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Science 12 August 2005:
Vol. 309. no. 5737, pp. 1059 - 1062
DOI: 10.1126/science.1114704
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Reports

Origin of Brittle Cleavage in Iridium

Marc J. Cawkwell,1* Duc Nguyen-Manh,2 Christopher Woodward,3,4 David G. Pettifor,5 Vaclav Vitek1

Iridium is unique among the face-centered cubic metals in that it undergoes brittle cleavage after a period of plastic deformation under tensile stress. Atomistic simulation using a quantum-mechanically derived bond-order potential shows that in iridium, two core structures for the screw dislocation are possible: a glissile planar core and a metastable nonplanar core. Transformation between the two core structures is athermal and leads to exceptionally high rates of cross slip during plastic deformation. Associated with this athermal cross slip is an exponential increase in the dislocation density and strong work hardening from which brittle cleavage is a natural consequence.

1 Department of Materials Science and Engineering, University of Pennsylvania, 3231 Walnut Street, Philadelphia, PA 19104–6202, USA.
2 European Atomic Energy Community/UK Atomic Energy Authority (EURATOM/UKAEA) Fusion Association, Culham Science Centre, Abingdon, OX14 3DB, UK.
3 Air Force Research Laboratory, Wright-Patterson Air Force Base, OH 45433–7817, USA.
4 Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208–3108, USA.
5 Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, UK.

* To whom correspondence should be addressed. E-mail: cawkwell{at}seas.upenn.edu

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Surface-controlled dislocation multiplication in metal micropillars.
C. R. Weinberger and W. Cai (2008)
PNAS 105, 14304-14307
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