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Size effects in LiF micron-scale single crystals of low dislocation density

Published online by Cambridge University Press:  31 January 2011

Edward M. Nadgorny ,
Dennis M. Dimiduk  and
Michael D. Uchic
Edward M. Nadgorny*
Affiliation:
General Dynamics Information Technology, Dayton, Ohio 45431-1231
Dennis M. Dimiduk
Affiliation:
Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson Air Force Base, Ohio 45433-7817
Michael D. Uchic
Affiliation:
Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson Air Force Base, Ohio 45433-7817
*
a)Address all correspondence to this author. e-mail: nadgorny@mtu.edu On sabbatical leave from Physics Department, Michigan Technological University, Houghton, MI 49931.
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Abstract

This study examines the size-dependent deformation response of pure LiF single crystals using microcompression testing. Microcrystals with an 〈001〉 orientation and sample diameter D ranging from 1 to 20 μm were fabricated by focused ion beam (FIB)-milling from bulk crystals having a low initial dislocation density. Both as-grown and γ-irradiated crystals were examined to characterize the effect of an increased point defect density on the size-affected plastic flow response. Similar to previously studied face-centered cubic (FCC)-derivative metals, both types of LiF microcrystals exhibit typical size-dependent plastic flow behavior: a dramatic size-dependent and statistically varying flow stress, atypically high strain hardening rates at small plastic strains, and fast intermittent strain bursts. The size-dependent strengthening obeys a power law, σ ∼ D−m, where m ≈ 0.8, and this rapid hardening results in engineering flow stresses of 650 MPa in 1-μm samples. The findings are evaluated against possible dislocation mechanisms that could be responsible for the observed size effects.

Keywords

DislocationsNanoscaleStress/strain relationship
Type
Outstanding Symposium Papers
Information
Journal of Materials Research , Volume 23 , Issue 11 , November 2008 , pp. 2829 - 2835
Copyright
Copyright © Materials Research Society 2008

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References

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