Anomalous bulk dealloying below the parting limit

Abstract

Dealloying has been extensively studied both as a corrosion degradation mechanism in structural materials, including those used in nuclear, aerospace, or marine environments, and as a versatile method to fabricate porous materials for catalysts and other functional applications. Classical dealloying theory in aqueous environments predicts a critical reactive-element concentration (parting limit) for continuous selective dissolution at temperatures where bulk diffusion does not dominate; this threshold is commonly reported around 50~60 at.%. Yet recent studies show that molten salt environments can generate extensive bulk dealloying below this threshold. Despite the importance of this anomalous dealloying behavior in many energy systems and electrochemical applications, its fundamental origin remains elusive. Here, we address this critical gap, revealing a grain boundary (GB)-assisted bulk dealloying mechanism. Using three-dimensional (3D) reconstruction of the dealloyed regions correlated with crystallographic and elemental analyses, we directly map the 3D GB-void architecture and reveal that diffusion-induced recrystallization (DIR) generates a high-density GB network, which then promotes molten-salt infiltration and can drive bulk dealloying far-below the conventionally reported parting limit, producing a distinctive morphology reminiscent of discontinuous precipitation (DP). Understanding this dynamic GB-void interplay is crucial for the prediction and control of dealloying in complex electrochemical environments.