Microstructure And Ion Irradiation Of Metal Multilayer Film

With the continuous development of human society,the scarcity of fossil energy becomes more serious,and nuclear energy shows great development.The optimization and upgrading of nuclear reactors have continuously increased the requirements for the anti-radiation performance of nuclear materials.Therefore,the design of highly radiation-resistant materials is an indispensable condition for the development of nuclear energy.The grain boundaries(GBs)can effectively absorb irradiation defects,which seriously affect the serviceability of the material.However,effect of different GBs on the radiation damage cascade has not been clearly revealed at the nanoscale.The cascade evolution caused by irradiation in twinned copper,ordinary grain boundary copper and single crystal copper was studied by atomic simulation,focusing on the number of interstitial atoms or vacancies stabilized in copper with different GBs.Understanding the mechanical properties and deformation behavior of nanotwinned Cu/high-entropy alloy(HEA)FeCoCrNi nano-multilayer materials provides a theoretical basis for further understanding and designing advanced metal-based materials with good radiation resistance.Tungsten has excellent high-temperature performance,so it would most likely be one of the candidates for the material of the polarizer of the plasma nuclear fusion device.However,the uniform nucleation of tungsten at nanoscale has not been clearly revealed.Through the annealing experiment combined with molecular dynamics simulation,the relationship between the microstructure,mechanical properties and cooling rate of tungsten metal was studied.This work provides a process for preparing tungsten with excellent mechanical properties by adjusting the solidification rate.The main research contents and results are as follows:(1)The radiation damage process in twinned copper,ordinary grain boundary copper and single crystal copper was studied.Using copper atoms as the primary collision atoms,the radiation displacement damage caused by the incident of ions with 5 ke V energy into twinned copper,ordinary grain boundary copper and single crystal copper was simulated at 298 K.Theresults show that the radiation displacement effect caused by ion incidence mainly produces point defects,and these types include vacancy and interstitial atom.It was confirmed that the grain boundaries in twinned copper and ordinary grain boundary copper can be used as effective defect sinks to eliminate vacancy.The law of Frankel logarithm is generated during the cascade collision: in single crystal copper,it increases rapidly and then decreases,and finally obtains a stable value;in twinned copper and ordinary grain boundary copper,it quickly increases to the peak value,and then decreases.As the time increases,it increases to the maximum value,finally gets a stable value.The order of their radiation resistance from high to low is: twinned copper>single crystal copper>common grain boundary copper.(2)The deformation behavior of nano-twinned Cu/HEA FeCoCrNi nano-multilayer materials was studied.In Cu/FeCoCrNi multilayer,the nucleation and slip of lattice dislocations in Cu layer dominate,and slip dislocations are deposited at twinning boundary.As the strain increases,dislocations are activated in HEA layer and deposited in interface,which ultimately promotes the sliding transport from the FeCoCrNi layer to the Cu layer.With the increase in the number of nano-twinned Cu/HEA FeCoCrNi layers,the flow stress decreases and maintains a constant value,which depends on sliding transfer and interface dislocation to control strain hardening.It provides theoretical guidance and structural design for the development of HEA multilayers with excellent radiation resistance.(3)The relationship between tungsten microstructure and mechanical properties at different cooling rates was studied.Atomic simulation results show that an amorphous structure can be obtained at a cooling rate greater than 50K/ps;a hybrid structure of the stable BCC phase and an amorphous phase can be formed at cooling rates in the range of 10–50K/ps;a stable BCC phase can be generated at a cooling rate lower than 10K/ps.On the one hand,the hybrid structure wins over the BCC structure by enhancing the critical tensile strain,limiting the nucleation of cracks and reducing the degree of damage;on the other hand,the hybrid structure can deliver a higher strength than an amorphous structure.