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1.
Internal oxidation of Cu-C and Ag-C composites
Gabrijela Čevnik, Gorazd Kosec, Ladislav Kosec, Rebeka Rudolf, Borut Kosec, Ivan Anžel, 2008, kratki znanstveni prispevek

Opis: The internal oxidation in copper-carbon and silver-carbon composites occurs when they are exposed to air or oxygen at high temperature. Solubility of carbon in copper or in silver is very low. The kinetics of oxidation at high temperature and activation energy were determined and the mechanism of internal oxidation was analysed. The kinetics of internal oxidation was determined for both cases and it is depended from the diffusion of oxygen following parabolic time dependence according to Wagner's theory. The activation energy for Cu-C composite is 70.5 kJ/mol, and for Ag-C composite is 50.1 kJ/mol, what is in both cases close to the activation energy for the volume diffusion of oxygen in copper or in silver. In both cases gas products are formed during the internal oxidation of composites. In the internal oxidation zone pores, bubbles occur. The carbon oxidates directly with the oxygen from solid solution as long there is a contact, which breaks down with the presence of gas products. Then the oxidation occurs over the gas mixture of CO and CO2.Pri visokih temperaturah kompoziti bakra in srebra z ogljikom na zraku ali v kisiku reagirajo po mehanizmu notranje oksidacije. Topnost ogljika v trdnem bakru in trdnem srebru je zelo majhna. Analizirali smo kinetiko oksidacije kompozitov, določili aktivacijsko energijo in mehanizem notranje oksidacije. Kinetika oksidacije je pri obeh skupinah materialov odvisna od difuzije kisika in sledi parabolični odvisnosti od časa v skladu z Wagnerjevo teorijo. Aktivacijska energija procesa je za kompozit Cu-C enaka 70,5 kJ/mol, za kompozit Ag-C pa 50,1 kJ/mol, kar je blizu aktivacijski energiji za volumsko difuzijo kisika v trdnem bakru oziroma srebru. Pri oksidaciji kompozita nastajajo plinski produkti. Oksidacija ogljika poteka neposredno s kisikom iz trdne raztopine, ko pa se zaradi nastanka plinske faze stik prekine, pa preko plinske zmesi CO in CO2.
Ključne besede: internal oxidation, internal oxidation zone, composite, copper, silver, diffusion, kinetics
Objavljeno: 31.05.2012; Ogledov: 1130; Prenosov: 15
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2.
Microstructure of rapidly solidified Cu-Al-Ni shape memory alloy ribbons
Gorazd Lojen, Ivan Anžel, Albert C. Kneissl, Elfride Unterweger, Borut Kosec, Milan Bizjak, 2005, izvirni znanstveni članek

Opis: Cu-Al-Ni shape memory alloys (SMAs) are currently the only available high temperature SMAs, showing a good resistance against functional fatigue. In polycrystalline state, they are very brittle and exhibit, in general, only small reversible deformations. By melt spinning, thin Cu-Al-Ni ribbons can be manufactured directly from the melt. Appropriate casting parameters can ensurea single layer columnar structure with a fibre texture, which significantly increases the maximal reversible strain in longitudinal direction. Cu-Al-Ni ribbons, containing 13, 14 and 15 wt.% Al were cast by free jet melt spinning. Because of the alloys' low thermal conductivity, the cooling rate was surprisingly low - considering the crystal grain size - significantly below 103 K/s. Therefore, wide ribbons having a single layer columnar and (except the ribbons containing 13 wt.% Al) completely martensiticstructure could not be obtained. Regardless the chemical composition, the ribbons have a single layer columnar structure only if the thickness does not exceed approximately 50 m, otherwise the structure consists of at least two layers of equiaxed grains. In as-cast condition, only ribbons containing 13 wt.% Al seem to be completely martensitic. Heat treatments at temperatures up to 900 °C improved the structure of 13 and 14 wt.% Al ribbons. All ribbons exhibit one-way shape memory effect in as-cast condition. Heat-treated ribbons containing 13 wt.% Al exhibited two-way shape memory effect already after one bending and heating cycle.
Ključne besede: metallurgy, shape memory alloys, Cu-Al-Ni alloy, microstructure, melt spinning
Objavljeno: 01.06.2012; Ogledov: 1057; Prenosov: 62
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3.
Nanofoils for soldering and brazing in dental joining practice and jewellery manufacturing
Karlo Raić, Rebeka Rudolf, Borut Kosec, Ivan Anžel, Vojkan Lazić, Aleksandar Todorović, 2009, izvirni znanstveni članek

