Experimental and theoretical study of lattice relaxation around refractory atoms in nickel

Abstract

The lattice relaxation around Mo, Ru, Hf, Ta, W and Re in Ni is investigated by means of X-ray absorption spectroscopy. For all of the investigated concentrations the substitutional lattice position is confirmed except for the higher Hf concentration where different phases are observed. An outward relaxation of the neighboring atoms is detected with clear trends of increasing nearest neighbor distances with decreasing valence for the 5d impurities, and separate trends for the 4d impurities. Ab initio supercell calculations within the linearized augmented plane wave formalism are used to complement the experimental results and allow for a better interpretation of the experimental trends in terms of the electronic structure of the impurity.

What is the role of rhenium in single crystal superalloys?

“…In this case, the L 3 edge of Re was used to detect the local environment surrounding the Re atoms in the specimens. Both studies clearly indicate that Re-Re first neighbour pairs are unlikely in the Ni lattice, as the data clearly indicates that Re is coordinated by 12 Ni atoms [27,28].…”

“…The presence of Re clusters in the Ni lattice was also investigated using extended x-ray absorption fine spectroscopy (EXAFS) [27,28]. In EXAFS, the local atomic structure surrounding atoms of a specific element can be probed by examining the oscillations in x-ray absorption coefficient immediately above the absorption edge of that element.…”

The time differential perturbed angular correlation study of the Ni–5at.% Hf alloy

“…2). Regarding our earlier EXAFS and XRD results on this alloy [1,2], it was attributed to the majority of Ta atoms in the paramagnetic HfNi 5 phase having the defect …”

“…Previous SEM and XRD analysis of the nickel-5 at.% hafnium alloy revealed the presence of two phases: the Ni(Hf) solid solution and the defective HfNi 5 phases [1]. The majority of Hf atoms appeared to be incorporated in the HfNi 5 phase as demonstrated by EXAFS investigation on this alloy [1,2].…”

“…[1,2]. These earlier investigations on structural properties and alloy formation in the Ni-5 at.% Hf alloy showed that the composition of this alloy is in accordance with the Ni-Hf phase diagram [3].…”