Grain-Size-Independent Plastic Flow at Ultrahigh Pressures and Strain Rates
Abstract
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 (∼1 07 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 μ 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.
- Publication:
-
Physical Review Letters
- Pub Date:
- February 2015
- DOI:
- Bibcode:
- 2015PhRvL.114f5502P
- Keywords:
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- 62.20.F-;
- 62.50.-p;
- 68.35.Gy;
- Deformation and plasticity;
- High-pressure effects in solids and liquids;
- Mechanical properties;
- surface strains