TY - JOUR
T1 - The Role of Lengthscale in the Creep of Sn-3Ag-0.5Cu Solder Microstructures
AU - Gu, Tianhong
AU - Gourlay, Christopher M.
AU - Britton, T. Ben
N1 - Funding Information:
TBB would like to thank the Royal Academy of Engineering for his research fellowship. We would like to thank EPSRC (EP/R018863/1) for funding. We would like to acknowledge Dr Sergey Belyakov for support in the initial fabrication of the samples. The assistance of Dr Te-Cheng Su in DIC studies is also gratefully acknowledged. The microscope and loading frame used to conduct these experiments was supported through funding from Shell Global Solutions and is provided as part of the Harvey Flower EM suite at Imperial.
Publisher Copyright:
© 2021, The Author(s).
PY - 2021/3
Y1 - 2021/3
N2 - Creep of directionally solidified Sn-3Ag-0.5Cu wt.% (SAC305) samples with near-<110> orientation along the loading direction and different microstructural lengthscale is investigated under constant load tensile testing and at a range of temperatures. The creep performance improves by refining the microstructure, i.e. the decrease in secondary dendrite arm spacing (λ2), eutectic intermetallic spacing (λe) and intermetallic compound (IMC) size, indicating a longer creep lifetime, lower creep strain rate, change in activation energy (Q) and increase in ductility and homogeneity in macro- and micro-structural deformation of the samples. The dominating creep mechanism is obstacle-controlled dislocation creep at room temperature and transits to lattice-associated vacancy diffusion creep at elevated temperature (TTM > 0.7 to 0.75). The deformation mechanisms are investigated using electron backscatter diffraction and strain heterogeneity is identified between β-Sn in dendrites and β-Sn in eutectic regions containing Ag3Sn and Cu6Sn5 particles. The size of the recrystallised grains is modulated by the dendritic and eutectic spacings; however, the recrystalised grains in the eutectic regions for coarse-scaled samples (largest λ2 and λe) is only localised next to IMCs without growth in size.
AB - Creep of directionally solidified Sn-3Ag-0.5Cu wt.% (SAC305) samples with near-<110> orientation along the loading direction and different microstructural lengthscale is investigated under constant load tensile testing and at a range of temperatures. The creep performance improves by refining the microstructure, i.e. the decrease in secondary dendrite arm spacing (λ2), eutectic intermetallic spacing (λe) and intermetallic compound (IMC) size, indicating a longer creep lifetime, lower creep strain rate, change in activation energy (Q) and increase in ductility and homogeneity in macro- and micro-structural deformation of the samples. The dominating creep mechanism is obstacle-controlled dislocation creep at room temperature and transits to lattice-associated vacancy diffusion creep at elevated temperature (TTM > 0.7 to 0.75). The deformation mechanisms are investigated using electron backscatter diffraction and strain heterogeneity is identified between β-Sn in dendrites and β-Sn in eutectic regions containing Ag3Sn and Cu6Sn5 particles. The size of the recrystallised grains is modulated by the dendritic and eutectic spacings; however, the recrystalised grains in the eutectic regions for coarse-scaled samples (largest λ2 and λe) is only localised next to IMCs without growth in size.
KW - digital image correlation
KW - microstructural evolution
KW - Pb-free solder
KW - polygonisation
KW - recrystallisation
UR - http://www.scopus.com/inward/record.url?scp=85100056260&partnerID=8YFLogxK
U2 - 10.1007/s11664-020-08697-4
DO - 10.1007/s11664-020-08697-4
M3 - Article
AN - SCOPUS:85100056260
SN - 0361-5235
VL - 50
SP - 926
EP - 938
JO - Journal of Electronic Materials
JF - Journal of Electronic Materials
IS - 3
ER -