Yankun Dou

The motion of edge dislocations and the interaction between edge dislocations and dislocation loops in pure V and TiVTa alloy are simulated in this work, with the aim to reveal the influences of the existence of \begin{document}$ \left\langle {111} \right\rangle $\end{document} dislocation loops, which are dominant in pure V, and \begin{document}$ \left\langle {100} \right\rangle $\end{document} dislocation loops, which are dominant in TiVTa alloy, on the irradiation properties of materials and the differences between the irradiation properties influenced by the two types of dislocation loops. The edge dislocations and \begin{document}$ \left\langle {100} \right\rangle $\end{document} loops and \begin{document}$ \left\langle {111} \right\rangle $\end{document} loops with different sizes are introduced into pure V and TiVTa alloy by using molecular dynamics simulation technology. The effects of loop type, loop size, and temperature on the interaction between edge dislocations and dislocation loops in pure V and TiVTa alloy are compared with each other and analyzed. The differences in interaction between dislocations and dislocation loops are summarized, and the reasons are revealed.The simulation results of edge dislocation motion reveal that the velocity of edge dislocations in the pure V decreases with temperature increasing, while the velocity of edge dislocations in the TiVTa alloy shows no significant relation to temperature. This is due to phonon-drag mechanism controlling the motion of edge dislocations in the pure V. In the TiVTa alloy, due to inevitable local chemical fluctuations, the phonon-drag mechanism and the nanoscale segment detrapping mechanism simultaneously control the motion of edge dislocations.The simulation results of the interaction between edge dislocations and dislocation loops show that there are two kinds of interaction mechanisms between dislocations and loops in pure V and TiVTa alloy: for small dislocation loops, dislocations tend to absorb the loops and continue to move; for large dislocation loops, dislocations tend to go through the loops and then move forward. With the size of dislocation loop increasing, the stress required for dislocations to detach from the dislocation loops also increases. With the increase of temperature, the stress required for dislocations to detach from the dislocation loops decreases. This is because the larger the size of the loops, the larger the contact area between dislocations and loops, and the greater the obstacle presented by the loops. With the increase in temperature, atomic vibrations are accelerated, and the hindrance of the loops is reduced.When comparing the interaction between \begin{document}$ \left\langle {100} \right\rangle $\end{document} loops and \begin{document}$ \left\langle {111} \right\rangle $\end{document} loops and dislocations, it is found that the hindrance of \begin{document}$ \left\langle {111} \right\rangle $\end{document} loops to dislocation movement is lower than that of \begin{document}$ \left\langle {100} \right\rangle $\end{document} loops, and the difference in the hindrance to dislocation between \begin{document}$ \left\langle {100} \right\rangle $\end{document} loops and \begin{document}$ \left\langle {111} \right\rangle $\end{document} loops is more significant in pure V than what is observed in TiVTa alloy. This is because the mobility of \begin{document}$ \left\langle {111} \right\rangle $\end{document} loops is higher than that of \begin{document}$ \left\langle {100} \right\rangle $\end{document} loops, the hindrance to dislocation motion of \begin{document}$ \left\langle {111} \right\rangle $\end{document} loops is lower than that of \begin{document}$ \left\langle {100} \right\rangle $\end{document} loops. However, in the TiVTa alloy, significant lattice distortion reduces the mobility of \begin{document}$ \left\langle {111} \right\rangle $\end{document} loops. Therefore, the hindrance of \begin{document}$ \left\langle {111} \right\rangle $\end{document} loops in the TiVTa alloy is lower than that of \begin{document}$ \left\langle {100} \right\rangle $\end{document} loops, but the difference between them is reduced compared with what is observed in pure V.

Among the currently developed multi-principal element alloys (MPEAs), Ti-V-Ta MPEA stands out because of its good high-temperature strength, good room-temperature plasticity, stable organizational structure, and low neutron activation, and becomes a first option for cladding material of special power reactors. The radiation resistance of Ti-V-Ta MPEA is the focus of current research. Dislocation loops are the main irradiation defects in Ti-V-Ta MPEA, which can significantly affect the mechanical properties. Therefore, clarifying the formation mechanism of dislocation loops in Ti-V-Ta HEA can help to understand its radiation resistance. The formation behavior of dislocation loops in Ti-V-Ta MPEA is studied based on molecular dynamics method in this work. Cascade overlap simulations with vacancy clusters and interstitial clusters are carried out. The cascade overlap formation mechanism of dislocation loops is analyzed and discussed. In Ti-V-Ta MPEA, the cascade overlap with defect clusters can directly produce different types of dislocation structures. The defect configuration after cascade overlap is determined by the primary knock-on atom (PKA) energy and the type and size of the preset defect clusters. Cascade overlap can improve the formation probability of \begin{document}$ \left\langle {100} \right\rangle $\end{document} dislocation loops in Ti-V-Ta MPEA. Cascade overlap with vacancy clusters is an important mechanism for the formation of \begin{document}$ \left\langle {100} \right\rangle $\end{document} vacancy dislocation loops, and the size of vacancy clusters is the dominant factor for the formation of \begin{document}$ \left\langle {100} \right\rangle $\end{document} vacancy dislocation loops. When the PKA energy is enough to dissolve the defect clusters, \begin{document}$ \left\langle {100} \right\rangle $\end{document} vacancy dislocation loops are more likely to form. Furthermore, cascade overlap with interstitial clusters in Ti-V-Ta MPEA is a possible mechanism for the formation of \begin{document}$ \left\langle {100} \right\rangle $\end{document} interstitial dislocation loops. This study can contribute to understanding the evolution behavior of irradiation defects in Ti-V-Ta MPEA, and provide theoretical support for designing the composition and optimizing the high-entropy alloys.