Effects Of Al,Ti And/or Zr On The Formation Of Nano-scale Oxides In FeCrAl-ODS Steels Prepared By Powder Metallurgy Method

Oxide dispersion strengthened(ODS)steel is one of the most promising candidate structural materials of generation IV nuclear fission reactors such as supercritical water-cooledreactors(SCWRs)and lead-cooled fast reactors(LFRs)and,moreover,it is one of the most promising structural materials of future fusion reactors because it has excellent resistance to corrosion,creep,irradiation and high temperature strength.The macroscopic properties of ODS steel depend on the phase and morphology of nano-sized oxides and the interface between metal and oxide.In this work,3.8Al–0.1Ti(Fe–15.5Cr–3.8Al–2W–0.1Ti–0.35Y₂O₃),3.7Al–0.1Ti–0.63Zr(Fe–15Cr–3.7Al–2W–0.1Ti–0.63Zr–0.35Y₂O₃)and 3.8Al–0.12Ti–0.44Zr(Fe–14.8Cr–1.82W–0.12Ti–3.8Al–0.44Zr–0.29Y₂O₃)were studied.Through HRTEM methods,the effects of the addition of Zr and the contents of Al,Ti and Zr on the phases of nano-oxides and the proportions of various types of oxides in FeCrAl-ODS steels were studied.The variation law and internal mechanism of the type and proportions of nano-sized oxides were analyzed and discussed.The main conclusions are as follows:(1)Most of the nano-sized particles in 3.8Al–0.1TiODS steel are Y–Al–O oxides,the number proportion is 88.7%.The Y–Al–O oxides are mainly composed of orthorhombic YAl O₃(YAP),hexagonal YAl O₃(YAH),monoclinic Y₄Al₂O₉(YAM)and cubic Y₃Al₅O₁₂(YAG)with the proportion is 38.6%,41.7%,4.6%and 3.8%,respectively.(2)Most of the oxides in 3.7Al–0.1Ti–0.63Zr ODS steel are Y–Zr–O oxides,accounting for 87.9%of the oxide particles.Y–Zr–O oxides can be divided into triangular?phase Y₄Zr₃O₁₂ and orthorhombic or cubic structure Y₂Zr₂O₇,accounting for 61.2%and26.7%,respectively.The amount of Y–Al–O oxide in 3.7Al–0.1Ti–0.63Zr ODS steel is4.2%.Compared with the amount of Y–Al–O oxide(?88.7%)in 3.8Al–0.1TiODS steel,it indicates that the minor addition of Zr can significantly inhibit the formation of Y–Al–O oxides and promote the formation of a large number of Y–Zr–O oxides.In addition,a small amount of large oxide particles was detected,mainly Zr O₂,with a proportion of3.0%.(3)In 3.8Al–0.12Ti–0.44Zr ODS steel,about 58.1%of the nanoparticles are composed of Y–Zr–O oxides,in which the number proportions of triangular?phase Y₄Zr₃O₁₂,cubic Y₂Zr₂O₇ and orthorhombic Y₂Zr₂O₇ are 32.0%,15.1%and 11.0%,respectively.About 17.4%of the nanoparticles are composed of Y–Al–O oxides with YAP accounting for 10.5%.In addition,a small amount of Y–Cr–O oxides were detected,mainly including YCrO₃ and YCrO₄,accounting for 0.6%and 0.6%,respectively.(4)A small amount of Y₂TiO₅ particles were detected in 3.7Al–0.1Ti–0.63Zr ODS steel,accounting for 4.9%.However,in 3.8Al–0.12Ti–0.44Zr ODS steel,about 18.6%of the particles are composed of Y–Ti–O oxides,mainly including orthorhombic Y₂TiO₅and YTi₂O₆,accounting for 7.0%and 7.6%,respectively.The results indicate that the Zr concentration decreases from 0.63 wt.% to 0.44 wt.%and,simultaneously,the Ti concentration increases from 0.10 wt.%to 0.12 wt.%,the proportion of Y–Ti–O oxides can be significantly increased.(5)The results of this paper reveal the variation of the types and the proportions of nano-sized oxides in FeCrAl-ODS steel with the contents of Al,Ti and Zr.This suggests that by adjusting the kinds of minor elements,the kinds and proportions of nano-sized oxides can be adjusted,which provides theoretical guidance and basis for optimizing the composition of ODS alloy and developing ODS steel with better properties.