Effects Of Zr And/or Ti Addition On The Nano-scale Particles In ODS Steels As The Fuel Cladding Materials Of Generation Iv Nuclear Fission Reactors

Superior performance is essential for the nuclear structural materials of Generation IV nuclear fission reactors because the service conditions are much more harsh,e.g.,much higher operation temperature,relative to light water reactors.Oxide dispersion strengthened steels are the most promising candidate cladding materials of Generation IV nuclear fission reactors because they have excellent resistance to creep and irradiation as well as very good stability in various physical and chemical environments due to the characteristic features,i.e.,highly dense dispersed ultrafine nano-sized oxides.High-Cr ODS steels can meet all the requirements of the cladding materials of super-critical pressurized water cooled reactors and lead-bismuth eutectic cooled fast breeder reactors because they have even higher strength and extraordinary compatibility with not only sodium but also super-critical pressurized water?SCPW?and lead-bismuth eutectic?LBE?.It has been demonstrated that the addition of minor reactive elements,e.g.,Ti and Zr,is very effective for improving the performance of high-Cr ODS steels,which is closely related to the effects of such oxide-formation elements on the nanoparticles.Therefore,the effects of Ti and/or Zr addition on the nano-sized oxides in high-Cr ODS steels were investigated in the present research work.This study divided into the following two parts:The first Part:The influencing mechanisms of Ti and/or Zr addition on nanoparticles in FeCrAl-ODS steels,including SOC-9?Fe-15Cr-4Al-0.1Ti-2W-0.35Y₂O₃?and ODS-Zr3?Fe-15Cr-4Al-2W-0.15Ti-0.5Zr-0.35Y₂O₃?,which can be used as the cladding materials of super-critical pressurized water cooled reactors,were investigated by using high resolution transmission electron microscopy?HRTEM?.The results are compared with those of SOC-14?Fe-15Cr-4Al-2W-0.1Ti-0.63Zr-0.35Y₂O₃?.The underlying mechanisms of the outstanding thermal stability and irradiation tolerance of the oxides as well as the superior strength and the excellent resistance of ODS-Zr3 to creep,irradiation in SCPW and LBE at high temperature are discussed.The following conclusions can be drawn:?1?The triangle crystal structure?-phase Y₄Zr₃O₁₂ particles are formed instead,and a small amount of luorite structure Y₂Zr₂O₇ particles were detcted in the bcc matrix,which become more obvious with the increase of Zr content.?2?The addition of 0.5 wt.%Zr intensively suppresses the formation of Y-Al-O oxide particle,which become more obvious with the increase of Zr conte nt.In addition,Y₂TiO₅,YTiO₃ and YTi₂O₆ particles are generated and are obviously much more promoted with the increasing of Ti content.?3?The number fraction of Y-Zr-O,Y-Ti-O and Y-Al-O complex oxides can be optimized by controlling Zr/Ti ratio and,consequently,the comprehensive performance of ODS steels can be improved.That is to say,the irradiation resistance and thermal stability can be significantly enhanced.It was found that the ratio of Y-Zr-O,Y-Ti-O and Y-Al-O complex oxides is about 5:3:1 with Zr/Ti ratio being³.33 in ODS-Zr3al oy.The second part:The influencing mechanisms of Ti addition and,moreover,the contents of W contents,on nanoparticles in FeCr-ODS steels,including SOC-5?Fe-15.95Cr-0.09Ti-0.34Y₂O₃?and SOC-P3?Fe-13.32Cr-1.9W-0.16Ti-0.33Y₂O₃?,which can be used as the cladding materials of sodium cooled fast reactors,were investigated by using high resolution transmission electron microscopy?HRTEM?.The unusual thermal stability and outstanding irradiation tolerance of the oxide oxide particles as well as the superior strength of FeCr-ODS with the increasing of Ti,are discussed.The following conclusions can be drawn:?1?The coherency of the nanoparticles was obviously improved with the Ti content increased from 0.09 wt.%to 0.16 wt.%.?2?In the SOC-P3 alloy,the vast majority of particles are composed of Y₂TiO₅?⁶5.95%?and Y₂Ti₂O₇?³0.4%?.However,in the SOC-5 alloy,the Y₂TiO₅ complex oxide accounts for⁹6.5%while the number fraction of Y₂Ti₂O₇ complex oxide is³%.A very small amount of large TiO₂ oxides were detected in the SOC-P3 and SOC-5al oys.