Directional solidification experiments on Cu-Sn peritectic alloys have been conducted at very low velocity in a high-thermal-gradient Bridgman furnace. The size of the samples has been reduced in order to decrease natural convection and the associated macrosegregation. At the lowest growth rates (0.5 and 0.58 lm s À1 ), eutectic-like a + b lamellar structures have been observed in near-peritectic composition alloys over several millimeters of growth. These structures resulted from a destabilization of a band structure in which a-and b-phases overlay each other. Electron backscattered diffraction measurements revealed that bands and lamellae of a solid phase are continuous and originate from a single nucleus.

Single pan thermal analyses (SPTA) have been performed on Cu-14.5 wt.% Sn, Cu-21.3 wt.% Sn and Cu-26.8 wt.% Sn peritectic alloys. For this purpose, a SPTA assembly has been built and calibrated. As the latent heat is a function of temperature and composition during solidification of alloys, a new heat flow model coupled to a Cu-Sn thermodynamic database has been defined for the calculation of the corresponding evolutions of the solid mass fraction, f s ðT Þ. To verify the accuracy of this model, a close comparison with a microsegregation model that includes back-diffusion in the primary a-solid phase has also been conducted successfully. The thermal analyses have finally shown that the Cu-Sn phase diagram recently assessed in the review of Liu et al. is the most reliable.

Abstract-The anisotropy of the solid-liquid interfacial energy plays a key role during the formation of as-solidified microstructures. Using the n-vector formalism of Cahn and Hoffman, this contribution presents the effect that anisotropy has on the equilibrium shapes of crystals and on surface tension equilibrium at triple lines. Consequences for heterogeneous nucleation of anisotropic crystals and for dendritic growth morphologies are detailed with specific examples related to Al-Zn and Zn-Al alloys.

SummaryThis paper presents a few examples of the application of electron back-scatter diffraction (EBSD) to solidification problems. For directionally solidified Al-Zn samples, this technique could reveal the change in dendrite growth directions from <100> to <110> as the composition of zinc increases from 5 to 90 wt%. The corresponding texture evolution and grain selection mechanisms were also examined. Twinned dendrites that form under certain solidification conditions in Al-X specimens (with X = Zn, Mg, Ni, Cu) were clearly identified as <110> dendrite trunks split in their centre by a (111) twin plane. In Zn-0.2 wt% Al hot-dip galvanized coatings on steel sheets, EBSD clearly revealed the preferential basal orientation distribution of the nuclei as well as the reinforcement of this distribution by the faster growth of <1010> dendrites. Moreover, in Al-Zn-Si coatings, misorientations as large as 10 • mm −1 have been measured within individual grains. Finally, the complex band and lamellae microstructures that form in the Cu-Sn peritectic system at low growth rate could be shown to constitute a continuous network initiated from a single nucleus. EBSD also showed that the α and β phases had a Kurdjumov-Sachs crystallographic relationship.

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