Journal
MATERIALS & DESIGN
Volume 137, Issue -, Pages 176-183Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.matdes.2017.09.062
Keywords
X-ray tomography; Hypereutectic Al-Si alloy; Primary silicon morphology; Twinning
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Funding
- National Natural Science Foundation of China [51775297]
- National Science and the Tsinghua University Initiative Scientific Research Program [20151080370]
- UK Royal Academy of Engineering/Royal Society through the Newton International Fellowship Scheme
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The 3-D morphology of the primary silicon particle (PSP) in a hypereutectic Al-20 wt% 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 froma 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. (C) 2017 Elsevier Ltd. All rights reserved.
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