5th International Conference on Advances in Solidification Processes (ICASP-5) 5th International Symposium on Cutting Edge of Computer Simulation of Solidification, Casting and Refining (CSSCR-5)

The formation of eutectic microstructures, composed of two phases or more, is often encountered during the solidification of industrial alloys. Fraction and characteristics of this structure have consequences on the subsequent phase transformations, mechanical strength and final end-use properties of metallic pieces. Consequently, estimation of eutectic growth kinetics is required in order to predict its development and internal scale during solidification processes. However, most of existing eutectic growth models are within the frame of the primary Jackson-Hunt theory [1] and systematically use linear approximations for thermodynamic properties and solidification front curvature effects. These approximations limit their application to low growth rate. In addition, these models also neglect variations of densities between phases and advection of liquid phase induced by shrinkage effect. An original model of directional growth for lamellar eutectics is presented. This model is based on the analysis and computation of thermodynamic equilibrium at the solidification front. Contrary to previous models, this new approach does not make use of linearization hypotheses for the alloy phase diagram. In addition this model considers variations of densities within phases along with the influence of curvature on thermodynamic equilibrium at the solidification front. The numerical implementation is made possible through a coupling with a thermodynamic software based on the CALPHAD approach. This new numerical model is applied to the Al-Al2Cu eutectic structure and compared to the Jackson-Hunt theory. Large differences between results of the present model and this theory are observed at high growth rate. Validations with experimental observations developed in a large range of growth velocities and reported in literature are also proposed. Analytical developments are finally provided in order to explain and estimate evolutions observed in eutectic microstructure evolution. The application of this model to multicomponent alloys will be discussed. [1] K.A. Jackson, J.D. Hunt, Lamellar and rod eutectic growth, Trans. AIME, 236 (1966), 1129–1142