Elemental Mapping and Phase Discrimination of Single Crystal Superalloys

Nickel-based single crystal superalloys are high-performance materials with excellent creep, fatigue and oxidation resistance that are designed to retain chemical and microstructural stability under extreme temperatures. Their phase stability greatly depends on the alloying elements and their distribution within the superalloy - both of these factors can be determined using Bruker's latest XFlash^® 7 Detector.

Ni-based single crystal superalloys consist of two phases, gamma and gamma-prime (written as γ and γ’), where γ forms the microstructural matrix and γ’ is the precipitating or intermetallic phase in a cuboidal form.

The elemental analysis of Nickel-based superalloys is challenging, because their matrix, located between regions of the precipitating phase, is only a few tens of nanometers in width. SEM EDS is a versatile technique that can be used for the qualitative and quantitative analysis or chemical characterization of such materials at the high spatial resolution required.

Here, we present elemental maps of a mechanically polished Ni-based superalloy sample that were acquired at a low SEM acceleration voltage of 3 kV. An EDS spatial resolution of approximately 15 nm was achieved for these measurements, allowing the two different phases to be clearly resolved.

The high collection efficency of the XFlash^® 7 EDS detector series allowed the detection and mapping of elements present at low concentration. EDS elemental mapping was used for phase discrimination. It was found that the superalloy's matrix was composed of mostly Cobalt and Chronium, with traces of Tungsten and Molybdenum, whereas the precipitating phase was found to primarily contain Nickel, Aluminium and Tantalum.