Theoretical studies of Ir₅Th and Ir₅Ce nanoscale precipitates in Ir

Abstract

Experimentally, it is known that very small amounts of thorium and/or cerium added to iridium metal form a precipitate, Ir₅Th/Ir₅Ce, which improves the high-temperature mechanical properties of the resulting alloys. We demonstrate that there are low-energy configurations for nanoscale precipitates of these phases in Ir, and that these coherent arrangements may assist in producing improved mechanical properties. One precipitate/matrix orientation gives a particularly low interfacial energy, and a low lattice misfit. Nanolayer precipitates with this orientation are found to be likely to form with little driving force to coarsen. The predicted morphology of the precipitates and their orientation with the matrix phase provide a potential experiment that could be used to test these predictions.

Keywords:

• iridium
• interface structure
• first-principles calculations
• grain boundary segregation
• nanostructures

Acknowledgements

We would like to thank E.P. George for useful discussion, and Hongbin Bei and Frederik Otto for comments on the manuscript. The research supported by the US Department of Energy (DOE), Basic Energy Sciences, Materials Sciences and Engineering Division. We also acknowledge computer time from the National Energy Research Scientific Computing Center (NERSC) of DOE. Lattice plots were made using VESTA [27] software.