Interactions Between Self-interstitial Dislocation Loop In Bcc-Fe And Surface And Crack Investigated By MD Simulation

Formation and evolution of interstitial dislocation loops induced by radiation damages in materials have been confirmed to seriously affect the performance of materials under irradiation.For example,in body-centered cubic(bcc)Fe based alloy,1/2<111> and <100> are mainly formed during the irradiation,which are related with various degradations of material properties.Thus,to understand their effects on radiation damages of material is always one of the hottest topics in nuclear material society.Meanwhile,under the irradiation,the micro-crack can also be formed in bulk and near the surface of the materials.In previous studies,although the radiation effects in structural materials used in nuclear reactors have been studied extensively,the interactions between the dislocation loop and surface,micro-crack,and its expansion have not been fully explored.In this work,the detailed interactions between the self-interstitial dislocation loop and surface,micro-crack and its expansion in bcc iron have been studied at atomic scale with the potential of Ackland-2004 Fe by molecular dynamics(MD)simulation method.DXA method of Ovito was used to analyze and characterize the defects and morphologies from the simulation results.The simulation results indicated that the factors including Burgers vector of loop,depth of loop to surface,the interaction between pre-existing <100> loops and temperature,all seriously affect the interaction between loop and surface.Especially,the present results show for the first time the evolution of Burgers vector of <100>loop from <100> to 1/2<111> and its 1D diffusion to surface.Based on these results,we also further explored the surface evolution after its interaction with loops.Further research results on the interaction between dislocation loop andmicro-crack indicate that the relative position between them,the slope of micro-crack,the size of loop and existence of free surface,would all affect the loop-micro-crack interaction and the related finally formed micro-structure after the interaction.Under the different conditions,the interactions either induce the formation of micro-scale complex radiation damage structure,or the absorption of dislocation by micro-crack,resulting in the rugged crack tips,which would affect the growth and expansion of micro-crack,the degradation of mechanical properties of materials under irradiation.Furthermore,the results can also be compared with the formation of dislocation and dislocation loop free zone near the crack tip observed experimentally,which can provide a new understanding to these phenomena.To explore whether the underlying reason induces the expansion of micro-crack on the slip plane or not,the simulation results indicate when the interaction between them dominates the whole process with the distance between them within the critical value,the dislocation network containing the <100> and 1/2<111> segments,would interact with the crack tip to inhibit the expansion of crack through the pinning effect.When the size of loop is different,the pining effect would also be available only when the interaction between loop core and crack tip is dominated with the distance between them within the critical value.All these results have provided new understandings of radiation damages on the surface of materials and irradiation assisted stress corrosion crack(IASCC)under irradiation.