High strain rate molecular dynamics simulations of pre-existing edge dislocation in Al, Cu and Ni: Arrhenius to non-Arrhenius transition

A Verma and SK Singh and NK Rawat and N Jain, MOLECULAR SIMULATION, 51, 396-406 (2025).

DOI: 10.1080/08927022.2025.2484321

In this article, the authors have conducted classical mechanics-based molecular dynamics simulations to compute edge dislocation velocity in three face centered cubic (FCC) metals that are Aluminium, Copper, and Nickel. The dislocation velocity trend was reported as a function of the temperatures in conjunction with variation in the strain rate values. Basically, the dislocation migration is assumed to be a thermally activated (Arrhenius) phenomenon, i.e. the dislocation velocity increases as the temperature values increase. We have predicted that for the higher strain rate regime, all three FCC elements showcase an anti- thermal (non-Arrhenius) behaviour i.e. the dislocation velocity is inversely proportional to the temperature. The phonon scattering mechanism has been thought of as the chief reason behind this compelling behaviour of dislocation drag. Interestingly, at lower strain rates, the authors perceived a transition from Arrhenius to non-Arrhenius dislocation migration behaviour at a certain critical temperature (Tc). In Aluminium and Copper, the shift from Arrhenius to non-Arrhenius behaviour occurred at approximately 150 K; whereas in Nickel, this transition is observed at around 300 K. We anticipate that with further lowering of the strain rates, the Tc would become even higher. This is mainly because the thermal fluctuations dominate at lower strain rates, whereas the phonon drag mechanism at higher strain rates. It was also noticed that the material possessing a higher Young's/bulk/shear modulus and melting temperature exhibited a higher Tc (the temperature at which Arrhenius behaviour of dislocation migration transits to non-Arrhenius).

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