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1.
High-cycle fatigue behaviour of the aluminium alloy 5083-H111
Branko Nečemer, Franc Zupanič, Tomaž Vuherer, Srečko Glodež, 2023, izvirni znanstveni članek

Ključne besede: aluminium alloys, rolling direction, high-cycle fatigue, fracture analysis
Objavljeno v DKUM: 04.04.2024; Ogledov: 128; Prenosov: 13
.pdf Celotno besedilo (8,97 MB)
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LCF behaviour of high strength aluminium alloys AA 6110A and AA 6086
Jernej Klemenc, Srečko Glodež, Matej Steinacher, Franc Zupanič, 2023, izvirni znanstveni članek

Opis: The proposed research presents the comprehensive investigation of the Low Cycle Fatigue (LCF) behaviour of two high-strength aluminium alloys of series AA 6xxx: the conventional alloy AA 6110A and the newly developed alloy AA 6086. Both alloys were characterised in the as-cast condition after homogenisation, extrusion, and T6 heat treatment. The quasi-static strength and hardness of the aluminium alloy AA 6086 were found to be significantly higher if compared to the AA 6110A alloys, while the ductility was a little bit smaller. The LCF tests showed that the AA 6086 alloy is more suitable for the high-cycle fatigue regime. On the other hand, the engineering advantage of the AA 6110A alloy is only for low-cycle fatigue applications if less than 100 loading cycles are expected in the service life of the analysed structure. The fatigue cracks formed predominantly on the α-AlMnSi intermetallic particles in both alloys, and, during LCF tests, exhibited small crack propagation. The area of the fatigue crack growth was much smaller than the area of the forced fracture. At smaller amplitude strains the fatigue striations were present at the fracture surface, while, at higher amplitude strains, they were not present. The obtained experimental results represent a good basis for engineering design applications of the analysed alloys AA 6086 and AA 6110A.
Ključne besede: aluminijeve zlitine, malociklično utrujanje, eksperimentalno testiranje, fraktografija, aluminium alloys, low cycle fatigue, experimental testing, fractography
Objavljeno v DKUM: 29.03.2024; Ogledov: 118; Prenosov: 12
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4.
Comparative study of the microstructure and properties of cast-fabricated and 3D-printed laser-sintered Co–Cr alloys for removable partial denture frameworks
Dejan Stamenković, Miljana Popović, Rebeka Rudolf, Milorad Zrilić, Karlo Raić, Kosovka Obradović-Đuričić, Dragoslav Stamenković, 2023, izvirni znanstveni članek

Opis: Since additive technologies in dentistry are gradually replacing metal casting technology, it is necessary to evaluate new dental constructions intended for the development of removable partial denture frameworks. The aim of this research was to evaluate the microstructure and mechanical properties of 3D-printed, laser-melted and -sintered Co–Cr alloys, and perform a comparative study with Co–Cr castings for the same dental purposes. The experiments were divided into two groups. The first group consisted of samples produced by conventional casting of the Co–Cr alloy. The second group consisted of 3D-printed, laser-melted and -sintered specimens produced from a Co–Cr alloy powder divided into three subgroups, depending on the technological parameters chosen for manufacturing (angle, location and heat treatment). Examination of the microstructure was carried out by classical metallographic sample preparation, using optical microscopy and scanning electron microscopy with energy dispersive X-ray spectroscopy (EDX) analysis. A structural phase analysis was also performed by XRD. The mechanical properties were determined using a standard tensile test. The microstructure observation showed a dendritic character in the case of castings, while in the case of 3D-printed, laser-melted and -sintered Co–Cr alloys, the microstructure was typical for additive technologies. The XRD phase analysis confirmed the presence of Co–Cr phases (ε and γ). The results of the tensile test showed remarkably higher yield and tensile strength values and slightly lower elongation of the 3D-printed, laser-melted and -sintered samples than those produced by conventional casting.
Ključne besede: Co–Cr dental alloys, 3D printing, laser melting and sintering, casting, microstructure, mechanical properties, characterization
Objavljeno v DKUM: 21.04.2023; Ogledov: 390; Prenosov: 33
.pdf Celotno besedilo (16,55 MB)
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5.
Influence of Heat Treatments on Microstructure of Electron Beam Additive Manufactured Ti-6Al-4V Alloy : magistrsko delo
Damir Skuhala, 2020, magistrsko delo

