Atomic structure of the crystalline/amorphous interface in a directionally crystallized Pd80Si20 alloy

An amorphous ribbon of Pd₈₀Si₂₀ alloy was directionally crystallized under an imposed temperature gradient of 25 K/mm with a growth velocity of 0.0785 mm/s, and the structure of the crystalline/amorphous interface was investigated by conventional and high-resolution transmission electron microscopy (TEM). Under these conditions, the amorphous Pd₈₀Si₂₀ crystallizes into a broken-lamellar eutectic of the Pd₃Si and Pd₉Si₂ equilibrium phases. The Pd₃Si phase is faceted and grows along the 010] direction by nucleation and propagation of unit-cell ledges parallel to the (010) terrace plane. The Pd₉Si₂ phase is largely coherent with Pd₃Si and grows along a high-index crystallographic direction. Microscopic facets were not observed on the Pd₉Si₂ phase either by conventional or high-resolution TEM, indicating that its crystalline/ amorphous interface is comparatively rough. These observations are related to the crystallography and interphase boundary (IPB) energies of the phases and discussed in terms of mechanisms of lamellar growth. Formerly Graduate Research Assistant, Department of Metallurgical Engineering and Materials Science, Carnegie Mellon University. This paper is based on a presentation made in the symposium “The Role of Ledges in Phase Transformations” presented as part of the 1989 Fall Meeting of TMS-MSD, October 1–5, 1989, in Indianapolis, IN, under the auspices of the Phase Transformations Committee of the Materials Science Division, ASM INTERNATIONAL.