1. Microstructure and indentation properties of single-roll and twin-roll casting of a quasicrystal-forming Al-Mn-Cu-Be alloyFranc Zupanič, Matjaž Macerl, Toshio Haga, Tonica Bončina, 2022, izvirni znanstveni članek Opis: In this investigation, strips of an experimental Al-Mn-Cu-Be alloy were manufactured by
high-speed single-roll and twin-roll casting to stimulate the formation of a quasicrystalline phase
during solidification. The strips were characterised by light microscopy, scanning and transmission
electron microscopy, microchemical analysis, and X-ray diffraction. Indentation testing was used to
determine the mechanical responses of the strips in different areas. A smooth surface was achieved
on both sides of the twin-roll-cast strip, while the free surface of the single-roll-cast strip was rough.
The microstructures in both strips consisted of an Al-rich solid solution matrix embedding several
intermetallic phases Θ-Al2Cu, Be4Al (Mn, Cu), Al15Mn3Be2 and icosahedral quasicrystalline phase
(IQC). The microstructure of the single-roll-cast strip was more uniform than that of the twin-roll-cast
strip. Coarse Al15Mn3Be2 particles appeared in both alloys, especially at the centre of the twinroll strip. These coarse particles adversely affected the strength and ductility. Nevertheless, both
casting methods provided high-cooling rates, enabling the formation of metastable phases, such as
quasicrystals. However, improvements in alloy composition and casting procedure are required to
obtain enhanced microstructures and properties.
Ključne besede: single-roll casting, twin roll casting, microstructure, quasicrystal, hardness, aluminium, characterisation
Objavljeno v DKUM: 24.03.2025; Ogledov: 0; Prenosov: 4
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2. Mixed-field radiation of 3-D MLC flash memories for space applicationsLorenzo Gonzales, Salvatore Danzeca, Salvatore Fiore, Iztok Kramberger, 2024, izvirni znanstveni članek Opis: This article presents the results of dynamic measurements of 3-D multilevel cell (MLC) NAND flash memories in a mixed-field radiation facility CERN High-energy AcceleRator Mixed field/facility (CHARM), CERN. The results show that the behavior of devices is comparable to tests with specific high energy particles, such as high energy protons, heavy ions, and to TID tests. The observed TID and single-event effects (SEEs) in flash memories from the existing relevant work are also observed in mixed field, making the environment suitable for an accelerated system level test. As the CHARM hadron energy spectrum is comparable to the low Earth orbit (LEO) environment, the facility is appropriate as an accelerated test for space applications. Furthermore, the volumetric characteristics of the devices can be observed in this 3-D radiation facility. Additionally, bad bit (BB) spread was observed, and the necessary radiation induced errors in NAND devices are discussed.
Ključne besede: bit error rate, flkash memories, memory controller, mixed field facility, multilevel cell, MLC, radiation hardness, single-event upsets, SEUs, space applications, total ionizing dose
Objavljeno v DKUM: 03.02.2025; Ogledov: 0; Prenosov: 6
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3. Simulation and mechanical properties of fine-grained heat-affected zone microstructure in 18CrNiMo7-6 steelTomaž Vuherer, Fidan Smaili, Edvard Bjelajac, Mirza Manjgo, Gorazd Lojen, 2022, izvirni znanstveni članek Opis: Heat-affected zones (HAZs) in real welds are usually quite narrow, and consequently most standard mechanical tests are difficult or even impossible. Therefore, simulated microstructures are often used for mechanical tests. However, the most often used weld thermal cycle simulator produces only a few millimeters wide area of simulated microstructure in the middle of specimens. Consequently, these kind of simulated specimen are not suitable for standard tensile tests, and even for Charpy impact tests, the simulated area can be too narrow. Therefore, to investigate the mechanical properties of a fine-grain heat-affected zone in 18CrNiMo7-6 steel, two methods were used for simulation of as-welded microstructures: (a) a weld thermal cycle simulator, and (b) as an alternative, though not yet verified option, austenitizing in a laboratory furnace + water quenching. The microstructures were compared and mechanical properties investigated. The grain sizes of the simulated specimens were 10.9 μm (water-quenched) and 12.6 μm (simulator), whereby the deviations from the real weld were less than 10%. Both types of simulated specimen were used for hardness measurement, Charpy impact tests, and fatigue tests. Water-quenched specimens were large enough to enable standard tensile testing. A hardness of 425 HV, yield strength Rp02 = 1121 MPa, tensile strength Rm = 1475 MPa, impact energy KV = 73.11 J, and crack propagation threshold ΔKthR = 4.33 MPa m0.5 were obtained with the water quenched specimens, and 419 HV, KV = 101.49 J, and ΔKthR = 3.4 MPa m0.5 with the specimens prepared with the simulator. Comparison of the results confirmed that the annealed and quenched specimens were suitable for mechanical tests of FG HAZs, even for standard tensile tests. Due to the use of simulated test specimens, the mechanical properties determined can be linked to the FG HAZ microstructure in 18CrNiMo7-6 steel.
