| Popis: |
Electron microscope techniques were used to investigate black and white oxide films, formed before and after the oxidation transition, on Zircaloy-2 in superheated steam at 673 and 773 K. The nodular corrosion appearing on black oxide films during oxidation transition has been also investigated. A compressive stress gradient distributed through the thickness of black oxide films was measured to be ∼500 MPa/μm in films with a thickness of 1.2 μm decreasing to ∼60 MPa/μm with an increase in film thickness to 2.1 μm when nodular corrosion appears. Monoclinic, cubic, and tetragonal lattice structures in black oxide films formed both at 673 and 773 K have been identified. The proportion of cubic and tetragonal phases decreases with the increase of temperature and turns into an exclusively monoclinic lattice structure in white oxide films after oxidation transition. The grain size in black oxide films is extremely fine ( |
