Crystal structure of oxide film of NZ2 alloy corroded in different mediums

The crystal structure transformation of oxide film during corrosion and the effect of the transformation on the corrosion resistance of NZ2 were investigated. The crystal structure of oxide film of NZ2, corroded by static autoclave test in 360°C lithiated water and 400°C steam, was analyzed by Raman spectroscopy. The results show that the oxide film of NZ2 consists mostly of m-ZrO₂, including a certain quantity of distorted t-ZrO₂ which is stabilized by the compressive stress. With the prolongation of corrosion time, the metal/oxide interface is moving forward. When the compressive stress in the oxide formed previously is not enough to stabilize t-ZrO₂, t-ZrO₂ will transform to m-ZrO₂, and the average content of t-ZrO₂ in oxide film decreases. From oxide/metal interface to the surface of oxide film, the content of t-ZrO₂ reduces gradually. When NZ2 is corroded in 360°C lithiated water, the transformation rate from t-ZrO₂ to m-ZrO₂ in oxide film is much lower than that in 400°C steam. The transformation from t-ZrO₂ to m-ZrO₂ decides the corrosion resistance of NZ2. The higher the transformation rate is, the lower t-ZrO₂ content in oxide film is, and the higher corrosion rate of NZ2.