On the characterization of eutectic grain growth during solidification

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On the characterization of eutectic grain growth during solidification M. Morua, M. Ramirez-Argaez and C. Gonzalez-Rivera C. Departamento de Ingeniería Metalúrgica, Facultad de Química, UNAM, 04510, México D.F. ABSTRACT The purpose of this work is to compare the results obtained from three methodologies intended to estimate kinetic parameters describing quantitatively the grain growth during equiaxed eutectic solidification in order to identify the best procedure to characterize grain growth kinetics. A heat transfer / solidification kinetics model is implemented to simulate the cooling and solidification of eutectic Al-Si and eutectic cast iron in sand molds. Using simulated cooling curves and volume grain density data generated by the model, the three methods are applied to obtain their predicted grain growth coefficients. The predicted results are compared with the grain growth coefficients used in the model. The outcome of this work suggests that two of the three methods under study represent the best option to obtain the kinetic parameters of equiaxed growth during eutectic solidification. INTRODUCTION The simulation of the cooling and solidification of alloys has been an important tool to improve metal processing productivity in the last decades. The prediction of the formation and evolution of the solidification microstructure is intimately linked to understanding of solidification kinetics. In this regard, different modeling approaches have been developed in the last couple of decades. A recent work by Nakajima et al. [1] discusses the methodological progress for computer simulation of solidification. The models used in computer simulations of solidification involve calculations on nucleation and growth kinetics which in turn depend on the availability of laws of nucleation and growth capable to reproduce the experimental behavior of the alloys of interest. The simulation software commonly available includes and uses material data for some generic alloys with compositions according to standard specifications. However a lack of data in existing databases regarding more specific alloy systems could be a restriction to the prediction capability of this computational tool. For this reason, identification of the more suitable methods to obtain experimental data to simulate the solidification and grain growth kinetics of specific alloys is an important task. Computer aided cooling curve analysis methods (CA-CCA) have been used to study solidification kinetics of various alloy systems of metallurgical interest. It has been found that Fourier thermal analysis (FTA) [2] is the most reliable CA-CCA method because it takes into account the presence of thermal gradients, giving a more realistic evolution of the solid fraction. FTA method has been described in detail elsewhere [2]. Briefly, two cooling curves obtained at two radial locations within a cylindrical sample with thermally isolated top and bottom during its cooling and solidification, are numerically processed. The FTA numerical processing starts with the gene

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