Designing Corrosion-Resistant CoCrNi Medium Entropy Alloys via Short-Range Order Modification

TL;DR

This study demonstrates that modifying short-range order in CoCrNi medium entropy alloys enhances corrosion resistance by improving passive film formation, with implications for designing durable materials in harsh aqueous environments.

Contribution

It reveals the direct link between chemical short-range order and corrosion resistance, introducing a method to tailor alloy properties through CSRO manipulation.

Findings

Aging increases Cr-Cr short-range order in the alloy.

Enhanced passive film formation improves corrosion protection.

Aged alloy shows superior performance in acidic NaCl solution.

Abstract

Equiatomic CoCrNi medium entropy alloys are known for their unique properties linked to chemical short-range order (CSRO), crucial in both percolation processes and/or nucleation and growth processes influencing alloy passivation in aqueous environments. This study combines extended x-ray absorption fine structure, atomistic simulations, electrochemical methods, x-ray photoelectron spectroscopy, and transmission electron microscopy to explore CSRO evolution, passive film formation, as well as its characteristics in the as-homogenized CoCrNi condition, both before and after aging treatment. Results reveal a shift in local alloying element bonding environments post-aging, with simulations indicating increased Cr-Cr CSRO in 2nd nearest neighbor shells. Enhanced passive film formation kinetics and superior protection of the aged alloy in harsh acidified 3 mol/L NaCl solution indicate improved aqueous passivation correlated with Cr-Cr CSRO. This work establishes a direct connection between alloy CSRO and aqueous passivation in CoCrNi, highlighting its potential for tailored corrosion-resistant applications.