Opis: This paper describes the development of novel, reactive Al-Au nano-multilayered foils, their possible application in different fields and a discussion of the nano-foils' suitability for dental and jewellery applications. Moreover, this study includes the rapid joining of similar and dissimilar materials, by placing multilayer nano-foils and two layers of solder or braze. The foils precisely control the instantaneous release of heatenergy for the joining and act as a controllable local heat source. The reactive foils' thickness is in the range 10 nm to less than 100 nm and they contain many nanoscale layers that alternate between materials with high mixing heats, such as Al and Au. The foil between the two solder/braze layers melts the solder/braze with the heat generated by the reaction and bonds the components. The use of reactive foils eliminates the need for a furnace and dramatically increases the soldering/brazing heating rate of the components being bonded. Thus, ceramics and metals can be fused over required areas without the thermal stresses that are encountered in furnace soldering or brazing. In addition, a completely new plasma technology is proposed for the manufacturing of nano-foils and the first results of the preliminary experimental testing are presented.
Ključne besede: ceramic-metal bonding, low-temperature, nano-foils, plasma technology, dentistry, jewellery
Objavljeno: 01.06.2012; Ogledov: 1204; Prenosov: 34
.pdf Celotno besedilo (175,31 KB)
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4.
Microstructural and phase analysis of CuAlNi shape-memory alloy after continuous casting
Mirko Gojić, Stjepan Kožuh, Ivan Anžel, Gorazd Lojen, Ivana Ivanić, Borut Kosec, 2013, izvirni znanstveni članek

Opis: The results of the characterization of a CuAlNi shape-memory alloy after continuous casting technology are shown. Using this procedure a bar with a diameter of 8 mm was manufactured. After solidification of the alloy the microstructure characterization was carried out using optic microscopy (OM), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) methods. Our results showed that the as-cast alloy consisted of the parent β1 and β1’ martensite phases. The martensite phase primary as the needle-like inside grains was observed. Martensite laths have different orientations inside particular grains. It was found that the average grains size is 98.78 µm. The grain diameter near to the external surface is higher than in the center. The average hardness of the alloy was 275 HV1.
Ključne besede: shape memory alloys, martensite, continuous casting, grain size
Objavljeno: 16.03.2017; Ogledov: 388; Prenosov: 39
.pdf Celotno besedilo (1,28 MB)
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5.
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: 03.07.2017; Ogledov: 131; Prenosov: 41
.pdf Celotno besedilo (733,12 KB)
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6.
Analysis of interface at explosive welded plates from low-carbon steel and titanium
Borut Kosec, Ladislav Kosec, Gabrijela Čevnik, Peter Fajfar, Mirko Gojić, Ivan Anžel, 2004, izvirni znanstveni članek

Opis: On the basis of experimentally obtained data, it was established that a very thin layer of a melt is generated at the explosive welding of two metals at the bond interface within which impurities flow at the bond during melting. Rapid cooling after the collision generates an alloy of different structure and very small grains of an average thickness app. 1 to 2 micro m. The generation of such an amorphous layer in the bond area has been noticed with various metal combinations and represents a fundamental mechanism of explosive welding of metals. Using the metallographic analysis, the development of the vortices which were formed by the explosive welding of low-carbon steel and titanium plates is described in the paper.
Ključne besede: metallurgy, explosion welding, plates, composites, low-carbon steel, titanium, melt, vortex
Objavljeno: 03.07.2017; Ogledov: 352; Prenosov: 45
.pdf Celotno besedilo (123,13 KB)
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7.
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: 03.07.2017; Ogledov: 257; Prenosov: 36
.pdf Celotno besedilo (97,32 KB)
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8.
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: 03.07.2017; Ogledov: 372; Prenosov: 52
.pdf Celotno besedilo (1,59 MB)
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9.
Microstructure of NiTi orthodontic wires observations using transmission electron microscopy
Janko Ferčec, Darja Jenko, 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: 03.07.2017; Ogledov: 351; Prenosov: 48
.pdf Celotno besedilo (869,15 KB)
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10.
Rhodium platings
Rebeka Rudolf, Bojan Budić, Dragoslav Stamenković, Miodrag Čolić, Andrej Ivanič, Borut Kosec, 2013, kratki znanstveni prispevek

Opis: Modern rhodium plating solutions are based on either sulphate or phosphate. Although in theory there are four possible combinations, in practice only three different rhodium electrolytes are used. These are based on dilutions of rhodium sulphate or phosphate concentrates with added sulphuric or phosphoric acid. These processes are be discussed in this paper with a demonstration of Rh platings in the Slovenian firm Zlatarna Celje d.d.
Ključne besede: rhodium, plating, jewellery, properties
Objavljeno: 03.07.2017; Ogledov: 337; Prenosov: 44
.pdf Celotno besedilo (750,35 KB)
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