Study On Ion Irradiation Effect Of Nickel-based Superalloy For Molten Salt Reactor

In recent years,the demand of social development for energy is increasing.As a high energy density,clean,low-carbon energy,nuclear energy will play an increasingly important role in meeting the future energy needs of mankind.Molten salt reactor,as one of the most promising fourth generation reactors,has attracted worldwide attention due to its good safety and high thermal conversion efficiency.However,due to the need to work in the harsh environment of high temperature and high radiation dose,the performance of structural materials of molten salt reactor is challenged.UNS N10003 nickel base alloy is considered as the most promising candidate material for molten salt reactor because of its excellent high temperature mechanical properties and high temperature stability.However,the structure and properties of UNS N10003 nickel base alloy under different irradiation conditions need to be studied.In this thesis,TEM,SEM,XRD,OM and Nano Indenter were used to characterize the microstructure evolution and macroscopic properties of the alloy before and after irradiation.The effects of irradiation dose and temperature on the irradiation hardening,defect evolution,lattice change and surface morphology of UNS N10003 alloy were studied.Conclusions are as followed:Firstly,the TEM samples of UNS N10003 alloy were irradiated by 1 MeV Xe²⁰⁺ions.When the irradiation dose was 0.5 dpa,obvious black spots appeared in the alloy.With the increasing of irradiation dose,the number of black spot defects decreases and dislocation loops and dislocations increase.When the irradiation dose reaches 5 dpa,the structure of light dark phase appears in the alloy.There are a lot of second phase in UNS N10003 alloy,which is confirmed to be M₆C by TEM.After ion irradiation,the phase tends to be amorphous;When the irradiation dose reaches 0.5 dpa,the second phase is amorphous.TEM samples after irradiation were studied by in-situ heating technique of TEM.The results show that when the irradiation dose is 0.5 dpa,the number of black spots decreases slowly when the temperature rises to 450?.With the temperature rising to 500?,the number of black spots begins to decrease sharply and dislocation loops are formed obviously;When the irradiation dose of 10dpa is heated in situ,the structure of the light dark phase does not change significantly when the temperature rises to 450?.When the temperature rises to 600?,the structure of the light dark phase is gradually destroyed.When the temperature rises to 700?,the structure of the light dark phase is no longer continuous.Secondly,the bulk samples of UNS N10003 were irradiated by 7 MeV Xe²⁶⁺ions.The results of GIXRD show that the crystal lattice of the samples does not change significantly until the irradiation dose is 10 dpa.No obvious effect of ion irradiation on the alloy surface was observed by optical microscope and scanning electron microscope.The hardness and modulus of the irradiated bulk samples were studied by nanoindentation.The results show that the hardening of the alloy occurs when the irradiation dose is 0.5 dpa,and the hardening degree increases with the increase of irradiation dose.However,the young's modulus of the alloy does not change significantly at different irradiation doses.Finally,TEM results show that the surface of the alloy is amorphous when the irradiation temperature is room temperature and the irradiation dose is 10 dpa and 15 dpa.The maximum range of ions in the room temperature sample with 10 dpa radiation dose is 1400 nm,which is consistent with the SRIM calculation results.The peak damage depth is 1200 nm,which is larger than the SRIM simulation results;The maximum range of ions in the sample with 15 dpa radiation dose is 1700 nm,and the peak damage area is 1500 nm,which are larger than the SRIM simulation results.The number of defects in the room temperature sample increases with the increasing of radiation dose.When the irradiation temperature is 600?and the irradiation dose is 10 dpa,there are obvious dislocation loops in the alloy.