Evolution of dendritic patterns during alloy solidification: onset of the initial instability

Area of Science:

• Materials Science
• Physics
• Solidification Science

Background:

• Directional solidification of binary alloys can lead to complex dendritic patterns from initially planar interfaces.
• Understanding the transition from planar to dendritic growth is crucial for materials processing and predicting microstructure.
• Previous theoretical models, like Warren and Langer's, provided frameworks for this phenomenon.

Purpose of the Study:

• To experimentally investigate the evolution of dendritic patterns from a planar solid-liquid interface.
• To quantitatively measure solute buildup and interface instability during directional solidification.
• To compare experimental findings with recent theoretical calculations by Warren and Langer.

Main Methods:

• Used a transparent organic crystal (succinonitrile doped with coumarin 152) as a model alloy.
• Employed fluorescence of coumarin 152 for direct observation of solute concentration profiles.
• Utilized UV absorption to induce thermal perturbations and measure linear growth coefficients.

Main Results:

• Detailed measurements of solute buildup ahead of the planar interface were performed.
• The instability of the planar solid-liquid front was observed and characterized.
• Experimental measurements of concentration profiles and linear growth coefficients agreed well with Warren-Langer predictions.

Conclusions:

• The experimental investigation validates the theoretical predictions of Warren and Langer regarding dendritic pattern formation.
• The study provides a detailed comparison between experimental observations and theoretical models of solidification instability.
• The methods used allow for precise measurements of key parameters governing the transition to dendritic growth.