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1.
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: 1173; Prenosov: 74
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2.
Microstructure and properties of shape memory alloys
Albert C. Kneissl, Elfride Unterweger, Gorazd Lojen, Ivan Anžel, 2005, izvirni znanstveni članek

Opis: This work addresses three topics: the generation of two-way shape memory effects in NiTi, NiTiW and CuAlNi wire materials and the investigation of the long term stability of these effects; investigations on thin CuAlNi films produced by PVD; investigation on thin CuAlNi ribbons produced by melt-spinning.
Ključne besede: metallurgy, shape memory alloys, properties, microstructure
Objavljeno: 01.06.2012; Ogledov: 971; Prenosov: 61
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3.
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In-situ monitoring of internal oxidation of dillute alloys
Mihael Brunčko, Ivan Anžel, Albert C. Kneissl, 2007, izvirni znanstveni članek

Opis: This paper presents a non-destructive measurement method that enables identification and characterization of phenomena during internal oxidation of metallic materials as well as monitoring the kinetics of internal oxidation using "in-situ" electrical resistance measurements. A special laboratory device, based on the unique measurement cell, for the electrical resistance measurements at high temperatures and the model for electrical resistance transformation into an instantaneous microstructure were developed. To accomplish this, the process of internal oxidation was divided into the sequence of the key partial reactions that were presented in the model as the parallel andžor serial connected time variable resistors in the electrical circuit. The validity of the transformation model was experimentally confirmedby internal oxidation of Ag-Sn (2 at.% Sn) alloy at different oxidation temperatures in air atmosphere. The comparison of the results obtained by "in-situ" electrical resistance measurements with those obtained by metallographic analysis and Wagnerćs theory shows that the novel method presents a more effective tool for monitoring of internal oxidation kinetics. The method identifies also the microstructural defects and their influences onthe kinetics of internal oxidation.
Ključne besede: metallurgy, Ag-Sn alloy, internal oxidation, electrical resistance
Objavljeno: 01.06.2012; Ogledov: 888; Prenosov: 22
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5.
Monitoring of directional solidification with simultaneous measurements of electrical resistance and temperature
Mihael Brunčko, Ivan Anžel, Alojz Križman, 2003, izvirni znanstveni članek

Opis: WE present the efficiency of simultaneous electrical resistance and temperature (ERT) measurements for monitoring the position, X, and the growth rate, V, of the solidification front during the directional solidification of alloys. On alaboratory device for directional solidification (Bridgman-type furnace), theeutectic Pb-Sn alloy was solidified at five different pulling rates, VP, with a constant imposed temperature gradient, GP. During directional solidification, the electrical resistance and the temperature changes were measured simultaneously in the experimental samples. The results of the experiments show that simultaneous measurement of ERT enables not only the determination of the average growth rate, V, during directional solidificationbut also its fluctuation over the total measurement length of the sample.
Ključne besede: metallurgy, Pb-Sn alloy, directional solidification, electrical resistance measurements, temperature measurements
Objavljeno: 01.06.2012; Ogledov: 1025; Prenosov: 68
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6.
The effect of nitrogen-ion implantation on the corrosion resistance of titanium in comparison with oxygen- and argon-ion implantations
T. Sundararajan, Zdravko Praunseis, 2004, izvirni znanstveni članek

Opis: Commercially pure (CP) titanium was surface modified with nitrogen-, argon- and oxygen-ion implantations in order to investigate the material's corrosion resistance in a simulated body fluid. Five doses were chosen for the ions, ranging from 5.1015 cm-2 to 2.5-1017 cm-2. In-vitro open-cyclic potential-timemeasurements and cyclic polarization studies were carried out to evaluate the corrosion resistance of the modified surface in comparison to an unmodified surface. Specimens implanted at 4.1016 cm-2 and 7.1016 cm-2 showed the optimum corrosion resistance, higher doses showed a detrimental effect on the corrosion resistance. Argon- and oxygen-ion implantation at these doses did not show any improved corrosion resistance, indicating the beneficial role of nitrogen on the corrosion resistance of titanium in the simulated body-fluid environment. Grazing-incidence X-ray diffraction (GIXD) was employed on the implanted specimens to determine the phases formed with the increasing doses. X-ray photoelectron spectroscopy (XPS) studies on the passive film of the implanted samples and on the unimplanted samples were analyzed in order to understand the role of nitrogen in improving the corrosion resistance. The results of the present investigation indicated that nitrogen-ion implantation can be used as a viable method for improving the corrosion resistance of titanium. The nature of the surface and the reason for the variation and the improvement in the corrosion resistance are discussed in detail.
Ključne besede: metallurgy, ion implantation, orthopedic implants, corrosion, titanium, nitrogen, oxygen, argon
Objavljeno: 10.07.2015; Ogledov: 1334; Prenosov: 51
.pdf Celotno besedilo (3,38 MB)
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7.
Fatigue properties of sintered DIN SINT-D30 powder metal before and after heat treatment
Marko Šori, Borivoj Šuštaršič, Srečko Glodež, 2014, izvirni znanstveni članek

Opis: The main focus of this study was to determine how heat treatment affects the dynamic properties of sintered steel. All the specimens were made of the DIN SINT-D30 metal powder, but only half of them were additionally heat treated. Flat specimens were cold pressed and sintered. The second set was additionally heat treated to increase the strength. After the static mechanical properties were determined, the fatigue strength was investigated in a pulsating machine with a load ratio of R = 0. Wöhler curves were plotted and the parameters for determining the fatigue life (of' and b) were calculated.
Ključne besede: powder metallurgy, fatigue, S-N curve
Objavljeno: 16.03.2017; Ogledov: 338; Prenosov: 60
.pdf Celotno besedilo (157,94 KB)
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8.
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: 394; Prenosov: 50
.pdf Celotno besedilo (123,13 KB)
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9.
Microstructure analysis of internally oxidized Cu-C composite
Rebeka Rudolf, Ladislav Kosec, Alojz Križman, Ivan Anžel, 2006, izvirni znanstveni članek

Opis: On the basis of experimentally obtained data, it was established that submicron-size bubbles are formed by the internal oxidation of Cu-C composite with fine dispersed graphite particles. They are homogeneously distributed in the Cu-matrix. This process starts with the dissolution of oxygen into the metal at the free surfaces, and continues with the diffusion of oxygen atoms into the volume of copper crystal lattice where they react with the graphite particles. The reactions of dissolved oxygen with carbon yield the gas products (CO2, CO), which cannot be dissolved in the crystal lattice of the matrix. The gas molecules, which are enclosed in the space previously occupied by the graphite, have a greater specific volume than the solid graphite. Consequently, compressive stresses arise in the copper matrix around the bubbles. The interaction of these stress fields with gliding dislocations during loading could improve the mechanical properties of the copper. The internal oxidation kinetic in Cu-C composite depends on the diffusion of oxygen in the copper matrix, and the penetration depth of the internal oxidation front indicates the parabolic nature of the process.
Ključne besede: metallurgy, Cu-C composites, internal oxidation, bubbles
Objavljeno: 03.07.2017; Ogledov: 235; Prenosov: 52
.pdf Celotno besedilo (1,20 MB)
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