Grain Refinement and Solidification Velocity of Supercooled Melts

Abstract

Using a high speed thermal imaging camera, solidification velocity of undercooling is accurately determined for a highly undercooled Ni70Cu30 binary concentrated single phase alloy. It is observed that the velocity of solidification is first continuously and smoothly increasing at the low and mediate undercoolings then increasing discontinuously to a maximum value at the high undercooling range. Thus, the solidifcation velocity-undercooling relation has an abrupt discontinuity, which is caused by nonequilibrium diffusion of solutes in the liquid side near the advancing solid liquid interface. Grain refinement of high undercooling is directly induced by recrystallization, which was in clear contrast with the remelting induced dendrite fragmentation in conventional alloys.