Abstract
The effects of Pt incorporation on the isothermal oxidation and diffusion behavior of low-sulfur aluminide bond coatings were investigated. Aluminide (NiAl) coatings and Pt-modified aluminide (Ni, Pt)Al coatings were synthesized on a low-sulfur, yttrium-free single-crystal Ni-based superalloy by a high-purity, low-activity chemical vapor deposition (CVD) aluminizing procedure. The isothermal oxidation kinetics and scale adhesion behavior of CVD NiAl and (Ni, Pt)Al were compared at 1150°C. Compositional profiles of alloying elements in the NiAl and (Ni, Pt)Al coatings before and after isothermal oxidation were determined by electron microprobe analysis. Platinum did not reduce oxide-scale growth kinetics. No significant differences in bulk refractory metal (W, Ta, Re, and Mo) distributions were observed as a result of Pt incorporation. Spallation of the alumina scale and the formation of large voids along the oxide-metal interface were commonly observed over the NiAl coating grain boundaries after 100 hours at 1150°C. In contrast, no spallation of Al2O3 scales occurred on (Ni, Pt)Al coating surfaces or grain boundaries, although the sulfur content in the CVD (Ni, Pt)Al coatings was higher than that of the CVD NiAl coatings. Most significantly, no voids were observed at the oxide-metal interface on (Ni, Pt)Al coating surfaces or cross sections after 200 hours at 1150°C. It was concluded that a major beneficial effect of Pt incorporation on an aluminide coatings oxidation resistance is the elimination of void growth at the oxide-metal interface, likely by mitigation of detrimental sulfur effects.
Original language | English |
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Pages (from-to) | 1727-1741 |
Number of pages | 15 |
Journal | Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science |
Volume | 32 |
Issue number | 7 |
DOIs | |
State | Published - 2001 |
Funding
Warnes and N. DuShane, Howmet Corporation, for conducting Pt electroplating; L.D. Chitwood and G. Garner, ORNL, for assisting with oxidation experiments; and L. Walker, ORNL, for the EPMA analysis. The authors also thank Ted Besman, Pete Tortorelli, and Mike Lance, ORNL, for reviewing the manuscript. This research was sponsored by the Advanced Gas Turbine Systems Program, DOE Office of Industrial Technologies, under Contract No. DE-AC05-96OR22464 with UT-Batelle Research Corporation.