Revealing the shock-induced complex phase transformations of tin and their impacts on spallation
Michael Scott Rafuse 
David Madukwe 
Richard D. Johnson Abstract
Spallation, a critical mode of dynamic fracture, remains a central focus in the study of material response under extreme conditions. While well studied in common metals, the spallation of tin (Sn), a group IV element exhibiting multiple solid phase along the shock-Hugoniot, presents significant challenges due to its complex pressure-temperature phase diagram. This complexity poses significant challenges for experimental characterization and reliability of interatomic potentials used in atomistic simulations. Consequently, the phase transition pathways and their influence on spallation in Sn remain poorly understood. In this work, we employ non-equilibrium molecular dynamics simulations using a first-principle accuracy machine learning potential to simulate the dynamic response of Sn at strain rates down to 5x10^9/s, which is comparable to experiments. Our simulations successfully capture critical behaviors such as shock-induced phase transitions and melting, and reproduce their experimental shock pressures. Meanwhile, the results clearly elucidate the β-to-bct transition pathway, revealing a two-stage mechanism mediated by an intermediate simple-hexagonal phase. Furthermore, we identify two distinct kinetic behaviors under phase transition conditions: phase transition-mediated amorphization and shock-induced supercooled melting. Both mechanisms are shown to originate from the large differences in the slopes of the melting lines between adjacent solid phases. These findings provide atomistic-scale evidence directly linking phase transformations to spallation failure, offering new insights into the fundamental physics of dynamic fracture in Sn.
Keywords : interatomic potentials, molecular dynamics simulation, phase diagrams, phase transformation
Note : Funding Information: The authors gratefully the funding by American Heart Association (AHA – 19TPA34850168) and by NIH (NHLBI - HL119371C).