Wavebreakers in excitable systems and possible applications for corrosion mitigation.

Abstract

Traveling waves of excitation arise from the spatial coupling of local nonlinear events by transport processes. In corrosion systems, these electro-dissolution waves relay local perturbations across large portions of the metal surface, significantly amplifying overall damage. For the example of the magnesium alloy AZ31B exposed to sodium chloride solution, we report experimental results suggesting the existence of a vulnerable zone in the wake of corrosion waves where local perturbations can induce a unidirectional wave pulse or segment. The evolution of these segments, combined with the absence of rotating spiral waves, imply subexcitable dynamics for which the segments' open ends tangentially retract. Using a simple excitable reaction-diffusion model, we identify parameters that replicate these experimental observations. Under these conditions, small protected disks act as wavebreakers, disrupting continuous fronts, which then shrink and disappear. We further explore different placement schemes of these wavebreakers to optimize potential corrosion mitigation. For constant surface coverage, many small wavebreakers prove more effective than a few large ones. A comparison of triangular, square, rectangular, hexagonal, aperiodic Penrose, and random lattice geometries indicates that triangular placements of wavebreakers are generally the optimal choice, while rectangular and random lattices perform poorly. Although wavebreakers were not demonstrated experimentally in this study, these findings provide concrete design guidance for the protection of alloy surfaces prone to wave-mediated corrosion.