Origin of Brittle Cleavage in Iridium

• Published in: Science (American Association for the Advancement of Science) Vol. 309; no. 5737; pp. 1059 - 1062
• Main Authors: Cawkwell, Marc J, Nguyen-Manh, Duc, Woodward, Christopher, Pettifor, David G, Vitek, Vaclav
• Format: Journal Article
• Language: English
• Published: Washington, DC American Association for the Advancement of Science 12.08.2005; The American Association for the Advancement of Science
• Subjects: Achondrites; Analysis; Chondrites; Condensed matter: structure, mechanical and thermal properties; Crystalline polymers; Dislocations; Energy; Exact sciences and technology; Face centered cubic lattices; Fatigue, brittleness, fracture, and cracks; Iridium; Lead; Mechanical and acoustical properties of condensed matter; Mechanical properties of solids; Metals; Oxygen; Physics; Plastic deformation; Plasticity; Screw dislocations; Shear stress; Structure; Sulfur; Tensile strength; Testing; Dislocation density; FCC lattices; Cleavage fracture; Atomistic model; Brittle fracture; Cross slip; Plasticity; Screw dislocations; Fracture mode
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.1114704

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.