Effects of Solidification Thermal Parameters on Microstructure and Mechanical Properties of Sn-Bi Solder Alloys
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- 作者：Bismarck Luiz Silva ; Vítor Covre Evangelista da Silva…
- 关键词：Sn ; Bi alloys ; solidification ; microstructure ; Bi precipitates ; tensile strength ; fracture surface
- 刊名：Journal of Electronic Materials
- 出版年：2017
- 出版时间：March 2017
- 年：2017
- 卷：46
- 期：3
- 页码：1754-1769
- 全文大小：
- 刊物类别：Chemistry and Materials Science
- 刊物主题：Optical and Electronic Materials; Characterization and Evaluation of Materials; Electronics and Microelectronics, Instrumentation; Solid State Physics;
- 出版者：Springer US
- ISSN：1543-186X
- 卷排序：46
文摘
Samples extracted along the length of directionally solidified (DS) castings of three Sn-xBi alloys (x = 34 wt.%Bi, 52 wt.%Bi and 58 wt.%Bi) were first evaluated metallographically and then subjected to scanning electron microscopy and energy-dispersive x-ray spectroscopy analyses. The characteristic length scale of both eutectic and dendritic phases forming the microstructure were determined and correlated with solidification thermal parameters (growth rate V, and cooling rate Ṫ). Tensile and Vickers hardness tests were performed to allow strength and ductility to be discussed as a function of both microstructure features and alloy solute content. The tertiary dendrite arm spacings along the length of the DS Sn-52 wt.%Bi alloy casting are shown to be lower than those obtained for the Sn-34 wt.%Bi alloy casting. The results of mechanical tests show that, with the decrease in the alloy Bi content, both tensile strength and hardness are improved. This is shown to be mainly attributed to the higher density of Bi precipitates decorating the Sn-rich dendrites, which are finer than the equivalent phase developed for the Sn-52 wt.%Bi alloy. However, the ductility is shown to be significantly improved for specimens associated with regions of more refined microstructure of the Sn-52 wt.%Bi alloy DS casting. A microstructure combining much branched dendrites, fine Bi particles within the β-Sn dendritic matrix and an important proportion of very fine eutectic formed by alternate Bi-rich and Sn-rich phase, seems to be conducive to this higher ductility. In this case, the fracture surface is shown to be more finely broken with presence of dimples for this particular condition, i.e., characteristic of a ductile fracture mode.