Revealing the dynamic responses of Pb under shock loading based on DFT-accuracy machine learning potential

TL;DR

The paper addresses how lead responds at the atomistic level to shock loading, a problem challenging to resolve with empirical potentials. It deploys a DF-accurate machine-learned potential (DP-PbSn) within non-equilibrium MD to simulate large-scale systems under shock along two crystallographic directions, capturing plasticity, phase transitions, and melting. The results reveal pronounced anisotropy: [001] shock drives rapid, reversible FCC↔BCC transformations via a Bain-path, while [011] shock produces slower, more persistent defects with a Pitsch-oriented FCC↔BCC relationship and eventual disorder at high strain rates. This work provides mechanistic insight into Pb’s dynamic response and establishes a transferable approach for studying other materials under extreme conditions.

Abstract

Lead (Pb) is a typical low-melting-point ductile metal and serves as an important model material in the study of dynamic responses. Under shock-wave loading, its dynamic mechanical behavior comprises two key phenomena: plastic deformation and shock induced phase transitions. The underlying mechanisms of these processes are still poorly understood. Revealing these mechanisms remains challenging for experimental approaches. Non-equilibrium molecular dynamics (NEMD) simulations are an alternative theoretical tool for studying dynamic responses, as they capture atomic-scale mechanisms such as defect evolution and deformation pathways. However, due to the limited accuracy of empirical interatomic potentials, the reliability of previous NEMD studies is questioned. Using our newly developed machine learning potential for Pb-Sn alloys, we revisited the microstructure evolution in response to shock loading under various shock orientations. The results reveal that shock loading along the [001] orientation of Pb exhibits a fast, reversible, and massive phase transition and stacking fault evolution. The behavior of Pb differs from previous studies by the absence of twinning during plastic deformation. Loading along the [011] orientation leads to slow, irreversible plastic deformation, and a localized FCC-BCC phase transition in the Pitsch orientation relationship. This study provides crucial theoretical insights into the dynamic mechanical response of Pb, offering a theoretical input for understanding the microstructure-performance relationship under extreme conditions.