Advanced Materials for the 21st Century , pp. 409-420, 1999.

The Limiting Strength Properties of Nanocrystalline Materials

R. W. Armstrong* and G. D. Hughes**
*Department of Mechanical Engineering
University of Maryland
College Park, MD 20742

**Laboratory for Physical Sciences
8050 Greenmead Drive
College Park, MD 20740.


Consideration is given to a number of exciting reasons for investigating the strength properties of ultrafine grain size materials, for example, as carefully pursued by J. R. Weertman and colleagues. One reason relates to the increased importance of the interfacial energy versus volume free energy of crystals at nanoscale grain sizes, now suggested to cotinect with reported observations of greater grain boundary and grain volume disorder in molecular dynamics modeling of nanocrystalline material. A second reason relates to the proposed transition from gain volume deformation mechanisms to localized grain boundary shearing at the nanoscale, connecting with a number of predictions obtained from the dislocation pile-up model for the Hall-Petch (H-P) reciprocal square root of grain size dependence for strength values when small numbers of dislocations are present in the pile-ups. Model limitations on strength properties are described and an estimate is given of the local pile-up stress influence on Coble-type diffusional creep at nanocrystal boundaries.

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