Grain-size-independent plastic flow at ultrahigh pressures and strain rates.
A basic tenet of material science is that the flow stress of a metal increases as its grain size decreases, an effect described by the Hall-Petch relation. This relation is used extensively in material design to optimize the hardness, durability, survivability, and ductility of structural metals. This Letter reports experimental results in a new regime of high pressures and strain rates that challenge this basic tenet of mechanical metallurgy. We report measurements of the plastic flow of the model body-centered-cubic metal tantalum made under conditions of high pressure (>100  GPa) and strain rate (∼10(7)  s(-1)) achieved by using the Omega laser. Under these unique plastic deformation ("flow") conditions, the effect of grain size is found to be negligible for grain sizes >0.25  μm sizes. A multiscale model of the plastic flow suggests that pressure and strain rate hardening dominate over the grain-size effects. Theoretical estimates, based on grain compatibility and geometrically necessary dislocations, corroborate this conclusion.
Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551, USA.
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Park
Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551, USA.
R E
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Rudd
Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551, USA.
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Cavallo
Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551, USA.
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Barton
Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551, USA.
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Arsenlis
Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551, USA.
J L
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Belof
Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551, USA.
K J M
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Blobaum
Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551, USA.
B S
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El-dasher
Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551, USA.
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Florando
Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551, USA.
C M
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Huntington
Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551, USA.
B R
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Maddox
Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551, USA.
M J
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May
Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551, USA.
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Plechaty
Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551, USA.
S T
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Prisbrey
Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551, USA.
B A
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Remington
Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551, USA.
R J
RJ
Wallace
Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551, USA.
C E
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Wehrenberg
Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551, USA.
M J
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Wilson
Atomic Weapons Establishment, Aldermaston, Reading RG7 4PR, United Kingdom.
A J
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Comley
General Atomics, 3550 General Atomics Court, San Diego, California 92121, USA.
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Giraldez
General Atomics, 3550 General Atomics Court, San Diego, California 92121, USA.
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Nikroo
General Atomics, 3550 General Atomics Court, San Diego, California 92121, USA.
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Farrell
General Atomics, 3550 General Atomics Court, San Diego, California 92121, USA.
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Randall
Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, New Mexico 87545, USA.
G T
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Gray
D008422:Materials Testing / Q000379:methods; D008670:Metals / Q000737:chemistry; D008962:Models, Theoretical; D010316:Particle Size; D013635:Tantalum / Q000737:chemistry*
D008670:Metals; D013635:Tantalum