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Comparison and implementation of thermo-mechanical fatigue damage models : magistrsko delo
Jure Vinkovič, 2021, magistrsko delo

Opis: The basis of the master thesis is an in-depth and comprehensive analysis of the scientific literature on damage models of thermo-mechanical fatigue. The aim of the thesis is to investigate and determine the suitability of damage models for their application in numerical simulations of components subjected to thermo-mechanical loading with in-phase, out-of-phase or constant temperature cycles. The theoretical background of material behavior under static and dynamic loads (e.g. low-cycle fatigue, high-cycle fatigue) is presented. The work also includes an overview of damage mechanisms typical of time-temperature varying loading conditions (e.g. cyclic softening and hardening of the material, mean stress relaxation, material creep, visco-plasticity, etc.). This is followed by a structured review of several damage models of thermo-mechanical fatigue (e.g. Neu-Sehitoglu, DTMF, Coffin-Manson, Ostergren, Smith-Watson-Topper, Unified Energy Approach, etc.). An overview of the experimental tests on aluminum alloy and cast iron carried out at temperatures up to 800 °C is given. The idea of processing the raw experimental data including the calibration procedure of the thermo-mechanical fatigue damage models is schematically illustrated and described. The basic mathematical laws of constitutive material models for both material types are given. In the conclusion of the MSc thesis, the correlations of the calibrated damage models are presented, which, together with the constructive opinions, give an important message on the application of the individual damage models depending on the type of material and the loading method.
Ključne besede: thermo-mechanical fatigue, constitutive material model, damage model, aluminum alloy, cast iron alloy, finite element method
Objavljeno v DKUM: 03.01.2022; Ogledov: 277; Prenosov: 0

Preparation and electrochemical characterization of aluminium liquid battery cells with two different electrolytes ($NaCl-BaCl_2-AlF_3-NaF$ and $LiF-AlF_3-BaF_2$)
Viktor Napast, Jože Moškon, Marko Homšak, Aljana Petek, Miran Gaberšček, 2015, izvirni znanstveni članek

Opis: The possibility of preparation of operating rechargeable liquid battery cells based on aluminium and its alloys is systematically checked. In all cases we started from aluminium as the negative electrode whereas as the positive electrode three different metals were tested: $Pb$, $Bi$, and $Sn$. Two types of electrolytes were selected: $Na_3AlF_6-AlF_3-BaCl_2-NaCl$ and $Li_3AlF_3-BaF_2$. We show that some of these combinations allowed efficient separation of individual liquid layers. The cells exhibited expected voltages, relatively high current densities and could be charged and discharged several times. The capacities were relatively low (120 mAh in the case of $Al-Pb$ system), mostly due to unoptimised cell construction. Improvements in various directions are possible, especially by hermetically sealing the cells thus preventing salt evaporation. Similarly, solubility of aluminium in alloys can be increased by optimising the composition of positive electrode.
Ključne besede: liquid batteries, aluminium, alloy, electrochemistry
Objavljeno v DKUM: 24.08.2017; Ogledov: 864; Prenosov: 297
.pdf Celotno besedilo (316,77 KB)
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The characterization of phase transformations in rapidly solidified Al-Fe and Cu-Fe alloys through measurements of the electrical resistance and DSC
Milan Bizjak, Ladislav Kosec, Borut Kosec, Ivan Anžel, 2006, izvirni znanstveni članek

