Influence of growth direction on the microstructure of unidirectionally solidified Cu-Pb monotectic alloy using zone-melt technique

Ichiro Aoi, Makoto Ishino, Makoto Yoshida, Hideharu Fukunaga, Hideo Nakae

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The influence of growth direction on the monotectic structure of the Cu-Pb alloy is studied. In order to examine the influence under a 1 g environment, both the upward (opposite to the direction of gravity) and downward (the direction of gravity) unidirectional solidifications (UDS) are carried out. In the case of the upward UDS, a banded structure, which consists of Pb-rich and Cu-rich layers, is observed. The L2 droplets pile up in front of the solid/liquid interface. On the other hand, in the downward UDS, the irregularly shaped L2 phase uniformly disperses in the specimen and no banded structure is found. The gravity macrosegregation of the L2 liquid is observed at the bottom of the molten alloy in the downward solidified specimen. This is caused by the difference in the density between the L1 and L2 phases. Furthermore, a mechanism for the formation of a banded structure is suggested. This mechanism suggests that the coalesced L2 phase covers the solid/liquid interface by producing a Pb-rich layer that permits an increase in the undercooling of the L1/L2 interface compared to the monotectic temperature. As nucleation of the α-Cu phase occurs on the Pb-rich layer, the coexisting three phases are then restored. The temperature at the growth front is also returned to the monotectic temperature. The repetition mentioned above will result in the banded structure found in the upward UDS.

Original languageEnglish
Pages (from-to)806-815
Number of pages10
JournalJournal of Crystal Growth
Issue number4
Publication statusPublished - 2001 Feb


ASJC Scopus subject areas

  • Condensed Matter Physics
  • Inorganic Chemistry
  • Materials Chemistry

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