Segregation-assisted spinodal and transient spinodal phase separation at grain boundaries

Reza Darvishi Kamachali,Dirk Ponge,Dierk Raabe,Alisson Kwiatkowski Da Silva,Eunan Mceniry,Baptiste Gault,Jörg Neugebauer

doi:10.1038/s41524-020-00456-7

Abstract

Segregation to grain boundaries affects their cohesion, corrosion, and embrittlement and plays a critical role in heterogeneous nucleation. In order to quantitatively study segregation and low-dimensional phase separation at grain boundaries, here, we apply a density-based phase-field model. The current model describes the grain-boundary thermodynamic properties based on available bulk thermodynamic data, while the grain-boundary-density profile is obtained using atomistic simulations. To benchmark the performance of the model, Mn grain-boundary segregation in the Fe–Mn system is studied. 3D simulation results are compared against atom probe tomography measurements conducted for three alloy compositions. We show that a continuous increase in the alloy composition results in a discontinuous jump in the segregation isotherm. The jump corresponds to a spinodal phase separation at grain boundary. For alloy compositions above the jump, we reveal an interfacial transient spinodal phase separation. The transient spinodal phenomenon opens opportunities for knowledge-based microstructure design through the chemical manipulation of grain boundaries. The proposed density-based model provides a powerful tool to study thermodynamics and kinetics of segregation and phase changes at grain boundaries.

Highlights

Grain boundaries (GBs) influence functional and structural properties of polycrystalline materials in different ways
The vast structural variability and high amenability of GBs to chemical changes renders them ideal objects for tuning their properties by solute segregation[3,4,5,6,7]
In a GB, atoms are forced to accommodate for the incompatible lattices of the two adjacent grains

Summary

INTRODUCTION

Grain boundaries (GBs) influence functional and structural properties of polycrystalline materials in different ways. In parallel to the conventional thermodynamic models, phasefield models have been developed to study GB-related phenomena which concentrate on the effect of non-local gradient energy terms within the GB region. Hu and Chen[55] developed a phase-field model for studying solute segregation and phase transition at dislocations. We use a density-based phase-field model within a GB plane fluctuates. This is, neglected in the to study interfacial segregation and phase separation. In this current treatment, assuming an average constant GB density value picture, the structurally defected GB region is represented by a ρGB corresponding to the GB type. Detailed derivation of the density-based theory can be found in ref

RESULTS

METHODS

Experiments and APT analysis

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