Abstract:
This study investigates the impact of the cooling rates, from 18 to 1.5 °C/s, on the as-cast microstructure of the CMSX-4 Ni-based superalloy, especially on morphological changes in primary γ′ precipitates in the dendrite core and border. Microstructural characterization along the height of directionally solidified samples included the measurement of grain density, secondary dendrite arm spacing, γ–γ′ eutectic morphology and volume fraction, solute segregation, and primary γ’ precipitate morphology & size in both dendrite core and border. A simple thermodynamic model was employed to investigate the morphological transitions observed during coarsening of primary γ′ precipitates, from sphere to cube, concave cube, octocube and solid-state dendrite. The γ–γ′ lattice misfit, the γ/γ′ elastic strain energy values within the γ matrix, and the critical precipitation sizes for morphological changes were extrapolated for the dendrite core and border. The thermodynamic model, which considers the balance between elastic and interfacial energies, does not completely explain the differences in size and shape of the primary γ′ particles between the dendrite border and core. The more varied γ′ particle morphologies in the dendrite border are due to faster precipitate coarsening, driven by lower Re and W contents, higher atomic diffusivity, increased solvus temperature, and reduced supercooling for the precipitation reaction.
Referência:
MOREIRA, Marcelo Ferreira; SOUZA, Gabriel Praça de; VENTURELLI, Bianca Nan,; FANTINI, Luiza de Brito; AZEVEDO, Cesar Roberto de Farias. Effect of the cooling rate on the microstructure of directionally solidified casting (CMSX-4 Ni superalloy). International Journal of Metalcasting, 21 p., Jan., 2024.
Acesso ao artigo no site do Periódico:
https://link.springer.com/article/10.1007/s40962-023-01249-6
