Stress-driven grain re-orientation and merging behaviour found in oxidation of zirconium alloy using in-situ method and MD simulation

It has been believed that ZrO2 columnar grains, which contribute to the reduction of oxygen diffusion in the oxide layer, are the result of grain growth, and the subsequent oxidation mechanism of zirconium alloy is also formed and developed on this basis. Here we report an in situ oxidation experiment carried out at 500 ℃ air condition demonstrating that large size ZrO2 grains were results of the merging of small size grains rather than growth of grains. We further show that original orientation of small size grains and dislocation motion play crucial roles in the merging process of small size grains. [Display omitted] •An in situ TEM oxidation at 500 ℃ air condition was carried out.•An atomic view of microstructure evolution mechanism of the oxide layer of zirconium has been reported.•The role of dislocation, initial orientation and stress in oxide microstructure evolution has been studied. It has been believed that ZrO2 columnar grains, which contribute to the reduction of oxygen diffusion in the oxide layer, are the result of growth of small grains, and the subsequent oxidation mechanism of zirconium alloy is also formed and developed on this basis. Here we report an in situ oxidation experiment carried out at 500 ℃ air condition demonstrating that large size ZrO2 grains was results of the merging of small size grains rather than growth of small grains. We further show that original orientation and dislocation motion play crucial roles in the merging process of small size grains.