Effects of chemical short-range order on the percolation model of passivation for binary alloys

Metallic alloys exhibit corrosion resistance due to the formation of a passive oxide film. To better understand passive film formation, we investigate the effects of chemical short-range order (SRO) on the aqueous passivation of face-centered cubic (FCC) binary alloys to account for chemical ordering/clustering in nominally random solid solutions. We analyze the effects of SRO on the percolation threshold, distribution of the total number of distinct clusters in the percolated structures, and the 2D–3D percolation crossover in binary alloy thin films. We find that these parameters are a function of SRO. We combine these results to develop a percolation crossover model with SRO to understand the electrochemical passivation behavior in binary alloys. Finally, we develop SRO maps over a range of compositions and temperatures from Monte Carlo simulations using a cluster expansion model trained on the mixing energy of Cu-Rh FCC alloy calculated using Density Functional Theory (DFT). When coupled with the percolation crossover model, such SRO maps demarcating regions of positive and negative Warren-Cowley SRO parameters can directly inform about the passive film formation behavior of binary alloys.