Dislocation dynamics investigation of the effects of composition inhomogeneity on yielding and dislocation density evolution in FeCrAl alloy

Abstract Composition inhomogeneities arise in multicomponent alloys during processing, e.g., spinodal alloys, during rapid solidification, e.g., in additive manufactured alloys, and/or when the alloys are subjected to extreme conditions, such as irradiation. These inhomogeneities have a strong impact on the mechanical response and strength of the alloys. In this paper, a framework for studying single crystal plasticity in inhomogeneous alloys using discrete dislocation dynamics (DDD) is presented. Virtual realizations of a single Fourier mode sinusoidal and stochastic composition fields are generated for testing the impact of composition inhomogeneity within a three-dimensional DDD framework. The composition fields are also utilized to determine internal coherency stress arising due to lattice parameter dependence on composition by solving an eigenstrain boundary value problem (BVP). Composition-aware dislocation velocities, determined from molecular dynamics (MD) simulations are utilized to model the composition dependent local lattice mobility of dislocations. The composition reconstruction scheme, internal coherency stress, and the composition-dependent dislocation velocities are coupled to DDD, and the effects of the composition fluctuations are studied on the stress-strain response and evolution of the dislocation densities in a model BCC FeCrAl alloy. The effects of the composition fluctuations on crystal plasticity are studied from the perspective of single dislocation and their collective dynamics. The influence of the inhomogeneous composition fields on the collective dynamics of dislocations is revealed through the statistics of cross-slip and the driving forces on the dislocations coming from the stress associated with composition fields, applied load, and dislocation-dislocation interactions.