Crystal nucleation and detachment from a chilling metal surface with vibration

A novel method of crystal nucleation and detachment from a vibrating chilling solid surface has been proposed to further increase the proportion of equiaxed grains in the solidification microstructure. Using a transparent NH₄Cl-H₂O alloy, the surface nucleation and evolution behaviors of dendrites were in situ observed. The effects of vibration frequency as well as amplitude on the equiaxed crystallographic morphology were experimentally studied, and the effects of the roughness of solid surface were also considered. The results show that exerting vibration to a chilling metal surface is an effective way to produce a lot of nuclei for forming equiaxed grains microstructure, and with higher vibration frequency and amplitude, much finer equiaxed grains are obtained. Moreover, nucleation on the chilling surface is a much localized behavior, some fixed positions on the chilling surface act as active nucleation sites, of which the number increases with a lowering chilling temperature.