Effect of solidification time on the structural evolution of undercooled single phase alloys

The Cu70Ni30 alloy melt was bulk undercooled by combining the glass fluxing technique with superheating-cooling cycles. Different solidification times , ranging from several seconds to several hundred seconds, were designed to investigate the structural evolution of the alloy in the undercooling rang e 0-250 K. The grain refinements at low and high undercoolings were all obs erved for all values of solidification time. The results indicate that the grain refinement at low undercoolings mainly originates from the dendrite r emelting driven by the chemical superheating rather than by solid-liquid in terface energy, and that at high undercoolings the refinement is not relate d to the dendrite remelting at all. (C) 1999 Elsevier Science B.V. All righ ts reserved.