Freckle criteria for the upward directional solidification of alloys

• Published in: Metallurgical and materials transactions. A, Physical metallurgy and materials science Vol. 32; no. 2; pp. 397 - 406
• Main Authors: WANHONG YANG, WEI CHEN, CHANG, Keh-Minn, MANNAN, Sarwan, DEBARBADILLO, John
• Format: Journal Article
• Language: English
• Published: New York, NY Springer 01.02.2001; Springer Nature B.V
• Subjects: Applied sciences; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Materials science; Metals. Metallurgy; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Physics; Solidification; Directional solidification; Theoretical study; Dendrites; Macrosegregation; Microstructure; Rayleigh number; Phase transitions; Dendritic structure; Solidification
• ISSN: 1073-5623; 1543-1940
• DOI: 10.1007/s11661-001-0271-y

Macrosegregation defect freckles result from the convective flow due to a density gradient in the mushy zone. Several freckle criteria were proposed in the literature for the evaluation of the freckle tendency of alloys and processes. These criteria were examined using experimental data of the upward directional solidification of Pb-Sn, Pb-Sb, and Pb-Sn-Sb systems. It is found that the freckle criterion given by Flemings and co-workers gives the best description of the freckle tendency. A Rayleigh number is derived from Flemings' criterion. The critical value of the Rayleigh number is found to be Ra sub cr approx =1.