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11.
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: 10.07.2015; Views: 611; Downloads: 64
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12.
Površina zlitine Cu-Sn-Zn-Pb po obsevanju z ultravijoličnim dušikovim laserjem
Franc Zupanič, Tonica Bončina, Davor Pipić, Višnja Henč-Bartolič, 2007, original scientific article

Abstract: Površino zlitine Cu-Sn-Zn-Pb smo obsevali z laserskimi impulzi dušikovega laserja (valovna dolžina 337 nm). Pri tem sta se spremenila tako topografija površine kot tudi mikrostruktura pod njo. Ker je s klasičnimi metalografskimi metodami zelo težko primerno pripraviti obsevano površino za mikroskopsko opazovanje, smo kot temeljno orodje za metalografsko preiskavo uporabili fokusirani ionski curek (FIB), kajti FIB lahko odstranjuje material na specifičnih mestih v mikro- in nanoobmočju in odkrije mikrostrukturo brez prejšnje metalografske priprave. To nam je omogočilo, da smo raziskali vpliv obsevanja z laserjem na spremembo oblike površine, ugotovili profil kraterjev ter mikrostrukturne spremembe v območju toplotnega vpliva.
Keywords: laserska ablacija, bakrova zlitina, fokusiran ionski curek, mikrostruktura, topografija površine
Published: 10.07.2015; Views: 805; Downloads: 88
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13.
The influence of cooling rate on the microstructure of an Al-Mn-Be alloy
Niko Rozman, Tonica Bončina, Ivan Anžel, Franc Zupanič, 2008, original scientific article

Abstract: In ternary Al-Mn-Be alloys a metastable quasicrystalline phase can form at relatively low cooling rates (≈ 100 K/s); however, besides the quasicrystalline phase other phases can also be present. We found that the investigated alloy is very prone to the formation of metastable phases, which are also quasicrystalline. Using different investigation methods we determined the type of phases, their shape, morphology, chemical composition and distribution. Special attention was given to the micro- and nano-sized quasicrystalline particles. When using slow cooling, Al10Mn3 and Be4AlMn were present; however, with a faster cooling rate a quasicrystal approximant and a quasicrystalline phase were formed.
Keywords: aluminium, quasicrystals, cooling rate, microstructure
Published: 10.07.2015; Views: 786; Downloads: 46
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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: 10.07.2015; Views: 708; Downloads: 68
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17.
Characterization of defects in PVD TiAlN hard coatings
Peter Gselman, Tonica Bončina, Franc Zupanič, Peter Panjan, Darja Kek-Merl, Miha Čekada, 2012, original scientific article

Abstract: PVD hard coatings are continuously gaining their importance in different fields of applications. In industrial use, they are often exposed to corrosive environments. Hard coatings possess inherently good corrosion resistance, but the substrate-hard coating systems may suffer from a severe corrosion attack due to the defects (craters, pin holes) in the coatings. On the sites, where defects extend through the coating, pitting corrosion can take place. These sites are drawbacks in the applications of hard coating. A PVD TiAlN hard coating was prepared on cold-work, tool-steel (AISI D2) substrates by sputtering using unbalanced magnetron sources. The growth defects incorporated into the coating were studied after the deposition and corrosion experiments. We used two methods: (1) scanning electron microscopy (SEM) for general overview of the coating topography and 2D-characterization of defects, and (2) scanning electron microscopy with a focused ion beam (SEM-FIB) for making serial cross-sections through the selected defects in order to provide images for a 3D-reconstruction of defects. In this work we tried to investigate the formation of a defect at a specific location and findout whether the selected defect causes pitting corrosion.
Keywords: trde prevleke, PVD prevleke, defekti, jamičasta korozija, mikrostruktura, PVD hard coating, defect, pitting corrosion, microstructure
Published: 10.07.2015; Views: 846; Downloads: 67
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18.
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: 937; Downloads: 95
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Lastnosti in mikrostruktura avstenitnih nerjavnih jeklenih peskov
Tonica Bončina, Franc Zupanič, Ivan Anžel, Alojz Križman, 2000, professional article

Abstract: V naši raziskavi smo primerjali lastnosti in mikrostrukturo dveh vrst litih avstenitnih nerjavnih jeklenih peskov. Jekleni peski A so bili izdelani z nizkotlačno asimetrično vodno atomizacijo v odprti komori, peski B pa s plinsko atomizacijo. Primerjava napak in obrabne obstojnosti med peski A in B je pokazala, da imajo peski B manjši delež votlosti, večji delež okroglosti in boljšo obrabno obstojnost. Peski A so prevlečeni z debelo oksidno plastjo, ki nastane zaradi reakcije delcev s kisikom ali vodno paro med sferoidizacijo ali po njej. To je tudi vzrok za velik delež peskov nepravilne oblike in votlosti pri peskih A. Čeprav imajo peski A in B koncentracijo zlitinskih elementov v predpisanih mejah, pa se mikrostrukturi razalikujeta. Manjši delež C, Mn in Ni v peskih A vpliva, da se v mikrostrukturi poleg avstenita pojavlja še delta ferit, medtem ko imajo peski B popolno avstenitno mikrostrukturo. Ustrezno kvaliteto avstenitnih nerjavnih jeklenih peskov se lahko doseže: - če poteka atomizacija v razmerah, pri katerih na površini delcev ne nastaja trdna oksidna plast - če je kemijska sestava nerjavnega jekla taka, da je mikrostruktura po atmomizaciji v celoti avstenitna (dovolj visoka koncentracija C, Mn in Ni pri dani koncentraciji Cr).
Keywords: avstenitni nerjavni jekleni peski, mikrostruktura, oksidna plast, atomizacija
Published: 01.06.2012; Views: 1087; Downloads: 75
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