2, The Stock Company A.A. Bochvar High-Technology Research Institute of Inorganic Materials, Moscow, , Russian Federation
A systematic study of post-quench ductility of sponge-based E110 samples subjected to steam oxidation at 1000°C, 1100°C, and 1200°C was performed by ring compression testing (RCT). For sponge-based E110 samples hydrogen pickup was not observed during steam oxidation.
Thus, it can be concluded that the ductility of oxidized samples, represented by the offset strain, gradually decreases as the oxygen pickup increases only. The samples oxidized at 1200°C are less ductile than those oxidized at lower temperatures at the same value of equivalent clad reacted. Microstructural examinations were performed on oxidized E110 specimens to correlate material performance with microstructure. Three different layers were observed: oxide layers on sample surfaces, a low oxygen layer in the middle of the cladding wall, and an oxygen rich layer between the oxide and low oxygen layers. Oxide layer thickness is observed to increase as the test time increases. Scanning electron microscopy study shows that the average oxygen content in the center 300 µm increases as the temperature increases for the samples having the same oxygen pickup. Microhardness measurements were performed at room temperature on the oxidized E110 samples. The hardness value of the middle 300 µm increases with both oxygen pickup and steam oxidation temperature. This indicates that more oxygen diffused into the middle of the prior beta layer at higher temperatures thereby reducing the ductility of the prior beta layer. The RCT data show that the strain values decrease as oxygen pickup increases and decreases as temperature increases. This observation is confirmed by the microhardness profile across the metal layer. Low hardness values at 1000°C indicate low oxygen concentration in the metal layer, in good agreement with the observation that the oxygen pickup at 1000°C is lower than that at 1100-1200°C. In addition to the as-received E110 cladding sample, pre-hydrided E110 cladding with hydrogen concentrations in the 100-150 wppm range was also investigated. The material behavior of pre-hydrided specimens is compared to the as-received E110.