Correlative analysis of grain boundary precipitates in Ni-based superalloy Rene 41

Both hot workability and in-service mechanical properties of Ni-based superalloys are strongly influenced by the presence of secondary phases precipitated within the matrix and at grain boundaries. Due to its remarkably high contents of alloying elements, Ni-based superalloy Rene acute accent 41 forms various precipitate phases at grain boundaries, including but not limited to various carbides and gamma' precipitates, and this may lead to grain boundary cracking. Better knowledge of the nature of these precipitates at different temperatures will enable manufacturing of Rene acute accent 41 aerospace parts with higher yield and better in-service properties. Limitations of conventional electron microscopy methods have previously impeded progress at this front. Previous studies on grain boundary precipitation in Rene acute accent 41 indicate the co-existence of two dominant types of grain boundary carbides, M6C at temperatures up to 1147 degrees C and M23C6 below 980 degrees C. However, recent state-ofthe-art thermodynamic simulations indicate that M6C is stable over a much wider temperature range. We propose a novel correlative approach using both convergent beam electron diffraction (CBED) and site-specific atom probe microscopy (APM) to distinguish grain boundary carbides in Rene acute accent 41 unambiguously. While CBED reveals space groups, APM enables chemical analyses with near atomic resolution in 3D. Our correlative microscopy combined with thermodynamic simulations confirms the presence of both M6C and M23C6 after annealing at 900 degrees C while only M6C is present at 1100 degrees C.

Automated summary

The performance of Ni-based superalloys is affected by the presence of precipitates at grain boundaries, especially in alloys like Rene 41 with high alloying elements. Different types of grain boundary carbides may exist at different temperatures, highlighting the significance of understanding these precipitates for manufacturing high-quality aerospace components.