Opis: For the characterization of the phase transformations in the alloys during the heat treatment the various methods of the thermal analyses are available. Thermogravimetry, differential thermal analysis (DTA) and the differential scanning calorimetry (DSC) are the most frequently used methods. The phase transformations proceed in two stages, i.e. nucleation and the growth of the new phase. Both processes are closely linked with the movement of the atoms. Rapidly solidified alloys often contain the elements with the low diffusivity. During the transition from the unstable to the stable state the energy changes are small, therefore the characterization of the changes by DTA, DSC is very difficult and could not be measured. During the heat treatment the phase transformations of the rapidly solidified alloys of Al-Fe and Cu-Fe were successfully detected by the simultaneous measurements of the electrical resistance, and were compared by the DSC method. By determination of the temperature regions of the phase transitions or temperatures, where the dynamics of the changes is maximal, the samples were heat treated and analysed by the scanning and transmission electron microscopy respectively.
Ključne besede: rapidly solidified Al-Fe alloy, rapidly solidified Cu-Fe alloy, transformations, electrical resistance, differential scanning calorimetry
Objavljeno v DKUM: 03.07.2017; Ogledov: 1550; Prenosov: 103
.pdf Celotno besedilo (1,71 MB)
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Mechanical properties and microstructure characterisation of Au-Pt dental alloy
Rebeka Rudolf, Tjaša Zupančič Hartner, Ladislav Kosec, Aleksandar Todorović, Borut Kosec, Ivan Anžel, 2008, izvirni znanstveni članek

Opis: Development of a dental alloy with high Au content is based on the ternary system of Au-Pt-Zn with a nominal composition of 86,9Au-9,9Pt-1,5Zn, and about 1,5 wt.% micro-alloying elements (In, Ir, Rh). The results analyses of different heat-treated states showed that the optimal mechanical properties and hardness of an Au-Pt-Zn alloy can be reached with combinations of heat treatment for 20 minutes at 723 K and then slowly cooling, if the alloy was annealed at 1223 K for 30 minutes and the water quenched. Research results confirmed that the microstructure of the Au-Pt-Zn alloy consists of two phases: α1-phase rich in Au (main phase) and α2-phase rich in Pt (minor phase). During XRD analysis and use of the Rietveld method, it was found that the α1-phase content is about 98,5 wt.% while the content of α2-phase is 1,5 wt.%. STA analyses show that the Au-Pt-Zn alloy has a solidus temperature of about 1292 K and a liquidus temperature of about 1412 K.
Ključne besede: Au dental alloy, properties, microstructure, characterization
Objavljeno v DKUM: 03.07.2017; Ogledov: 834; Prenosov: 92
.pdf Celotno besedilo (1,59 MB)
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Effect of cooling rate on the microstructure of an Al94Mn2Be2Cu2 alloy
Tonica Bončina, Boštjan Markoli, Franc Zupanič, 2012, izvirni znanstveni članek

Opis: In this study the effect of the cooling rate on the microstructure of Al94 Mn2 Be2 Cu2 alloy was investigated. The vacuum induction melted and cast alloy was exposed to different cooling rates. The slowest cooling rate was achieved by the DSC (10 K·min^−1), the moderate cooling rate succeeded by casting in the copper mould (≈1 000 K·s−1) and the rapid solidification was performed by melt spinning (up to 10^6 K·s^−1). The microstructure of the DSC-sample consisted of α-Al matrix, and several intermetallics: τ1-Al29 Mn6 Cu4 , Al4 Mn, θ-Al2 Cu and Be4 Al(Mn,Cu). The microstructures of the alloy at moderate and rapid cooling consisted of the α-Al matrix, i-phase and θ-Al2 Cu. Particles of i-phase and θ-Al2 Cu were much smaller and more uniformly distributed in melt-spun ribbons.
Ključne besede: Al-alloy, metallography, microstructure, cooling rate, solidification
Objavljeno v DKUM: 03.07.2017; Ogledov: 576; Prenosov: 80
.pdf Celotno besedilo (231,30 KB)
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Analysis of a strain rate field in cold formed material using the visioplasticity method
Leo Gusel, Rebeka Rudolf, Borut Kosec, 2009, kratki znanstveni prispevek

