11. Effect of heat treatment on thermal conductivity of additively manufactured AISI H13 tool steelSamo Tome, Blaž Karpe, Irena Paulin, Matjaž Godec, 2024, objavljeni znanstveni prispevek na konferenci Povzetek: AISI H13 is commonly used for tooling, where higher wear resistance, thermal fatigue resistance, or hot toughness is required. Such examples include forging dies, plastic molds, hot shear blades, high-pressure die casting, and extrusion dies. Thus, thermal conductivity is one of the most important factors for hot work tools. Typically, the work cycle of a hot work tool designed for forging consists of four main phases: the forging stroke, with which the die imparts its shape onto the part, a brief pause while the die is reset to its original position, a lubrication phase, and a post lubrication dwell phase. During the forging phase, a significant amount of heat is transferred to the die while it is in contact with the part. This heat must then be dispelled for the part to return to a working temperature. While somewhat different, other hot work processes mentioned above are similar in that the hot work tool gets heated to a high temperature due to the contact with the object of deformation. The process of additive manufacturing (AM) promises better, more efficient tool production with features like conforming cooling channels, which would reduce the thermal fatigue of tools, prolonging tool life. However, the powder bed fusion (PBF) method creates a columnar microstructure, which has a detrimental effect on the thermal conductivity of H13 tool steel. Our investigation focused on the beneficial effect of heat treatment, specifically annealing at different temperatures, on the thermal conductivity of AM-produced H13 parts.
Ključne besede: SLM, thermal conductivity, tool steel, heat treatment
Objavljeno v DiRROS: 28.02.2024; Ogledov: 136; Prenosov: 73
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12. 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, izvirni znanstveni članek Povzetek: 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.
Ključne besede: total hip arthroplasty, modular neck, Ti6Al4V alloy, CoCrMo alloy, corrosion
Objavljeno v DiRROS: 07.02.2024; Ogledov: 257; Prenosov: 134
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13. 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, izvirni znanstveni članek Ključne besede: Martensitic stainless steel, deep cryogenic treatment, microstructure, mechanical properties, microstructural transformations, phase transformation
Objavljeno v DiRROS: 02.02.2024; Ogledov: 184; Prenosov: 92
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14. 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, izvirni znanstveni članek Ključne besede: hybrid additive manufacturing, Ti6Al4V, tensile properties, defects, microstructure, phase transformation
Objavljeno v DiRROS: 02.02.2024; Ogledov: 169; Prenosov: 89
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15. 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, izvirni znanstveni članek Ključne besede: stainless steel, AISI 304L, deep cryogenic treatment (DCT), microstructure, mechanical properties, fatigue, residual stress
Objavljeno v DiRROS: 02.02.2024; Ogledov: 204; Prenosov: 90
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16. 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, izvirni znanstveni članek Ključne besede: soft magnetic alloy, differential scanning calorimetry, oxygen, high-temperature phase, microstructure, eutectics
Objavljeno v DiRROS: 02.02.2024; Ogledov: 164; Prenosov: 76
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17. 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, izvirni znanstveni članek Ključne besede: Ti6Al7Nb implant alloy cementless hip endoprostheses, roughness, Al2O3 grit blasting, surface and subsurface implant contamination, cytotoxicity, aseptic loosening, infection, osseointegration
Objavljeno v DiRROS: 01.02.2024; Ogledov: 189; Prenosov: 78
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18. Improving the surface properties of additive-manufactured Inconel 625 by plasma nitridingDanijela Anica Skobir Balantič, Črtomir Donik, Bojan Podgornik, Aleksandra Kocijan, Matjaž Godec, 2023, izvirni znanstveni članek Povzetek: 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.
Ključne besede: additive manufacturing, powder-bed fusion, plasma nitriding, expanded austenite, wear and corrosion resistance, Ni-based alloy
Objavljeno v DiRROS: 31.01.2024; Ogledov: 212; Prenosov: 85
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19. Relevance of inter-particle interaction in directed energy deposition powder streamTijan Mede, Matjaž Godec, 2024, izvirni znanstveni članek Povzetek: 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.
Ključne besede: DED, powder stream, grain collisions, DEM
Objavljeno v DiRROS: 31.01.2024; Ogledov: 136; Prenosov: 82
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20. 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, izvirni znanstveni članek Ključne besede: aluminium alloys, hot rolling, microstructure, EBSD, burst test
Objavljeno v DiRROS: 06.05.2022; Ogledov: 524; Prenosov: 140
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