Journal
PHYSICAL REVIEW LETTERS
Volume 114, Issue 6, Pages -Publisher
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevLett.114.065502
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- U.S. Department of Energy by Lawrence Livermore National Laboratory [DE-AC52-07NA27344]
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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 (similar to 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 mu m 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.
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