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Hall-Petch analysis of dislocation pileups in thin material layers and in nanopolycrystals

Published online by Cambridge University Press:  06 March 2013

Ronald W. Armstrong*
Affiliation:
Department of Mechanical Engineering, Center for Energetic Concepts Development, University of Maryland, College Park, Maryland 20742
*
a)Address all correspondence to this author. e-mail: rona@umd.edu
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Abstract

A potential order-of-magnitude increase in Hall-Petch (H-P)-based strength level for nanoscale grain-size structures is an important enabler of electronic thin film material design applications. Dislocation pileups of smaller lengths in such thin film materials are blocked in a screw orientation at the through-thickness grain boundaries of relatively larger grains. For fully nanopolycrystalline materials, both strength and strain rate sensitivity measurements exhibit complementary H-P reciprocal square root of grain size dependencies. An additional increase in strength level is predicted for transition from a pileup to a single dislocation loop expanding against the grain boundary obstacle. In opposition, disordered grain boundaries are responsible for a reduced H-P stress intensity, kε. And at the limiting high stresses reached at lower-limiting nanoscale grain sizes, reversed H-P dependences are obtained both for the strength and strain rate sensitivity.

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Articles
Copyright
Copyright © Materials Research Society 2013 

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References

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