Study On Improving High Temperature Oxidation And Acid Corrosion Resistance Of Fe-Cr-Ni Medium Entropy Alloy For Nuclear Power By Rare Earth Ce

Nuclear power has become one of the important energy sources used by mankind.Nuclear power is an important part of the power industry.However,each hot end component of the reactor should be able to operate stably for tens of thousands of hours,which puts forward high requirements for the material selection of high temperature and corrosion resistant components of nuclear power plant.Therefore,the research on nuclear power components is very important.In this study,the high temperature oxidation and acid solution corrosion behavior of Fe-Cr-Ni medium entropy alloys（MEA-Ce and MEA）with and without rare earth were compared and analyzed.We use the scanning electron microscope（SEM）to observe the surface and cross section of oxide scale,the cross section element composition was analyzed by energy dispersive spectroscopy（EDS）,and the phase composition of oxidation products was analyzed by X-ray diffraction（XRD）and X-ray photoelectron spectroscopy（XPS）,The high temperature oxidation mechanism of Fe-Cr-Ni medium entropy alloy and the effect of rare earth elements on high temperature oxidation properties were discussed.It is found that the oxidation kinetics curves of the two medium entropy alloys basically accord with the parabolic law.Under this law,the high temperature oxidation kinetics is usually controlled by the diffusion of cations or anions through the oxide scale.The addition of rare earth elements changes the mass transfer mechanism of ions（mainly the outward transfer of cations into the inward transfer of anions）,which also makes the oxidation weight gain of MEA-Ce less at different temperatures.After the fitting of oxidation kinetics,it was found that the oxidation activation energy of MEA was 418.7 k J·mol^-1 and that of MEA-Ce was 467.6k J·mol^-1.It can be seen that the high temperature oxidation resistance of MEA-Ce was better than that of MEA after the addition of rare earth elements.After adding rare earth elements,the MEA-Ce oxide film is more uniform and compact,the oxide film is complete without holes and cracks,and the content of protective spinel oxide is higher.From the section direction of oxide film,rare earth elements make more Si O₂dispersed at the interface between MEA-Ce matrix and oxide film,and the pinning effect is more significant than MEA,which can effectively slow down the further oxidation of matrix.Comprehensive analysis of XRD and XPS results show that the oxide film of two medium entropy alloys can be divided into three layers.The outer oxide layer is mainly composed of dense（Fe,Mn）cr2o4 spinel,the inner layer is composed of dense continuous Cr2O3,and the internar oxide layer is dispersed Si O₂.For the acid corrosion resistance,MEA-Ce and mea were compared by means of scanning electron microscope（SEM）,energy dispersive spectroscopy（EDS）,X-ray photoelectron spectroscopy（XPS）,electrochemical impedance spectroscopy（EIS）and potentiodynamic polarization,the corrosion behavior of them in sulfuric acid solution was analyzed,and the protective ability of the passive film of the two materials was compared,The corrosion mechanism of Fe-Cr-Ni medium entropy alloy in sulfuric acid solution and the effect of rare earth elements on acid corrosion resistance were discussed.It is found that in 0.1 mol/L H₂SO₄ solution,the corrosion current density of MEA-Ce is lower than mea by two orders of magnitude,and its charge transfer resistance is 1.56 times that of MEA.For the passivation film formed by the two materials after charging for 2 hours at+400 m V_SHE potential,the content of Cr and Ni in MEA-Ce E passivation film is higher,the content of Fe and Mn is lower,and the Cr+Ni/Fe+Mn cation ratio is 1.34 times that of MEA,forming a passivation film with more corrosion resistance.After immersion in 0.1 mol/L H₂SO₄solution at room temperature for 30 days,the surface corrosion of MEA is more serious than that of MEA-Ce,and large corrosion pits appear,which indicates that the protection of passive film formed by mea after immersion in solution is worse than that of MEA-Ce.Therefore,it can be further verified that MEA-Ce is more corrosion resistant than MEA in 0.1 mol/L H₂SO₄ solution after the addition of rare earth elements.