About this Abstract |
| Meeting |
11th International Symposium on Superalloy 718 and Derivatives 2026: Legacy, Innovations, and Future Directions
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| Symposium
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Superalloy 718 and Derivatives 2026: Legacy, Innovations, and Future Directions
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| Presentation Title |
Influence of Al:Nb Ratio on Microstructure and Mechanical Properties in New Polycrystalline Ni Superalloys |
| Author(s) |
Annie M. L. Andersson, George J. Wise, Mark C. Hardy, Howard J. Stone |
| On-Site Speaker (Planned) |
Annie M. L. Andersson |
| Abstract Scope |
Developing Ni-based superalloys with improved high-temperature performance beyond Alloy 718, while retaining cast-and-wrought processability, requires detailed understanding of compositional effects on phase evolution and mechanical properties. This study investigates how varying the Al:Nb ratio affects the microstructure and hardness of two potential new such alloys aged between 750-850°C. Lower Al:Nb ratios promoted δ and γ'' formation: Alloy 1 (Al:Nb = 0.69) formed δ under all conditions, while Alloy 2 (Al:Nb = 1.00) formed δ only at higher temperatures or extended ageing times. γ'' was also observed in Alloy 1, forming flat caps on hemispherical γ' precipitates, suggesting interfacial nucleation.
γ' precipitate sizes were smaller in Alloy 1 for all ageing conditions. Activation energies for γ' coarsening were calculated using a Lifshitz-Slyozov-Wagner model, with values decreasing linearly from 278 kJ/mol to 216 kJ/mol as Al:Nb ratio increased. This trend aligns with the higher diffusivity of Al compared to Nb and reflects faster coarsening at higher Al content.
Hardness measurements reflected the combined effects of phase content and precipitate size. Alloy 1 reached peak hardness after extended ageing at 750°C, while Alloy 2 peaked at 800°C. Despite a lower γ' volume fraction, Alloy 1 exhibited comparable hardness to Alloy 2, attributed to additional strengthening from the δ phase. These findings highlight the complex interplay between Al:Nb ratio, phase stability, coarsening kinetics, and mechanical response in these Ni superalloys. |
| Proceedings Inclusion? |
Definite: At-meeting proceedings |