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Onset of sidebranching in directional solidification.
Blas Echebarria1, Alain Karma, Sebastian Gurevich
1Departament de Física Aplicada, Universitat Politècnica de Catalunya, Av. Dr. Marañón 44-50, 08028 Barcelona, Spain.
Summary
Sidebranching in directional solidification arises from either noise or deterministic oscillations. Increasing thermal gradients reduce sidebranching onset by promoting tip blunting and noise amplification.
Area of Science:
- Materials Science
- Physics
- Computational Modeling
Background:
- Directional solidification is crucial for materials processing.
- Sidebranching instability affects the quality of solidified materials.
- Previous experimental studies have observed sidebranching in dilute alloys.
Purpose of the Study:
- Investigate the origins and dynamics of sidebranching.
- Explore the roles of noise and deterministic oscillations.
- Examine the influence of realistic alloy parameters and thermal gradients.
Main Methods:
- Utilized a computationally efficient phase-field formulation.
- Simulated sidebranching in 2D and 3D thin-sample geometries.
- Analyzed the bifurcation of growth solutions and noise-induced transitions.
Main Results:
- Identified two primary mechanisms for sidebranching: noise amplification and deterministic oscillations.
- Observed oscillatory solutions bifurcating subcritically from steady-state solutions.
- Demonstrated that noise-induced sidebranching amplitude saturates nonlinearly due to overlapping diffusion fields.
- Found that increased thermal gradients reduce sidebranching onset velocity and wavelength by promoting tip blunting.
Conclusions:
- Sidebranching in directional solidification is a complex phenomenon driven by distinct mechanisms.
- The phase-field model accurately reproduces experimentally observed behaviors.
- Thermal gradients play a counterintuitive role in suppressing sidebranching through tip blunting and noise amplification.
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