2015/02/12 by H.-S. Park, Robert E. Rudd, R. M. Cavallo +21 · 84 citations
Materials Science · Earth and Planetary Sciences · #High-Velocity Impact and Material Behavior #Microstructure and mechanical properties #High-pressure geophysics and materials #Materials science #Grain size #Strain rate #Plasticity #Flow stress #Tantalum #Strain hardening exponent #Grain boundary strengthening #Composite material #Hardening (computing) #Ductility (Earth science) #Severe plastic deformation #Metallurgy #Creep #Grain boundary #Microstructure
paper · open access · doi:10.1103/physrevlett.114.065502
published in Physical Review Letters 114(6), 065502 (American Physical Society)
openalex publication_date 2015/02/12 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
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.