Effects of Zr Content on the Microstructure of FeCrAl ODS Steels

FeCrAl oxide dispersion strengthened (ODS) steels are an important kind of cladding material for accident-tolerant fuels. Their radiation resistance and mechanical properties are closely related to the grain size and dispersed second phases. In order to tailor the microstructure and provide an experimental basis for the composition design of FeCrAl ODS steels, in this paper FeCrAl ODS steels with different Zr contents were prepared by mechanical alloying and the subsequent hot isostatic pressing (MA-HIP) process. The effects of Zr content on the grain size distribution and the precipitation of dispersed second phases in FeCrAl ODS steels were investigated by electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM). The results showed that the grain size decreased first and then increased as the Zr content increased, and that the average grain size achieved the minimum value of 2.092 μm when the Zr content was 0.6 wt.%. The Zr content had a negligible effect on the grain orientation of FeCrAl ODS steels, but the dispersed second phase changed from the Al2Y4O9 phase with monoclinic structure to the Y4Zr3O12 phase with hexagonal structure as the Zr content increased

Addition of niobium in Fe-13Cr-4.5Al-2Mo alloy used as ATF cladding: Effect on high temperature water corrosion and in-situ electrochemistry

Niobium addition in candidate accident tolerant fuel (ATF) cladding FeCrAl alloy has received much attention, but its effect on high temperature water corrosion behavior has not been revealed. Four alloys with different Nb content (0 wt%, 0.5 wt%, 1.0 wt% and 1.5 wt%) based on Fe-13Cr-4.5Al-2Mo model alloy were designed, and the corrosion behavior was investigated by in-situ electrochemistry and microscopy. The in-situ electrochemistry analyses, including open circuit potential (OCP), polarization and electrochemical impedance spectrum, were carried out in 360 °C/19.0 MPa lithiated and borated water connected with a loop system to monitor the water chemistry. The oxide films formed after immersion for 85 days were deeply investigated by focused ion bombarding and transmission electron microscopy. Results have shown that OCP decreased with elevated temperature and corrosion potential increased with time. FeCrAl alloys have satisfactory corrosion resistance because of small corrosion currents and thin oxide films. Only monolayer multicrystal spinel oxide forms on FeCrAl alloys. Slight Nb addition (0.5 wt% and 1.0 wt%) benefits the corrosion resistance due to relatively large impedance of oxide and delayed oxidation of Fe2Nb particles. Porosities with Fe depletion were spotted in oxide and especially severe in 1.5 wt%-Nb alloy. Cathodic Tafel kinetics and corrosion mechanisms of FeCrAl were further discussed