Nanocrystalline and Ultra-Fine Grained Tungsten for Kinetic Energy Penetrator and Warhead Liner Applications

Report No. ARL-RP-180
Authors: Kyu Cho; Laszlo Kecskes; Robert Dowding; Brian Schuster; Qiuming Wei; Ruslan Z. Valiev
Date/Pages: June 2007; 14 pages
Abstract: For the first time, we have demonstrated adiabatic shear localization in pure, ultra-fine grain (UFG) and nanocrystalline (NC) tungsten (W). Fabricated by severe plastic deformation (SPD), microstructural and mechanical property analyses of the W samples show that the combination of fine grain size, stored strain energy, ultra-high strength, little or no work hardening capacity leads to a unique flow softening behavior. It is further hypothesized that, while maintaining material ductility, grain refinement and redistribution of pre-existing impurities, segregated along grain boundaries (GBs), are equally critical for localized flow softening to occur. The UFG and SPD W results serve as minimum property benchmarks for shear localization to occur. In turn, these are used to define the experimental protocols and parameters for use in alternate fabrication procedures such as rapid consolidation of UFG or NC W powders. Preliminary results indicate that additional development of high-purity W nanopowders and appropriate grain-growth inhibitors will be required for this latter approach to successfully produce UFG and NC W microstructures.
Distribution: Approved for public release
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Last Update / Reviewed: June 1, 2007