Molecular Dynamic Simulation Of Radiation Resistance Of Nickel-based Alloys

With the development of economy,the demand for energy is increasing with the continuous improvement of human living level.However,the global fossil energy is facing the crisis of exhaustion.Finding alternative clean reproducible energy to solve the energy crisis has become one of the hot topics in global.Nuclear energy is recognized as the most ideal alternative clean energy,because of its advantages such as cleanliness,environmental protection and high efficiency.As the key components in nuclear reactors,structural materials are generally exposed to special conditions such as high temperature,corrosive media,and irradiation,which directly determine the safety and service life of nuclear reactors.Therefore,the research and development of structural materials are very important in the application and development of advanced nuclear reactors.At present,Ni-based alloys have important application prospects as future advanced nuclear reactor structural materials,so it is necessary to study the radiation resistance of Ni-based alloys.In this thesis,the irradiation resistance of pure Ni,binary Ni alloys,ternary Ni amorphous,and ternary single-phase concentrated solid-solution alloy was studied by molecular dynamics simulations.Firstly,we studied the effects of three symmetrical grain boundaries and doped He atoms on the cascade defects of pure Ni alloys.The simulation results show that the symmetric grain boundaries of ?11(113)and ?19(331)have an"adsorption"effect on the irradiation-induced interstitial atoms and doped He atoms,which results in the distribution of interstitial atoms and vacancy defects in different regions and then reduces the defect recombination rate.However,the symmetric grain boundary of ?3(111)has a minor effect on the irradiation defects in Ni.At the same time,we also found that the distribution of He clusters in the symmetric grain boundaries of ?11(113)and ?19(331)promotes the formation of dislocation loops in pure Ni.Secondly,to simulate the irradiation effects of Ni Mo alloys,we use MAEAM potential function models to construct Ni Ni,Mo Mo and Ni Mo potential functions and detailed comparison with experimental values,DFT values and existing potential function results.These results show that the physical properties obtained by the MAEAM potential function are in good agreement with the experimental values and the DFT results.Compared with the existing potential function,our potential function can describe the relative performance of defects with higher accuracy.Furthermore,the constructed potential function was used to studied the irradiance resistance of Ni and Ni Mo alloys,and analyzed the formation and distribution of irradiated defects.The results showed that this potential function can be applied to the cascade simulation of Ni Mo alloy systems.Next,we studied the relationship between the glass-forming ability(GFA)and the irradiation performance in Ni-Zr-Mo ternary amorphous.In this work,we focused on the effect of the element addition on microstructures and GFA of Ni-based alloys.The results show that with the increasing of Mo contents,GFA first increases up to the maximum value(f_Mo=0.21),and then the GFA decreases when Mo element is added,which is consistent with the existing theoretical and experimental results.What's more,the additive Mo atoms don't just replace the largest Zr atoms,but remarkably change the atomic structure and chemical order,resulting in a more stable,compact and complex system.We verified that the proposed topologically close-packed(TCP)cluster can effectively and accurately describe the GFA of the system by calculating the electron state density through the first-principle molecular dynamics method,while the icosahedron(ICO)clusters cannot accurately represent the relationship between the GFA of the system and the Mo content.Furthermore,we simulated the cascade collision process of Ni₆₄Zr_36-xMo_x,and analyzed the structures by TCP clusters and indicated that the more TCP clusters,the better the GFA and the stronger the radiation resistance.Finally,we made a comparative study of the radiation resistance between Ni and Ni Co Fe ternary single-phase concentrated solid-solution alloy.The results show that Ni Co Fe single-phase concentrated solid-solution alloy has a slower energy dissipation during the cascade process compared with pure Ni,and the migration and movement of interstitial defect clusters is a three-dimensional model.Then there are a few the residual defects after irradiation,therefore this system remains a high recombination rate of defects and an improved radiation resistance.And then the dislocation reaction in Ni and Ni Co Fe single-phase concentrated solid-solution alloy was further analyzed to explain the mechanism of complex dislocation loops/networks induced by irradiation.In summary,this article comparatively studies the radiation resistance of pure Ni,Ni-based alloy,Ni-based amorphous and Ni-based single-phase concentrated solid-solution alloy.The atomic simulation studies revealed the mechanism of structural evolution during the irradiation of different Ni-based alloy systems and the physical fundamentals for the good radiation resistance of the Ni-based amorphous and Ni-based single-phase concentrated solid-solution alloy.Importantly,a new method of adjusting the composition of amorphous alloys was proposed to selectively control the structure of amorphous alloys and GFA to obtain good radiation resistance,which can provide a guidance for the manufacture of amorphous alloys towards exploring designing the advanced nuclear reactor structural materials in the future.