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Comparison of NiTi orthodontic archwires and a determination of the charasteristic properties
Janko Ferčec, Matija Kos, Mihael Brunčko, Ivan Anžel, Branislav Glišić, Evgenija Marković, Rebeka Rudolf, 2014, original scientific article

Abstract: The aim of this paper was to analyse the characteristic properties of six different, commercially available nickel-titaniumorthodontic wires with a diameter of 0.305 mm (0.014"). The characteristic properties were determined by usingsemi-quantitative EDX analyses, DSC analyses for a determination of the phase temperatures, and a tensile test to obtain themechanical properties of the wires. The investigation of the chemical composition showed an equiatomic NiTi alloy. Analysesof phase temperatures showed that the nickel-titanium orthodontic wires were, in an austenitic microstructure, exhibiting asuperelastic effect in the oral environment. The uniaxial tensile stressstrain curves showed different values for the beginningand the end of the transformation range during the loading.
Keywords: shape-memory alloy, phase transformation, thermal analysis, tensile test
Published in DKUM: 21.12.2015; Views: 1021; Downloads: 87
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Shapes of the icosahedral quasicrystalline phase in melt-spun ribbons
Tonica Bončina, 2013, short scientific article

Abstract: The shapes of icosahedral quasicrystalline (IQC) particles were determined in melt-spun ribbons of alloys based on the Al-Mn-Be alloy system. The sizes of the quasicrystalline particles ranged from a few tenths of nanometres up to 1m. Therefore, different methods were employed for characterizing their shapes: projection of quasicrystalline particles using transmission electron microscopy (TEM), cross-sections of IQCs on metallographically polished surfaces, and observation of deep-etched samples and extracted particles using a scanning electron microscope (SEM). It was discovered that icosahedral quasicrystalline particles preferentially grow in three-fold directions and have a tendency for faceting and adopting the shape of a pentagonal dodecahedron. The evolution of quasicrystalline shapes is systematically presented.
Keywords: Al-alloy, metallography, ribon, icosahedral quasicrystalline phase, shape, melt-spinning
Published in DKUM: 10.07.2015; Views: 1019; Downloads: 86
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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, original scientific article

Abstract: 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.
Keywords: metallurgy, shape memory alloys, Cu-Al-Ni alloy, microstructure, melt spinning
Published in DKUM: 01.06.2012; Views: 1855; Downloads: 104
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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, original scientific article

Abstract: 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.
Keywords: focussed ion beam, FIB, metallography, melt-spinning, shape memory alloy, Cu-Al-Ni
Published in DKUM: 31.05.2012; Views: 1384; Downloads: 25
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