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Effect of cooling rate on the microstructure of an Al94Mn2Be2Cu2 alloy
Tonica Bončina, Boštjan Markoli, Franc Zupanič, 2012, original scientific article

Abstract: In this study the effect of the cooling rate on the microstructure of Al94 Mn2 Be2 Cu2 alloy was investigated. The vacuum induction melted and cast alloy was exposed to different cooling rates. The slowest cooling rate was achieved by the DSC (10 K·min^−1), the moderate cooling rate succeeded by casting in the copper mould (≈1 000 K·s−1) and the rapid solidification was performed by melt spinning (up to 10^6 K·s^−1). The microstructure of the DSC-sample consisted of α-Al matrix, and several intermetallics: τ1-Al29 Mn6 Cu4 , Al4 Mn, θ-Al2 Cu and Be4 Al(Mn,Cu). The microstructures of the alloy at moderate and rapid cooling consisted of the α-Al matrix, i-phase and θ-Al2 Cu. Particles of i-phase and θ-Al2 Cu were much smaller and more uniformly distributed in melt-spun ribbons.
Keywords: Al-alloy, metallography, microstructure, cooling rate, solidification
Published in DKUM: 03.07.2017; Views: 963; Downloads: 97
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Faze v kvazikristalni zlitini $Al_{64,4}Cu_{22,5}Fe_{13,1}$
Tonica Bončina, Boštjan Markoli, Ivan Anžel, Franc Zupanič, 2007, original scientific article

Abstract: V ternarnem sistemu Al-Cu-Fe se pojavlja t.i. i-faza (ikozaedrični kvazikristal), ki je termodinamsko ravnotežna faza in s tem sestavni del ravnotežnega faznega diagrama. Na enofazno področje i-faze meji veliko število intermetalnih faz, ki so lahko glede na sestavo zlitine, razmere pri strjevanju in toplotni obdelavi v stabilnem ali metastabilnem ravnotežju z i-fazo. Sinteza enofazne kvazikristalne zlitine je mogoča samo v ozkem koncentracijskem območju in pri primernem načinu toplotne obdelave, zato je poznavanje in ugotavljanje faz ključnega pomena. V raziskavi smo izdelali zlitino $Al_{64,4}Cu_{22,5}Fe_{13,1}$ in vzorce toplotno obdelali na različne načine. Posamezne faze in druge mikrostrukturne značilnosti smo ugotovili z ustrezno metalografsko pripravo vzorcev in metodami svetlobne mikroskopije (SE), vrstične elektronske mikroskopije (SEM), mikrokemične analize (EDS), rentgenske fazne analize (XRD), presevne elektronske mikroskopije (TEM) ter mikrotrdote. Faze smo ločevali tudi glede na njihovo morfologijo in mikrotrdoto (nanoidentifikacija). Prisotnost i-faze smo potrdili z metodama XRD in TEM.
Keywords: Al-Cu-Fe, kvazikristali, metalografija
Published in DKUM: 10.07.2015; Views: 1174; Downloads: 109
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Structure of the continuously cast Ni-based superalloy GMR 235
Franc Zupanič, Tonica Bončina, Gorazd Lojen, Boštjan Markoli, Savo Spaić, 2007, original scientific article

Abstract: In this work we characterized the structure of continuously cast small cross-section rods (O10 mm) of the Ni-based superalloy GMR 235. In the microstructure prevailed dendritic columnar ?-grains with ?'-precipitates. In the interdendritic regions MC-carbide and M3B2-boride were identified. The inverse macrosegregation was very faint, except at the secondary witness marks and natural corrugations. It was found that the alternating drawing mode had much greater influence on microstructure than other casting parameters. Special attention was given to explanation of processes leading to formation of surface marks (primary and secondary witness marks and natural corrugations). Formation of hot tears and appearance of inverse segregation is also discussed.
Keywords: Ni-based superalloy, solidification, microstructure, continuous casting, surface marks
Published in DKUM: 01.06.2012; Views: 1684; Downloads: 102
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Microstructure of Al-Mn-Be melt-spun ribbons
Franc Zupanič, Tonica Bončina, Borivoj Šuštaršič, Ivan Anžel, Boštjan Markoli, 2008, original scientific article

