A novel mechanism for nodular corrosion of Zircaloy-4 corroded in 773 K superheated steam

Abstract Corrosion resistance of Zircaloy-4 plate specimens in 773 K/10.3 MPa superheated steam is anisotropic. The rolling surface (S N ) mainly suffers uniform corrosion, while the surface perpendicular to transversal direction (S T ) and the surface perpendicular to rolling direction (S R ) mainly suffer nodular corrosion. A novel mechanism of nodular corrosion related to Sn segregation at the interface between oxide and matrix (O/M) is proposed. The anisotropic nodular corrosion results from the anisotropy of Sn segregation at the O/M interfaces formed on S N , S R and S T surfaces with different grain orientations. Finally, some reported results about nodular corrosion in zirconium alloys are discussed.