Surface growth, inner defects and interface mixing of Cr coating on Zr alloy irradiated by 5 MeV protons at 400°C

Surface, inner and interface damages of Cr coatings irradiated by 5 MeV protons were characterized by XRD, SEM, TEM and nanoindentation in this work. After irradiation, a Cr₇C₃ growth layer with refined grains was formed on the surface due to the separation and redeposition of diffused Cr atoms. Irradiation-induced defects in the Cr coatings were voids, dislocations, and bubble-vacancies complexes. Importantly, irradiation softening was found for the arc-ion plated Cr coating, which should be due to the deformation recovery and recombination of inherent sinks and irradiation defects. At the coating-substrate interface, the ZrCr₂ C14 phase, a multilayered interface and the preferential diffusion were found, meaning chained or layered Cr atoms may dominate the interface diffusion. In mechanism, formation mechanisms of irradiation defects are analyzed and the irradiation-enhanced diffusion, ballistic collision and the sharpening effect are employed to explain the interface mixing. A correlation coefficient of the anisotropic diffusion is proposed in the Cr flux equation for explaining the (110)-dominated diffusion. The results show that irradiation effects of coatings depend on the inherent defects and preferred orientation produced in the preparation process of coatings.