Microstructure factors affecting the corrosion of Zr alloys

The effects of alloying elements, precipitates and processing parameters on the corrosion behavior of Zr alloys have been studied to establish the database for developing corrosion-resistant fuel claddings. Many types of Zr alloys containing various alloying elements were manufactured with different processing parameters. Corrosion tests for the manufactured Zr alloys were performed under the condition simulating the PWR coolant by using a circulating loop as well as static autoclaves. The microstructure of the alloys was observed by a transmission electron microscopy. The types of precipitates in the alloys were identified by analyzing the selected area diffraction pattern and the chemical composition from the energy dispersive X-ray spectroscopy. The relationship between the microstructure and the corrosion behavior showed that the corrosion resistance of Zr alloys was determined primarily by Nb content and precipitate characteristics. The change of Nb content and annealing temperature during the manufacturing process resulted in the change of the precipitate characteristics, which in turn determined the corrosion behavior of Zr alloys. The corrosion resistance of the Nb-containing Zr alloys was apparently degraded with a formation of β-Zr phase and an increase of the precipitate size, which resulted from the increase of intermediate and final annealing temperature. (author)