THE EFFECT OF ENHANCED GRAVITY LEVELS ON MICROSTRUCTURAL DEVELOPMENT IN PB-50 WT PCT SN ALLOYS DURING CONTROLLED DIRECTIONAL SOLIDIFICATION

The Pb-50 wt pct Sn alloys were directionally solidified at 21.1 mum s -1 through a temperature gradient of approximately 3.5 K mm-1. With th e aid of a centrifuge, the solidifying dendritic interfaces were subje cted to constant gravity levels, opposite to the growth direction, up to 15.3 times that of Earth's. Microstructural examination revealed no significant change in the secondary dendrite arm spacing, the interde ndritic eutectic spacing, or the primary dendrite trunk diameter as a function of increasing gravity level; the primary dendrite arm spacing , however, decreased significantly. The primary spacing decrease is ar gued to result from suppressing convection in the bulk liquid or by mo dification of the rejected solute layer as a result of enhanced buoyan cy.