Self-assembly of metal-ceramic nanocomposites within Cr-based coatings exhibiting superior oxidation resistance in high-temperature atmosphere

The deposition of coatings is considered the most promising solution to improve the high-temperature oxidation resistance of the commercially used Zircaloy nuclear fuel cladding. However, in high-temperature conditions, although metallic coatings possess good adhesion to the cladding, their oxidation resistance is poor. On the contrary, ceramic coatings exhibit better oxidation resistance but lower structural stability. To effectively address these issues, in this work, a carbon-doped metallic multi-layered Cr/CrAl coating was designed to operate stably during routine working conditions. Unexpectedly, the developed coating can be self-assembled into metal-ceramic nanocomposite structures at elevated temperatures like a loss-of-coolant accident (LOCA). The self-assembled Cr₂AlC MAX phase and the Cr_xC ceramic nanoparticles within the transformed Cr₂Al coating lead to superior oxidation and corrosion resistance in high temperatures. An oxidized weight gain at 1200 °C steam oxidation experiments is only 18.5 % of that of the bare Zircaloy. Moreover, the coating displayed excellent density and good adhesion strength without any cracking effect near the interface between the coating and the substrate. In-depth first-principles calculations demonstrate that the superb oxidation resistance of the coating originated from the prevention of Al diffusion by the Cr₂Al intermetallic compounds and the Cr_xC ceramic nanoparticles. Our work provides valuable insights and paves the way for developing novel self-assembling coatings with excellent oxidation resistance required for accident-tolerant fuel cladding.