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Abstract

Using density functional theory (DFT), we studied the C segregation behavior to three low-Σ symmetrical tilt grain boundaries (STGBs) in bcc-Fe. For each GB, we examined potential segregation sites and demonstrated that the most stable segregation sites always possess the greatest coordination number and maximum nearest Fe-C neighbor distance. Thereby a geometric criterion for predicting the segregation sites for more general GBs is suggested. We rationalized the geometric criterion by splitting the solution energy into chemical and mechanical contribution. The chemical contribution is shown to be related to the coordination number, whereas the mechanical contribution is related to the Fe-C bond length. The effect of C on the GB energies depends on the GB structure. The open GBs are stabilized by C segregation and the GB energy continuously decreases by increasing the C concentration while the compact GB shows an opposite trend.