Effect of Cr segregation on grain growth in nanocrystalline α-Fe alloy: A multiscale modeling approach

We present a multiscale modeling framework that integrates density functional theory (DFT) with a phase-field model (PFM) to explore the intricate dynamics of grain growth in nanocrystalline $\alpha$-Fe single-phase alloy in the presence of chromium (Cr) segregation. Simulated results for equilibrium segregation in stationary grain boundary (GB) agree with the Mclean isotherm, validating our model. Polycrystal simulations featuring nanocrystalline grains at different temperatures reveal that the grain growth kinetics depends on the ratio of Cr diffusivity to intrinsic GB mobility. Without Cr segregation at GB, the relationship between the square of average grain size ($d^2$) and time ($t$) demonstrates a linear correlation. With Cr segregation at GB, the $d^2$ vs. $t$ plot initially follows the same linear growth trajectory as observed without segregation up to a threshold grain size, beyond which it deviates with a decreasing slope. The threshold grain size decreases with increasing temperature from 700K to 900K. Notably, at 1000K, grain growth without and with Cr segregation both follow a linear trajectory, the latter having a smaller slope from the beginning. We develop an analytical formulation based on Cahn’s solute drag theory to predict grain growth in the presence of solute segregation at GB and use it to validate our simulation results.