Effects Of Minor Elements And Consolidation Temperature On FeCrAl-ODS Steel Nano Oxides

ODS steel has been considered as the most promising candidate material for the next generation of nuclear fuel cladding due to its excellent creep strength,corrosion resistance,radiation resistance and good physical and chemical thermal stability.The macroscopic performance of ODS steel depends on the phase,morphology,and interface of the dispersed nanometer-scale oxides.The methods to control the phase and morphology of nanometer-scale oxides and,moreover,the oxide/matrix heterogeneous interfaces include the addition of minor active elements and the adjustment of consolidation temperature.In this paper,in order to study the effects of the contents of Zr and Ti on the nanometer-scale oxides in FeCrAl-ODS steels,the phase and morphology of nanometer-scale oxides and,moreover,the oxide/matrix interfaces in SOC-14?Fe-15Cr-2W-0.09Ti-4Al-0.63Zr-0.35Y₂O₃?andZr-3?Fe-15Cr-2W-0.12Ti-4Al-0.49Zr-0.33Y₂O₃?were analyzed by high resolution transmission electron microscopy?HRTEM?.Moreover,in order to study the effect of the consolidation temperature on the nanometer-scale oxides in FeCrAl-ODS steels,the phase and morphology of nanometer-scale oxides and,moreover,the oxide/matrix interfaces in SOC-9?1150^oC?and SOC-9-ET-1?1050^oC?ODS steel with identical chemical compositions,i.e.,Fe-15.5Cr-2W-0.09Ti-3.8Al-0.35Y₂O₃,by HRTEM.The results are as follows:?1?Compared with SOC-14,the proportion of Y-Zr-O complex oxides in Zr-3alloy decreases from 87.43%to 54.74%,and the proportion of Y-Ti-O complex oxides increases from 5.71%to 33.36%.Therefore,the proportions of Y-Zr-O and Y-Ti-O complex oxides in FeCrAl-ODS steels could be adjusted by changing the contents of Ti and Zr for improving the irradiation resistance and thermal stability.The Y-Ti-O complex oxides obviously increase even when the content of Ti is adjusted only slightly.?2?By comparing Zr-3 with SOC-14,it can be concluded that when the Ti content increases from 0.09%to 0.12%,and the Zr content decreases from 0.63%to 0.49%with the content of Al keeping constant,the proportion of Y-Al-O complex oxides increased from 3.43%to 11.9%,indicating the decrease of the Zr content makes the suppression effect of Zr addition on the formation of Y-Al-O complex oxides become weaker.?3?The addition of Zr into FeCrAl-ODS steels can not only significantly improve the dispersion morphology of the oxides,providing opportunities for the recombination of point defects generated during irradiation,but also lead to the formation of a large amount of Y₄Zr₃O₁₂ complex oxides with very good radiation resistance,which can greatly improve the radiation stability of the materials.?4?By comparing SOC-9-ET-1 with SOC-9,the proportion of YAlO₃?YAH,yttrium-aluminum-hexagonal?was increased from 55%to 89.5%and,moreover,the proportion of YAlO₃?YAP,yttrium-aluminum-hexagonal?particles was decreased from 38%to 4.5%when the extrusion temperature was reduced from 1150^oC to 1050^oC.This indicates that the reduction of consolidation temperature can effectively promote the formation of YAH particles,leading to the improved thermal stability and radiation resistance of FeCrAl-ODS steels.?5?By comparing SOC-9-ET-1 with SOC-9,when the consolidation temperature decreases from 1150^oC to 1050^oC,the coherency of the nanometer-scale oxides is enhanced very remarkably and,moreover,the size and the volume number density of the nanometer-scale oxides significantly reduces and increases,respectively,leading to the greatly improved the dispersion morphology.