Directional solidification of highly undercooled eutectic Ni_(78.6)Si_(21.4) alloy

摘要

The directional solidification of highly undercooled eutectic Ni_(78.6)Si_(21.4) alloy is firstly achieved. In contrast with the conventional solidification, it occurs under a negative gradient at the solid/liquid interface. The essential condition for the processing is that the thermal diffusion in liquid plays a dominant role in the crystal growth. A directional solidification Ni_3Si dendrite structure is obtained at the undercooling of 72 K. The other directional solidification a-Ni dendrite is derived at the undercooling of 195 K. Thermodynamic modeling of homogeneous nucleation is applied in undercooled eutectic Ni_(78.6)Si_(21.4) alloy. It is found that Ni_3Si is easier nucleation than a-Ni in undercooled eutectic Ni_(78.6)Si_(21.4) melt. Calculated dendrite growth velocities confirm the predicted tendency of dendrite growth on the foundation of LKT/BCT theories.