Complex eutectic growth and Bi precipitation in ternary Sn-Bi-Cu and Sn-Bi-Ag alloys

Author(s)

Silva, Bismarck Luiz ; Garcia, Amauri ; Spinelli, Jose Eduardo

• Document type: Journal article
• Source: Journal of Alloys and Compounds; v. 691, p. 600-605, JAN 15 2017.
• Web of Science Citations: 18

Abstract

Sn-34 wt%Bi, Sn-34 wt%Bi-2wt%Ag and Sn-34 wt%Bi-0.7 wt%Cu alloys have been directionally solidified (DS) under a broad range of solidification cooling rates. Microstructures have been characterized with emphasis on both eutectic growth and precipitation of Bi within the beta-Sn dendritic matrix. The eutectic growth, for all alloys examined, is shown to be associated with the coexistence of coarse and fine lamellar structures with different length-scale of lamellar spacing (lambda). Experimental growth relations of l vs. the cooling rate have been proposed. The length-scale of the lamellae in the fine eutectic ranges from 0.8 to 2.5 mm while in the coarse eutectic from 1.8 to 4.0 mm. Taking as reference the Sn-Bi alloy, both the spacing between Bi precipitates (lambda(p)) and the fine eutectic spacing (lambda(fine)) increase with Cu and Ag additions, whereas lambda(coarse) remains roughly unaltered. Both ternary Sn-Bi-Ag and Sn-Bi-Cu alloys are shown to have worse distributions of both lamellae in the fine eutectic and of precipitates within Sn-rich dendrites, which resulted in decrease in hardness. (C) 2016 Elsevier B.V. All rights reserved. (AU)

• FAPESP's process: 13/08259-3 - Microstructure and mechanical behavior of Sn-Bi-Cu and Sn-Bi-Ag lead-free solder alloys
• Grantee: Bismarck Luiz Silva
• Support Opportunities: Scholarships in Brazil - Doctorate
• FAPESP's process: 15/11863-5 - Microstructure evaluation of ternary Al-Si-Cu, Sn-Bi-Sb and Zn-Sn-Cu and its correlations with mechanical properties
• Grantee: José Eduardo Spinelli
• Support Opportunities: Regular Research Grants