Effect of Si on the structure and oxidation behavior of Cr-Si coatings on Zry-4 under high temperature steam environment

Under loss of coolant accident (LOCA), zirconium alloy (Zry-4) is easily oxidized by high temperature steam, which makes its performance deteriorate. To improve the oxidation resistance of Zry-4 under LOCA, Cr-Si coatings with different Si content were deposited on Zry-4 by magnetron sputtering, and the effects of Si content on the steam oxidation resistance of the Cr-Si coatings were investigated. With the fluctuation of Si content inside the coating, there appears different lattice structure. Some amorphous phases and lattice distortions in the coatings with moderate Si content were discovered by TEM, which were beneficial to limit O diffusion in the lattice. However, in the coatings with the higher Si content, the lattice distortions transform into dislocations, which contributes to the O diffusion. The oxidation kinetics of the coated samples proved that the Cr-Si coating with lattice distortion was more consistent with the parabolic law and showed excellent oxidation resistance. In addition, the results of first-principles calculations supported the above view that the O diffusion energy in the lattice increases after the introduction of Si.