Semi-Solid Metal (SSM) casting is a promising technology offering an opportunity to manufacture net-shape, complex geometry metal components in a single operation. However, the absence of foundry guidelines and limited design data for SSM casting makes it challenging to predict the performance of both process and components. The objective of this research was to develop and offer new solutions to material processing-related issues in the electronics industry. By investigating the opportunities afforded by the recently developed RheoMetalTM rheocasting process, a better understanding of the critical factors needed for an effective manufacturing process and optimised component characteristics was achieved. A study of the evolution of microstructure at different stages of the RheoMetalTM process demonstrated the influence of multistage solidification on the microstructural characteristics of the rheocast components. The microstructure of a slurry consists of the solute-lean and coarse globular α-Al particles with a uniform distribution of alloying elements, suspended in the liquid matrix. Additional solute-rich α-Al particles were identified as being a consequence of discrete nucleation events taking place after the initial slurry production. In the final components, macrosegregation was observed in the form of variations in the ratio of solute-lean coarse globular α-Al particles and solute-rich fine α-Al particles in both longitudinal and transverse directions. The relation between microstructural characteristics and material properties was established by determination of the local properties of a rheocast component. The fracture of a rheocast telecom component was strongly affected by microstructural inhomogeneity. In particular, macrosegregation in the form of liquid surface segregation bands and sub-surface pore bands strongly affected the fracture behaviour. Thermal conductivity measurements revealed that regions of the component with a high amount of solute-lean globular α-Al particles showed higher thermal conductivity. The effect of the local variation in thermal conductivity on the thermal performance of a large rheocast heatsink was evaluated by simulation. The results clearly show the importance of considering material inhomogeneity when creating a robust component design.

<p>Predmet izučavanja ove disertacije obuhvatio je ispitivanje uticaja starenja stabilizovanog/solidifikovanog&nbsp; (S/S)&nbsp; sedimenta&nbsp; zagađenog te&scaron;kim metalima i arsenom, i efikasnost primenjenih imobilizacionih agenasa (Portland cement, kreč, leteći pepeo, zeolit, montmorilonit i kaolinit) nakon dugogodi&scaron;njeg starenja S/S sme&scaron;a. Shodno tome ispitana je dugoročna stabilnost i postojanost dobijenih S/S sme&scaron;a sa aspekta izluživanja pomenutih metala, promene u minerolo&scaron;kim i strukturnim karakteristikama, kao i uticaj su&scaron;enja i zrenja materijala na pomenute parametre. Istraživanja u disertaciji obuhvatila su dve faze. Prva faza imala je za cilj procenu rizika i&nbsp; početnu karakterizaciju netretiranog sedimenta primenom analize pseudo-ukupnog sadržaja metala kojom je utvrđen sadržaj metala u početnom uzorku sedimenta. Druga faza uključivala je primenu tretmana stabilizacije i solidifikacije na kontaminirani sediment dodavanjem različitih imobilizacionih agenasa. Analize su se vr&scaron;ile nakon 7 i 28 dana od primenjenog S/S tretmana, kao i nakon 7 godina sa ciljem da se utvrdi uticaj vi&scaron;egodi&scaron;njeg starenja i zrenja monolitnih sme&scaron;a na mobilnost metala i strukturne karakteristike sme&scaron;a. U&nbsp; okviru&nbsp; druge faze istraživanja ispitana je toksičnost S/S sme&scaron;a primenom DIN i TCLP testova izluživanja, dok je test toksičnosti primenom bakterija Vibrio Fischeri&nbsp; doprineo u&nbsp; sagledavanju&nbsp; procene rizika S/S sme&scaron;a po organizme. Nakon 28 dana i 7 godina kori&scaron;ćena je sekvencijalna ekstrakcija za&nbsp; određivanje mobilnost i biodostupnost metala u monolitnim matriksima. U cilju&nbsp; utvrđivanja mikrostukturnih karakteristika sedimenta primenjena je rendgenska difrakciona analiza (XRD) za ispitivanje kristalnih struktura&nbsp; S/S sme&scaron;a i detekciju mineralnog sastava. Pomoću elektronskog mikroskopa i energodisperzivnog detektora&nbsp; sa X-zrakom (SEM/EDS) određena je kvalitativna i kvantitativna distribucija metala i&nbsp; drugih elemenata od interesa, dok se za identifikaciju formiranih funkcionalnih grupa u monolitnim sme&scaron;ama primenio spektrometar sa infracrvenom Furijeovom transformacijom (FTIR). Na osnovu dobijenih rezultata zaključeno je da se mobilnost te&scaron;kih metala i arsena značajno smanjila nakon 7 godina za sme&scaron;e tretirane cementom (C5), krečom (L10), letećim pepelom (F30) i kaolinitom&nbsp; (K20), a efekat stabilizacije je pokazan transformacijom metala iz direktne toksične frakcije u&nbsp; stabilnije oblike. Sme&scaron;e C5 i K20 ispoljavaju&nbsp; najmanje toksične efekate od svih sme&scaron;a, jer je procenat inhibicije&nbsp; na&nbsp; bioluminiscentnim&nbsp; bakterijama manji od 13%, dok je u pogledu izdržljivosti monolitna sme&scaron;a C5 pokazala najveću pritisnu čvrstoću od svih sme&scaron;a. Dobijeni podaci su neprocenjivi za dobijanje stvarnog uvida u dugoročnu efikasnost&nbsp; primenjenog&nbsp; tretmana i mogućnost bezbedne upotrebe ili odlaganja dobijenih S/S sme&scaron;a sa aspekta za&scaron;tite životne sredine, kao i ekonomski i ekolo&scaron;ki prihvatljivog upravljanja opasnim otpadom.