Three-dimensional visualization and characterization of morphology and internal microstructural features of primary silicon crystals in a cast Al–Si base alloy

• Published in: Journal of crystal growth 2009-09, Vol.311 (19), p.4454-4461
• Main Authors: Singh, H., Gokhale, A.M., Mao, Y., Tewari, A., Sachdev, A.K.
• Format: Article
• Language: English
• Subjects: A1. Crystal morphology; A1. Optical microscopy; A1. Solidification; A2. Bulk crystal growth; A2. Growth from melt; B1. Metals; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Growth from melts; zone melting and refining; Materials science; Methods of crystal growth; physics of crystal growth; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Physics; Solidification
• ISSN: 0022-0248; 1873-5002
• DOI: 10.1016/j.jcrysgro.2009.08.001

Primary Si crystals are usually present in the cast microstructures of near-eutectic, eutectic, and hyper-eutectic Al–Si base alloys. Three-dimensional digital images of individual primary Si crystals present in a permanent mold cast unmodified Al-12 wt% Si-1 wt% Ni base alloy are reconstructed using a combination of montage serial sectioning and three-dimensional digital image processing techniques. Octahedral, prismatic, and plate-like three-dimensional morphologies of the primary Si crystals are present in the microstructure. Some of the primary Si crystals contain interior regions/islands of Al-alloy that are completely enclosed in the corresponding Si crystals indicating certain variations in the crystal growth velocities during the evolution of these crystals. The boundaries of these interior regions/islands are non-faceted smooth and curved indicating re-melting of the Al-rich islands and re-dissolution of some Si near these internal boundaries in the Al-alloy as a result of the heat generated by liquid-to-solid transformation of Si away from the islands.