Experimental evidence for a zigzag bifurcation in bulk lamellar eutectic growth

We present real-time observations of the directional-solidification patterns of a transparent nonfaceted eutectic alloy (CBr4-C2Cl6) in bulk samples. The growth front of the two-phase solid is observed from the top through the liquid and the glass wall of the container with a long-distance microscope. We show that, in near-eutectic CBr4-C2Cl6 alloys, the upper stability limit of the stationary lamellar patterns is due to a zigzag bifurcation, which occurs at an interlamellar spacing of about 0.85lambda(m), where lambda(m) is the minimum-undercooling spacing. The zigzag patterns undergo a lamella breakup instability leading to the creation of new lamellae at about 1.1lambda(m). On the other hand, the lower stability limit of the stationary patterns is due to the same instability as in thin samples, namely, a lamella termination instability that occurs at about 0.7lambda(m).