Zr₂Al₃C₄ Coatings on Zirconium-alloy Substrates with Enhanced Adhesion and Diffusion Barriers by Al/Mo-C Interlayers

Zircaloy coating is one of the crucial technical ways to improve the accident tolerance of nuclear fuel cladding, which enables the zirconium-water reaction problems to be solved. Zr 2 Al 3 C 4 coating is one type of candidate solutions to improve the high-temperature oxidation resistance of zirconium claddings. However, little study has been performed on the synthesis of Zr 2 Al 3 C 4 coatings on zirconium alloy substrates due to the inter-diffusion, as well as the difference of the thermal expansion coefficients between the Zr 2 Al 3 C 4 coating and the substrates. In this study, Zr 2 Al 3 C 4 coatings were prepared through room-temperature magnetron sputtering and post annealing on zirconium alloy (ZIRLO) substrates with magnetron-sputtered Al/Mo-C interlayers. The effects of Al/Mo-C interlayers on phases and microstructures of Zr-Al-C coatings after annealing were studied by different methods. It is found that the coatings without interlayer are broken and no Zr 2 Al 3 C 4 phase is formed due to significant interdiffusion between the Zr-Al-C coating and the substrate during annealing at 800 for 3 h. The Al/Mo-C interlayers prevented elemental diffusion between Zr-Al-C coatings and substrates during the post-annealing process. The Al/Mo-C interlayers act as diffusion barriers and greatly reduce the stoichiometric deviations from Zr 2 Al 3 C 4 phase, which facilitates the formation of the Zr 2 Al 3 C 4 phase in the final coating. Moreover, this diffusion-barrier layers contribute to eliminating cracks induced by the difference of the thermal expansion coefficients between the Zr 2 Al 3 C 4 coatings and substrates. At the same time, the adhesions between Zr-Al-C coatings with Al/Mo-C interlayers and substrates were improved after annealing, with their strength exceeding 30 N.