Connectivity of Phases and Growth Mechanisms in Peritectic Alloys Solidified at Low Speed: an X-Ray Tomography Study of Cu-Sn

Abstract

The variety of microstructures that form at low solidi cation speed in peritectic alloys, -bands, islands or even coupled (or cooperative) growth of the primary alpha- and peritectic beta-phases-, have been previously explained by nucleation-growth mechanisms. In a recent investigation on Cu-Sn, a new growth mechanism was conjectured on the basis of 2-dimensional optical microscopy and Electron Back-Scattered Diffraction (EBSD) observations made in longitudinal sections. In the present contribution, X-ray tomography has been used to confi rm this mechanism: alpha- and beta-phases can be totally inter-connected in 3 dimensions and bands (or islands) can result from an overlay mechanism, rather than from a nucleation events sequence. When the lateral growth of a new layer is too fast, an instability can lead to the formation of a lamellar structure as for eutectic alloys.