Abstract
Platinum-modified aluminide bond coatings are widely used and yet there is little fundamental understanding about the important compositional factors which control their oxidation resistance and, ultimately, their performance. Due to the complex nature of the substrate-TBC system, it is difficult to perform carefully controlled experiments. Therefore, cast, model alloys have been tested in order to better understand the role of minor impurity elements, Pt and the Al content which decreases during service due to oxidation and interdiffusion with the substrate. While the importance of Y, S and their ratio have been previously studied, a similar relationship between Hf and C also appears to be an important factor for forming an adherent alumina scale. Using a series of Ni-Al alloys, a clear degradation in oxidation resistance is shown when the γ′ phase begins to form. At lower Al levels, the formation of Ni-rich oxides signaled the onset of reduced scale adhesion and this problem was particularly acute for two-phase, β-γ′ Ni-Al alloys. The addition of Pt appeared to improve oxidation resistance of Ni-Al alloys by improving the selective oxidation of Al and thereby lowering the critical Al content needed to suppress Ni-rich oxide formation. However, two-phase Ni-Al-Pt alloys showed a reversible phase transformation near 1100°C that may explain the macroscopic deformation observed in this alloy after thermal cycling. Rather than stresses in the scale, the phase transformation may explain the deformation observed in aluminide bond coatings. Finally, based on the apparent limitations of β-phase aluminide bond coatings, preliminary results are presented on γ + γ′ compositions with high (20-30at.%) Pt contents to selectively form adherent alumina scales. Coatings based on these compositions could be more durable because of less interdiffusion with the superalloy substrate.
Original language | English |
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Pages | 597-606 |
Number of pages | 10 |
State | Published - 2004 |
Event | SUPERALLOYS 2004 - Tenth International Symposium on Superalloys - Champion, PA, United States Duration: Sep 19 2004 → Sep 23 2004 |
Conference
Conference | SUPERALLOYS 2004 - Tenth International Symposium on Superalloys |
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Country/Territory | United States |
City | Champion, PA |
Period | 09/19/04 → 09/23/04 |
Keywords
- Aluminide coatings
- Hafnium effect
- Oxidation resistance
- Platinum diffusion coating
- Platinum effect