1. Influence of surface preparation of aluminum alloy AW-5754 and stainless steel X5CRNI18-10 on the properties of bonded jointsNataša Zdravković, Damjan Klobčar, Dragan Milčić, Matevž Zupančič, Borut Žužek, Miodrag Milčić, Aleksija Ðurić, 2024, izvirni znanstveni članek Povzetek: Adhesive bonding has proven to be a reliable method of joining materials, and the development of new adhesives has made it possible to use bonding in a variety of applications. This article addresses the challenges of bonding metals such as the aluminum alloy EN AW-5754 and the stainless steel X5CrNi18-10. In this study, the effects of laser cleaning and texturing on the surface properties and strength of two bonded joints were investigated and compared with mechanical preparation (hand sanding with Scotch-Brite and P180 sandpaper). The bonded joints were tested with three different epoxy adhesives. During the tests, the adhesion properties of the bonded surface were determined by measuring the contact angle and assessing the wettability, the surface roughness parameters for the different surface preparations, and the mechanical properties (tensile lap-shear strength). Based on the strength test results, it was found that bonded joints made of stainless steel had 16% to 40% higher strength than aluminum alloys when using the same adhesive and surface preparation. Laser cleaning resulted in maximum shear strength of the aluminum alloy bond, while the most suitable surface preparation for both materials was preparation with P180 sandpaper for all adhesives.
Ključne besede: adhesive bonding, surface preparation, aluminum alloy AW-5754, stainless steel X5CrNi18-10, epoxy adhesives
Objavljeno v DiRROS: 20.12.2024; Ogledov: 259; Prenosov: 147
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2. Influence of isothermal annealing in the 600 to 750 °C range on the degradation of SAF 2205 duplex stainless steelJaka Burja, Borut Žužek, Barbara Šetina, 2024, izvirni znanstveni članek Povzetek: We studied the effect of isothermal annealing (600–750 °C, 1 to 1000 min) on the microstructure
and mechanical properties of SAF 2205 duplex stainless steel. Impact toughness was found
to be significantly more affected than hardness by annealing. Annealing at 750 °C for 1000 min
resulted in a more than 90% decrease in impact toughness, while hardness only increased by 25%.
Tensile strength increased up to 100 MPa, but elongation decreased by more than 50% under the
same conditions. Sigma phase formation was minimal at lower temperatures (650 °C and below)
but increased significantly at higher temperatures. At 750 °C and 1000 min of annealing, the ferrite
content dropped from 50% to 16%. These findings suggest that annealing temperature and time need
to be carefully controlled to avoid a reduction in impact toughness and ductility caused by sigma
phase precipitation. The harmful effect of sigma phase precipitation on mechanical properties was
directly shown.
Ključne besede: duplex stainless steel, sigma phase, precipitation kinetics, mechanical properties, isothermal annealing
Objavljeno v DiRROS: 24.07.2024; Ogledov: 511; Prenosov: 408
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4. 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: 903; Prenosov: 487
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5. High-temperature oxidation of boiler steels at 650 °CJaka Burja, Barbara Šetina, Borut Žužek, Tilen Balaško, 2023, izvirni znanstveni članek Povzetek: 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.
Ključne besede: high-temperature oxidation, thermogravimetric analysis, kinetics, CALPHAD, boiler steels, SEM, EBSD
Objavljeno v DiRROS: 26.01.2024; Ogledov: 1050; Prenosov: 441
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