Atomistic study on the dynamic response of the void or helium bubble in aluminum under compression and tension

WD Wu and JL Shao, JOURNAL OF APPLIED PHYSICS, 127 (2020).

DOI: 10.1063/5.0004698

This work investigates the deformation and dynamic property of the pre- existing void or helium (He) bubble in aluminum (Al) under compression and tension with molecular dynamics simulations, where both the uniaxial and triaxial loadings at a high strain rate are considered. Under compression, the void completely collapses by plastic deformation and after that a recrystallization process is found. The He bubble undergoes a finite collapse because of its internal pressure. Solidification of the He bubble is also observed at a sufficiently high pressure. Moreover, stacking fault tetrahedrons (SFTs) are found under the triaxial compression, instead of the shear dislocation loops under the uniaxial compression. Under tension, the volume of the void or He bubble is nearly proportional to the strain before instability and begins to grow sharply after instability. The instability volumes of the void or He bubble and the corresponding strains approximately satisfy a linear reduction distribution. When the pre-existing void collapses completely, new void nucleation will appear under tension. Interestingly, the triaxial tension produces a large void from the vertex of SFTs, while uniaxial tension produces many small voids at the intersection of the stacking faults. As for the He bubble, it will first be elongated along the tension direction under uniaxial tension. With the increase of tension strain, the void or He bubble grows into an irregular polyhedron and tends to be isotropic for both uniaxial and triaxial tension. In the meantime, the He atoms will deposit on the boundary eventually because the attraction between He and Al is included. In addition, the difference of temperature and pressure between the He bubble and Al matrix is discussed, and an empirical model is proposed to describe the He bubble pressure during the loading process.

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