Migration mechanisms of BCC vanadium grain boundaries under temperature gradients: insights from molecular dynamics...

Processing techniques such as annealing or sintering, as well as high-temperature operational environments like nuclear reactor cladding, are influenced by temperature gradient conditions, which drive grain boundary migration toward the thermal gradient, thereby altering material properties. The high melting point of body-centered cubic (BCC) transition metal vanadium (~ 2194 K) enables simulations across a wide temperature gradient range without phase transformations, allowing a focused investigation of the effects of temperature gradients and grain boundary structure on migration rate. We employed molecular dynamics simulations to investigate the atomic rearrangement and migration behavior of different types of grain boundaries in vanadium metal under temperature gradient driving forces. The study revealed that the grain boundary structure significantly affects the migration rate below the disordering transition temperature (approximately 0.5-0.7 $T_m$ ). Low-misorientation grain boundaries can be described by dislocation structures, where temperature gradients induce sliding of 1/2 < 111 > screw dislocations while < 100 > edge dislocations hardly slide or climb. Some high-misorientation grain boundaries enable coordinated atomic motion through hexagonal or square lattice structures. Above the disordering transition temperature, local disordering occurs, and excess free volume and vacancies facilitate a transition from hopping-like atomic motion to collective string-like atomic motion or atomic diffusion. Additionally, grain boundary roughening transitions promote structural disordering, significantly enhancing migration rates. These findings elucidate the temperature-dependent nature and multi-mechanism synergy of grain boundary migration in vanadium, providing a theoretical foundation for optimizing microstructure and mechanical properties.

In this study, molecular dynamics simulations were utilized to investigate the influence of grain boundary structure on migration behavior in BCC vanadium under temperature gradients. The simulations were performed using LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator) software with an Embedded Atom Method (EAM) potential to model interatomic interactions. Bicrystal models with various grain boundary types (e.g., Σ5, Σ31a) were constructed using Atomsk and subjected to temperature gradients of 500-1100 K and 600-1600 K, with a time step of 1 fs. Structural dynamics and migration behavior were analyzed using LAMMPS and visualized with the OVITO software, providing detailed insights into microstructural evolution under thermal gradients.