Atomistic Modeling of Dislocation Plasticity in Metals and Alloys

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.

This thesis focuses on the robust and efficient quantification of energy barriers to dislocation motion in metals and alloys. The work combines advanced computational methods, such as the nudged elastic band (NEB) method and molecular dynamics (MD) simulations, to investigate rate-controlling mechanisms at the atomic scale.

The research begins with the development of the NEB method to calculate Peierls barriers for dislocation glide in face-centered cubic (FCC) nickel, identifying how these barriers decrease with increasing shear stress. The study then expands to model dislocation-obstacle interactions, exploring mechanisms like vacancy cluster cutting and cross-slip, using stress-controlled and strain-controlled simulations to reveal activation energies and rate-limiting processes.

In addition to atomistic modeling, the thesis presents a statistical analysis of short-range order (SRO) and short-range clustering (SRC) in binary and ternary alloy systems. This analysis demonstrates how alloy structures, such as NiCr and NiCrCo, exhibit SRO and SRC, which in turn affect dislocation glide and alloy strength.

Further, the thesis evaluates dislocation glide barriers in A600 alloys, providing detailed insights into the mechanical behavior of these complex alloys under shear loads. Finally, MD simulations of dislocation mobility in nickel and A600 reveal how mobility and threshold stress decrease with increasing temperature, highlighting the thermal effects on alloy performance.

To conclude, this thesis has developed and applied advanced computational techniques to quantify the energy barriers and dislocation mobility in Ni and Ni-based alloys. These results offer a mechanistic understanding of dislocation motion and interaction with defects, and also provide quantitative input or mechanistic support for dislocation dynamics and crystal plasticity modeling. This research establishes a solid foundation for future research into the rate-controlling mechanisms of dislocation motion in metals and alloys, contributing to the broader field of materials science.