14330 14350 14370 14390 14410 14430 14450 14470

Wave number (cm-1)

TGO Adherence

Considerable literature[5'21-33] describes the improved oxidation resistance associated with alloying additions for MCrAlY, nickel aluminide (NiAl) coatings and superalloys. Figure 7 shows the improvement in oxidation and spallation resistance of MCrAlY coated specimens and turbine blades.[21] However, controversy exists concerning the mechanisms associated with the improvement, e.g, pegging, neutralization of sulfur segregation, reduced oxidation rate, microstructural enhancement of TGO, inhibition of interdiffusion. Pint and coworkers[5'24] at Oak Ridge National Laboratory (ORNL) have shown that the addition of Hf improved the oxidation resistance of Pt-Al coatings. Preliminary results indicate that the addition of both Si and Hf can significantly improve oxidation resistance of the Pt-Al coatings.[34] This work will study for the first time the synergistic benefit of Si and Hf to Pt-Al coatings for both stand-alone and TBC coatings.

Figure 7. (a) Single crystal turbine blades showing superior coating durability of the Si,Hf added MCrAlY coating (left) vs. the failed MCrAlY coating (right) after 2500 endurance engine cycles. (b) This superiority can be attributed to the synergetic benefits of Si and Hf shown by the progressive failure stages described on the y-axis.[21]

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13. A.G. Evans, M.Y. He and J.W. Hutchinson, Acta Metall., 1997, vol. 45, pp. 3543.

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19. D.R. Clarke, V. Sergo and M.Y. He, Elevated Temperature Coatings: Science and Technology III, ed. J. M. Hampikian and N. B. Dahotre, TMS, Warrendale, PA, 1999, pp. 67.

20. J.C. Schaeffer, NASA Conference Publication, No. 207429, 1998, pp. 99.

21. D.K. Gupta and D.S. Duvall, Superalloy 1982, pp. 711.

22. K G. Schmitt-Thomas and M. Hertter, Surf. Coat. Technol, 1999, vol. 120, pp. 84.

23. J.H.W. de Wit and P.A. van Manen, Mater. Sci. Forum, 1994, vol. 154, pp. 109.

24. B.A. Pint, Oxid. Metals, 1997, vol. 48, pp. 303.

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26. R. Streiff, O. Cerclier and D.H. Boone, Surf. Coat. Technol., 1987, vol. 32, pp. 111.

27. E. Lang, The Role of Active Elements in the Oxidation Behavior of High Temperature Metals and Alloys, 1988.

28. J.A. Haynes, Y. Zhang, W.Y. Lee, B.A. Pint, I.G. Wright and K.M. Cooley, Elevated Temperature Coatings: Science and Technology III, ed. J. M. Hampikian and N. B. Dahotre, TMS, Warrendale, PA, 1999, pp. 185.

29. T.A. Taylor, D.F. Bettridge, R. C. Tucker, Jr., U.S. Patent 5,455,119, 1995.

30. B.A. Nagaraj, W.B. Connor, R.W. Jendrix, D.J. Wortman, L.W. Plemmons, U.S. Patent 5,427,866, 1995.

31. B.G. McMordie and T.A. Kircher, U.S. Patent 5,65,0,235, 1997.

32. W.C. Basta, D C. Punola and B.M. Warnes, U.S. Patent 5,658,614, 1997.

33. C S. Giggins, Jr. and B.H. Kear, U.S. Patent 4,086,391, 1978.

34. K. Murphy, Private Communications, 2000.

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37. Y.H. Sohn, K. Schlichting, K. Vaidyanathan, E. Jordan and M. Gell, Metall. Mater. Trans., in Press.

2.2 Objectives

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