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Materials 2012, 5(11), 2151-2175; doi:10.3390/ma5112151

Creep Behavior of a Sn-Ag-Bi Pb-Free Solder

* ,
Sandia National Laboratories, PO Box 5800, Albuquerque, NM 87185, USA
* Author to whom correspondence should be addressed.
Received: 28 July 2012 / Revised: 27 September 2012 / Accepted: 18 October 2012 / Published: 2 November 2012
(This article belongs to the Special Issue Creep and Fracture of Engineering Materials and Structures)
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Compression creep tests were performed on the ternary 91.84Sn-3.33Ag-4.83Bi (wt.%, abbreviated Sn-Ag-Bi) Pb-free alloy. The test temperatures were: −25 °C, 25 °C, 75 °C, 125 °C, and 160 °C (± 0.5 °C). Four loads were used at the two lowest temperatures and five at the higher temperatures. The specimens were tested in the as-fabricated condition or after having been subjected to one of two air aging conditions: 24 hours at either 125 °C or 150 °C. The strain-time curves exhibited frequent occurrences of negative creep and small-scale fluctuations, particularly at the slower strain rates, that were indicative of dynamic recrystallization (DRX) activity. The source of tertiary creep behavior at faster strain rates was likely to also be DRX rather than a damage accumulation mechanism. Overall, the strain-time curves did not display a consistent trend that could be directly attributed to the aging condition. The sinh law equation satisfactorily represented the minimum strain rate as a function of stress and temperature so as to investigate the deformation rate kinetics: dε/dtmin = Asinhn (ασ) exp (−ΔH/RT). The values of α, n, and  ΔH were in the following ranges (±95% confidence interval): α, 0.010–0.015 (±0.005 1/MPa); n, 2.2–3.1 (±0.5); and ΔH, 54–66 (±8 kJ/mol). The rate kinetics analysis indicated that short-circuit diffusion was a contributing mechanism to dislocation motion during creep. The rate kinetics analysis also determined that a minimum creep rate trend could not be developed between the as-fabricated versus aged conditions. This study showed that the elevated temperature aging treatments introduced multiple changes to the Sn-Ag-Bi microstructure that did not result in a simple loss (“softening”) of its mechanical strength.
Keywords: tin-silver-bismuth (Sn-Ag-Bi) solder; creep deformation; aging tin-silver-bismuth (Sn-Ag-Bi) solder; creep deformation; aging
This is an open access article distributed under the Creative Commons Attribution License (CC BY) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Vianco, P.; Rejent, J.; Grazier, M.; Kilgo, A. Creep Behavior of a Sn-Ag-Bi Pb-Free Solder. Materials 2012, 5, 2151-2175.

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