Elaboration of self-healing coatings for the development of robust materials in nuclear conditions

This study aims to improve oxidation resistance of nuclear fuel claddings in accident conditions. In this context, Cr-Al-C and Cr₂AlC coatings deposition and their behavior were studied. Firstly, we investigated the influence of HiPIMS process parameters on the properties of the plasma and the deposited films. Despite more intense ionic fluxes due to the HiPIMS process, coatings do not crystallize without an additional energy supply. Partially crystallized Cr₂AlC thin films were obtained by a 500 C annealing of as-deposited Cr-Al-C coatings. This two-step process is a viable solution to protect nuclear claddings with Cr₂AlC coating while maintaining the metallurgical properties of the zirconium based substrates. Secondly, the assessment of the oxidation resistance of as-deposited and annealed coatings revealed significant protective effect against rapid oxidation under dry and wet air at high temperatures (up to 1200 C) owing to the formation of a continuous oxide layer. During the first stages of oxidation, this layer is made of α-Al₂O₃ and Cr₂O₃ for as-deposited coating while only α-Al₂O₃ is present for the annealed one. Because of Al depletion, coatings later deteriorate and form a residual and porous intermediate chromium carbide (Cr₇C₃) layer which further fully oxidizes. It was shown that the inward diffusion of Al with Zr also accelerates the coating deterioration. To improve the oxidation resistance of these coatings, multilayered architectures were developed. Adding a molybdenum interlayer as diffusion barrier globally decreased the oxidation resistance of the coating. In contrast, topping Cr-Al-C and Cr₂AlC with a Cr layer improved oxidation behavior over single-layer coatings. (author)