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Characterization of Cu-Al-Ni melt-spun ribbons using a focussed ion beam (FIB)
Franc Zupanič, Elfride Unterweger, Albert C. Kneissl, Ivan Anžel, Gorazd Lojen, 2007, izvirni znanstveni članek

Opis: This work investigates the possibilities for applying a focussed ion beam (FIB) for the metallographic preparation and characterization of Cu-Al-Ni melt-spun ribbons. Two alloys were selected for this reason: CuAl13Ni4 and CuAl15Ni4. The microstructure of the first alloy was fully martensitic and the microstructure of the second consisted of two phases: martensite and ▫$\gamma_2$▫. It was discovered that with FIB-etching the microstructures of both alloys can be clearly revealed on polished cross-sections of the melt-spun ribbons, as well as on their wheel-side and air-side surfaces. However, better results were obtained when the etched surface was smoother, and finer details were visible when using smaller ion currents. In addition, a study was made into the influence of platinum deposition on the quality of 3D-cross sections. It was found that Pt-deposition is necessary when the edge of the trench should be straight and sharp, and the surface of the 3D cross-section smooth. However, in this case, the microstructure of the ribbons free surface cannot be seen.
Ključne besede: focussed ion beam, FIB, metallography, melt-spinning, shape memory alloy, Cu-Al-Ni
Objavljeno: 31.05.2012; Ogledov: 899; Prenosov: 18
URL Povezava na celotno besedilo

Microstructural changes during vacuum carburizing of steels
Mihael Brunčko, Ivan Anžel, Albert C. Kneissl, 2011, izvirni znanstveni članek

Objavljeno: 01.06.2012; Ogledov: 648; Prenosov: 56
URL Povezava na celotno besedilo

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: 1176; Prenosov: 74
URL Povezava na celotno besedilo

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: 975; Prenosov: 61
URL Povezava na celotno besedilo

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: 895; Prenosov: 22
URL Povezava na celotno besedilo

Microstructural investigation of melt-spun NiTi based ribbons
Kambiz Mehrabi, Mihael Brunčko, Albert C. Kneissl, 2012, izvirni znanstveni članek

Opis: In order to get small-dimensioned shape memory alloys (SMAs) with good functional and mechanical properties, a rapid solidification technique was employed. This paper discusses the use of different melt-spinning procedures for the preparation of proper thin NiTi ribbons. Metallographic characterization of SMAs is an important way to evaluate material properties, therefore the effect of alloy composition and different conditions of melt-spinning process (crucible, melting time and temperature) on the various inclusions and microstructure of NiTi alloys was investigated. Specimens for metallographic studies were cut from the longitudinal cross sections of melt-spun ribbons. The microstructures and different phases were examined by optical, scanning and transmission electron microscopy and the influence of the processing methods on microstructures of ribbons will be discussed.
Objavljeno: 10.07.2015; Ogledov: 369; Prenosov: 38
URL Povezava na celotno besedilo

Characterization of oxidation resistance of stainless steels at high temperature by metallographic examinations and in-situ electrical resistance measurements
Mihael Brunčko, Rebeka Rudolf, Kambiz Mehrabi, Albert C. Kneissl, Ivan Anžel, 2013, izvirni znanstveni članek

Opis: Practically all metals and alloys survive high-temperature exposure by growing oxide scales and/or by precipitation of the oxide particles in the matrix. Formed products can grow in shape of external oxide layers on surfaces, or as discrete oxide particles precipitated in a metal matrix. The first case represents external oxidation, and the other case is called internal oxidation. These processes are very important, because they determine the properties and applicability of metallic materials. Generally, they are undesired, because they cause deterioration of the mechanical properties and decomposition of metallic material. On the other side, the controlled process of external oxidation could be used for formation of protective coatings and the internal oxidation for dispersion strengthening of materials. In this paper we present monitoring of hightemperature oxidation of X12Cr13 stainless steel by in-situ electrical resistance measurements at different annealing temperatures in the air atmosphere. We determined the kinetics of oxide scale formation and its morphology with additional metallographic examination made by optical and scanning electron microscopy. The results of this research work show that in-situ monitoring and characterization of high-temperature oxidation present a strong tool that will contribute to a better fundamental understanding of the phenomena that occur during high-temperature oxidation of metallic materials.
Objavljeno: 10.07.2015; Ogledov: 387; Prenosov: 42
URL Povezava na celotno besedilo

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