Tuning chemical short-range order for stainless behavior at reduced chromium concentrations in multi-principal element alloys

TL;DR

This study demonstrates that tuning the chemical short-range order in multi-principal element alloys by adding small amounts of aluminum can significantly enhance their corrosion resistance, approaching that of traditional stainless steel.

Contribution

It introduces a novel approach to improve alloy passivation by controlling CSRO, enabling reduced chromium content while maintaining stainless behavior.

Findings

Adding 0.03-0.06 mole fraction of Al alters Cr-Cr CSRO.

Modified CSRO leads to passivation similar to 304L stainless steel.

Electrochemical and structural analyses support the CSRO-based passivation mechanism.

Abstract

Single-phase multi-principal element alloys (MPEAs) hold promise for improved mechanical properties as a result of multiple operative deformation modes. However, the use of many of these alloys in structural applications is limited as a consequence of their poor aqueous corrosion resistance. Here we introduce a new approach for significantly improving the passivation behavior of alloys by tuning the chemical short-range order (CSRO) parameter. We show that the addition of only 0.03 to 0.06 mole fraction of Al to a (FeCoNi)0.9Cr0.1 alloy changed both the magnitude and sign of the Cr-Cr CSRO parameter resulting in passivation behavior similar to 304L stainless steel containing twice the amount of Cr. Our analysis is based on comparing electrochemical measures of the kinetics of passive film formation with CSRO characterizations using time-of-flight neutron scattering, cluster expansion methods, density functional theory and Monte Carlo techniques. Our findings are interpreted within the framework of a recently proposed percolation theory of passivation that examines how selective dissolution of the non-passivating alloy components and CSRO results in excellent passive films at reduced levels of the passivating component.