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Title: On secondary dendrite arm coarsening in peritectic solidification
Authors: Ma, D.
Xu, W.
Ng, S.C. 
Li, Y. 
Keywords: Coarsening
Dendrite arm spacing
Gibbs-Thomson effect
Peritectic reaction
Peritectic transformation
Issue Date: 15-Jan-2005
Citation: Ma, D., Xu, W., Ng, S.C., Li, Y. (2005-01-15). On secondary dendrite arm coarsening in peritectic solidification. Materials Science and Engineering A 390 (1-2) : 52-62. ScholarBank@NUS Repository.
Abstract: A model for isothermal coarsening of secondary dendrite arms in peritectic reaction and transformation (liquid + primary-phase → peritectic-phase) is proposed to evaluate the secondary dendrite arm spacing (λ2) of the primary phase in directional solidification of peritectic alloys. The model defines three stages for thin-arm dissolution (or thick-arm coarsening), i.e. the initial, intermediate and final stages: The initial thin-arm dissolution through the primary phase is sustained solely by the Gibbs-Thomson effect; the intermediate thin-arm dissolution through the peritectic phase is driven by Gibbs-Thomson effect but retarded by the peritectic reaction and transformation; the final dissolution through the primary and peritectic phases is enhanced by the Gibbs-Thomson effect and the phase transformation. The kinetics of peritectic reaction and transformation were found to be crucial to determine the thin-arm dissolution, which were characterized by the reaction constant (f) and the diffusion coefficient of solute in solid peritectic-phase (DS), respectively. The present model shows that λ2 Vm is constant for a given Pb-Bi peritectic alloy, where V is growth velocity, and the factor, m, ranges from 1/3 to 1/2, rather than that normally observed (e.g. 1/3) for single-phase solidification. It is also notable that the calculated λ2 for a Zn-7.37 wt.% Cu peritectic alloy was reasonably consistent with our earlier experiments for various growth velocities. © 2004 Published by Elsevier B.V.
Source Title: Materials Science and Engineering A
ISSN: 09215093
DOI: 10.1016/j.msea.2004.07.032
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