Fabrication of Cr2AlC Coatings at Zircaloy-4 at KIT

Cr₂AlC, one of the alumina-forming MAX phases, was synthesized and examined as potential protective coating on Zircaloy-4 substrates to against high-temperature oxidation. The Cr₂AlC coatings are synthesized by magnetron sputtering using elemental nanoscale multilayer stacks, and subsequent ex-situ thermal annealing in argon. Formation of a single Cr₂AlC MAX phase after annealing at 550°C was confirmed. The coatings have a 1.5 μm thick Cr overlayer. The Cr overlayer aims to eliminate potential fast hydrothermal dissolution of Al during normal operation. The total thickness of the coatings is around 6.5 μm with a 500 nm thick Cr interlayer as bonding layer and diffusion barrier. The high-temperature oxidation tests evidence high adherence, excellent oxidation resistance up to at least 1200°C and autonomous self-healing capability via the growth of a protective a protective Al₂O₃ scale beneath Cr₂O₃. Thus, Cr₂AlC-based coatings on Zr alloys have promising application prospects as one type of ATF claddings for improved accident tolerance. (author)