A critique of rhenium clustering in Ni–Re alloys using extended X-ray absorption spectroscopy

The extended X-ray absorption fine structure (EXAFS) technique is used to study the local atomic structure around the solute atoms in a number of binary nickel alloys, with the solute atoms taken from the 5d series of transition metals. Particular emphasis is placed on the Ni–Re system, in view of the strong influence of Re on the high-temperature properties of Ni-based superalloys. Analysis of the EXAFS data indicates that Re is coordinated by Ni atoms; no evidence is found for any clustering of Re in this system. The EXAFS analysis is complemented by first-principles density functional theory calculations, which predict a positive energy for Re dimer formation in the Ni matrix. The reported results indicate that Re clustering is not an explanation for its key role in promoting creep resistance in these materials.