Atomistic Simulation Studies Of The Creep Mechanical Properties Of Austenitic Nanocrystalline Fe-Ni-Cr Alloy

Due to gradual depletion of fossil fuels,nuclear power,as a clean and efficient electric energy,has broad application prospects.China is vigorously promoting independent nuclear power technology,and the installed capacity of nuclear power is constantly expanding.The radioactive core is located in the center of the reactor pressure vessel,which requires the reactor pressure vessel to be safe and reliable in the operation period,and the reactor pressure vessel must not undergo creep fracture.SA508 steel has excellent mechanical properties and has become one of the major materials for manufacturing pressure vessels.Atomistic scale creep simulation and irradiation damage simulation can observe the real-time evolution of microstructures and the dynamic response of cascade atoms in the whole deformation process,and understand the deformation mechanism of materials.In this paper,the creep behaviors and mechanism of austenitic nanocrystalline Fe-Ni-Cr alloy are studied by molecular dynamics simulation.Based on the molecular dynamics method,the creep behaviors of austenitic nanocrystalline Fe-Ni-Cr alloy are studied,and the effects of stress,grain size and temperature on creep mechanism are discussed.The results show that the creep curves have primary creep stage and steady-state creep stage due to the existence of defects such as vacancy,dislocation and grain boundary.Steady-state creep rate increases with the increase of temperature,grain size refinement and increase of applied stress.With the refinement of grain size and the increase of temperature,the stress exponent will change from 1 to 2,which means that the creep mechanism changes from diffusion creep to grain boundary slip creep.The grain size exponent increases with the increase of temperature and stress.The creep mechanism changes from lattice diffusion creep to grain boundary diffusion creep and grain boundary slip creep.When the temperature and stress are higher,the creep mechanism becomes dislocation creep.The microstructures of the corresponding creep mechanisms are also analyzed.The diffusion creep mechanisms are proved by the calculation of diffusion coefficient,diffusion activation energy and creep activation energy.The effects of PKA energy(low energy),temperature and grain size on the irradiation damage and the effect of irradiation on creep behaviors of austenitic nanocrystalline Fe-Ni-Cr alloy are studied by molecular dynamics method.The defects of polycrystalline materials will increase in the simulated time scale due to the existence of grain boundaries,and most of defects distributed at the grain boundaries,which is different from the stable defects formed by the annihilation of defects in single crystal materials.With the increase of PKA energy,the collision cascade becomes more severe.The induced sub-cascade and defects increase with higher temperature.At the end of the simulation,there is a power-law relationship between the number of total defects and the reciprocal of grain size.This is because with the refinement of grain size,the atoms at the grain boundaries are much more,and more defects induced at the grain boundary.A large number of defects are formed in the material after irradiation,and the creep strain and steady-state creep rate are raised.Irradiation has little effect on the stress exponent and grain size exponent,because the defects induced by cascade collision only account for a small proportion compared with the defects induced by grain boundaries.Compared with creep condition at high temperature and high stress,low energy irradiation has little effect.