Mixing enthalpy near grain boundaries in Fe-Cr alloy: The results of atomistic simulation

Energy characteristics of symmetric tilt (twin) grain boundaries (GBs) Σ5(210) and Σ5(310) with the tilt axis [001] and boundaries Σ3(111) and Σ3(112) with the tilt axis [11¯0] in a bcc random binary FeCr alloy have been studied using atomistic simulation. The simulation has been carried out based on DFT calculations and two-band semi-empirical potential. We have proposed the formula for calculating the mixing enthalpy near GBs. The relationship between the mixing enthalpy and the energy of the boundary in the alloy has been revealed. Both simulation methods have shown a decrease in the mixing enthalpy near a GB compared to the ideal crystal. Moreover, DFT has predicted a stronger decrease in the mixing enthalpy compared to estimates based on semi-empirical interaction. Based on the obtained dependences of the mixing enthalpy on the alloy composition, phase diagrams for the considered GB regions have been constructed. It has been shown that the GB region is characterized by a higher equilibrium concentration of chromium, and the precipitates of the α'-phase have a lower concentration of chromium compared to the bulk. The smallest difference in equilibrium compositions has been observed for the Σ5(310) and Σ3(112) boundaries, and the largest one for the Σ3(111) boundary, which has the highest energy among considered GBs.