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Solidification Modeling of Microsegregation
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
2018 (English)Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
Abstract [en]

A phase transformation from liquid to solid phase takes place when the material solidifies. Limited diffusion during this phase transition causes microsegregation, which is aphenomenon during solidification that leads to the formation of secondary phases andconcentration gradients. This affects the properties of the material and how it is to be treatedin further processing steps. Due to the complexity of the solidification process, a modelingapproach has been used for investigation of microsegregation.

The Scheil-Gulliver model assumes negligible diffusion in the solid phase but an exchange ofsolute during back-diffusion can have an important influence on solidification. While the Brody-Flemings model considers this, it is questionable in its assumptions. A new proposedmodel by John Ågren that considers multicomponent diffusion effects have been implementedusing the Matlab-Toolbox for Thermo-Calc.

The model is used to perform solidification simulations for the binary Al-2.1Cu and theternary Al-2.1Cu-1Si system (at%) and the results are compared to the Scheil-Gulliver modeland DICTRA simulations. The Ågren model gives excellent results for the binary system athigh cooling rates. It does however show deviations from the DICTRA results at lowercooling rates and for the ternary system.

Abstract [sv]

När ett material stelnar sker en fasomvandling från flytande till fast fas. Begränsad diffusionunder denna fasövergång orsakar mikrosegring, vilket är ett fenomen under stelningsförloppetsom skapar sekundära faser och koncentrationsgradienter. Detta påverkar egenskaperna hosmaterialet and hur den ska behandlas under senare processteg. På grund av komplexiteten avstelningsprocessen har modellering använts för att undersöka mikrosegring.

Scheil-Gulliver modellen antar att det inte sker någon diffusion i fast fas men ett utbyte avinlösta ämnen kan ha ett viktigt inflytande på stelningsförloppet. Fastän Brody-Flemingsmodellen tar hänsyn till detta så är den tveksam i sina antaganden. En ny föreslagen modell avJohn Ågren betraktar diffusionseffekter för ett multikomponent system och denna harimplementerats med hjälp av Matlab-Toolbox för Thermo-Calc.

Modellen har använts för att simulera stelning för ett binärt Al-2.1Cu och ett ternärt Al-2.1-1Si system (at%) och resultaten har jämförts med Scheil-Gulliver modellen och DICTRAsimuleringar. Ågren modellen ger utmärkta resultat för det binära systemet vid högakylhastigheter. Modellen visar däremot avvikelser från DICTRA vid låga kylhastigheter samtför det ternära systemet.

Place, publisher, year, edition, pages
2018. , p. 25
Keywords [en]
Solidification, casting, microsegregation, Thermo-Calc, DICTRA
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-231496OAI: oai:DiVA.org:kth-231496DiVA, id: diva2:1228826
Educational program
Master of Science in Engineering - Materials Design and Engineering
Supervisors
Examiners
Available from: 2018-06-29 Created: 2018-06-28 Last updated: 2018-06-29Bibliographically approved

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