Experimental and Numerical Modeling of Segregation in Metallic Alloys

• Published in: Metallurgical and Materials Transactions A
• Main Authors: Mosbah, Salem, Bellet, Michel, Gandin, Charles-André
• Other Authors: Carpenter Technology Corporation, Carpenter, Centre de Mise en Forme des Matériaux (CEMEF), Mines Paris - PSL (École nationale supérieure des mines de Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2010
• Subjects: SEM image; Solid-phase; South pole; Spherical domain; Strong correlation; Structure formations; Temperature curves; Undercooled melt; Alumina plates; Composition measurements; Cooling rates; Coupling scheme; Dendrite arm spacing; Dendritic structures; Distribution maps; Electromagnetic levitation; Energy dispersive X-ray spectrometry; Equiaxed grains; Eutectic structures; Experimental techniques; FE method; Finite-element models; Grain nucleation; Heat extraction rate; Levitated droplet; Liquid phasis; Mass exchange; Metallic alloys; Metallurgical characterization; Mushy zone; Numerical modeling; Phase nucleation; Scanning electron microscopes; Segregation model; [SPI.MAT]Engineering Sciences [physics]/Materials; South Pole
• Online Access: https://hal-mines-paristech.archives-ouvertes.fr/hal-00509607; https://hal-mines-paristech.archives-ouvertes.fr/hal-00509607/document; https://hal-mines-paristech.archives-ouvertes.fr/hal-00509607/file/Mosbah-Bellet-Gandin_MMTA2010_av.pdf; https://doi.org/10.1007/s11661-009-0141-6

International audience Electromagnetic levitation (EML) has been used as an experimental technique for investigating the effect of the nucleation and cooling rate on segregation and structure formation in metallic alloys. The technique has been applied to aluminum-copper alloys. For all samples, the primary phase nucleation has been triggered by the contact of the levitated droplet with an alumina plate at a given undercooling. Based on the recorded temperature curves, the heat extraction rate and the nucleation undercooling for the primary dendritic and the secondary eutectic structures have been determined. Metallurgical characterizations have consisted of composition measurements using a scanning electron microscope (SEM) equipped with energy dispersive X-ray spectrometry and the analysis of SEM images. The distribution maps drawn for the composition, the volume fraction of the eutectic structure, and the dendrite arm spacing (DAS) reveal strong correlations. Analysis of the measurements with the help of a cellular-automaton (CA)-finite-element (FE) model is also proposed. The model involves a new coupling scheme between the CA and FE methods and a segregation model accounting for diffusion in the solid and liquid phases. Extensive validation of the model has been carried out on a typical equiaxed grain configuration, i.e., considering the free growth of a mushy zone in an undercooled melt. It demonstrates its capability of dealing with mass exchange inside and outside the envelope of a growing primary dendritic structure. The model has been applied to predict the temperature curve, the segregation, and the eutectic volume fraction obtained upon single-grain nucleation and growth from the south pole of a spherical domain with and without triggering of the nucleation of the primary solid phase, thus simulating the solidification of a levitated droplet. Predictions permit a direct interpretation of the measurements.