Line-length-dependent dislocation mobilities in an FCC stainless steel alloy

Using molecular dynamics simulations, we compute the mobility of an edge dislocation in a random FCC Fe0.70Ni0.11Cr0.19 alloy over temperatures from 100 to 900 K and shear stresses up to 600 MPa. Dislocation mobilities are shown to be intrinsically length-dependent when the line length is below a minimum value, with shorter lines having a reduced mobility. We show that this minimum line length is sensitive to both temperature and stress. We develop a drag model with terms accounting for solute, phonon, and singular drag mechanisms, and fit the model to MD data in the length-independent regime. Using the drag parameters from this fit, we implement a kinetic Monte Carlo (kMC) model for dislocation motion in the solute-drag-dominated regime. The kMC model is then used to explain the length dependence of the mobility and further characterize the statistical solute environment experienced by the dislocation. Our methods and findings are readily extensible to other crystal structures (e.g., HCP, BCC).