Role of chemical disorder in slowing down diffusion in complex concentrated alloys

The advent of multiprincipal element alloys (MPEAs) has sparked significant interest in physical metallurgy. These alloys, distinguished by their high configurational entropy aimed at minimizing free energy, have raised intriguing questions regarding the interplay of chemical disorder and chemical short-range order (CSRO) in kinetics of MPEAs. Particularly, the widely assumed phenomenon of sluggish diffusion has come under scrutiny. Here we employ atomistic simulations to quantitatively evaluate the impact of CSRO on diffusion in a representative medium-entropy alloy. We introduce a physical order parameter to establish a quantitative correlation between CSRO and diffusivity. Surprisingly, our simulations suggest that CSRO, rather than chemical disorder, serves to suppress and localize defect diffusion. The observed link between diffusion activation energy and CSRO provides a rationale for the observed deceleration in diffusion due to chemical ordering. A linear relationship between diffusion activation energy and activation entropy is unveiled, aligning with the Meyer-Neldel rule, and replicating experimental results. These insights help clarify the intricate role of chemical disorder in plastic deformation of chemically disordered materials. © 2024 American Physical Society.