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21.
Thermal stability of Al-Mn-Be melt-spun ribbons
Gorazd Lojen, Tonica Bončina, Franc Zupanič, 2011, objavljeni povzetek znanstvenega prispevka na konferenci

Ključne besede: icosahedral quasicrystals, aluminium alloys
Objavljeno: 01.06.2012; Ogledov: 885; Prenosov: 42
URL Povezava na celotno besedilo

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Microstructure of Al-Mn-Be melt-spun ribbons
Franc Zupanič, Tonica Bončina, Borivoj Šuštaršič, Ivan Anžel, Boštjan Markoli, 2008, izvirni znanstveni članek

Opis: 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.
Objavljeno: 01.06.2012; Ogledov: 1166; Prenosov: 64
URL Povezava na celotno besedilo

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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, izvirni znanstveni članek

Opis: 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.
Ključne besede: Ni-based superalloy, solidification, microstructure, continuous casting, surface marks
Objavljeno: 01.06.2012; Ogledov: 812; Prenosov: 64
URL Povezava na celotno besedilo

27.
Morfologija karbida MC in borida M3B2 v liti Ni-superzlitini GMR 235
Franc Zupanič, 2002, izvirni znanstveni članek

Opis: V tem delu smo raziskali morfologijo karbida MC in borida M3B2 v litem stanju nikljeve superzlitine GMR 235. Normalne in globoko jedkane metalografske vzorce ter tudi elektrolizno ekstrahirane karbide in boride smo opazovali predvsem na vrstičnem elektronskem mikroskopu. Zaradi značilnosti strjevanja te zlitine, ki se začne s primarno kristalizacijo trdne raztopine na osnovi niklja - faze y, sta se karbid in borid v glavnem nahajala v meddendritnem prostoru. Njuna velikost in oblika sta bili odvisni od hitrosti ohlajanja kakor tudi od anizotropije njunih lastnosti (površinske energije...) ter mehanizmov in kinetike rasti. Pri manjših ohlajevalnih hitrostih je na morfologijo karbidov izrazito vplivala anizotropija površinske energije. Zato so bili delci oktaedrične oblike kot tudi močno razvejeni dendriti MC-karbida pretežno obdani s habitusnimi ravninami {I II}. Pri večjih hitrostih ohlajanjaso nastali skeletni karbidi s številnimi vejami v smereh , ki so se pogosto razvejile. V ternarnem evtektiku (y + MC + M,B,) je imel MC-karbid obliko tankih ploščic. Borid M3B2 je bil navzoč v okviru ternarnega evtektika. Kristaliti borida so bili sestavljeni iz vzporednih lamel, ki so se pogosto razvejile. Pri povečani hitrosti ohlajanja je postala njihova oblika bolj nepravilna.
Ključne besede: nikljeva superzlitina, morfologija, karbidi, boridi, GMR 235
Objavljeno: 01.06.2012; Ogledov: 835; Prenosov: 46
.pdf Celotno besedilo (308,23 KB)
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28.
Lastnosti in mikrostruktura avstenitnih nerjavnih jeklenih peskov
Tonica Bončina, Franc Zupanič, Ivan Anžel, Alojz Križman, 2000, strokovni članek

Opis: 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).
Ključne besede: avstenitni nerjavni jekleni peski, mikrostruktura, oksidna plast, atomizacija
Objavljeno: 01.06.2012; Ogledov: 954; Prenosov: 55
.pdf Celotno besedilo (2,74 MB)
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29.
Thermal stability of Al-Mn-Be melt-spun ribbons
Gorazd Lojen, Tonica Bončina, Franc Zupanič, 2012, izvirni znanstveni članek

Opis: 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.
Ključne besede: quasicrystal, Al-Mn-Be alloy, thermal stability
Objavljeno: 10.07.2015; Ogledov: 682; Prenosov: 54
.pdf Celotno besedilo (777,98 KB)
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30.
Characterization of defects in PVD TiAlN hard coatings
Peter Gselman, Tonica Bončina, Franc Zupanič, Peter Panjan, Darja Kek-Merl, Miha Čekada, 2012, izvirni znanstveni članek

Opis: 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.
Ključne besede: trde prevleke, PVD prevleke, defekti, jamičasta korozija, mikrostruktura, PVD hard coating, defect, pitting corrosion, microstructure
Objavljeno: 10.07.2015; Ogledov: 642; Prenosov: 48
.pdf Celotno besedilo (716,32 KB)
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