Effect of Convective Instability in Directionally Solidified Hypermonotectic Al-In Alloys

Abstract

Aligned composite growth of In-rich fibers in an Al-rich matrix can be achieved in hypermonotectic Al-In alloys through directional solidification under interfacially stable conditions, i.e. a sufficiently high thermal gradient to growth rate ratio. During vertically upwards directional solidification, however, a solute depleted boundary layer is expected to develop at the solidification front. In the Al-In system and most other immiscible alloy systems, this solute depleted boundary layer results in an unfavorable density gradient with a more dense liquid above a less dense liquid. This convectively unstable situation is expected to lead to flow iii the liquid in advance of the solidification front. The effect of this flow on the morphology and compositional uniformity along the length of hypermonotectic Al-In samples will be presented. In addition, this study will investigate the feasibility of directionally solidifying vertically downwards to eliminate convection caused by the destabilizing solutal field.