Research On The Precipitation Hardening Behavior Of FeCr Alloy Used As Fuel Cladding

FeCr alloy exhibits excellent high temperature oxidation resistance,It shows lower reaction activity with high temperature water,which is different from zirconium cladding.Therefore generation of hydrogen would be reduced significantly under severe accident circumstance.Nowdays FeCr alloy has been recognized as one of the candidate materials for accident tolerance fuels.However,irradiation induced hardening and embrittlement are also shortcomings that cannot be ignored,which reduces service life and reload cycle.Research on the mechanisms of irradiation hardening and mechanical properties of FeCr alloy will provide helpful guidance for its engineering applications.In this paper,Fe14Cr,Fe20Cr,Fe14Cr5Al,Fe20Cr5Al alloys were prepared by arc smelting and aged at 500℃for 50h,100h,150h and 200h respectively.The aged samples were used to analyze the hardening effect of theα’precipitated phase,and the aged samples were irradiated with He ions at two dose rates.The mechanism of radiation hardening was analyzed by means of microhardness,nanoindentation,X-ray diffraction,positron annihilation technology and transmission electron microscope.The microhardness test results of the aged samples show that the increase of the aging time increases the microhardness of the alloy,and the increase of the Cr content also increases the hardness of the alloy.This is because long-term aging and high content of Cr are easier to precipitateα’phase,and the increase in hardness is due to the second phase hardening effect ofα’phase;the addition of Al makes the hardness of the alloy drop significantly,indicating that Al can inhibitα’Of precipitation.The results of positron lifetime spectroscopy showed that the short lifetime in the sample did not change much and decreased slightly,indicating that the aging process had little effect on the vacancy density in the sample.The 200h-aged Fe20Cr sample was analyzed by transmission electron microscopy,and rod-shaped,dispersed precipitation phases were observed.The content of 40%Cr-rich phase was in the transition stage from nucleation growth to spinodal decomposition.The Fe14Cr sample was subjected to 300Ke V He+ion irradiation experiments at room temperature,the total fluence was 5.29E16cm^-2,and the dose rate was 1.47E13cm^-2s^-1 and7.31E14cm^-2s^-1,respectively.The nanoindentation test results after irradiation show that the dose rate has a significant effect on the hardness of the alloy.The hardness of the sample under low dose rate irradiation increases more,and the hardness of the irradiated layer is greater.The change trend of the elastic modulus in the two samples is basically the same.As the indentation depth increases,the elastic modulus shows a downward trend.The XRD results show obvious three strong peaks of FeCr,which represent（110）（200）（211）crystal planes.The corresponding crystal grain size of each crystal plane is calculated.The results show that the crystal grain size increases slightly with aging time.