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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: 03.07.2017; Views: 394; Downloads: 66
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Effect of AlTi5B1 and AlSr10 additions on the fluidity of the AlSi9Cu3 alloy
Matej Steinacher, Franc Zupanič, Mitja Petrič, Primož Mrvar, 2014, original scientific article

Abstract: This work studies the effect of the AlTi5B1 and AlSr10 additions on the fluidity and the solidification time of the AlSi9Cu3 casting alloy. The fluidity was investigated by determining the flow length in a spiral-shaped mould. The solidification time was measured with a thermocouple positioned at the ingate bottom. An individual pouring into the preheated (200 °C) metallic mould was done at different pouring temperatures ((640, 670, 700, and 710) °C). In all the cases, the fluidity was improved with the increasing pouring temperatures. An addition of the AlTi5B1grain refiner to the basic alloy reduced both the grain size and the fluidity, whilst the solidification time was similar to that of the basic alloy. On the other hand, an addition of the AlSr10 modifier refined the ßSi eutectic phase, increased the fluidity and prolonged the solidification time in comparison to the basic alloy. The fluidity was proportional to the solidification time. Thus, by carrying out a simple thermal analysis and determining the solidification time, it is possible to predict the fluidity.V delu je predstavljen vpliv dodatkov AlTi5B1 in AlSr10 na livnost in strjevalni čas livne aluminijeve zlitine AlSi9Cu3. Livnost smo preiskovali z merjenjem dolžine toka taline v kovinski kokili s spiralno livno votlino, medtem ko smo strjevalni čas merili s termoelementom, ki je bil vstavljen na dnu lijaka. Talino smo pri različnih livnih temperaturah ((640, 670, 700 in 710) °C) ulivali v predgreto kokilo (200 °C). Livnost je v vseh primerih naraščala z naraščanjem livne temperature. Dodatek udrobnilnega sredstva AlTi5B1 k osnovni zlitini je zmanjšal tako velikost kristalnih zrn kot livnost, medtem ko je bil strjevalni čas podoben kot v osnovni zlitini. Dodatek modifikatorja AlSr10 je zmanj{al velikost evtektične faze ßSi, povečal livnost ter podaljšal strjevalni čas v primerjavi z osnovno zlitino. Livnost je bila sorazmerna strjevalnemu času, tako da lahko z enostavno termično analizo in določanjem strjevalnega časa napovemo livnost preiskovane zlitine.
Keywords: AlSi9Cu3 alloy, grain refinement, modification, fluidity, solidification time
Published: 15.03.2017; Views: 622; Downloads: 76
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Influence of a random field on particle fractionation and solidification in liquid-crystal colloid mixtures
Vlad Popa-Nita, Paul van der Schoot, Samo Kralj, 2006, original scientific article

Abstract: The influence of a random-anisotropy (RA) type disorder on the phase separation of nematogen-colloid mixtures is studied theoretically by combiningthe phenomenological Landau-de Gennes, Carnahan-Starling, and hard-sphere crystal theories. We assume that the colloids enforce the RA disorder on the surrounding thermotropic liquid-crystal (LC) molecules. We adopt the Imry-Ma argument according to which the lower-temperature phase exhibits a domain-type pattern. The colloids impose a finite degree of orientational ordering even in the isotropic (paranematic) phase. In the ordered phase they give rise to a domain-type structure, resulting in the distorted nematic (speronematic) phase. The RA field opposes the phase separation tendency. With increasing disorder the difference between the paranematic and speronematic ordering decreases. Consequently there is a critical disorder, above which both phases become identical from the orientation point of view, but have different concentrations of colloids. We have also estimated another characteristic value of disorder above which the isotropic phase can exist only in a liquid state, the crystal phase being suppressed completely.
Keywords: liquid crystals, transitions, segregation, mixing, random fields, solidification, complex fluids
Published: 07.06.2012; Views: 947; Downloads: 68
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Monitoring of directional solidification with simultaneous measurements of electrical resistance and temperature
Mihael Brunčko, Ivan Anžel, Alojz Križman, 2003, original scientific article

Abstract: WE present the efficiency of simultaneous electrical resistance and temperature (ERT) measurements for monitoring the position, X, and the growth rate, V, of the solidification front during the directional solidification of alloys. On alaboratory device for directional solidification (Bridgman-type furnace), theeutectic Pb-Sn alloy was solidified at five different pulling rates, VP, with a constant imposed temperature gradient, GP. During directional solidification, the electrical resistance and the temperature changes were measured simultaneously in the experimental samples. The results of the experiments show that simultaneous measurement of ERT enables not only the determination of the average growth rate, V, during directional solidificationbut also its fluctuation over the total measurement length of the sample.
Keywords: metallurgy, Pb-Sn alloy, directional solidification, electrical resistance measurements, temperature measurements
Published: 01.06.2012; Views: 1256; Downloads: 83
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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: 01.06.2012; Views: 1098; Downloads: 83
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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: 31.05.2012; Views: 1444; Downloads: 72
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