  Ultrathin passive films effectively prevent the chemical attack of stainless
steel grades in corrosive environments; their stability critically depends on
the interplay between structure and chemistry of the constituents Fe-Cr-Mo. In
particular, nanoscale inhomogeneities along the surface can have a tremendous
impact on material failure, but are yet barely understood. Addressing a
stainless-type glass-forming Fe50Cr15Mo14C15B6 alloy and utilizing a
combination of complementary high-resolution analytical techniques, we relate
near-atomistic insight into different gradual nanostructures with time- and
element-resolved dissolution behavior. The progressive elemental segregation on
the nanoscale is followed in its influence on the concomitant degree of
passivity. A detrimental transition from Cr-controlled passivity to
Mo-controlled breakdown is dissected atom-by-atom demonstrating the importance
of nanoscale knowledge for understanding corrosion.
