Study on Nb interlayer as CrZr diffusion barrier layer at high-temperature

Abstract

The study examined the diffusion mitigation effect and mechanical properties of the Nb interlayer prepared by magnetron sputtering as a CrZr diffusion barrier through annealing experiment, high-temperature air oxidation experiment and ring compression tests. The results show that the presence of an Nb interlayer significantly alleviates the CrZr interdiffusion, especially prevents the CrZr interdiffusion in the 1200 °C air environment and stabilizes the interface structure in the 1400 °C air environment. After undergoing air oxidation at 1200 °C, the Cr/Nb-coated samples showed the structure of Cr₂O₃, Cr, Cr₂Nb Laves phase, Nb, (Zr, Nb) miscibility gap, β-Zr, α-Zr(O), and ZrO₂ layers. During a certain period of argon annealing at 1332 °C, the increase in the thickness of the interlayer of the Cr/Nb coating, especially for samples containing micron sized Nb layer, is smaller than that of Cr-coated samples, indicating that the presence of the Nb layer is effective in alleviating the CrZr contact reaction to a certain extent. During the ring compression tests, the Cr/Nb coating is still firmly bonded to the Zr alloy cladding tube even under large deformation, and the micron-scale Nb layer releases part of the stress, resulting in short crack clusters on the surface of the coating instead of a large number of through-wall cracks. In summary, the Nb layer has the potential to be used as a diffusion barrier for CrZr interface, and the details of Nb as a diffusion barrier are discussed.