Physics

Molecular dynamics simulation of shock wave propagation in pure aluminum and aluminum with $\theta'$ precipitates

P. A. Bezborodova, A. E. Mayer, V. S. Krasnikov

Chelyabinsk State University, Chelyabinsk, Russia

Abstract: Nowadays, molecular dynamics (MD) simulations are fruitfully used to reveal atomistic details of the shock-wave (SW) loading of various materials including metal alloys. In the part of alloys, most of MD studies are dedicated to solid solutions and concentrated alloys with uniform nanostructure. Although precipitation hardening is the predominant strategy for dilute alloys, the precipitation strengthened alloys are not currently well described by means of MD simulations of SW loading. Here we make first step in this direction by performing a comparative study of the SW propagation in pure dislocation-free aluminum single crystal and that with $\theta '$ precipitates as the main strengthening phase in Al-Cu alloys. We consider a single particle velocity of $1000$ m/s behind SW front, a single impact direction of $[100]$, a single precipitate diameter of $5$ nm and a single initial temperature of $300$ K. It is shown that the $\theta '$ precipitates provokes easer nucleation of dislocations and voids due to the inherent tensile and shear stresses localized in their vicinities. This heterogeneous nucleation enhances the dislocation density and plastic relaxation rate resulting in weaker elastic precursor. Besides, the elastic precursor in aluminum with precipitates reveals clear attenuation in contrast with the case of pure aluminum, where the homogeneous nucleation as the incipience of plasticity maintains the elastic precursor amplitude at a certain constant level. On the other hand, the easer nucleation of voids under tension in the reflected rarefaction wave does not decrease the spall strength of Al-Cu alloy, which, on the contrary, is about $4\%$ higher than in pure aluminum. The void growth hindering by the $\theta '$ precipitates overbalance the easer void nucleation and leads to the increase in spall strength.

Keywords: Aluminum, aluminum-copper alloy, $\theta '$ precipitates, shock wave, spall fracture, nucleation of dislocations, nucleation and growth of voids, plasticity and fracture, molecular dynamics.

UDC: 539.3

Received: 20.10.2024
Revised: 15.02.2025

Language: English

DOI: 10.47475/2500-0101-2025-10-3-580-594