Effect of solidification temperature range on the dendritic growth mode

Electromagnetic levitation technique was used to undercool bulk samples of Co-20% Cu and Co-60% Cu alloys and high undercoolings up to 303 and 110 K were achieved,respectively.The dendritic growth velocities were measured as a function of undercooling.The dendrite growth velocity of the Co-20% Cu alloy was much higher than that of the Co-60% Cu alloy.The experimental data were analyzed on the basis of the LKT/BCT dendritic growth model by taking into account non-equilibrium interface kinetics.It has been revealed that a transition from solute diffusion controlled dendritic growth to thermal diffusion controlled dendritic growth occurs at an undercooling of about 66 K for the Co-20% Cu alloy,whereas the dendrite growth in Co-60% Cu alloy proceeds in a solute diffusion controlled mode within a large solidification temperature range,and the solutal undercooling plays a dominant role.It is thus deduced that certain distinct solidification temperature ranges may be responsible for the different solidification modes for the two alloys.