In-situ observation of cellular growth under rapid solidification conditions

Dynamic studies on the rapid solidification of binary CBr4-C2Cl6 alloys at different hypoeutectic compositions were performed. The samples were solidified in fine glass tubes with a square cross-section by pulling the tube rapidly from a hot into a cold zone. Applying pulling velocities up to 30 mm s−1, local solidification velocities from 0.3 to 2 mm s−1 depending on the cooling temperature were achieved. Independent of concentration and solidification velocity, the observed interface morphologies revealed either a cylindrical or elongated cellular pattern, which are often separated by a boundary in pulling direction. The occurrence of these morphologies was found to change instantaneously. The spacings of the cylindrical and the elongated cells were measured as a function of concentration and solidification velocity. The results are discussed with respect to a recent theory for cellular growth.