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A Combined Ab Initio and Bond-Order Potentials Study of Cohesion in Iridium

Published online by Cambridge University Press:  15 February 2011

Marc J. Cawkwell ,
Duc Nguyen-Manh ,
Vaclav Vitek  and
David G. Pettifor
Marc J. Cawkwell
Affiliation:
Department of Materials Science and Engineering, University of Pennsylvania, 3231 Walnut Street, Philadelphia, PA 19104-6272, U.S.A.
Duc Nguyen-Manh
Affiliation:
Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, United Kingdom.
Vaclav Vitek
Affiliation:
Department of Materials Science and Engineering, University of Pennsylvania, 3231 Walnut Street, Philadelphia, PA 19104-6272, U.S.A.
David G. Pettifor
Affiliation:
Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, United Kingdom.
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Abstract

The extremely high melting point and excellent resistance to oxidation and corrosion offered by iridium suggest numerous applications of this transition metal in static components at high temperatures and in aggressive environments. However, the mechanical and physical properties of f.c.c. Ir exhibit numerous anomalies when compared to other metals that crystallize in the f.c.c. structure. Notable examples include a negative Cauchy pressure, 1/2 (C12 – C44), brittle transgranular cleavage after a period of plastic flow even in pure single crystals and anomalous [ΆΆ0] branches in the phonon spectra. Atomistic studies of extended defects are needed to elucidate the origin of anomalous mechanical properties, such as brittleness. For this purpose we developed a Bond-Order Potential (BOP), an O(N) tight-binding formalism, employing physically transparent parameterizations that use experimental and ab initio data, generated in this study using the Full Potential Augmented Plane Wave plus Local Orbitals (APW+lo) method. The constructed BOP reproduces then both equilibrium as well as a variety of nonequilibrium properties of Ir and represents an excellent description of cohesion in f.c.c. Ir. This description of interatomic interactions is imminently suitable for studies of defects, such as dislocations and grain boundaries, that control plastic deformation and fracture.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 779: Symposium W – Multiscale Phenomena in Materials - Experiments and Modeling Related to Mechanical Behavior , 2003 , W5.5
Copyright
Copyright © Materials Research Society 2003

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