The Effect Of Plastic Deformation On Corrosion Behavior Of SIMP Steel In Liquid Lead-bismuth And The Mechanism Of The Study

Liquid lead bismuth eutectic（LBE;Pb 44.5 Bi 55.5,wt.%）has superior thermal and hydraulic properties and chemical stability,it is an important core coolant for lead-cooled fast reactors（LFR）in Generation IV reactors.In addition,liquid LBE has properties such as high neutron yield and low neutron absorption cross section,which makes it one of the important scattering target materials.Despite the advantages of liquid LBE as a coolant or scattering target material,its strong corrosion problem on structural materials is still one of the major bottlenecks limiting the development of advanced nuclear energy systems.The corrosion mechanisms of liquid lead-bismuth alloys on structural materials are mainly oxidation,dissolution and abrasion.LBE corrosion mechanism is influenced by the chemical composition,surface state and microstructure of the structural material,in addition to the state of the liquid lead bismuth,such as temperature,liquid metal dissolved oxygen concentration and flow rate,etc.In practical engineering reactor structural materials are often made by plastic processing,and different deformation parameters will affect their surface state and microstructure.Therefore,it is important to study the effects and mechanisms of plastic deformation on liquid metal corrosion for the selection of structural materials and service performance assessment of lead-cooled fast reactors.Although some research works have been carried out by researchers to explore the effects of plastic deformation on the corrosion behavior of liquid LBE,these studies are not systematic enough.In particular,It should be noted that there is a lack of clear understanding of the physical mechanisms by which plastic deformation affects corrosion.Therefore,systematic research work needs to be further developed.In this study,SIMP steel,a new structural material for nuclear applications jointly developed by the Institute of Modern Physics and the Institute of Metals Research of the Chinese Academy of Sciences,was selected for the study,and the corrosion experiments of SIMP steel with different rolling deformation（0%,10%,30%,50%,70%）at different temperatures（350°C,450°C,550°C）in saturated oxygen liquid LBE of different durations（100-2000 h）were carried out.Then the microstructure and composition of the corrosion layer were characterized by scanning electron microscopy（SEM）,energy dispersive X-ray spectrometer（EDX）,X-ray diffractometer（XRD）and electron probe microanalyzer（EPMA）,and the corrosion behavior and mechanism of SIMP steel in liquid LBE with different rolling deformation were investigated from the perspectives of thermodynamic formation mechanism and kinetic change trend.The effects of rolling deformation,temperature,time and alloy composition on the corrosion behavior of SIMP steels were systematically investigated.The focus is on the oxidation corrosion mechanism of SIMP steel in liquid LBE and comparing the anti-corrosion performance of SIMP in liquid LBE with different rolling deformation.The main results obtained are as follows:（1）Oxidation corrosion occurred in SIMP steels with different rolling deformation at 350°C,450°C and 550°C in saturated oxygen liquid LBE,and multilayer structural oxide layers were formed on the surface of the samples.When the samples were corroded in saturated oxygen liquid LBE at 550℃for 100-700 h,the formed oxide layer was a double-layer structure,with Fe-Cr spinel as the inner oxide layer and magnetite as the outer oxide layer;after 1000 h of corrosion,the oxide layer formed on the surface of the samples was divided into outer oxide layer,inner oxide layer and IOZ layer.The oxide layer formed on the surface of the samples can be divided into two layers,consisting of an outer layer of magnetite（Fe₃O₄）and an inner layer of Fe-Cr spinel,when corroded in saturated oxygen liquid LBE at450°C and 350°C for 100-2000 h.（2）The oxide layer formed on the surface of SIMP steel at different rolling deformation increases with time during the corrosion of liquid LBE at different temperatures.It was found that in liquid LBE at 450°C and 550°C,the oxidation kinetic curves of pristine SIMP steel and rolled-down 10%SIMP steel approximately followed a linear pattern,and the oxidation kinetic curves of rolled-down 30%,50%and 70%SIMP steel approximately followed a parabolic pattern.The oxidation kinetic curves of SIMP steels with different rolling deformation in liquid LBE at350°C are approximately parabolic in shape.（3）SIMP steels introduce grain boundaries and dislocations during rolling deformation,which can provide"short-circuit"channels for atomic diffusion.Rolling increases the diffusion rate of elements such as Fe,Cr,O and Si in the matrix,and SIMP exhibits different growth rates of oxide layers with different rolling deformation amounts of elements.Rolling improved the LBE corrosion resistance of SIMP steels in liquid LBE at 550°C and 450°C.In liquid LBE at 350°C,rolling reduced the LBE corrosion resistance of SIMP steels.