Lamellar eutectic growth with anisotropic interphase boundaries: Experimental study using the rotating directional solidification method

Abstract

International audienceWe report on an experimental study of the effects of interphase boundary anisotropy on eutectic microstructures using a new methodology called rotating directional solidification (RDS), which consists of rotating a thin sample with respect to a fixed unidirectional thermal gradient. The systems used are thin, large eutectic grains of the CBr4-C2Cl6 and In-In2Bi lamellar eutectic alloys. The shape of the observed RDS lamellar trajectories turns out to be a reproducible eutectic-grain-dependent feature, in agreement with the theoretical prediction that these trajectories are approximately homothetic to the Wulff form of the interphase boundary in the sample plane. We show that different modes of lamellar growth, ranging from quasi-isotropic to (crystallographically) locked, exist in different eutectic grains of the two alloys studied. A detailed characterisation of these modes is given, with particular attention to the as-yet poorly understood aspects of locked lamellar growth. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved

Interphase anisotropy effects on lamellar eutectics: A numerical study

“…In a steady-state condition, the (lam ellar) tilt angle 0, is defined by tan 9, = Vd/ V . On the basis o f in situ directional solidification observations using thin sam ples o f m etallic and transparent organic eutectic alloys, a conjecture was form ulated recently that relates the value o f 6, to the anisotropy o f the free energy o f the interphase boundaries (interfacial anisotropy) [20,21]. The m ain underlying hypotheses are that (i) only the solid-solid interfaces are anisotropic (i.e., in a nonfaceted alloy, the anisotropy o f the solid-liquid interfaces has a negligible effect on the lam ellar grow th dynam ics) and (ii) the solid-liquid interface keeps virtually the same shapew ith m irror sym m etry about the m idplane o f a lam ella-as for standard (nontilted) lam ellae.…”

“…In Sec. V, we will discuss separately (i) a way to estimate the accuracy of measurements of the interphase boundary Wulff plot using experimental observations with the so-called rotating directional-solidification method [21] and (ii) possible reasons for the absence of hysteretic behavior in the high-anisotropy case in the PF simulations. Conclusions and perspectives are presented in Sec.…”

Phase-field modeling of eutectic structures on the nanoscale: the effect of anisotropy

“…As reported in Refs. [22][23][24], the tilting angle of the phase boundary may considerably differ from the actual tilting angle. This is demonstrated for different anisotropy strengths in Fig.…”

“…The initial front direction is conserved here owing to the restriction by the boundary condition. To mimic the local situation in the experiments [23], in which a circular disc was rotated so that the solidification front was in a fixed temperature gradient, here we varied the orientation of the long axis of the anisotropy relative to the direction of the long side of the simulation box. Here observed: (i) The usual critical anisotropy [s0 = 1/(2 n  1) for n-fold symmetry] that corresponds the limit for the occurrence of excluded orientations in the equilibrium shape (see e.g., [52]), yielding here 1/3.…”

“…A broad variety of the eutectic systems show interfaces with anisotropic interfaces. Recent papers [22][23][24][25][26] address the effect of anisotropy of the solid-solid and solid-liquid interfaces on the eutectic pattern; reporting e.g., the existence of locked and unlocked relative orientations in the case of supercritical anisotropy [22][23][24].…”