</p> / <p>The subject of study in this dissertation included to investigate the&nbsp; effect&nbsp; of&nbsp; aging&nbsp; of&nbsp; stabilized/solidified&nbsp; (S/S)&nbsp; sediment&nbsp; contaminated with&nbsp; heavy&nbsp; metals&nbsp; and&nbsp; arsenic,&nbsp; and&nbsp; the&nbsp; efficacy&nbsp; of&nbsp; the&nbsp; applied immobilization&nbsp; agent&nbsp; (Portland&nbsp; cement,&nbsp; lime,&nbsp; fly&nbsp; ash,&nbsp; zeolite, montmorillonite and kaolinite) after long-term aging of S/S mixtures. The<br />long&nbsp; -&nbsp; term stability and stability of the obtained S/S mixtures from the aspect of leaching of the mentioned metals, changes in mineralogical and structural characteristics,&nbsp; as&nbsp; well&nbsp; as&nbsp; the&nbsp; influence&nbsp; of&nbsp; drying&nbsp; and maturation of the material on the mentioned parameters were examined. The&nbsp; research&nbsp; in&nbsp; the&nbsp; dissertation&nbsp; included&nbsp; two&nbsp; phases.&nbsp; The&nbsp; first&nbsp; phase aimed&nbsp; at&nbsp; risk&nbsp; assessment&nbsp; and&nbsp; initial characterization&nbsp; of&nbsp; untreated sediment using pseudo-total metal content analysis which determined the<br />metal content in the initial sediment sample.&nbsp; The second phase involved applying&nbsp; stabilization&nbsp; and&nbsp; solidification&nbsp; treatments&nbsp; to&nbsp; the&nbsp; contaminated sediment&nbsp; by&nbsp; adding&nbsp; various&nbsp; immobilizing&nbsp; agents.&nbsp; The&nbsp; analyzes&nbsp; were performed after 7 and 28&nbsp; days from the applied S/S treatment, as well as after 7 years in order to determine the influence of perennial aging and maturation&nbsp; of&nbsp; monolithic&nbsp; mixtures&nbsp; on&nbsp; metal&nbsp; mobility&nbsp; and&nbsp; structural characteristics&nbsp; of&nbsp; the&nbsp; mixtures.&nbsp; In&nbsp; the&nbsp; second&nbsp; phase&nbsp; of&nbsp; the&nbsp; study,&nbsp; the toxicity&nbsp; of&nbsp; S/S&nbsp; mixtures&nbsp; using&nbsp; DIN&nbsp; and&nbsp; TCLP&nbsp; leaching&nbsp; tests&nbsp; was examined, while&nbsp; the&nbsp; toxicity&nbsp; test&nbsp; using&nbsp; bacteria&nbsp; Vibrio&nbsp; Fischeri contributed&nbsp; to&nbsp; the assessment&nbsp; of&nbsp; the&nbsp; risk&nbsp; of&nbsp; S/S&nbsp; mixtures&nbsp; to&nbsp; organisms. After&nbsp; 28 days&nbsp; and&nbsp; 7 years,&nbsp; sequential extraction was&nbsp; used to&nbsp; determine the mobility and bioavailability of metals in monolithic matrices. In order to&nbsp; determine&nbsp; the&nbsp; microstructural&nbsp; characteristics&nbsp; of&nbsp; the&nbsp; sediment,&nbsp; x-ray diffraction analysis (XRD) was used to examine the crystal structures of&nbsp; S/S mixtures and&nbsp; to detect the mineral composition.&nbsp; The qualitative and quantitative&nbsp; distribution&nbsp; of&nbsp; metals&nbsp; and&nbsp; other&nbsp; elements&nbsp; of&nbsp; interest&nbsp; was determined using an electron microscope and an energy-dispersive X-ray detector&nbsp; (SEM&nbsp; /&nbsp; EDS),&nbsp; while&nbsp; an&nbsp; infrared&nbsp; Fourier&nbsp; transform spectrometer(FTIR) was used to identify the formed functional groups in monolithic mixtures. Based on the obtained results, it was concluded that the mobility of heavy metals and arsenic decreased significantly after 7 years&nbsp; for&nbsp; mixtures&nbsp; treated&nbsp; with&nbsp; cement&nbsp; (C5),&nbsp; lime&nbsp; (L10),&nbsp; fly ash&nbsp; (F30) and&nbsp; kaolinite&nbsp; (K20),&nbsp; and&nbsp; the&nbsp; stabilization&nbsp; effect&nbsp; was&nbsp; shown&nbsp; by transformation&nbsp; of&nbsp; metals&nbsp; from&nbsp; direct&nbsp; toxic&nbsp; fractions&nbsp; into&nbsp; more&nbsp; stable forms. Mixtures&nbsp; C5&nbsp; and&nbsp; K20&nbsp; exhibit&nbsp; the&nbsp; least&nbsp; toxic&nbsp; effects&nbsp; of&nbsp; all mixtures, because the percentage of inhibition on bioluminescent bacteria is less than 13%, while in terms of durability, the monolithic mixture C5 showed&nbsp; the&nbsp; highest&nbsp; compressive&nbsp; strength&nbsp; of&nbsp; all&nbsp; mixtures.&nbsp; The&nbsp; obtained data are invaluable for gaining real insight into the long-term efficiency of the applied treatment and the possibility of safe use&nbsp; or disposal of the obtained&nbsp; S/S&nbsp; mixtures&nbsp; from&nbsp; the&nbsp; aspect&nbsp; of&nbsp; environmental&nbsp; protection,&nbsp; as well&nbsp; as&nbsp; economically&nbsp; and&nbsp; ecologically&nbsp; acceptable&nbsp; hazardous&nbsp; waste management.</p>