Phase Field Method Simulation Of The Evolution Of Iron-based Alloy Irradiated Void Structure And Its Stress Effect

Iron-based and iron-nickel-based medium and high-temperature alloys have excellent high-temperature structural stability and radiation resistance,and are often used as components in nuclear reactor cores under high-temperature,high-pressure,and high-irradiation environments.Irradiation produces abundant vacancies and interstitial atoms and other radiation defects.Temperature and pressure induce radiation damage to tissues,resulting in material embrittlement,softening,swelling and other radiation effects,causing material failure and threatening the safe use of nuclear energy.Therefore,the effective control of radiation-damaged tissue has become a key issue for nuclear reactor safety,and revealing the evolutionary law of vacancy clusters into cavities and regulating them has become the core of the safe service of nuclear materials.Irradiation experiments are expensive and difficult to capture in situ observations.In view of the particularity of irradiation,irradiation experiments cannot meet the requirements for the evolution of the microstructure in the core cladding materials.The phase field method can capture the dynamic evolution of the irradiation-induced microstructure process.Aiming at the iron-based and iron-nickel-based irradiated void structures,this paper uses the coupled rate theory phase field method to study the effects of temperature,radiation dose,alloy composition and stress state on the evolution of voids.The main results obtained in the thesis are as follows.The study of the Fe-Cr alloy cavity nucleation and growth law and the influence of temperature and irradiation dose on the evolution of the void revealed that there is a clear positive correlation between the irradiation dose and the incubation period.The higher the irradiation dose,the shorter the incubation period.The relationship between the incubation period and the temperature is more complicated.When the temperature is relatively low,the incubation period is shortened when the temperature rises,and when the temperature continues to rise to a higher temperature,the incubation period is prolonged.The advection term is introduced into the Cahn-Hilliard conservative field model to simulate the influence of temperature gradient on void migration during irradiation.Vacancies and interstitial atoms diffuse from the low-temperature zone to the high-temperature zone in the opposite direction of the temperature gradient,and the vacancy concentration in the high-temperature zone is significantly higher than that in the low-temperature zone,resulting in preferential nucleation of cavities in the high-temperature zone.When there is a temperature gradient,the void continuously migrates from the low temperature region to the high temperature region driven by the heat flow,and the morphology of the void gradually changes during the migration process.Take Fe-Cr and Fe-Ni two alloys as examples to study the difference in irradiated structure caused by the difference in alloy composition.Cr is beneficial to inhibit the vacancy concentration and the nucleation of voids in the system;Ni can inhibit the clustering of vacancies and extend the void Nucleation and incubation period enhances the anti-radiation performance.The superposition of the stress field generated by the high-pressure environment and the uneven stress field of the material structure affects the nucleation,size and distribution of the voids.The phase field equations of coupled linear elastic strains are constructed,and the effects of applied stress field and dislocation stress field on the evolution of voids in core cladding materials are constructed.The orientation diffusion of vacancies under the action of elastic stress is manifested in the morphology of the voids,which changes the morphology of the voids.Under the action of applied stress and dislocation stress,the diffusion of vacancies and interstitials is accelerated,and the voids are easier to nucleate,which accelerates the evolution of voids.