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Flow Effect on Si Crystals and Mn-Phases in Hypereutectic and Eutectic Al-Si-Mn Alloys

Mikołajczak Piotr

Archives of Foundry Engineering

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2023

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Vol. 23, iss. 4

72--86

EN

During mold filling and casting solidification, melt flow caused by gravity is present. Otherwise, forced flow may be a method applied for casting properties improvement. The flow effect generated by an electromagnetic field on the growing phases and a whole microstructure in Al-Si-Mn alloys was studied by slow solidification conditions. The hypereutectic and eutectic alloys were chosen to allow independent growth or joint growth of forming: Si crystals, Mn-rich α-Al15Si2Mn4 phases and Al-Si eutectics. In eutectic alloys, where Mn-phases precipitate as first and only one till solidus temperature, flow decreased number density of pre-eutectic α-Al15Si2Mn4. In the hypereutectic alloys, where Mn-phases grow in common with Si crystals, forced convection increased the overall dimension, decreased number density of pre-eutectic Mn phases and strengthened the tendency to growth in the outside of the sample. In the alloys, where Si crystals grow as first, stirring reduce number density of Si and moved them into thin layer outside cylindrical sample. Also by joint growth of Si crystals and Mn-phases, in hypereutectic Mn/Si alloy, flow moved Si crystals outside, reduced number density and increased the dimension of crystals. Stirring changed also AlSi eutectic spacing, specific surface Sv of α-Al and secondary dendrite arm spacing λ2. The results gave insight of what transformation under stirring take place in simple Al-Si-Mn alloys, and helps to understand what modifications in technical alloys may occur, that finally lead to changes in castings microstructure and properties. The possibility to control dimension, number density and position of Mn-phases and Si crystals is completely new and may help by metallurgical processes, continuous casting of billets and in the production of Si for the solar photovoltaic industry.

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Investigation of the influence of liquid phase motion on the solidification process in the three-dimensional region

Węgrzyn-Skrzypczak Ewa

Journal of Applied Mathematics and Computational Mechanics

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2021

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Vol. 20, nr 1

103--111

EN

In this paper, the numerical model of solidification process with the motion of the liquid phase is presented. The mathematical description of the considered problem is based on the heat conduction equation with convective term and the Navier-Stokes equations with continuity equation. The numerical model uses the Finite Element Method (FEM). The simulations of the solidification process with or without the fluid motion effect are presented and discussed.

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Microstructural and Mechanical Characterization of Solidified Austenitic Stainless Steels

Celik A. G., Polat S., Atapek S. H., Haidemenopoulos G. N.

Archives of Foundry Engineering

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2017

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Vol. 17, iss. 3

163--167

EN

Among the family of stainless steels, cast austenitic stainless steels (CASSs) are preferably used due to their high mechanical properties and corrosion resistance. These steels owe their properties to their microstructural features consisting of an austenitic matrix and skeletal or lathy type δ-ferrite depending on the cooling rate. In this study, the solidification behavior of CASSs (304L and 316L grades) was studied using ThermoCalc software in order to determine the solidification sequence and final microstructure during cooling. Theoretical findings were supported by the microstructural examinations. For the mechanical characterization, not only hardness measurements but also tribological studies were carried out under dry sliding conditions and worn surfaces were examined by microscopy and 3D profilometric analysis. Results were discussed according to the type and amount of microstructural features.

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Możliwości zagospodarowania popiołów z termicznego przekształcania osadów ściekowych w kotłach fluidalnych

Borowski G., Gajewska M., Haustein E.

Inżynieria i Ochrona Środowiska

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2014

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T. 17, nr 3

393--402

PL

Problem zagospodarowywania osadów ściekowych dotyczy głównie ich wykorzystania rolniczego, w tym rekultywacji terenów zdegradowanych. Zmiana wymagań prawnych i środowiskowych spowodowała konieczność poszukiwań nowych sposobów ich unieszkodliwiania. W Polsce od kilku lat obserwuje się wzrost zainteresowania termiczną metodą przekształcania osadów ściekowych. Zastosowana technologia spalania fluidalnego sprzyja zmniejszeniu ilości wytwarzanych i zdeponowanych osadów ściekowych. Ich termiczne przekształcanie nie eliminuje jednak problemu występowania m.in. metali ciężkich w uzyskanych popiołach, a jedynie prowadzi do związania ich w formy bardziej stabilne, ograniczając w ten sposób stopień szkodliwości dla środowiska naturalnego. W artykule zaprezentowano metodę zestalania popiołów powstałych z termicznego przekształcania osadów ściekowych w blokach cementowych. Analizując właściwości popiołów z fluidalnego spalania osadów ściekowych, zaproponowano koncepcję alternatywnego rozwiązania - ich przetworzenie w postać zeszklonych mikrokulek. Proponowana metoda zapewni neutralizację substancji niebezpiecznych w nich zawartych. Omówiono potencjalne korzyści ekologiczne i ekonomiczne oraz wymieniono dziedziny potencjalnego wykorzystania gospodarczego w zależności od wielkości średnic mikrokulek. Mikrokulki szklane mogą być, między innymi, stosowane w przemyśle tworzyw sztucznych do uzyskania wytrzymałych wyrobów z PCV, a także jako zamiennik tzw. proppantów w procesie szczelinowania hydraulicznego przy wydobyciu gazu łupkowego i ropy naftowej.

EN

The problem of sewage sludge processing relates mainly to its agricultural use, including the restoration of degraded land. Changing the legal and environmental requirements made it necessary to search for new techniques of disposal. In Poland, for several years there has been increased interest in using thermal treatment of sewage sludge. The used technology of fluidized bed combustion helps to reduce the amount of generated and deposited sludge. The thermal processing does not eliminate the problem of occurrence of heavy metals in the ash obtained, only results in binding them in the more stable form, thus reducing the degree of harmfulness to the environment. The paper presents a method for solidification of ash from the incineration of sewage sludge in cementitious compositions. Analyzing the characteristics of ashes from fluidized bed combustion of sewage sludge, there was proposed the concept of alternative solutions - processing in the form of vitrified microspheres. The proposed method provides neutralizing the hazardous substances contained therein. The potential environmental and economic benefits, and outlined areas of potential economic use, depending on the size of the diameter of the microspheres, were discussed. Glass microspheres may be, inter alia, used in the plastics industry to get durable PVC products, and also as a replacement of ‘proppants’ in hydraulic fracturing of the shale gas and oil.