Convective effects on columnar dendritic solidification -- A multiscale dendritic needle network study

TL;DR

This paper introduces a multiscale dendritic needle network model that incorporates buoyant flow to study crystal growth dynamics, microstructure selection, and oscillatory behaviors in solidification processes under various conditions.

Contribution

The paper develops a novel multiscale Dendritic Needle Network model that includes buoyant flow, enabling detailed analysis of microstructure selection and oscillatory growth in solidification.

Findings

Flow velocity close to crystal growth velocity induces oscillations.

Primary dendrite spacing influences oscillatory behavior.

Model reproduces experimental and phase-field results.

Abstract

Gravity-induced buoyancy, inevitable in most solidification processes, substantially alters the dynamics of crystal growth, such that incorporating fluid flow in solidification models is crucial to understand and predict key aspects of microstructure selection. Here, we present a multi-scale Dendritic Needle Network (DNN) model for directional solidification that includes buoyant flow in the liquid, and apply it to a range of alloys and growth conditions. After a brief presentation of the model, we study the selection of stable primary dendrite arm spacings in Al-4at.%Cu and in Ti-45at.%Al alloys under different gravity levels, comparing both applications to published phase-field results and experimental measurements. Then, we simulate the oscillatory growth behavior recently reported via X-ray in situ imaging of directional solidification of nickel-based superalloy CMSX-4. In this last application, the DNN simulations manage to reproduce the oscillatory growth behavior, and hence permit identifying the fundamental mechanisms behind the oscillatory growth regime. In particular, we show that sustained oscillations occur when the average liquid flow velocity is close to the crystal growth velocity, and that primary dendritic spacings also play a crucial role in the oscillatory behavior.