Spacing Characterization in Al-Cu Alloys Directionally Solidified Under Transient Growth Conditions

TL;DR

This study investigates how dendritic spacing in Al-Cu alloys changes under transient solidification conditions, revealing step-wise evolution patterns confirmed by experiments and phase field simulations.

Contribution

It provides new experimental and simulation evidence showing dendritic spacing evolves in a step-wise manner during transient growth, aligning with theoretical predictions.

Findings

Spacing evolves in an almost step-wise fashion.

Dendrite instabilities are confined to sub-domains.

Rapid growth condition changes prevent whole-system adaptation.

Abstract

We study spacing selection in directional solidification of Al-Cu alloys under transient growth conditions. New experimental results are presented which reveal that dendritic spacing versus solidification rate evolves in an almost step-wise fashion, consistent with previous theoretical predictions of Langer and co-workers. Phase field simulations of directional solidification with dynamical growth conditions approximating those in the experiments confirm this behavior. Changes in dendrite arm spacing is shown to be consistent with dendrite instabilities confined, initially, to sub-domains, rather than the entire system. This is due to the rapid variation in growth conditions, which prevent the system from adapting as a whole but, rather, in a succession of quasi-isolated domains.