Nanocrystalline materials prove stable enough to be used in for ballistic protection

The unique properties and strength of nanocrystalline materials have been studied for decades, but their use has been severely limited by a lack of microstructural stability and a tendency to deform and breakdown under extreme pressure.

Hornbuckle et al. used laser-driven flyer plates to shock a promising thermo-mechanically stable nanocrystalline copper tantalum (NC-Cu-Ta) alloy, studying the mechanical and physical characteristics of the material under extreme pressures. Though the material incurred small changes in its structure after initial short-duration shocks, the authors found the microstructures of the NC-Cu-Ta alloy remained undamaged at moderate shock velocities and pressures. The material displayed a high tolerance for defect accumulation under the extreme testing conditions.

The ability to maintain a lower defect concentration under shock compression provides an archetype from which materials can be developed that go beyond conventional theory. Smaller grain sizes may then prove to yield higher mechanical strength as compared to coarser grained alloys.

“Achieving the thermo-mechanical stability of nanocrystalline metals and alloys is a game changing advancement. This research could have lifesaving applications in the development of high energy absorbing materials, which would provide protection for military vehicles or could even be applied to race cars,” said author B. C. Hornbuckle.

The laser-driven flyer plates were tested at velocities of 0.8 and 2.4 kilometers per second and beyond the previously studied strain rate of 10⁵ s⁻¹. Analysis of the impact was performed using high speed video and advanced electron microscopy.

“Currently, our work is very fundamental, and moving forward, we would like to conduct large scale testing on other materials,” said Hornbuckle.

Source: “Laser shocking of nanocrystalline materials: Revealing the extreme pressure effects on the microstructural stability and deformation response,” by B. C. Hornbuckle, S. W. Dean, X. Zhou, A. Giri, C. Williams, K. N. Solanki, G. B. Thompson, and K. A Darling, Applied Physics Letters (2020). The article can be accessed at https://doi.org/10.1063/5.0008107 .