Opis: In this paper the visioplasticity method is used to find the complete velocity and strain rate distributions from the experimental data, using the finite-difference method. The data about values of strain rates in plastic re- gion of the material is very important for calculating stresses and the prediction of product quality. Specimens of copper alloy were extruded with different lubricants and different coefficients of friction and then the strain rate distributions were analysed and compared. Significant differences in velocity and strain rate distributions were obtained in some regions at the exit of the deformed zone.
Ključne besede: forward extrusion, copper alloy, visioplasticity, strain rate, lubrication
Objavljeno v DKUM: 03.07.2017; Ogledov: 497; Prenosov: 102
.pdf Celotno besedilo (733,12 KB)
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In situ TEM study of precipitation in a quasicrystal-strengthened Al-alloy
Tonica Bončina, Franc Zupanič, 2017, izvirni znanstveni članek

Opis: Precipitation kinetics and mechanisms within an Al-Mn-Be-Cu quasicrystal strengthened alloy at 300°C were studied using in-situ transmission electron microscopy. The alloy was cast into a copper mould. Quasicrystalline precipitates formed throughout the Al-rich solid solution, whilst heterogeneous formations of Al2Cu and T-phase occurred on icosahedral quasicrystalline particles formed during solidification. The formation of quasicrystalline particles and T-phase was limited by manganese diffusivity, whilst that of Al2Cu by copper diffusivity. The precipitation produced only a small hardening effect.
Ključne besede: Al-alloy, quasicrystal
Objavljeno v DKUM: 09.05.2017; Ogledov: 901; Prenosov: 306
.pdf Celotno besedilo (1,07 MB)
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The influence of the morphology of iron powder particles on their compaction in an automatic die
Borivoj Šuštaršič, Matjaž Godec, Črtomir Donik, Irena Paulin, Srečko Glodež, Marko Šori, Milan Ratej, Nada Javornik, 2015, strokovni članek

Opis: Fe- and steel-based powder metallurgy (P/M) products, such as steel gears, spurs, locking mechanisms, porous filters, sliding bearings and bushes, as well as other machine parts and structural elements, are mainly produced with the so-called conventional sintering technology. It is the most efficient technology for the mass production of small, complex, functional and structural parts. Therefore, it is the most convenient and popular among all of the P/M technologies. The most important end-user of sintered parts is the automotive industry. However, small, complex, sintered parts can also be frequently used in the furniture and household industries, precise mechanics, articles for recreation and sports. A fine, iron-based powder mixture or prealloyed powder is first automatically uniaxial-die compacted (ADC) into the final shape of the product with a mechanical or hydraulic press and then sintered in a protective atmosphere at approximately 1100 °C. The metal powder mixture must have the appropriate engineering properties given by the chemistry and particle morphology, enabling a fast and reliable die-compaction process. The most important are a high tap density, a good powder flowability and a low compressibility. All this gives the green compacts an appropriate final shape with a smooth surface, a relatively high and uniform green density, as well as a green strength without internal flaws and cracks. In the case of very small two-or-more-heights products, for example, spur gears with a low module, it is very difficult to obtain a uniform green density at acceptable compaction pressures. Often small cracks are formed at height crossings and big differences in the green density appear in smaller or thinner regions. In the frame of our investigation we analysed the influence of the selected prealloyed commercial iron powder’s morphology and its technological properties on automatic die compaction, as well as the sintering process in the case of small two-level sintered gear dimensions of 5/40–7/10×7mm with module m = 0.5. The original iron powder was sieved and the finest powder particle fraction (< 45 µm) was compared with the original powder mixture considering ADC and sintering process. It was found that the selection of the finer powder mixture could not contribute to the improvement in the overall ADC process, as well as a better green compact. In the present paper the results of our investigations are presented and the reasons why a finer powder mixture cannot contribute much to an improvement of the conventional sintering process.
Ključne besede: Fe-based alloy powders, particles, morphology, microstructure, automatic die compaction, sintering
Objavljeno v DKUM: 27.03.2017; Ogledov: 890; Prenosov: 321
.pdf Celotno besedilo (1,18 MB)
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Morphological and microstructural features of Al-based alloyed powders for powder-metallurgy applications
Borivoj Šuštaršič, Irena Paulin, Matjaž Godec, Srečko Glodež, Marko Šori, Jože Flašker, Albert Korošec, Stanislav Kores, Goran Abramović, 2014, strokovni članek

