocjančič, 2023, original scientific article Abstract: In this paper, we present the mechanisms of premature fracture of modular neck stems in two case studies: (I) when the neck and stem are both made of the same Ti6Al4V alloy, and (II) when the neck and stem are made from two different alloys, CoCrMo and Ti6Al4V alloy. Our study integrates two orthopedic patients who have undergone primary uncemented THA for usual indications in two orthopedic centers (Community Health Centre and University Medical Centre). Both centers are part of the national public health care system. Both surgeries were performed by two skilled orthopedic surgeons with more than 10 years of experience in THA. The survivorship of the modular neck of cast CoCrMo alloy was 24 months. The survivorship of the modular neck from Ti6Al4V alloy was 84 months. Multivariate analyses were performed to assess the differences in the fretting, corrosion, and fatigue of the two prematurely failed modular neck stems: stereo light microscopy (SLM), scanning electron microscopy (SEM), X-ray energy-dispersive spectroscopy (EDS), and electron backscatter diffraction (EBSD). Patient demographic information, including sex, age, body mass index, survivorship of implants, and reason for the revision, was collected from medical records. We found that fretting and fatigue occurred on both neck-stem retrievals due to additional galvanic corrosion, but the CoCrMo/Ti6Al4V alloy system suffered more corrosion due to additional galvanic corrosion and fractured earlier than the Ti6Al4V/Ti6Al4V metal alloy system. Both metallic alloy systems used in this application are known to be highly corrosion-resistant, but the bio-tribo-corrosion processes need to be understood in detail and characterized so that appropriate improvements in design and materials can be made. Keywords: total hip arthroplasty, modular neck, Ti6Al4V alloy, CoCrMo alloy, corrosion Published in DiRROS: 07.02.2024; Views: 254; Downloads: 133 Full text (5,12 MB) This document has many files! More... |
12. Austenite reversion suppression with deep cryogenic treatment : a novel pathway towards 3rd generation advanced high-strength steelsPatricia Jovičević Klug, Matic Klug Jovičević, Lars Thormählen, Jeffrey McCord, Michael Rohwerder, Matjaž Godec, Bojan Podgornik, 2023, original scientific article Keywords: Martensitic stainless steel, deep cryogenic treatment, microstructure, mechanical properties, microstructural transformations, phase transformation Published in DiRROS: 02.02.2024; Views: 178; Downloads: 90 Full text (13,70 MB) This document has many files! More... |
13. Hybrid additive manufacturing of Ti6Al4V with powder-bed fusion and direct-energy depositionSimon Malej, Matjaž Godec, Črtomir Donik, Matej Balažic, René Zettler, Thomas Lienert, Laurent Pambaguian, 2023, original scientific article Keywords: hybrid additive manufacturing, Ti6Al4V, tensile properties, defects, microstructure, phase transformation Published in DiRROS: 02.02.2024; Views: 165; Downloads: 88 Full text (18,54 MB) This document has many files! More... |
14. Complex interdependency of microstructure, mechanical properties, fatigue resistance, and residual stress of austenitic stainless steels AISI 304LPatricia Jovičević Klug, Matic Klug Jovičević, Michael Rohwerder, Matjaž Godec, Bojan Podgornik, 2023, original scientific article Keywords: stainless steel, AISI 304L, deep cryogenic treatment (DCT), microstructure, mechanical properties, fatigue, residual stress Published in DiRROS: 02.02.2024; Views: 198; Downloads: 89 Full text (5,90 MB) This document has many files! More... |
15. Solidification behavior of Fe-6.5Si alloy powder for AM-SLM processing, as assessed by differential scanning calorimetryDarja Steiner Petrovič, Črtomir Donik, Irena Paulin, Matjaž Godec, Maja Vončina, Martin Petrun, 2023, original scientific article Keywords: soft magnetic alloy, differential scanning calorimetry, oxygen, high-temperature phase, microstructure, eutectics Published in DiRROS: 02.02.2024; Views: 160; Downloads: 76 Full text (9,05 MB) This document has many files! More... |
