On the growth mechanism of the primary silicon particle in a hypereutectic Al-20wt%Si alloy using synchrotron X-ray tomography

Publication date: 5 January 2018
Source:Materials & Design, Volume 137
Author(s): J. Wang, Z. Guo, J.L. Song, W.X. Hu, J.C. Li, S.M. Xiong
The 3-D morphology of the primary silicon particle (PSP) in a hypereutectic Al-20wt%Si alloy was characterized using synchrotron X-ray tomography. It was found that the most probable particle morphology always had a shape factor of 0.85, indicating either a regular octahedron or a twinned shape with a/h=2.5 (a was the edge length and h was the distance between the outer surface and the {111} plane). A growth transition model was then developed to describe the growth mechanism for the PSPs. It is believed that both octahedral and twinned shapes are a transition from a so-called facetted growth unit, which has a morphology of just half octahedron and evolves from a spherical nucleation. Further growth of the silicon particles can lead to the formation of hollow hoppers due to the mismatch of the growth velocity along different directions.

Graphical abstract

http://ift.tt/2hGuG8m