Phase-field simulation of high-temperature corrosion of binary Zr-2.5Sn alloy

Abstract

Due to the small neutron absorption cross section and excellent thermal creep performance, zirconium alloy is one of the most important cladding materials for fuel rods in commercial fission reactors. However, quantitative analysis of the effects of temperature and grain boundaries on the corrosion microstructure evolution of zirconium alloys is still needed. It is of great significance to establish a phase field simulation for the corrosion process of polycrystalline zirconium alloy and systematically investigate the thermodynamic impact. In this study, the phase field model of the corrosion process in zirconium alloys was developed by incorporating corrosion electrochemistry to calculate the interfacial energy at the metal-oxide and oxide-fluid boundaries. Then model was then employed to investigate the uniform corrosion behavior on the surface of Zr-2.5Sn alloy, which demonstrated that the corrosion kinetics curve followed a cubic rule. Subsequently, the influence of temperature on the corrosion thickening curve of zirconium alloys was examined, and good agreement between simulation and experimental results was achieved. It was observed that during early stages of oxide layer formation, there is a high growth rate with minimal temperature dependence; however, as the oxide layer thickness increases, temperature becomes a significant factor affecting its growth rate, with higher temperatures resulting in faster corrosion rates. Furthermore, an investigation into the effect of polycrystalline zirconium alloy matrices on corrosion rates revealed that grain boundaries accelerate oxide layer thickening due to enhanced oxygen diffusion rates. Along these grain boundaries towards the metal matrix at metal-oxide interfaces, regions with higher O<sup>2-</sup> concentrations form an O<sup>2-</sup> band which primarily influences oxidation-corrosion rates during initial oxidation stages.