Surface oxidization effect on the mechanical behavior of aluminum nanopowders under triaxial compression test

In this paper, the impression of surface oxidization on the aluminum nanopowders is investigated using the reactive molecular dynamics (MD) method under the triaxial compression tests. Validation of the computational model is examined with the experimental results, which demonstrates an acceptable accuracy of the numerical simulations. The MD simulations are performed in three stages; relaxing the nanopowders at 300 K and 0.1 MPa, confining the nanopowders under hydrostatic pressure, and imposing the deviatoric stress through the triaxial compression. Evolutions of the relative density with pressure, stress with strain, and dislocation density with strain are derived together with the distributions of the radial distribution function and the pressure contours to characterize the mechanical behavior of nanopowders during the compression tests. The effect of the oxide shell thickness of the nanopowders at different compression paths is studied from the mechanical and crystallographic points of view. The results highlight that the hardness of nanopowders increases, and its ductility decreases as the oxide shell thickness increases. The microstructural analysis demonstrates that the crystalline structure of the alumina shell changes mainly during the hydrostatic pressure, while the crystalline structure of the aluminum core is primarily affected during the triaxial compaction.