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1.
Characterization of cast Al86Mn3Be11 alloy
Tonica Bončina, Boštjan Markoli, Franc Zupanič, 2009, original scientific article

Abstract: An Al86Mn3Be11 alloy cast into copper mould was subjected to metallographic investigation. The as-cast microstructure consisted of a quasicrystalline icosahedral phase (i-phase), Be4AlMn phase and, occasionally, a hexagonal phase. Al-rich solid solution represented the dominant phase. The chemical compositions of phases were determined using AES. The composition of the Be4AlMn slightly deviated from the stoichiometric composition, whereas the composition of the i-phase was approximately Al52Mn18Be30, containing an appreciable amount of Be. The average composition of the hexagonal phase was Al66Mn21Be13. Deep etching and particle extraction provided a deep insight into the three-dimensional morphology of the i-phase and the hexagonal phase, whereas Be4AlMn was slightly attacked by the etchant. The i-phase was present predominantly in the form of dendrites and a rodlike eutectic phase. The hexagonal phase was primarily in the form of hexagonal platelets, whereas Be4AlMn was rather irregular in shape. The morphology of the i-phase can be explained by predominant growth in 3-fold directions and the lowest energy of the 5-fold planes, leading to the faceting and adopting a pentagonal dodecahedron shape. The brightnesses of phases in the backscattered electron images were rationalized by determining their backscattering coefficients. TEM investigation showed considerable phason strain in the i-phase, and the polycrystalline nature of the Be4AlMn phase.
Keywords: aluminium alloys, deep etching, metallography, particle extraction, quasicrystal
Published: 31.05.2012; Views: 1302; Downloads: 67
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2.
Metallographic techniques for the characterization of quasicrystalline phases in aluminium alloys
Tonica Bončina, Boštjan Markoli, Ivan Anžel, Franc Zupanič, 2008, original scientific article

Abstract: Several Al-alloys strengthened by quasicrystalline phases have been developed over the last few years showing the considerable potential for practical application. Therefore there is a strong need for developing new metallographic methods or adapting the traditional ones in order to identify and characterize quasicrystalline phases in a reliable, quick and economical way. This paper describes different techniques: the classical metallographic method, deep etching, particle extraction technique and cross-sectioning using focused ion beam (FIB), and discusses their advantages and disadvantages when identifying quasicrystalline particles. It was discovered that particle extraction techniques are very powerful methods for the identification of phases according to their morphology, and preparation of quality samples for X-ray diffraction (XRD). Transmission electron microscopy (TEM) analyses are also possible provided the extracted particles are thin enough.
Keywords: alluminium alloys, quasicrystal, metallography, deep etching, particle extraction
Published: 31.05.2012; Views: 1401; Downloads: 84
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Thermal stability of Al-Mn-Be melt-spun ribbons
Gorazd Lojen, Tonica Bončina, Franc Zupanič, 2012, original scientific article

Abstract: As with other kinds of finely dispersed, small particles, icosahedral quasicrystals (IQCs) also have a distinct strengthening effect, which can be utilised to enhance the mechanical properties of aluminium alloys. In Al-Mn-Bealloys, IQCs already form at moderate cooling rates, which can be utilised when using some conventional casting processes, like mould or injection casting. In this case, however, crystalline intermetallic phases are also present and the mechanical properties are inferior to those of two-phase aAl-IQC alloys. Two-phase microstructures are feasible using rapid solidification techniques, e.g., melt spinning. Further processing often involves technologies (consolidation, extrusion etc.), which include the influence of heat. The alloy must not be overheated in order to preserve the strengthening effect of the metastable IQC-particles. In this investigation the Al-Mn-Be alloy was melt-spun using a free-jet melt spinner. Subsequently, the thermal stability of the IQCs was explored by annealing the ribbons for 24h at different temperatures. The samples were examined in the as-cast and heat-treated conditions using a dual-beam, scanning electron microscope (SEM-FIB), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). It was discovered that in the as-cast condition, the ribbons had a two-phase microstructure, consisting of an aAl matrix and finely dispersed IQCs. During annealing at temperatures up to 400 °C, the IQCs did not decompose and the phase composition remained unchanged. Annealing at 500 °C and at higher temperatures caused a decomposition of the IQCs, and only the crystalline intermetallic phases Al6Mn and Be4AlMn could be found in the aAl matrix.
Keywords: quasicrystal, Al-Mn-Be alloy, thermal stability
Published: 10.07.2015; Views: 794; Downloads: 66
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5.
In situ TEM study of precipitation in a quasicrystal-strengthened Al-alloy
Tonica Bončina, Franc Zupanič, 2017, original scientific article

Abstract: 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.
Keywords: Al-alloy, quasicrystal
Published: 09.05.2017; Views: 509; Downloads: 205
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