[SY-G5] Metallic materials under extreme pressure: Interplay of plasticity and phase transitions
Invited
Shock waves are ubiquitous in various fields of activity including space science and engineering. They are of key interest for materials engineering, where shock-induced phase transitions may be used to produce new materials with increased strength which might be stable at ambient conditions.
As prototypical materials, we consider iron and iron-carbon alloys showing a pressure induced phase transformation from the bcc to the hexagonal close-packed phase at around 13 GPa depending on the carbon content. We study waves in polycrystalline Fe using an interatomic potential that faithfully incorporates this phase transition at the desired equilibrium pressure.
Our simulations show that the phase transformation is preceded by plastic activity, leading to the so-called 3-wave structure: An elastic compression wave is followed by a plastic wave which then leads to a phase-transformation front. We show that the phase transformation from bcc to hcp and vice-versa helps to drive twinning and decreases the probability of multiple spallation and crack formation. In agreement with experiments, the fracture surface is influenced by the phase transition showing smooth spall surfaces.
Despite large differences in material properties, shock waves in aluminium nanofoams exhibit, similar to polycrystalline iron, a 3-wave structure indicating three wave regimes: an elastic precursor is pursued by plastic activity in the filaments before eventually the foam structure is crushed and a compact material results. The collapse of the foam is well described by an analytical compaction model.
As prototypical materials, we consider iron and iron-carbon alloys showing a pressure induced phase transformation from the bcc to the hexagonal close-packed phase at around 13 GPa depending on the carbon content. We study waves in polycrystalline Fe using an interatomic potential that faithfully incorporates this phase transition at the desired equilibrium pressure.
Our simulations show that the phase transformation is preceded by plastic activity, leading to the so-called 3-wave structure: An elastic compression wave is followed by a plastic wave which then leads to a phase-transformation front. We show that the phase transformation from bcc to hcp and vice-versa helps to drive twinning and decreases the probability of multiple spallation and crack formation. In agreement with experiments, the fracture surface is influenced by the phase transition showing smooth spall surfaces.
Despite large differences in material properties, shock waves in aluminium nanofoams exhibit, similar to polycrystalline iron, a 3-wave structure indicating three wave regimes: an elastic precursor is pursued by plastic activity in the filaments before eventually the foam structure is crushed and a compact material results. The collapse of the foam is well described by an analytical compaction model.