Darvishmotevally, Parisa, Saadati, Mohammad, Cormier, Jonathan et Jahazi, Mohammad.
2025.
« Morphology evolution of plate-like precipitates in a polycrystalline Ni-based superalloy ».
Journal of Alloys and Compounds, vol. 1040.
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Résumé
The formation of a dendrite arm-like interface, called protrusions, between plate-like precipitates and the surrounding matrix was studied in AD730™ Ni-based superalloy. The evolution in the morphology and reprecipitation sequence of γ′ particles after solution heat treatment has been investigated using Electron Backscatter Diffraction (EBSD), Field Emission Scanning Electron Microscopy (FE-SEM), Transmission Electron Microscopy (TEM), and Energy-Dispersive Spectroscopy (EDS). For the first time, atomic-scale investigations using High- Resolution Transmission Electron Microscopy (HR-TEM) revealed that protrusions tend to nucleate on the facet interface of the existing plate-like particles with a high coherency to the matrix. An analysis based on the application of the Brook equation was conducted, and a correlation was established between the frequency of protrusions and dislocation spacing, supporting the proposed dislocation-driven nucleation mechanism. TEM analysis revealed a gradient in chemical composition at the matrix-protrusion interface, which and analyzed in the framework of the dissolution and growth theories of precipitates. The results indicated that the protrusion occurred in a growth process during cooling, leading to the depletion of the main precipitating elements in the matrix in the adjacent zones. Using diffusion theory, element-specific diffusion behavior was analyzed, and it was revealed that Nb diffusion plays a critical role in protrusion evolution and governs the depletion of γ′-forming elements (Ni, Al, Ti, Nb) near the interface. The precipitation sequence and composition are analyzed in terms of the diffusion of γ′-forming elements. The evolution in the chemical composition of different precipitates indicated that the protrusions form after the precipitation of plate-like γ’ and before that of secondary γ’ on plate-like precipitates with about 0.27 % misfit. Based on the obtained results, it was concluded that the formation mechanism of protrusions is nucleation on misfit dislocations at the precipitate-matrix interface, and growth on {111} facet planes of plate-like precipitates. Additionally, the level of matrix supersaturation controls their growth kinetics.
| Type de document: | Article publié dans une revue, révisé par les pairs |
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| Professeur: | Professeur Jahazi, Mohammad |
| Affiliation: | Génie mécanique |
| Date de dépôt: | 07 oct. 2025 12:12 |
| Dernière modification: | 15 oct. 2025 13:52 |
| URI: | https://espace2.etsmtl.ca/id/eprint/32331 |
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