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The FeNiCr alloys hold application potential in advanced reactors, however, irradiation hardening severely impacts their safety during service. To further enhance the irradiation hardening theory of the FeNiCr alloys, the interaction mechanism between 1/2{111} edge dislocation and 1/3 Frank dislocation loops in the equiproportional multi-principal solid solution Fe33Ni33Cr alloy and the influencing factors were investigated through the molecular dynamics (MD) simulations. Based on the model proposed by Osetsky and Bacon, a face-centered cubic cell with the x, y, and z axes of , , and was constructed with Fe33Ni33Cr as the matrix, and dislocation and dislocation loop were inserted into the cell. By varying the diameter of the dislocation loops and the temperature of the system, the diagram of the interactions and the stress-strain curves were obtained through MD simulation, and the influences of the size of the loops and temperature on the interaction process between the dislocation and dislocation loops were studied. The results indicate that the multi-principal component effect in the Fe33Ni33Cr alloy leads to stress fluctuations during dislocation slip, and the presence of the dislocation loops can cause the dislocation to have a significant stress peak during its slip process, that is, it has a remarkable hindering effect on the dislocation movement, thereby contributing to the irradiation hardening. At the three typical temperatures (300, 600, and 900 K), the critical shear stress of the interaction between the dislocation and dislocation loops is lower at high temperatures than at low temperatures. The reason is that the atomic thermal vibration caused by the temperature increase promotes dislocation motion, and the structural change during the reaction between dislocation and dislocation loops also has a considerable influence on the stress. The interaction between the dislocation and the dislocation loops at 300 K and 600 K is unfault mechanism. In the interaction process, the stacking fault in the Frank dislocation loop disappears and it transforms into a perfect loop, which further enhances the pinning effect of the dislocation loop. Additionally, the effect of dislocation loop size on dislocation slip was studied by comparing the interaction process diagram and the corresponding points on the stress-strain curve. When the diameter of the dislocation loop is 2, 4, and 6 nm, the change of the size of the dislocation loops increases the interaction area between the dislocation and the dislocation loop, and eventually the obstruction ability of the dislocation loop is strengthened. It is worth noting that when the size of the dislocation loop is 2 nm and 4 nm, the interaction leads to generating superjogs, and the generation of new structures increases the resistance of the dislocation to slip freely in the matrix. At the same time, the absorption mechanism which makes new structure increase the stress of the interaction process, resulting in a smaller critical shear stress difference due to the change in the size of the dislocation loops.

Low activation ferritic martensitic steel is considered as one of the candidate structural materials for the fourth generation reactor and fusion reactor. Low activation ferritic martensitic steel is based on Fe-Cr alloy, in which W is an important solute element. Irradiation embrittlement at low temperature is one of the important problems limiting the service of low-activation ferrite martensitic steels. The precipitated clusters during the service process cause hardening and embrittlement of the material due to the obstruction of dislocation movement by the precipitated clusters. An in-depth understanding of cluster precipitation behavior during service is helpful to understand the irradiation embrittlement of low-activation ferrite martensitic steels at low temperature. In order to simulate the precipitation kinetics of Fe-Cr alloy, by introducing composition-dependent pair potential, some improvements were made on the MIET_AKMC software developed by ourselves. The precipitation kinetics of coherent Cr-rich precipitates/clusters in Fe-Cr(8%, 10%, 16%, 20%)-W(0%, 1%, 2%) alloys during thermal ageing was simulated using the atomic kinetic Monte Carlo (AKMC) method. After thermal ageing, Cr precipitate into clusters to form Cr-rich precipitates/clusters, while W is still in a solid solution state. At the beginning of coarsening process, the radius of clusters, which was about (0.57±0.03) nm, was independent on simulation temperature and the initial Cr content in the box. The precipitation process of Cr cluster can be divided into three stages: nucleation, growth and coarsening. The Cr concentration in box and simulation temperature have an influence on the precipitation rate of Cr clusters. The presence of W can delay the precipitation kinetic process and the effect is most significant when Cr content is about 10%. This is due to that when Cr content is about 10%, the absolute value of the short-range order parameter for Fe-Cr has a maximum, quite independent of the composition and the temperature. The delay effect of W was related with the stronger binding energy between W and vacancy. For the binding energy between Cr and vacancy is 0.06 eV, while the binding energy between W and vacancy is 0.14 eV. From the simulation results, it can be deduced that W is benefit for materials performance, expect for solution strengthening, it can delay the precipitation process of Cr-rich clusters, which is harmful for materials performance.