Phase-field Study Of Mechanical Behaviors On Semi-coherent Interface In Irradiation Material

The thermonuclear reaction produces a large amount of inert gas element helium(He).Large quantities of He atoms will diffuse and aggregate into He cdusters even He bubbles owing to the insolubility of He atoms in metals.Those precipitations can seriously affect the mechanical properties of the material,resulting in swelling,embrittlement,hardening and so on,thereby shortening the service life of the materials and restricting the development of nuclear science and technology.Therefore,it is important to explore and understand the formation and evolution of He bubbles on the semi-coherent interface dislocation network for the design of radiation-resistant materials.It is found that defects such as vacancies,voids,grain boundaries and dislocation networks are beneficial to the nucleation of the He bubbles,and the He atoms tend to diffuse and accumulate on the dislocation network to form a periodic bubble array.At present,a large number of methods such as molecular dynamics and Monte Carlo simulation have been carried out to study the microscopic process of bubble formation.Atomic simulation can obtain the basic physical parameters of defects,but it is limited to time and space scales and cannot directly describe the long-term behavior between defects.The continuum model simplifies the processing of short-range atomic interactions between defects,such as dislocation core structures.Phase field method can not only use the microelastic theory to deal with the long-range elastic action on the continuous scale,but also use the atomic simulation results as input to deal with the short-range atomic action of the defect.Based on this,this paper uses the phase field microelastic theory and the Peierls-Nabarro model to study the interaction mechanism between defects.Firstly,the phase field model of dislocations is established,and the formation mechanism of dislocation networks with different orientations on semi-coherent interface under lattice mismatch and torsion mismatch is studied.Based on the model,we develop an improved phase-field model to study the segregation of He atoms at dislocation networks that takes dissociation of dislocation into account.It is found that the diffusion of He atoms is closely related to the periodically distributed stress field of the dislocation networks.In addition,the model is used to study the effects of mismatch value,rotation angle,stacking fault energy and layer thickness on helium bubbles distribution and morphology,therefore we can adjust He bubbles array distribution and He bubbles growth modes.These simulation results shall enrich our understanding on the mechanical behavior of helium in irradiated materials and provide theoretical guidance for designing radiation resistant materials.Furthermore,the interaction between a dissociated edge dislocation and a spherical void or inclusion is a micromechanical mechanism that causes hardening of face-centered cubic crystals materials under irradiation,a good understanding of the interaction mechanisms between dislocation and spherical inclusion is indispensable for studying material hardening.In this paper,we establish a phase field model of dislocation bypassing a spherical void,and simulate the effects of stacking fault energy and applied shear stress on the interactions.In addition,we consider the influence of spherical inclusion internal modulus on the interaction between a dislocation and spherical inclusion.All calculation results provide a new idea for understanding material hardening.