Study Of Effect Of Minor Reactive Elements On Structure Of Crystal And Heterogeneous Interface Of Nanoparticles In Oxide Dispersion Strengthened (ODS) Steels

Oxide dispersion strengthened?ODS?steel is one of the most promising cladding materials of Generation IV nuclear fission reactors such as supercritical water-cooled reactors?SCWRs?and lead-cooled fast reactors?LFRs?and,moreover,it is one of the most promising structural materials of the blanket of future fusion reactors due to its excellent performance in ultra-severe conditions.They exhibit high superior mechanical properties?e.g.,very good temperature strength and excellent creep resistance?;high resistance to irradiation hardening,irradiation swelling,and irradiation embrittlement;high resistance to corrosion in hot pressurized water,lead-bismuth eutectic and supercritical pressurized water;good thermal stability etc.The overall macroscopic behavior of ODS alloy can be strongly influenced by the phase and morphology of nanoparticles and,moreover,the metal/oxide interface structure.Therefore,the structures of the crystal and the interfaces of nanoparticles in three types of ODS steel,e.g.,a Ti-added FeCr-ODS steel,a Zr-added FeCrAl-ODS and a Hf-added FeCrAl-ODS steel,were studied by high resolution transmission electron microscopy?HRTEM?.The phases of the nanoparticles were identified and the corresponding proportions of various kinds of oxides were determined according to the results of statistical analyses of the HRTEM characterization.The knowledge is crucial to understanding of the formation mechanisms of various kinds of oxides and,moreover,the underlying reasons of the unusual thermal and irradiation stabilities of the oxides.The concluding remarks are:For Ti-added FeCr-ODS steel,i.e.,SF?Fe–14Cr–0.16Ti–2W–0.33Y₂O₃??1?About 64.7%of the nanoparticles are composed of Y–Ti complex oxides with the proportions of Y₂TiO₅ and Y₂Ti₂O₇ oxides of about 50.4%and 1.7%,respectively.The addition of small amount of Ti addition,i.e.,0.16 wt.%,into FeCr-ODS steel containing 0.33 wt.%Y₂O₃ promotes significant formation of Y₂TiO₅ complex oxide,instead of Y₂Ti₂O₇ complex oxide.?2?About 27.7%and 22.7%of the nanoparticles are composed of hexagonal Y₂TiO₅ and orthogonal Y₂TiO₅ oxides,respectively.The oxides have very good thermal and irradiation stabilities and,moreover,very strong capability for managing helium.?3?The proportions of TiO2 and Y2O3 are as high as 16.0%and 11.7%,respectively.However,the total proportion of Y–Cr complex oxides is as low as 7.6%with the number fractions of orthogonal YCrO3 oxide and tetragonal YCrO4 oxide of 3.4%and 4.2%,respectively.It is the first time to find tetragonal YCrO4 oxide in Fe–Cr–Ti–W–Y2O3 ODS steels.?4?About 7.6%and 5.0%of the nanoparticles are composed of orthorhombic YTiO₃ and orthorhombic YTi₂O₆ oxides,respectively.It is the first time to find orthorhombic YTi₂O₆ oxide in Fe–Cr–Ti–W–Y₂O₃ ODS steels.For Zr-added FeCrAl-ODS steel,i.e.,SL1?Fe–15Cr–4Al–2W–0.12Ti–0.44Zr–0.29Y₂O₃??1?About 62.9%of the nanoparticles are composed of Y–Zr complex oxides with the proportions of cubic Y₂Zr₂O₇?C?,orthogonal Y₂Zr₂O₇?O?and?-Y₄Zr₃O₁₂2 oxides of about 13.6%,18.8%and 30.5%,respectively.?-Y4Zr3O12 has the highest proportion,but a large amount of Y₂Zr₂O₇ has also been found,and the orthogonal Y₂Zr₂O₇ was found in FeCrAl-ODS-Zr for the first time.?2?About 5.3%nanoparticles are composed of Y–Al complex oxides.The addition of Zr?0.44 wt.%?to FeCrAl-ODS steel can significantly inhibit the formation of Y–Al composite oxide.?3?A fairly high proportion of the nanoparticles are composed of Y–Ti complex oxides?¹6.2%?,mainly including Y₂TiO₅ oxide?¹1.0%?with orthorhombic structure.A small amount of Ti?0.12 wt.%?can promote significant formation of Y–Ti–O.For Hf-added FeCrAl-ODS steel,i.e.,SL2?Fe–15Cr–2W–0.1Ti–4Al–0.62Hf–0.35Y₂O₃??1?The highest proportion of the nanoparticles,i.e.,51.0%,are composed of Y₂Hf₂O₇ oxide with anion-deficient fluorite structure.The oxide has very small size,excellent thermal stability and irradiation tolerance.?2?The proportion of Y–Al–O complex oxide is³2.0%,containing²5.5%YAlO₃?YAP?and⁶.5%YAlO₃?YAH?.The addition of Hf?0.62 wt.%?to FeCrAl-ODS steel can significantly inhibit the formation of Y–Al complex oxides,but the addition of Zr?0.44 wt.%?is more effective in suppressing the formation of Y–Al complex oxides.?3?A fairly high proportion of the nanoparticles are composed of Y–Ti complex oxides?¹7%?,mainly including Y₂TiO₅ oxide and YTiO₃ oxide with orthorhombic structure.A small amount of Ti?0.10 wt.%?can promote significant formation of Y–Ti–O.Orthogonal Y₂TiO₅ nanoparticles have good thermal stability and resistance to amorphization.