Opis: Additive manufacturing of metallic parts is increasing in popularity and starting to emerge as a new competitive manufacturing process. Printed structures from Ti-6Al-4V titanium alloy, produced by electron beam additive manufacturing (EBAM), possess columnar prior β grains and layer bands, alongside an ultrafine lamellar microstructure, which is prone to low ductility and thus requiring thermal post-processing. Several heat treatments were performed in α + β and β field, in one or multiple stages. The results showed that bi-lamellar microstructure can be obtained, and that selection of annealing temperature and cooling rate determines the morphology, thickness, and distribution of both primary and secondary α features. Mechanical properties were evaluated on three selected heat treatments. Annealing of the As-built condition was performed at 710°C (HT1) and 870°C (HT2), resulting in lamellar microstructure with basketweave morphology. In two-stage heat treatment (HT3), the temperature in the first stage has exceeded β transus, while in the second, annealing was performed again at 870°C. The microstructure was characterized as a mixture of lamellar and bi-lamellar with large α colonies inside the rearranged prior β grains. Air cooling was performed in all HT from the final annealing stage. Strength and hardness have decreased with increasingly coarser microstructural features, while fracture toughness was improved, except in HT1, where the decrease in the fracture toughness was mainly attributed to reduced intrinsic toughening. As-built and HT1 conditions were effected by microstructural texture, causing inconsistent fracture morphology, reduced crack roughness and scattering in results. The influence of texture was decreased by coarser microstructure in HT2, while crack tortuosity was increased. Very unpredictable fracture behaviour was observed in HT3 due to large α colonies, as their orientation determines the areas of ductile or cleavage crack propagation.
Ključne besede: Titanium alloys, Ti-6Al-4V, additive manufacturing, EBAM, heat treatments, microstructural optimization, mechanical properties, fracture toughness
Objavljeno v DKUM: 11.05.2020; Ogledov: 1729; Prenosov: 275
.pdf Celotno besedilo (25,14 MB)

6.
Force measurements on teeth using fixed orthodontic systems
Rebeka Rudolf, Janko Ferčec, 2013, pregledni znanstveni članek

Opis: The fixed orthodontic appliance consists of brackets that are bonded to the teeth. When the wire is engaged in the slot of the brackets, it generates forces for orthodontic tooth movement. The change in periodontal blood supply provides a biological response which leads to remodelling of the alveolar bone and the orthodontic tooth movement. Many variables influencing orthodontic treatment cannot be controlled fully, such as growth and tissue response to appliances. However, the force placed on the tooth should be a controllable variable, and a careful study of the physics underlying clinical applications can help in reducing undesirable side effects. The properties of orthodontic wires such as: strength, stiffness, elasticity and spring-back define their clinical usefulness. The ideal orthodontic wire should exhibit the following properties: large spring-back, low stiffness, good formability, high stored energy, biocompatibility and environmental stability, low surface friction, and the capability of being welded or soldered to auxiliaries. The ideal arch wire has not been introduced yet. Once the wire is activated or bent, it is the unloading or deactivating forces that produce the orthodontic tooth movement. For these reasons, it is necessary to know the force level caused by each individual wire used in orthodontic treatment. Finally, the purpose of this paper is a presentation of force measurements which are generated by different super-elasticity NiTi wires.
Ključne besede: force measurements, orhodontic system, teeth, NiTi alloys
Objavljeno v DKUM: 09.08.2017; Ogledov: 1246; Prenosov: 342
.pdf Celotno besedilo (1,33 MB)
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7.
Synthesis and characterization of hardened Cu-Fe-Ni-P alloy
Goran Brovč, Goran Dražić, Blaž Karpe, Igor Đorđević, Gorazd Lojen, Borut Kosec, Milan Bizjak, 2015, izvirni znanstveni članek

