Improved embedded-atom model potentials of Pb at high pressure: application to investigations of plasticity and phase transition under extreme conditions

Abstract

Local stress relaxation mechanisms of crystals are a long-standing interest in the field of materials physics. Constantly encountered inelastic deformation mechanisms in metals under dynamic loadings, such as dislocation, deformation twinning and phase transition, have been extensively discussed separately or as some of their combinations. Recently, virtual melting is found to be a dominant local stress relaxation mechanism under extreme strain rates. However, these deformation mechanisms have never been investigated in the same metal at an atomic level due to the lack of high pressure interatomic potentials. In this work, an embedded-atom model potential of Pb is developed and tested for high pressure applications. The developed potential of Pb could not only reproduce many energetic, elastic and defective properties at ambient conditions well, but also correctly describe face-centered cubic (fcc)-hexagonal close packed (hcp) and hcp-body-centered cubic phase transition of Pb under high pressures. Shock Hugoniot, as well as equation of states for fcc and hcp phase, also agrees well with the literature ones up to more than 100 GPa. With the developed potential, non-equilibrium molecular dynamic simulations are conducted to investigate dynamic behaviors of Pb single crystal under ramp-shock compressions. Depending on applied strain rates, dislocation-mediated plasticity, phase transition and virtual melting, constantly reported by experiments or theoretical investigations, are observed in our results. Additionally, a new phase transition mechanism of Pb subjected to the ramp compressions is uncovered.

Phase transformations, fracture, and other structural changes in inelastic materials

“…The VM phenomenon in a shock wave was confirmed and further elaborated in MD simulations for single crystal Cu, Al, Ta, Pb in [46,151,441,443] and for polycrystalline Be in [84].…”

A study on the degassing mechanism of Pb-based alloy under ultrasonic treatment

“…1 Except for experiments, we have carried out numerical simulations on the melting process of Pb metal materials under atomistic level. Based on the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) [6][7][8] , we investigate the hole vanishment in the melt structure, which is performed under the different states of a sinusoidal wave. The cubic Pb structure contains 128,833 Pb atoms, the whole model is a polycrystal one before melting, it contains 12 grains inside each box with threedimensional sizes of 25.0117×25.0117×25.0117nm.…”

Response embedded atom model potential of Pb at finite temperature: application on the dislocation mobility

“…Embedding energy is usually an unknown function of electron density (r i ), and several forms can be chosen. In this current REAM potential, the function of embedding energy [27,28] is expressed as…”