Opis: Besides advanced nano steels, polymers and ceramics, recently also light metals, i.e., Al, Mg and Ti based materials, have been recognized as future materials for different kinds of advanced applications. Al and its alloys have an acceptable price, excellent corrosive resistance, good mechanical and other physical properties. Therefore, they are also used in the powder-metallurgy (P/M) field. The P/M technology of Al materials is very demanding and has its own specifics compared to the sintering technology of iron and steel. A relatively large quantity of Al-based alloy powder is formed during the sand blasting of slugs and discs in the Talum Al factory, Kidričevo, Slovenia. Therefore, we analysed and investigated its practical usability for a production of advanced products using P/M technology. The formed Al-based powder was compared with the commercially available Al-based powders that are generally used for conventional sintering technology. In the first part of this paper we explain which types of Al-based powders are used for the production of sintered parts, what the required parameters are and why we considered them. Then, the results of theoretical thermodynamic analyses and investigations of the morphological and microstructural characteristics of the selected commercial Al-based powders are given, as well as their comparison with the Al powder formed during the sand blasting and its potential for P/M applications.
Ključne besede: Al-based alloy powders, morphology, microstructure, LM characterisation, SEM/EDS characterisation
Objavljeno v DKUM: 17.03.2017; Ogledov: 1053; Prenosov: 104
.pdf Celotno besedilo (4,85 MB)
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Effect of AlTi5B1 and AlSr10 additions on the fluidity of the AlSi9Cu3 alloy
Matej Steinacher, Franc Zupanič, Mitja Petrič, Primož Mrvar, 2014, izvirni znanstveni članek

Opis: This work studies the effect of the AlTi5B1 and AlSr10 additions on the fluidity and the solidification time of the AlSi9Cu3 casting alloy. The fluidity was investigated by determining the flow length in a spiral-shaped mould. The solidification time was measured with a thermocouple positioned at the ingate bottom. An individual pouring into the preheated (200 °C) metallic mould was done at different pouring temperatures ((640, 670, 700, and 710) °C). In all the cases, the fluidity was improved with the increasing pouring temperatures. An addition of the AlTi5B1grain refiner to the basic alloy reduced both the grain size and the fluidity, whilst the solidification time was similar to that of the basic alloy. On the other hand, an addition of the AlSr10 modifier refined the ßSi eutectic phase, increased the fluidity and prolonged the solidification time in comparison to the basic alloy. The fluidity was proportional to the solidification time. Thus, by carrying out a simple thermal analysis and determining the solidification time, it is possible to predict the fluidity.V delu je predstavljen vpliv dodatkov AlTi5B1 in AlSr10 na livnost in strjevalni čas livne aluminijeve zlitine AlSi9Cu3. Livnost smo preiskovali z merjenjem dolžine toka taline v kovinski kokili s spiralno livno votlino, medtem ko smo strjevalni čas merili s termoelementom, ki je bil vstavljen na dnu lijaka. Talino smo pri različnih livnih temperaturah ((640, 670, 700 in 710) °C) ulivali v predgreto kokilo (200 °C). Livnost je v vseh primerih naraščala z naraščanjem livne temperature. Dodatek udrobnilnega sredstva AlTi5B1 k osnovni zlitini je zmanjšal tako velikost kristalnih zrn kot livnost, medtem ko je bil strjevalni čas podoben kot v osnovni zlitini. Dodatek modifikatorja AlSr10 je zmanj{al velikost evtektične faze ßSi, povečal livnost ter podaljšal strjevalni čas v primerjavi z osnovno zlitino. Livnost je bila sorazmerna strjevalnemu času, tako da lahko z enostavno termično analizo in določanjem strjevalnega časa napovemo livnost preiskovane zlitine.
Ključne besede: AlSi9Cu3 alloy, grain refinement, modification, fluidity, solidification time
Objavljeno v DKUM: 15.03.2017; Ogledov: 844; Prenosov: 98
.pdf Celotno besedilo (642,42 KB)
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