Opis: In the manufacturing industry of electrical contacts, the prohibition of the use of toxic metals (Cd, Be), and desire to avoid the alloying with precious metals (Ag) has created a need for new alloys with good electrical conductivity and high mechanical properties at elevated temperatures. As a potentially useful material for this purpose, we have analyzed the continuously cast Cu-Fe-Ni-P alloy in various heat treatment conditions. Sequence of phase transformations during heat treatment was followed by 4 point D.C. electrical resistivity measuring method, and analyzed by scanning (SEM) and transmission (TEM) electron microscopy. Measurements of Vickers hardness and electrical conductivity after various heat treatment procedures indicate on high potential of Cu-Fe-Ni-P alloys as a material for electrical contacts.
Ključne besede: copper alloys, precipitation hardening, electrical contacts, electrical conductivity
Objavljeno v DKUM: 03.07.2017; Ogledov: 2234; Prenosov: 93
.pdf Celotno besedilo (454,32 KB)
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8.
Microstructure of NiTi orthodontic wires observations using transmission electron microscopy
Janko Ferčec, Darja Feizpour, Borut Buchmeister, Franc Rojko, Bojan Budič, Borut Kosec, Rebeka Rudolf, 2014, izvirni znanstveni članek

Opis: This work presents the results of the microstructure observation of six different types of NiTi orthodontic wires by using Transmission Electron Microscopy (TEM). Within these analyses the chemical compositions of each wire were observed in different places by applying the EDS detector. Namely, the chemical composition in the orthodontic wires is very important because it shows the dependence between the phase temperatures and mechanical properties. Micro- structure observations showed that orthodontic wires consist of nano-sized grains containing precipitates of Ti2Ni and/or TiC. The first precipitated Ti2Ni are rich in Ti, while the precipitated TiC is rich in C. Further investigation showed that there was a difference in average grain size in the NiTi matrix. The sizes of grains in orthodontic wires are in the range from approximately 50 to 160 nm and the sizes of precipitate are in the range from 0,3 μm to 5 μm.
Ključne besede: orthodontic wires, nickel-titanium orthodontic wire, NiTi wire, shape memory alloys, SMA wires, microstructure, transmission electron microscopy, TEM, average grain size
Objavljeno v DKUM: 03.07.2017; Ogledov: 1431; Prenosov: 120
.pdf Celotno besedilo (869,15 KB)
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9.
Internal oxidation of silver alloys with tellurium, selenium and sulphur
Gorazd Kosec, Ladislav Kosec, Ivan Anžel, Vasilij Gontarev, Borut Kosec, Milan Bizjak, 2005, izvirni znanstveni članek

Opis: Silver alloys with tellurium, selenium and sulphur fulfil the conditions for the internal oxidation. Microstructure of these alloys consists of matrix (dilute solid solution) and particles of intermetallic compounds. Internal oxidation of ternary alloys is very similar to that of the binary alloys, but there are also distinctions in thermodynamics properties of alloying elements. At the direct oxidation of the particles of the intermetallic compound the phenomena of the selective oxidation was observed. Concentration of more reactive elements is increasing in the oxidized part of the particles of the intermetallic compound (Te in AgTeSe alloys). Therefore the precipitated oxides formed with diffusional internal oxidation are richer with less reactive alloying element (Se in AgTeSe alloy). In the precipitated oxide particles the concentration of selenium is more than twice higher than of tellurium.
Ključne besede: internal oxidation, silver, alloys, compound, particle
Objavljeno v DKUM: 03.07.2017; Ogledov: 1060; Prenosov: 98
.pdf Celotno besedilo (97,32 KB)
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10.
Superplastic deformation of an X7093 Al alloy
Srdjan Tadić, Aleksandar Sedmak, Radica Prokić-Cvetković, Abdsalam Eramah, Rebeka Rudolf, 2014, izvirni znanstveni članek

Opis: We have investigated the superplastic deformation mechanism of a powder-metallurgy, high-zinc X7093 Al alloy. The objective was to examine the rate-controlling mechanisms that govern its superplastic deformation. The investigations were carried out in the temperature range 490–524 °C and strain rates of 4.17 × 10–5 s–1 to 2.1 × 10–2 s–1. The maximum ductility was slightly more than 500 % at 524 °C and 4.2 × 10–4 s–1. The values of the stress exponent (n) and the activation energy (Q) indicated that the deformation is rate-controlled by the climb within the grain-boundary diffusion path. The existence of a temperature-dependent threshold stress was confirmed.
Ključne besede: superplasticity, Al alloys, deformation mechanisms
Objavljeno v DKUM: 23.03.2017; Ogledov: 1281; Prenosov: 81
.pdf Celotno besedilo (580,64 KB)
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