Formation of semisolid globular structures under shearing

To understand the formations of the globular semi-solid structure in a stirred/sheared melt, extensive in-situ microstructure observations of succinonitrile-5at.%water transparent alloy and Sn-15wt.%Pb alloy were conducted using three specially designed apparatus. A analyses of spherical growth in an undercooling melt with strong convection was accounted for through added a convective loss of solute term in the solute transfer equation. The equation was numerically resolved, and the result indicates that, when the convective loss of solute induced by the tangential flow in front of a spherical crystal is taken consideration in the solute transfer equation, the concentration gradient at the solid/liquid interface decrease. And this leads to an increase in the interfacial morphological The theoretical analyses are in good agreement with the experimental results. More importantly, it is found in experiment that a step change in shearing rate can induce violent disturbances and thermal fluctuations in the melt, which promotes the formation of semi-solid globular structures.