Role of pre-existing dislocation network on the shock responses of single crystal tantalum

R Li and K Wang and YF Huang and YW Liao and WJ Zhu and WR Zhang and SL Yao, MECHANICS OF MATERIALS, 211, 105504 (2025).

DOI: 10.1016/j.mechmat.2025.105504

Tantalum exhibits complex shock plasticity involving competition between dislocation slip and deformation twinning. While this coupling is recognized, the role of pre-existing dislocation networks remains unclear. We systematically investigate how pre-existing dislocations affect shock response in 001-oriented Ta single crystals. Pre-existing dislocations, particularly screw segments, facilitate deformation twin nucleation and growth. However, high-density dislocation networks relax stress via slip and reactions, inhibiting twin propagation. These networks significantly enhance attenuation of the Hugoniot elastic limit (HEL) under low-velocity shocks, but their attenuating effect on the elastic precursor decreases with increasing shock velocity. At low speeds, stress relief primarily occurs through glide and reactions of pre-existing dislocations. As velocity increases, dislocation multiplication dominates, raising flow stress rapidly. Upon reaching the critical stress for twin nucleation, twinning plasticity surges, causing a sharp flow stress decline-contrasting dislocation-dominated behavior. Deformation twinning saturates at a specific twin fraction, after which flow stress converges irrespective of initial dislocation density. A quantitative relationship between the resolved shear stress required for twin nucleation and initial dislocation density is proposed for higher- scale simulations. Furthermore, pre-existing dislocations influence spallation. At low shock velocities (<0.7 km/s), lower dislocation density Ta exhibits higher spall strength. At high velocities (>0.7 km/s), void nucleation becomes more uniform, diminishing spall strength differences across initial dislocation densities. This work deepens understanding of dislocation-twin interplay and spallation in the presence of pre-existing networks, providing key insights for tailored material design.

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