Understanding the damage and failure of structural materials under extreme mechanical loads such as hypervelocity impact, which combines high strain rates, tri-axial stress, and temperature, is important for a range of applications including space exploration and defense. Niobium (Nb) is a BCC transition metal of interest for such applications due to its high melting point, high strength, and good resistance to corrosion and creep. Its alloys with other transition metals, such as NbTi, also provide many advanced mechanical properties for applications under extreme conditions. Experiments have revealed the dependence of spallation failure of BCC metals on the strain rate and shock strength, and high-resolution TEM studies have revealed many of the underlying microscopic processes, including phase transformations, shear bands, and deformation twins. Despite this progress and the insight provided by atomistic simulation studies a detailed mechanistic understanding of the spallation process of metals under extreme conditions is still lacking. This work seeks to fill this gap via large-scale molecular dynamics (MD) simulations.
We examined the performance of current interatomic potentials for Nb and NbTi under shock conditions via MD simulations in various static and dynamic processes and validated the models against available experimental data or high-accuracy electronic structure simulation results. We used the best-performing potentials for Nb and NbTi on a series of large-scale MD simulations and characterized the process of spallation with atomistic detail. We characterized the spall strength and strain as a function of shock strength and tested models used to extract these properties from experiments against the detailed data extracted from the MD simulations