16. The impact of Al2O3 particles from grit-blasted Ti6Al7Nb (alloy) implant surfaces on biocompatibility, aseptic loosening, and infectionBoštjan Kocjančič, Klemen Avsec, Barbara Šetina, Darja Feizpour, Matjaž Godec, Veronika Kralj-Iglič, Rok Podlipec, Andrej Cör, Mojca Debeljak, John T. Grant, Monika Jenko, Drago Dolinar, 2023, original scientific article Keywords: Ti6Al7Nb implant alloy cementless hip endoprostheses, roughness, Al2O3 grit blasting, surface and subsurface implant contamination, cytotoxicity, aseptic loosening, infection, osseointegration Published in DiRROS: 01.02.2024; Views: 189; Downloads: 78 Full text (16,21 MB) This document has many files! More... |
17. Improving the surface properties of additive-manufactured Inconel 625 by plasma nitridingDanijela Anica Skobir Balantič, Črtomir Donik, Bojan Podgornik, Aleksandra Kocijan, Matjaž Godec, 2023, original scientific article Abstract: As a surface-hardening technique, plasma nitriding is a common procedure for improving the properties of
conventional Ni-based alloys. The diffusion of nitrogen hardens a layer on the surface of the alloy, leading to
better wear resistance and a higher coefficient of friction, as well as a higher surface hardness. This study reports
the effect of plasma nitriding on additive-manufactured (AM) Inconel 625 (IN625) compared to its conventional
manufactured and nitrided counterparts. The samples produced with the laser powder-bed fusion (LPBF) process
were subsequently plasma nitrided in the as-built condition, stress-relief annealed at 870 °C and solution treated
at 1050 °C. The plasma nitridings were carried out at 430 °C and 500 °C for 15 h. The growth kinetics of the
nitride layer of the AM samples depends on the prior heat treatments and is faster in the as-built state due to the
specific cellular structure. The lower nitriding temperature leads to the formation of expanded austenite in the
nitride layer, while at the higher nitriding temperature, the expanded austenite decomposes and CrN precipitation
occurs. The XRD and SEM analyses confirmed the presence of two layers: the surface layer and the
diffusion layer beneath. The lower nitriding temperature caused the formation of expanded austenite or a
combination of expanded austenite and CrN. The higher nitriding temperature led to the decomposition of the
expanded austenite and to the formation/precipitation of CrN. The higher nitriding temperature also decreased
the corrosion resistance slightly due to the increased number of precipitated Cr-nitrides. On the other hand, the
wear resistance was significantly improved after plasma nitriding and was much less influenced by the nitriding
temperature. Keywords: additive manufacturing, powder-bed fusion, plasma nitriding, expanded austenite, wear and corrosion resistance, Ni-based alloy Published in DiRROS: 31.01.2024; Views: 205; Downloads: 84 Full text (7,98 MB) This document has many files! More... |
18. 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: 136; Downloads: 82 Full text (1,65 MB) This document has many files! More... |
19. The influence of the hot-rolling technique for EN AW-8021B aluminium alloy on the microstructural properties of a cold-rolled foilJakob Kraner, Tomaž Smolar, Darja Volšak, Marjana Lažeta, Robert Skrbinek, Damijan Fridrih, Peter Cvahte, Matjaž Godec, Irena Paulin, 2021, original scientific article Keywords: aluminium alloys, hot rolling, microstructure, EBSD, burst test Published in DiRROS: 06.05.2022; Views: 522; Downloads: 138 Link to file |
20. The influence of the plasma-nitriding temperature on the microstructure evolution and surface properties of additive-manufactured 18Ni300 maraging steelMatjaž Godec, Francisco Ruiz-Zepeda, Bojan Podgornik, Črtomir Donik, Aleksandra Kocijan, Danijela Anica Skobir Balantič, 2022, original scientific article Keywords: maraging steel, powder bed fusion, plasma nitriding, microstructure, wear resistance, corrosion resistance Published in DiRROS: 06.05.2022; Views: 598; Downloads: 208 Full text (6,68 MB) This document has many files! More... |