In-situ measurements of dendrite tip shape selection in a metallic alloy

TL;DR

This study employs high-resolution synchrotron radiography and advanced image processing to measure dendrite tip shapes in a metallic alloy in situ, revealing key parameters influencing microstructure during solidification.

Contribution

It introduces a novel in-situ measurement approach for dendrite tip shapes in metals, overcoming previous resolution and noise limitations, and quantifies shape selection parameters.

Findings

Dendrite tip shape selection parameter σ* = 0.0768

Interface energy anisotropy ε4 = 0.015

Tip shape amplitude coefficient A4 ≈ 0.004

Abstract

The size and shape of the primary dendrite tips determine the principal length scale of the microstructure evolving during solidification of alloys. In-situ X-ray measurements of the tip shape in metals have been unsuccessful so far due to insufficient spatial resolution or high image noise. To overcome these limitations, high-resolution synchrotron radiography and advanced image processing techniques are applied to a thin sample of a solidifying Ga-35wt.%In alloy. Quantitative in-situ measurements are performed of the growth of dendrite tips during the fast initial transient and the subsequent steady growth period, with tip velocities ranging over almost two orders of magnitude. The value of the dendrite tip shape selection parameter is found to be $\sigma^* = 0.0768$, which suggests an interface energy anisotropy of $\varepsilon_4 = 0.015$ for the present Ga-In alloy. The non-axisymmetric dendrite tip shape amplitude coefficient is measured to be $A_4 \approx 0.004$, which is in excellent agreement with the universal value previously established for dendrites.