Thermosolutal convection-induced freckle formation in steady and unsteady directional solidification: Analysis in Sn-Ni peritectic alloy

摘要

Peritectic alloys have attracted more and more attention during past decades due to their growing applications. However, different from the current analysis on other alloys, freckle formation is witnessed in two regions in Sn-Ni peritectic alloy during directional solidification: the former (latter) one before (after) peritectic reaction. Besides, compared with the steady growth condition, fewer freckles can be observed in deceleration growth while more freckles are formed in acceleration growth. In addition, it has been demonstrated that the dendritic morphology is greatly influenced by the Gibbs-Thomson (G-T) and temperature gradient zone melting (TGZM) effects. A Rayleigh number R-aP in consideration of both effects was proposed. The prediction of R-aP in the mushy zone shows two maximums during peritectic solidification, confirming the freckle formation in two regions in this work. Furthermore, the influence of unsteady growth condition on the freckle formation can also be successfully predicted by R-aP. (C) 2021 Elsevier B.V. All rights reserved.