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Solute segregation can profoundly affect the thermodynamic stability and cohesive properties of the grain boundaries (GBs) in Fe-based alloys. In the present work, first-principles calculations based on density functional theory (DFT) are performed to understand the atomistic mechanisms of the solute-GB interactions under the dilute limit condition. The segregation effects of six transition metal elements (Cr, Ni, Cu, Zr, Ta, and W) on the Σ3 111 [1 1-0] tilt boundary in BCC Fe are systematically studied by examining GB energy, solute segregation energy, and GB cohesion. The solute segregation energy is verified to be composed of a combination of the strain and electronic contributions rather than either of them alone, even for the solute elements with large atomic volume. The potential effects of the FCC/BCC polymorphic phase transformations on the solute segregation behaviors are also discussed. The dynamic …