SUMMARY

Dislocations play a crucial role in the plasticity of crystalline solids. Recent studies on dislocation processes in compositionally complex alloys, also called high-entropy alloys, have sparked interest in quantitatively determining energy barriers of dislocation movements in metals and alloys. However, traditional methods like molecular statics, molecular dynamics (MD), and coarse-grained models face timescale or accuracy limitations when determining these energy barriers. To overcome these challenges, we will employ the nudged elastic band (NEB) method, which is rooted in transition state theory and allows for the atomistically accurate determination of energy barriers as a function of applied loading.
In the proposed thesis research, we will develop strain- and stress-controlled NEB methods, ensuring the robust and efficient application of NEB methods for calculating Peierls barriers in a representative face-centered cubic single crystal of Ni. Subsequently, we will apply these NEB methods to calculate stress-dependent energy barriers for stacking fault tetrahedra (SFT) cutting and cross slip in Ni, considering different SFT sizes and spacings. The corresponding rate-limiting processes will be identified. Alloy systems introduce greater complexity due to the local variations in element distributions. To address this complexity, we will conduct Monte Carlo simulations to investigate short-range ordering and short-range clustering using statistical auto- and cross-correlation function analysis. Peierls barriers and mobility in Ni-based alloys will be determined using MD simulations and NEB calculations. Traditional embedded atom method potentials and machine-learning potentials will be utilized in both static and dynamic simulations.
This Ph.D. thesis research will demonstrate the robust and efficient quantification of energy barriers to dislocation motion in metals and alloys. Our approach is general and can be applied to investigate rate-controlling mechanisms in compositionally complex alloys for achieving outstanding mechanical properties in the future.