Dislocation Nucleation and Room Temperature Deformation of Single Crystal Iridium

The brittleness of Ir single crystal in nature has attracted more attention because it is a fcc metal. In this paper, nanoindentation experiments were performed on the (100) and (110) planes of Ir single crystal. The results show that the dislocation activation volumes of Ir single crystal are calculated to be 1.09 x 10(-3) nm(3) and 1.23 x 10(-3 )nm(3) for the (100) and (110) planes, respectively, based on the first pop-in data from load-displacement curves. These results clearly demonstrate that the formation of dislocation is probably nucleated heterogeneously from point-like defects, while for the homogeneous nucleation, the activation energy should reach 60.57 eV, and the activation radius reaches 1.971 nm. In the plastic deformation of Jr single crystal, the deformation dislocation density is found to be the order of 10(14) m(-2), which agrees with the previously reported data, implying that the anomalously high dislocation density does not exist in this nanoindentation experiment. The brittle fracture of Ir in nature may be attributed to the extremely small dislocation activation volume, leading to a large number of dislocation sources and severe dislocation interaction.