There is significant evidence that these precipitates’ exact character has a significant effect on mechanical and environmental stability, especially in high-temperature applications, despite their small volume fraction. Due to preferential elemental segregation of high Z-number elements, these all exhibit high backscatter scanning electron microscope (SEM) contrast. In the literature, refractory-rich grain boundary precipitates may be referred to as a ‘carbide’ without any effort to differentiate between M 23C 6, M 6C, or boride structures. These phases form through all stages of alloy processing, from initial casting through to final aging treatments. Toward this endeavor we require precise knowledge of chemistry, distribution, and structure of intra/intergranular precipitates, particularly carbides and borides. 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.Įngineering grain boundary character is essential to optimization of superalloy microstructure and performance. The identified phases are dissimilar to those predicted using ThermoCalc. Only correlative chemical and structural fingerprinting is necessary and sufficient to fully define a phase. 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. An M 2B boride also exhibiting Mo and W segregation is observed at B levels above approximately 0.085 at. pct. It is found that the principal carbide in these alloys is Mo and W rich with the M 6C structure. Structure is derived from electron backscatter diffraction (EBSD) with pattern template matching, and chemistry obtained with energy dispersive X-ray spectroscopy (EDS). 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.
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