Steps, kinetic anisotropy, and long-wavelength instabilities in directional solidification

Area of Science:

• Materials Science
• Solidification Physics
• Crystallography

Background:

• Directional solidification of binary alloys is crucial for materials processing.
• Interface kinetics and anisotropy significantly influence solidification morphology.
• Understanding instabilities is key to controlling material properties.

Purpose of the Study:

• To investigate the impact of anisotropic interface kinetics on long-wavelength instabilities during binary alloy directional solidification.
• To analyze the conditions leading to planar front stabilization and novel instabilities.
• To explore the dynamical behavior and preferred orientations of the crystal-melt interface.

Main Methods:

• Linear stability theory applied to a vicinal interface model.
• Analysis of the neutral stability curve and control parameters (morphological number).
• Derivation of generalized evolution equations and application of bifurcation analysis and numerical computations.

Main Results:

• Anisotropy stabilizes planar fronts for small segregation coefficients.
• Novel instabilities emerge at high solidification rates.
• Neutral stability curves exhibit complex behavior, including isolas.
• Bifurcation analysis indicates anisotropy promotes supercritical bifurcations and preferred interface orientations.

Conclusions:

• Anisotropic interface kinetics play a critical role in solidification instabilities.
• The study reveals conditions for both stabilization and destabilization of the solidification front.
• Finite-amplitude deformations under anisotropy lead to preferred interface orientations, impacting crystal growth.