On the Nonequilibrium Interface Kinetics of Rapid Coupled Eutectic Growth
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loys are a type of important engineering materials. The performances of these materials are closely correlated to their microstructures formed upon coupled eutectic growth.[1–5] Comprehensive understanding of the coupled eutectic growth behaviors are crucial in tailoring the microstructures and, in turn, the performances of these materials. So far, great effort has been devoted to modeling the coupled growth of the eutectic alloys.[6–12] The most well-known analytical model was established by Jackson and Hunt[6] (JH model). The JH model was developed based on two assumptions: (1) lamellar spacing of the two eutectic phases is much smaller than the solute diffusion length, and (2) solidification occurs at a sufficiently small interface undercooling (DT) so that the composition ahead of the solid/liquid (S/L) interface is approximately the same as the eutectic composition. This
H. DONG, Y.Z. CHEN, G.B. SHAN, Z.R. ZHANG, and F. LIU are with the State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an 710072, P.R. China. Contact e-mail: [email protected] and [email protected] Manuscript submitted December 22, 2016. Article published online June 5, 2017 METALLURGICAL AND MATERIALS TRANSACTIONS A
model establishes a quantitative relationship among the DT, the lamellar spacing (k), and the growth velocity (V) of the eutectic phases. However, due to the adopted assumptions, the JH model is only suitable for describing the coupled eutectic growth at a small V. To overcome this deficiency, Trivedi et al.[7] (TMK model) modified the JH model based on two types of eutectic phase diagrams: (1) a cigar-shaped phase diagram where the liquidus and solidus are parallel below the equilibrium eutectic temperature and (2) a phase diagram where the equilibrium partition coefficients of the two eutectic phases are constant and equal. However, the TMK model does not consider the effect of atom-attachment kinetics at the S/L interface, which can be significant when the growth V is high or the eutectic phases contain intermetallic compounds. Given this, Li and Zhou[8] (LZ model) introduced a kinetic undercooling (DTk) into the TMK model to account for the effect of atom-attachment kinetics at the S/L interface on the coupled growth. On the other hand, considering that under the rapid solidification condition, e.g., laser surface remelting, the eutectic alloys may grow at a high V where the solute trapping effect can be significant, Kurz and Trivedi[9] developed a model (KT model) involving the solute trapping effect at the S/L interface. The preceding models have been widely used to describe the coupled growth behaviors of the eutectic
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alloys. However, when the eutectic phases showing sluggish atom-attachment kinetics at the S/L interface, e.g., intermetallic compounds, form at high solidification velocities, both the effects of atom-attachment kinetics and solute trapping at the S/L interface will be significant. In this case, these models are not able to provide a rational description of
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