Studies On The Developing Of Interatomic Potentials And Simulations Of Primary Radiation Damage In Vanadium Alloys

Vanadium(V)-based materials are considered candidates for future fusion reactor structures due to their high thermal conductivity,good thermal creep,and high resistance to radiation swelling.The irradiation resistance of fusion reactor structural materials has a major impact on their safety and service life.Compared to traditional VTi-Cr alloys,recent studies have shown that traditional V-Ti-Ta alloys,V-Ti-Ta mediumentropy alloys(MEAs)and V-Ti-Ta-Nb high-entropy alloys(HEAs)have higher compressive strength,higher oxidation resistance and better wear resistance.There are limitations in the experimental study of the irradiation resistance of these alloys,such as high costs and difficulties in microscopic characterization,and there is an urgent need to combine multi-scale computational simulations to investigate the irradiation resistance and mechanisms of new V alloy materials.Highly accurate and computationally efficient potentials for interatomic interactions are a key basis for multi-scale simulations of the irradiation properties of V alloys,which cannot be carried out effectively due to the lack of potentials for V alloys.Therefore,we have developed potentials for the elements Ti and Nb,and further developed potentials for the V-Ti,V-Ta,V-Nb,V-Ti-Ta and V-Ti-Ta-Nb alloy systems in combination with the potentials for elements V and Ta already developed by the group.These potentials are in Finnis-Sinclair form and the short-range interatomic interactions are described by ZBL functions.The developed Nb and Ti elemental potentials were tested to describe well the lattice constants,cohesion energies,bulk moduli,elastic constants,vacancy and interstitial formation energies of the materials,and to reasonably predict properties such as vacancy migration energy,surface energy and stacking fault energy.The constructed alloy potentials provide a reasonable description of the typical defect properties of the solute Ti,Ta and Nb atoms in V as well as the enthalpy of formation,elastic constants and bulk modulus of the binary alloy.The construction of highly accurate potentials provides a key basis for molecular dynamics simulations of primary damage in irradiated V alloys.Firstly,primary irradiation damage to pure V was investigated using the constructed potentials.The fraction of vacancy clustering and vacancy cluster size was found to be higher than the fraction of interstitial clustering and interstitial cluster size,mainly due to the more dispersed distribution of interstitial defects after the collisional cascade,the smaller difference between the binding energy of interstitial clusters and vacancy clusters and the lower vacancy migration energy.The dislocation loops produced by the collision cascade are mainly 1/2<111> interstitial and vacancy-type dislocation loop,including a small proportion of <100> vacancy-type dislocation loops.Compared to pure tungsten,collision cascades in V are more prone to vacancy-type dislocation loops,mainly because the formation energy of vacancy-type dislocation loops in V is close to that of voids containing the same number of vacancies,whereas the formation energy of vacancy-type dislocation loops in tungsten is much higher than that of voids.The results of the collision cascade establish the cornerstone for understanding the primary irradiation damage and subsequent defect evolution studies of pure V.Secondly,primary irradiation damage of V-5Ti,V-5Cr and V-5Ta alloys was then investigated and compared with pure V.The results show that the addition of solute atoms has no significant effect on the number of Frenkel pairs,the defect clustering fraction,the defect size and the defect type produced by the collisional cascade.The long-time evolution of defects by the defect-driven method revealed that the addition of solute atoms significantly suppressed the motion of defects,resulting in smaller defect cluster sizes in the alloy.Finally,primary irradiation damage was investigated in V-5Ti-5Ta alloys,V-Ti-Ta MEA and V-Ti-Ta-Nb HEA.The results show that compared to pure V and V-5Ti-5Ta alloy,the collision cascades of V-Ti-Ta MEA and V-Ti-Ta-Nb HEA take longer to reach the thermal peak state,take longer to stabilize,and end up with a slightly higher number of residual Frenkel defect pairs and lower defect clustering and defect sizes.The number of dislocation loops in the V-Ti-Ta MEA and V-Ti-Ta-Nb HEA is much lower than that in the pure V and V-5Ti-5Ta alloy,mainly because the binding energy of interstitial and vacancy-type dislocation loop is much lower in the V-Ti-Ta MEA and V-Ti-Ta-Nb HEA than in the pure V and V-5Ti-5Ta alloy systems.In summary,in this dissertation,elemental potentials for Ti and Nb,and alloy potentials for V-Ti,V-Ta,V-Nb,V-Ti-Ta and V-Ti-Ta-Nb are constructed.The potentials meet the needs of defect interaction and collision cascade simulation studies in V alloys and expand the library of potentials for V alloys.The collisional cascade processes in primary irradiation damage of pure V,V-based binary alloys,V-5Ti-5Ta alloy,V-Ti-Ta MEA and V-Ti-Ta-Nb HEA were studied using the developed potentials to obtain detailed information on the number,type and structure of defects.The results of the above study provide the basis for understanding modelingling of primary irradiation damage and subsequent defect evolution over time in V alloy systems.Compared to pure V and traditional V-5Ti-5Ta alloy,the V-Ti-Ta MEA and V-Ti-Ta-Nb HEA exhibit superior irradiation resistance during the primary irradiation damage phase.The results of this dissertation provide a theoretical basis for accelerating the development of V alloys and the optimization and design of advanced V alloys irradiation-resistant materials.