EVOLUTION OF CHARACTERISTIC PATTERN PARAMETERS IN DIRECTIONAL SOLIDIFICATION OF THIN SAMPLES OF A DILUTE AL-CU ALLOY

The evolution of solidification patterns (cells, dendrites) with pulli ng velocity is analyzed on X-ray topographs taken in situ and in real time during directional growth of thin samples of a dilute Al-Cu alloy . Systematic measurements of major characteristic parameters (primary spacing, tip radius) are also carried out. The results are compared wi th data on the same alloy system available from the literature, which permits us to bring out the influence of convection in the melt on the se parameters and on the cell-dendrite transition.