Ključne besede: weld joint, fine-grained HAZ, simulation of microstructure, hardness, impact toughness, tensile properties, fatigue crack growth, 18CrNiMo7-6 steel
Objavljeno v DKUM: 05.12.2024; Ogledov: 0; Prenosov: 8
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4. Comparison of the mechanical properties of hardfacings made by standard coated stick electrodes and a newly developed rectangular stick electrodeEdvard Bjelajac, Andrej Skumavc, Gorazd Lojen, Mirza Manjgo, Tomaž Vuherer, 2024, izvirni znanstveni članek Opis: Cladding with a stick electrode is one of the oldest arc processes for adding a deposit on a base material. The process is suitable for outdoor working, but the disadvantages are low productivity and large dilution rates. In this work, a simple solution is proposed, which would enable cladding of a larger area with one pass and decrease the dilution rate at the same time—a new type of electrode was developed, exhibiting a rectangular cross-section instead of a round one. Hardfacings, welded with E Fe8 electrodes according to EN 14 700 Standard were welded on mild steel S355 J2 base material with three different coated stick electrodes. The first one was a commercially available, standard, round hardfacing electrode, the second was the same, but with a thinner coating, and the third one was a newly developed rectangular electrode. All three types had equal cross-sections of the metallic core and the same type of coating. Manufacturing of the rectangular electrodes in the laboratory is explained briefly. One- and multi-layer deposits were welded with all three types. Differences were observed in the arc behavior between the round and rectangular electrodes. With the rectangular electrode, the microstructure of the deposit was finer, penetration was shallower, and dilution rates were lower, while the hardness was higher, residual stresses predominantly compressive, and the results of instrumented Charpy impact tests and fracture mechanics tests were better.
Ključne besede: hardfacing, dilution rate, hardness, Charpy impact toughness, residual stress, fracture toughness
Objavljeno v DKUM: 14.05.2024; Ogledov: 298; Prenosov: 28
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5. Dispersoids in Al-Mg-Si alloy AA 6086 modified by Sc and YFranc Zupanič, Sandi Žist, Mihaela Albu, Ilse Letofsky-Papst, Jaka Burja, Maja Vončina, Tonica Bončina, 2023, izvirni znanstveni članek Ključne besede: aluminijeve zlitine, toplotna obdelava, mikrostruktura, disperzoidi, dilatometrija, trdota, aluminium alloy, heat treatment, microstructure, dispersoids, dilatometry, DSC, hardness
Objavljeno v DKUM: 05.04.2024; Ogledov: 183; Prenosov: 21
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6. Influence of kinematic factors of friction stir welding on the characteristics of welded joints of forged plates made of EN AW 7049 A aluminium alloyMilenko Perović, Sebastian Baloš, Dražan Kozak, Darko Bajić, Tomaž Vuherer, 2017, izvirni znanstveni članek Opis: In this paper, the influence of rotation speed and welding speed on the impact strength, microstructure and cross section micro hardness of FSW welded joints of Al-Zn-Mg-Cu high strength aluminium alloy is studied. Rotation speed was varied from 750 min−1 to 850 min−1 and welding speed from 60 mm/min to 80 mm/min. It was found that the energy of crack propagation is up to three times higher than the energy of crack initiation. This ratio was found by testing the Charpy notched specimens taken from left and right from the weld centre, 4 mm from the notch in a direction opposite to a direction of welding. Micro hardness distribution in the nugget does not show large dissipation of value regardless if the measuring point is in the upper or lower section of the nugget. Weld microstructure characteristics and zones are clearly defined at the basis of grain size and material flow.
Ključne besede: dynamic recrystallization, friction stir welding, impact strength, micro hardness distribution
Objavljeno v DKUM: 12.07.2017; Ogledov: 1551; Prenosov: 409
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7. Weldability prediction of high strength steel S960QL after weld thermal cycle simulationMarko Dunđer, Tomaž Vuherer, Ivan Samardžić, 2014, izvirni znanstveni članek Opis: This paper presents weld thermal cycle simulation of high strength steel S960QL, and describes influence of cooling time t8/5 on hardness and impact toughness of weld thermal cycle simulated specimens. Furthermore, it presents analysis of characteristic fractions done by electron scanning microscope which can contribute to determination of welding parameters for S960QL steel.
Ključne besede: high strength steels, S960QL steel, weldability, weld thermal cycle simulation, hardness, toughness
Objavljeno v DKUM: 03.07.2017; Ogledov: 2986; Prenosov: 170
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10. Prediction of the hardness of hardened specimens with a neural networkMatej Babič, Peter Kokol, Igor Belič, Peter Panjan, Miha Kovačič, Jože Balič, Timotej Verbovšek, 2014, izvirni znanstveni članek Opis: In this article we describe the methods of intelligent systems to predict the hardness of hardened specimens. We use the mathematical method of fractal geometry in laser techniques. To optimize the structure and properties of tool steel, it is necessary to take into account the effect of the self-organization of a dissipative structure with fractal properties at a load. Fractal material science researches the relation between the parameters of fractal structures and the dissipative properties of tool steel. This paper describes an application of the fractal dimension in the robot laser hardening of specimens. By using fractal dimensions, the changes in the structure can be determined because the fractal dimension is an indicator of the complexity of the sample forms. The tool steel was hardened with different speeds and at different temperatures. The effect of the parameters of robot cells on the material was better understood by researching the fractal dimensions of the microstructures of hardened specimens. With an intelligent system the productivity of the process of laser hardening was increased because the time of the process was decreased and the topographical property of the material was increased.
Ključne besede: fractal dimension, fractal geometry, neural network, prediction, hardness, steel, tool steel, laser
Objavljeno v DKUM: 17.03.2017; Ogledov: 2032; Prenosov: 152
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