Quantitative Precipitate Classification and Grain Boundary Property Control in Co/Ni-Base Superalloys

Abstract

A correlative approach is employed to simultaneously assess structure and chemistry of (carbide and boride) precipitates in a set of novel Co/Ni-base superalloys. Structure is derived from electron backscatter diffraction (EBSD) with pattern template matching, and chemistry obtained with energy dispersive X-ray spectroscopy (EDS). It is found that the principal carbide in these alloys is Mo and W rich with the M6C structure. An M2B boride also exhibiting Mo and W segregation is observed at B levels above approximately 0.085 at. pct. These phases are challenging to distinguish in an SEM with chemical information (EDS or backscatter Z-contrast) alone, without the structural information provided by EBSD. Only correlative chemical and structural fingerprinting is necessary and sufficient to fully define a phase. The identified phases are dissimilar to those predicted using ThermoCalc. We additionally perform an assessment of the grain boundary serratability in these alloys, and observe that significant amplitude is only obtained in the absence of pinning intergranular precipitates.

Multi-length-scale study on the heat treatment response to supersaturated nickel-based superalloys: Precipitation reactions and incipient recrystallisation

“…Elemental mapping using STEM-EDS showing net counts (with background subtraction) in Figure 2 Clearly, many carbon particles are observed; the distribution also demonstrates a directionality that is parallel to the cellular alignment in its corresponding SE image. Considering the transition metal enrichment at cell boundaries, those carbon particles are believed to be carbides, and are mostly likely to be the Ti/Nb/Ta rich MC type, as reported on similar alloys [42,43]. In addition, the boron map is similar to carbon whose distribution exhibits the same directionality, however, its presence is found both in particles and segregation to cell boundaries, consistent with reports elsewhere [44].…”

Review of Microstructure–Mechanical Property Relationships in Cast and Wrought Ni‐Based Superalloys with Boron, Carbon, and Zirconium Microalloying Additions

“…The development of experimental and data analysis approaches to address these shortcomings may not only be applicable to cast and wrought Ni-based superalloys but may be employed to solve similar challenges in Fe-based and Al alloys. [234][235][236][237][238][239][240][241] 6. Conclusions…”