Dislocation properties in BCC refractory compositionally complex alloys from atomistic simulations

Abstract

Body-centered cubic (BCC) refractory compositionally complex alloys (RCCAs) have emerged as promising candidates for aerospace, nuclear energy, and automotive applications due to their exceptional high-temperature strengths. It is well-known that dislocations play a critical role in the mechanical properties of refractory alloys. In this study, we examine the fundamental properties of edge and screw dislocations, including core energies and dislocation shear stresses (DSSs) in MoNbTi, NbMoTaW, and CrTaVW, at various temperatures using atomistic simulations with the state-of-the-art machine-learned interatomic potentials (MLIPs). Our findings reveal that at high temperatures, the DSS of edge dislocations exceed those of screw dislocations in MoNbTi and NbMoTaW alloys. This behavior is attributed to cross-kink diffusion and annihilation in screw dislocations, which leads to a more significant decrease in DSS as temperature increases. Furthermore, the DSS values of screw dislocations at low temperatures and those of edge dislocations at high temperatures closely align with experimental yield strengths. These results show that edge dislocations are primarily responsible for the high-temperature strengths of some of the RCCAs and are crucial for tuning their mechanical properties. Additionally, we observe that screw dislocations exhibit lower core energies than edge dislocations across all temperatures in the investigated alloys, indicating their greater thermodynamic stability. These findings underscore the importance of considering different types of dislocations at various temperature regimes in BCC RCCAs, which is essential for guiding alloy design within the vast compositional space.