Abstract: Microstructures of two alloys with the nominal compositions of Al92Mn3Be5 and Al89Mn6Be5 were characterized in the initial as-cast condition (after vacuum induction melting and casting) and after melt spinning. In the initial conditions, both alloys consisted of an aluminum-rich solid solution and two metastable intermetallic phases: Be4AlMn and Al10Mn3(Be). Both alloys melted over a rather large temperature range (between 230 °C and 310 °C). This was the main reason for the presence of unmelted particles in the melt-spun ribbons. Nonetheless, with the use of optimized melt-spinning parameters a microstructure composed of the Al-rich solid solution and finely dispersed quasicrystalline particles in ribbons with thicknesses ranging from 30-200 m was achieved. The dispersion of quasicrystalline particles was finest on the wheel side of the thinnest ribbons, attaining microhardness values between 250HV and 300 HV.
Published in DKUM: 01.06.2012; Views: 2081; Downloads: 123
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Quasicrystal-strengthened cast Al-alloys
Franc Zupanič, Tonica Bončina, Niko Rozman, Boštjan Markoli, 2011, original scientific article

Keywords: aluminium, quasicrystal, strengthening, mechanical properties
Published in DKUM: 01.06.2012; Views: 2286; Downloads: 35
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The solidification path of the complex metallic Al-Mn-Be alloy
Boštjan Markoli, Tonica Bončina, Franc Zupanič, 2010, published scientific conference contribution

Abstract: The solidification paths of the Al86.1Mn2.5Be11.4 and Al84Mn5.1Be10.9 alloys, melt spun, cast into a copper mould and controlled cooled (during DSC) were investigated by means of light-optical microscopy (LOM), differential scanning calorimetry (DSC) combined with thermogravimetry (TG) or simultaneous thermal analysis (STA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Auger electron spectroscopy (AES) and the X-ray diffraction (XRD) line in Elletra Trieste, Italy. The constitutions of samplesfrom both alloys were examined in all three states, i.e., after melt spinning, after casting into a copper mould and after differential scanning calorimetry. It was established that in the cast and controlled-cooled specimens the alloys consisted of an aluminium-rich ▫$alpha$▫Al-matrix, and the Al4Mn and Be4AlMn phases. In the case of casting and DSC the primary crystallization began with the precipitation of the Be4AlMn phase, followed by what can most likely be characterized as a uni-variant binary eutectic reaction L > (Be4AlMn + Al4Mn). The solidification process continued with an invariant ternary eutectic reaction, where the remaining melt (L) formed the heterogeneous structure (▫$alpha$▫Al + Al4Mn + Be4AlMn) or a ternary eutectic. When extremely high cooling rates were employed, as is the case with melt-spinning,the constituting phases of both alloys were precipitated in a very small form and the Be4AlMn phase was completely absent in the form of primary polygonal particles and replaced by the icosahedral quasicrystalline phase or the i-phase. There was also no evidence of the Al4Mn phase. The distribution, size and shape of all the constituents in the melt-spun alloys also varied from the contact surface towards the free surface of the ribbons. The smallest constituents were established at the contact surface, measuring less than 0.1 ▫$mu$▫m, to 0.5 ▫$mu$▫m at the free surface. The grains of the aluminium-rich matrix had mean diameters of less than 20 ▫$mu$▫m, close to the freesurface, down to 1 m at the contact surface.
Keywords: complex Al-Mn-Be alloys, metallography, solidification
Published in DKUM: 31.05.2012; Views: 2033; Downloads: 96
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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 in DKUM: 31.05.2012; Views: 2322; Downloads: 96
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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 in DKUM: 31.05.2012; Views: 2147; Downloads: 116
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