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Brittle fracture in fcc metals is uncommon. It is not common knowledge that single crystals or iridium, a high melting point fcc metal, fail by brittle cleavage at room temperature. Furthermore, polycrystalline iridium fails predominantly by brittle intergranular fracture at temperatures below 1000/sup 0/C. With the aid of several models of brittle fracture we have demonstrated that cleavage in iridium is intrinsic, resulting from apparently very strong and directed atomic binding forces. Intergranular fracture in iridium has been generally assumed to arise from the segregation of harmful impurities to the grain boundaries. It was demonstrated using Auger electron spectroscopy that impurity segregation to grain boundaries in iridium was not necessary for grain boundary fracture to occur, thereby demonstrating that intergranular brittle fracture in polycrystalline iridium is also intrinsic and not impurity related.
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