High Temperature Steam Oxidation Behavior of Cr-coated Zr Fabricated by Filtered Cathodic Vacuum Arc Ion Deposition

Abstract:

A Cr coating of about 4 μm thick was successfully prepared on pure zirconium by filtered cathodic vacuum arc ion deposition technology (FCVAD), and the high-temperature oxidation properties of bare and Cr-coated Zr were measured using a thermogravimetric analyzer (TGA) in steam environment at different temperatures. Their phase composition, microstructure and composition distributions before and after the steam oxidation tests were characterized by X-ray diffraction analyzer (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS). It was found that the mass gain per unit area of Cr-coated Zr was only 1/4, 1/6 and 4/9 of that of bare Zr after 3600 s exposure in 900, 1000 and 1100℃ steam environment, respectively. In the initial stage of steam oxidation, a compact and uniform Cr₂O₃layer was formed on the surface of Cr layer, significantly reducing oxygen or steam diffusion inwards. After Cr coating was completely oxidized into Cr₂O₃, Zr substrate was gradually oxidized, but the Cr₂O₃ at Cr₂O₃/Zr interface was reduced to form Cr. In addition, the oxidation activation energy of the Cr-coated Zr was up to 293.17 kJ/mol.

Key words:Pure zirconium; Filtered cathodic vacuum arc ion deposition; Cr coating; High-temperature steam oxidation; Oxidation kinetics