The use of a directional solidification technique to investigate the interrelationship of thermal parameters, microstructure and microhardness of Bi-Ag solder alloys

Author(s)

Spinelli, Jose Eduardo ^[1] ; Silva, Bismarck Luiz ^[1] ; Cheung, Noe ^[2] ; Garcia, Amauri ^[2]

Affiliation

^[1] Univ Fed Sao Carlos, Dept Mat Engn, BR-13565905 Sao Carlos, SP - Brazil

^[2] Univ Estadual Campinas, Dept Mfg & Mat Engn, BR-13083970 Campinas, SP - Brazil

• Document type: Journal article
• Source: MATERIALS CHARACTERIZATION; v. 96, p. 115-125, OCT 2014.
• Web of Science Citations: 7

Abstract

Bi-Ag alloys have been stressed as possible alternatives to replace Pb-based solder alloys. Although acceptable melting temperatures and suitable mechanical properties may characterize such alloys, as referenced in literature, there is a lack of comprehension regarding their microstructures (morphologies and sizes of the phases) considering a composition range from 1.5 to 4.0 wt.%Ag. In order to better comprehend such aspects and their correlations with solidification thermal parameters (growth rate, v and cooling rate, T), directional solidification experiments were carried out under transient heat flow conditions. The effects of Ag content on both cooling rate and growth rate during solidification are examined. Microstructure parameters such as eutectic/dendritic spacing, interphase spacing and diameter of the Ag-rich phase were determined by optical microscopy and scanning electron microscopy. The competition between eutectic cells and dendrites in the range from 15 to 4.0 wt.%Ag is explained by the coupled zone concept. Microhardness was determined for different microstructures and alloy Ag contents with a view to permitting correlations with microstructure parameters to be established. Hardness is shown to be directly affected by both solute macrosegregation and morphologies of the phases forming the Bi-Ag alloys, with higher hardness being associated with the cellular morphology of the Bi-2.5 and 4.0 wt.%Ag alloys. (C) 2014 Elsevier Inc. All rights reserved. (AU)

• FAPESP's process: 13/13030-5 - Microstructure, thermal parameters, segregation and mechanical properties of lead-free Sn-based, Zn-based and Bi-based solder alloys
• Grantee: José Eduardo Spinelli
• Support Opportunities: Regular Research Grants
• 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