Effects Of Al And Ti Content On The Formation Of Nano-oxides In FeCr-ODS Steel

ODS steel has been one of the most promising candidate cladding materials for Generation IV nuclear fission reactors due to its excellent high temperature stability,radiation tolerance and creep resistance etc.The outstanding overall performance of ODS steel mainly depends on the phase,morphology and metal/oxide interface structures of the nanoparticles.Therefore,it is very important to study the effect of minor reactive elements on the phase,morphology and metal/oxide interface structures of the nano-sized oxides in ODS steel.In this work,3.8Al-ODS steel(Fe-15.42Cr-0.1Ti-3.8Al-0.35Y₂O₃),0.09Ti-ODS steel(Fe-15.95Cr-0.09Ti-0.35Y2O3)and0.16Ti-ODSsteel(Fe-13.32Cr-0.16Ti-1.9W-0.35Y₂O₃)were studied.Through HRTEM methods,the effects of the co-addition of Al and Ti and,moreover,only the addition of Ti on the crystal structure,morphology and metal/oxide interface structures of nanoparticles in ODS steel were investigated,respectively.The main conclusions are as follows::(1)About 89.6%of nanoparticles in 3.8Al-ODS are composed of Y-Al-O complex oxides with YAl O₃(YAH)accounting for about 85.7%.YAl O₃(YAP)and Y₄Al₂O₉(YAM)were detected with proportions of?2.6%and?1.3%,respectively.In addition,Y-Ti-O complex oxides were found with a proportion of about 10.4%,including orthogonal structure Y₂TiO₅ oxide and orthogonal structure YTi₂O₆ oxide with proportions of?6.5%and?3.9%respectively.(2)In FeCr-ODS steel containing both Al and Ti elements,when the content of Al element is much higher than that of Ti element,the nanoparticles produced are mainly of Y-Al-O complex oxides.What's more,appropriately reducing the content of Al and Ti elements can not only make more YAH phases with better thermal stability in the alloy,but also generate a certain amount of of Y-Ti-O complex oxides in the alloy.(3)About 59.0%of nanoparticles in 0.09Ti-ODS steel are Y-Ti-O complex oxides with orthogonal structure Y₂TiO₅ accounting for about 32.0%.Hexagonal structure Y₂TiO₅ oxides and orthogonal structure YTiO₃ oxides were detected with proportions of?14.0%and 9.0%,respectively.In the 0.16Ti-ODS steel,about 64.7%of nanoparticles are Y-Ti-O complex oxides with hexagonal structure Y₂TiO₅ accounting for about27.7%.Orthogonal structure Y₂TiO₅ oxide and orthogonal structure YTiO₃ oxide were detected with proportions of?22.7%and?7.6%,respectively.In addition,YCr O₄ and YCr O₃ complex oxides,as well as simple structure TiO₂ and Y₂O₃ oxide particles were detected in both ODS steels.(4)In FeCr-ODS steel,only Ti element is added to form Y-Ti-O composite oxide particles,and when the ratio of Ti element to Y₂O₃ is small,Y₂TiO₅ composite oxide particles with orthogonal or hexagonal structure are mainly formed.What's more,it is further confirmed that the ratio of Ti to Y₂O₃ after adding Ti element will determine the final structure of Y-Ti-O complex oxides.With the continuous decrease of its ratio,the structure type is changed from pyrochlore phase?Y₂TiO₅ phase?YTiO₃ phase gradually changed.(5)Meanwhile,it can also be found that after the addition of Al and Ti elements in ODS steel,when the Al content is relatively large,Y-Al-O composite oxide particles are mainly generated,while the formation of Y-Ti-O composite oxide particles will be greatly restrained.