On secondary dendrite arm coarsening in peritectic solidification

D. Ma*, W. Xu, S. C. Ng, Y. Li

*Corresponding author for this work

Research output: Contribution to journalArticle

35 Citations (Scopus)

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.

Original languageEnglish
Pages (from-to)52-62
Number of pages11
JournalMaterials Science and Engineering A
Volume390
Issue number1-2
DOIs
Publication statusPublished - 15 Jan 2005
Externally publishedYes

Keywords

  • Coarsening
  • Dendrite arm spacing
  • Gibbs-Thomson effect
  • Peritectic reaction
  • Peritectic transformation

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