The high temperature impact response of tungsten and chromium

Investigators using shock response of metals to reveal processes at the atomic level report studies demonstrating multiple new phenomena, including completely opposite effects of annealing on FCC and BCC metals, unexpected temperature and strain rate dependencies and non-smooth (kinked) dependence of the amplitude of elastic precursor wave on propagation distance. Their results are reported in the Journal of Applied Physics.

According to co-author Eugene B. Zaretsky, they built on previous foundational work. In 1997 co-author Kanel, reported substantial, almost linear growth of Hugoniot elastic limit in single crystal aluminum with temperature, from RT and virtually up to the melting point (Kanel Effect), directly proving the existence of phonon viscous drag control of dislocation motion later confirmed in the pair’s work with polycrystalline FCC metals. Motivated by similarities of impact responses of different BCC metals, they chose tungsten and chromium, conducting planar impact tests on samples of different thicknesses, shock-loaded from different initial temperatures using VISAR (Velocity Interferometer System for Any Reflector) instrumentation.

By examining elastic-plastic shock waves in polycrystalline tungsten and chromium at varying temperatures, Zaretsky and Kanel demonstrated that, after annealing, the ramping elastic wave is transformed into a jump-like wave, substantially increasing the metals’ elastic limits and indirectly confirming the non-planar structure of the dislocation cores in BCC metals. They also found that decay is fast at propagation distances less than ∼1 mm (tungsten) or ∼0.5 mm (chromium) but lowers at greater distances. The stress where this transition takes place coincides with the Peierls stress of the active glide system and is characterized by unique temperature dependence for all BCC metals studied.

According to Zaretsky, this work significantly contributes to our understanding of yield properties of metals in shock compression research, particularly regarding annealing.

Source: “The high temperature impact response of tungsten and chromium,” by E. B. Zaretsky and G. I. Kanel, Journal of Applied Physics (AIP-2) (2017). The article can be accessed at https://doi.org/10.1063/1.4997674 .