High-temperature oxidation and hydrothermal corrosion of textured Cr2AlC-based coatings on zirconium alloy fuel cladding

Y Alumina-forming MAX phase coatings reveal great potential for accident tolerant fuel (ATF) cladding applications due to their favorable physical and mechanical properties and excellent high-temperature oxidation resistance. The feasibility of Cr2AlC MAX phase as protective coating on zirconium-alloy fuel claddings was explored focusing on high-temperature oxidation resistance in steam and hydrothermal corrosion performance in autoclave. Single-phase and basal-plane textured Cr2AlC coatings (similar to 6 mu m thick) were synthesized on Zircaloy-4 substrate by thermal annealing of specifically designed, magnetron-sputtered Cr/C/Al elemental multilayers at 550 degrees C for 10 min. Additionally, a second Cr/Cr2AlC bilayer coating design was fabricated aiming to eliminate potential rapid hydrothermal dissolution of Al during normal operating conditions. Micro-cracking appeared on both annealed coatings owing to thermal expansion differences between coating layer and substrate. Growth of an adherent and dense alpha-Al2O3 scale during high-temperature oxidation in steam and of a thin passivating Cr2O3 layer during hydrothermal corrosion in an autoclave imply excellent combined oxidation and corrosion resistance of the textured Cr2AlC coatings on Zircaloy-4. A self-healing capability via growth of alumina filling the micro-crack (annealing-induced) gaps was observed during high-temperature oxidation. However, partial delamination was seen for both coatings after short autoclave exposure and their mechanical properties (fracture toughness and adhesion strength) need further enhancement. Overall, tailored Cr2AlC-based (multilayered) coatings can be attractive candidates as potential type of coated ATF claddings.

Automated summary

The research shows that tailored Cr2AlC MAX phase coatings exhibit excellent oxidation and corrosion resistance in high-temperature oxidation and hydrothermal corrosion environments, making them promising candidates for coated accident tolerant fuel claddings. The coatings demonstrate a self-healing capability during high-temperature oxidation, but further enhancement of their mechanical properties is needed to address partial delamination observed during short autoclave exposure.