  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.
