In Situ Particle Layer Formation in a Al-Mn-Si Ternary Eutectic Alloy: Ground Reference and Microgravity Experiments

A special type of divorced eutectic growth mode (symbiotic growth) in a ternary Al-Mn-Si alloy, triggered by addition of titanium boride (TiB2) has been studied under both ground and microgravity conditions. During directional solidification, α (AlMnSi) particles nucleate ahead of the planar solidification front and are pushed and later engulfed by the interface forming a banded particle layer structure. The presence of fine titanium boride particles (clusters) in front of the growing α (AlMnSi) particles makes the interaction between the intermetallic α (AlMnSi) particles and solidification front much more complex than most proposed models for particle/interface interactions. Microgravity experiments can eliminate the gravity related effects and thus provide an opportunity to better understand the formation mechanism of symbiotic growth. In this study, hypoeutectic Al-1Mn-3Si alloys with addition of 0.33 wt% TiB2 were directionally solidified in ESA Solidification and Quenching Furnace (SQF) on board of the International Space Station (ISS). The ground experiment was conducted in a replica of this furnace prior to the microgravity experiments. Non-destructive X-ray tomography and its 3D reconstruction software was used to characterize the particles and their distribution. Comparison between ground and microgravity experiment results is presented. The particle pushing and engulfment of symbiotic growth is discussed based on a particle pushing and engulfment model.