Microstructure evolution in equiaxed dendritic growth

Abstract

Microstructure evolution in equiaxed dendritic solidification is investigated through the study of free dendritic growth in a supercooled melt. A detailed measurement of microstructural features (such as side-branch spacings, envelope shape, projection area, and contour length) of freely growing succinonitrile dendrites is performed using images from the microgravity experiment of Glicksman and co-workers. The measurements show that the microstructure evolution of an equiaxed dendrite is divided into two regimes: an initial linear regime and a subsequent non-linear coarsening regime. It is found that unique scaling relations exist between the measured geometry parameters and the primary tip radius or speed for both regimes. The underlying mechanisms involved in dendritic structure evolution are discussed. In addition, using the phase-field method, we perform numerical experiments to investigate the effects of melt convection on equiaxed dendritic growth. The dendrite tip operating state (i.e. the tip velocity and radius) is quantitatively evaluated as a function of the flow velocity and dendrite orientations and compared with Microscopic Solvability Theory. Other structural features (such as the side-branches) of an equiaxed dendrite in the presence of flow are also examined in order to show how convection influences microstructure evolution in equiaxed dendritic growth.