Coupled nucleation of dual-phase lamellar structure

Abstract

<p>Although lamellar structures widely exist in materials, the existing nucleation knowledge has failed to describe the nucleation process of lamellae. This is because it involves the simultaneous formation of two different phases whose early-stage nuclei are always anisotropic and ordered. We report here a coupled nucleation of lamellae in a eutectoid TiAl system, demonstrating the coupled formation of a pair of anisotropic and ordered ��₂ + �� lamellae from the matrix, and each pair nucleates independently and heterogeneously. The coupled pair has been identified by alternative segregation of Nb in the interface using atom probe tomography. The nucleation kinetics have been confirmed by atomistic simulations and in situ high-energy synchrotron X-ray diffraction. A theoretical model has been proposed for this heterogeneously coupled nucleation, offering potential applications in various systems or phase transitions involving anisotropic, ordered, or lamellar structures. This coupled nucleation model represents a significant enhancement to the existing nucleation theory.</p>