LAUSR

ABSTRACT Solidification velocities as a function of initial bulk undercoolings were systematically investigated using high speed thermal imaging of highly undercooled pure Ni and Ni-Cu alloy samples. For pure Ni, the dendrite growth velocity increased continuously to a maximum value of about 52 m s−1 at a maximum undercooling of 320 K. For Ni-Cu alloy, the dendrite growth velocity first increased continuously and then discontinuously to a maximum value of about 55 m s−1 at 300 K. A clear discontinuity appeared in the growth velocity-undercooling curve is considered to be caused by the finite speed of solute diffusion in the bulk liquid ahead of the migrating solid–liquid interface.