Atom Probe Tomography Analysis of Possible Rhenium Clustering in Nickel-Based Superalloys

Abstract

A local electrode atom probe is used to characterise a number of binary and commercial nickel-based alloys, specifically to determine whether rhenium atoms form solute clusters in these materials. The data are analysed via a statistical approach and results are compared to simulations which take the typical efficiency of the atom probe and the scatter in atomic positions into account. Thus, even the smallest clusters can -in principle -be detected by the algorithm. The analysis demonstrates conclusively that rhenium is not prone to clustering in the nickel lattice above the level associated with the random distribution of Re atoms. A similar conclusion applies to the other 5d elements (Ta, W, Ir and Pt) analysed in this study.

What is the role of rhenium in single crystal superalloys?

“…No clusters were detected. The same approach was adopted to study the distribution of Re in the γ phase of CMSX-4 where, similarly to the binary alloys, clusters were not found [24,25]. A sensitivity analysis of the approach on simulated 3DAP datesets revealed that sparse clusters (3.5 · 10 24 m −3 ) with 1 nm diameter should be evident, even when considering the detection efficiency and spatial resolution of the tool [24,25].…”

“…A maximum-separation friends-offriends algorithm was used to evaluate the presence of Re clusters in the data. The results were compared to simulated atom probe datasets [24] and randomised versions of themselves [25] (see Fig. 4).…”

“…Warnken used phase field simulations to establish whether the Re enrichment observed close to the γ /γ interfaces of uncrept CMSX-4 specimens [24,25] should be attributed to the coarsening of the γ secondary precipitates during heat treatment or to the growth of the γ secondary precipitates when cooling from service temperature. Simulations were made using the MICRESS TM , coupling the Thermo-Tech TM TTNI version 6 database and the NIST Ni superalloy mobility database to accurately represent the thermodynamics and kinetics of CMSX-4.…”

“…3b), but the heterogeneities observed may also be due to an nonhomogeneous distribution of Re. Recently, more 3DAP studies have been carried out to determine whether Re clusters may be present in the γ phase of Ni-based superalloys [24,25]. A number of Ni-X binary alloys (where X is Ta, W, Re, Ir and Pt), with 10 wt.% nominal solute content, were analysed using a direct-flightpath 3DAP.…”

Grain boundary segregation in Al–Mn electrodeposits prepared from ionic liquid

“…A ladder diagram is a cumulative presentation of solute content along a one-dimensional line, plotting the number of solute atoms encountered as a function of the total number of atoms encountered. Such ladder diagrams have been extensively used for identifying different phases as well as clustering in APTdata [23,53,54]. The slopes of these ladder diagrams are indicated inFigure 5, and represent the local concentration; in every case there is a clear signal of Mn segregation at the grain boundary, and the amount of grain boundary segregation ranges from 3 to 6 at.% higher than the composition in the neighboring grains.To get better statistics on the grain boundary and grain compositions, we constructed and analyzed 180 ladder diagrams such as those ofFigure 5, to assemble composition distributions unique to the boundary or the grains.…”