Grain boundary structural variations amplify segregation transition and stabilize co-existing spinodal interfacial phases

Grain boundaries (GBs)'s role in determining the functional and mechanical properties of polycrystalline materials is inscribed in both their structure and chemistry. Upon solute segregation, the structure and composition of a GB can change concurrently. We study the co-evolution of GB's structure and segregation by enhancing the density-based phase-field model to account for the in-plane structural variations in the GB. Significant mutual coupling is revealed between the GB's chemical and structural states during Mn segregation in Fe-Mn alloys. We found that the structural degrees of freedom in a GB (the ability of the GB structure to respond to the chemical variation) amplifies Mn segregation transition, even when the GB structure stays unchanged. When the GB structure is not uniform, that is the usual case, the coupling between GB structure and segregation evolution also enables the spinodally formed low- and high-Mn phases (upon segregation transition) to co-exist within the GB region. These findings explain the stabilizing mechanism of pronounced interfacial segregation fluctuations, experimentally evidenced in Fe-Mn GBs, and give new insights on the structural sensitivity of GBs' segregation phenomena and the mutual chemo-structural interplay. (c) 2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

The role of grain boundaries (GBs) in determining the properties of polycrystalline materials is influenced by their structure and chemistry. In this study, we investigate the co-evolution of GB structure and segregation in Fe-Mn alloys. We find that the coupling between the chemical and structural states of GBs amplifies Mn segregation transition, even when the GB structure remains unchanged. When the GB structure is non-uniform, low- and high-Mn phases can coexist within the GB region. These findings provide insights into the structural sensitivity of GB segregation and the chemo-structural interplay.