Phase Field Simulation Of Irradiation-Induced Dislocation Loop Climbing And Grain Boundary Cr Segregation In Fe-cr Alloys

In the process of service,nuclear reactor materials are subjected to high temperature.high pressure and the impact of highly irradiated particles.As a result,the organization and mechanical properties of the materials in service are changed,resulting in material failure and other serious problems.which poses a great threat to the efficient and safe use of nuclear energy.The impact of high-energy particles(neutrons,ions,electrons)on materials will produce a large number of point defects(vacancy and gap atoms),which gradually evolve into holes,helium bubbles,dislocation loop and other radiation damage tissues through cluster aggregation,recombination or interaction with other deficiency traps(dislocation,precipitation,grain boundaries,etc.).lrradiation embrittlement,irradiation hardening and swelling of materials were caused.Ferritic/martensitic steel(F/M steel,BCC structure)has excellent properties such as anti-swelling.anti-corrosion and creep,and is one of the potential alternative structural materials for fourthgeneration nuclear reactors.However,F/M steel is prone to embrittlement under low-temperature irradiation.which greatly limits its development and application.A large number of experiments and theoretical calculations show that the radiation brittle damage of materials is mainly related to radiation defect clusters(cavities,dislocation rings,etc.),irradiation induced solute segregation and precipitation.Therefore,in this paper,Fe-Cr alloy is taken as the research object.Based on linear elasticity theory and interface theory,the phase field method is used to construct the interstitial dislocation loop and grain boundary model,and the interstitial dislocation loop climbing growth,solute segregation and irradiation-induced solute segregation and precipitation are studied respectively.The main achievements of the paper are as follows:A phase field model suitable for<001>gap dislocation loop climbing growth and solute segregation was established.The effects of temperature,elastic energy and dislocation gradient on gap dislocation loop climbing growth and Cr segregation were systematically simulated.The simulation results show that with the change of temperature,the size and shape of the gap dislocation loop and the Cr segregation around the dislocation loop will also change.The size of the dislocation loop at high temperature is larger than that at low temperature.The anisotropic growth of dislocation loop is driven by the existence of elastic energy,which is consistent with the experimental results.The results also show that the increase of the gradient coefficient accelerates the climb growth of the dislocation loop,and the dislocation loop changes from elliptic shape to lens shape.In this paper,a model of irradiation-induced solute segregation at grain boundaries was established by modifying the kinetic equation of Cr atom with Darken equation,and the enrichment or dilution of Cr near grain boundaries was studied.The simulation results show that irradiation dose rate and temperature affect the enrichment or dilution state of Cr at the grain boundary,and have certain effects on the nucleation and growth of Cr-rich second phase.Irradiation accelerates the migration rate of Cr atom to or from the grain boundary,and with the increase of irradiation dose rate,Cr segregation or dilution at the grain boundary becomes more obvious.Taking Fe-10Cr as an example,the effect of temperature on the segregation and dilution of Cr around the grain boundary was simulated.The results show that Cr is enriched at the grain boundary when the temperature is less than 600K,and Cr is less than 500K,and the segregation is not obvious.When the temperature is higher than 600k,Cr element is depleted at the grain boundary,and the degree of Cr element dilution increases with the increase of temperature.