Stability of lamellar eutectic growth in thick samples

Abstract

The growth front of a transparent non-faceted eutectic (CBr₄–C₂Cl₆) is observed from the top in real time in thick samples during directional solidification. We study the stability of the lamellar patterns at near-eutectic concentrations as a function of the spacing λ and the pulling velocity V. The domain of stability of the symmetrical (straight) lamellar patterns is limited by an Eckhaus instability followed by eliminations of lamellae at λ/λ _m  ≈ 0.7, where λ _m  ∝ V ^−0.5 is the minimum-undercooling spacing, and a zigzag bifurcation at λ/λ _m  ≈ 0.85. A lamella break-up instability occurs at λ/λ _m  ≈ 1.1. Wall effects and topological defects play a major role during transients. No important anisotropy effect is observed, except near eutectic grain boundaries.

Acknowledgements

The authors thank M. Plapp and A. Parisi for communicating their unpublished numerical results, M. Perrut for contributions to the observations, and C. Perez and C. Picard for technical help. This research was supported by the Centre National d’Etudes Spatiales, France.