In situ investigation of unidirectional solidification in Sn–0.7Cu and Sn–0.7Cu–0.06Ni

The dynamics of off-eutectic solidification are studied in two Pb-free solders using synchrotron X-ray radiography and post mortem scanning electron microscopy. The early stages of growth revealed the onset of coupled growth and phase competition. In Sn–0.7 wt.% Cu, the βSn–Cu 6Sn 5 eutectic then gr...

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Bibliographic Details
Published in:Acta materialia 2011-06, Vol.59 (10), p.4043-4054
Main Authors: Gourlay, C.M., Nogita, K., Dahle, A.K., Yamamoto, Y., Uesugi, K., Nagira, T., Yoshiya, M., Yasuda, H.
Format: Article
Language:English
Subjects:
Copper
Curvature
Eutectic composition
Eutectic solidification
Eutectics
Intermetallic compounds
Invariants
Soldering
Solders
Solidification
Synchrotron radiation
Tin
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Summary:The dynamics of off-eutectic solidification are studied in two Pb-free solders using synchrotron X-ray radiography and post mortem scanning electron microscopy. The early stages of growth revealed the onset of coupled growth and phase competition. In Sn–0.7 wt.% Cu, the βSn–Cu 6Sn 5 eutectic then grew with Cu 6Sn 5 rods leading the βSn phase, with a range of rod spacings and local interface curvatures. However, these nonfaceted–faceted eutectic features were exhibited much more weakly than in the Al–Si and Fe–C eutectics, despite primary Cu 6Sn 5 crystals exhibiting marked faceting. In Sn–0.7 wt.% Cu–0.06 wt.% Ni, primary intermetallic laths grew ahead of a rod-like βSn–(Cu,Ni) 6Sn 5 univariant eutectic front. The univariant eutectic had a narrow freezing range and a similar spacing to the invariant eutectic at the same velocity. Composition measurements suggest that the univariant eutectic groove descends in the direction of the Sn + Cu 6Sn 5 binary eutectic point.
ISSN:1359-6454
1873-2453
DOI:10.1016/j.actamat.2011.03.028