In order to improve high-temperature oxidation and corrosion resistance of critical superalloy components in turbine engines innovative processing methods must be devised to improve coating and materials properties at a higher reliability and lower costs. Whether or not thermal barrier coating are applied to the engine components, the resistance to oxidation and hot corrosion relies on metallic coatings protecting the superalloy substrate.^[1] These metallic coatings are commonly either diffusion aluminides or MCrAlY overlays (where M=Ni, Co, Fe, Ni+Co, etc…).^[2],[3] Compared with diffusion coatings, MCrAlY coatings are more flexible in terms of composition selection for achieving a more balanced combination of coating properties and having a lower ductile to brittle transition temperature, which makes them more resistant to cracking upon thermal cycling.² Several techniques have been developed to deposit an MCrAlY coating (which commonly contain 18 to 22% Cr, 8 to 12% Al, and up to 0.5% Y) including physical vapor deposition,^[4] electrolytic codeposition,^[5],[6] electrophoresis,^[7] and autocatalytic electroless deposition^[8], of which electrolytic codeposition appears to be a promising, low cost, non-line of sight approach.^[9] Furthermore, electrolytic codeposition can be used to incorporate varying percentages of existing elements (Cr, Al, Y) or be used to incorporate other elements of interest (Re, Si, Ta, Nb, W, C…). Therefore this approach has the potential to enable the formation of previously unidentified metallic material systems that could inhibit corrosion and oxidation to temperatures in excess of 760°C (1400°F).

The potential of this scalable, low-cost, electrolytic codeposition approach to produce state-of-the-art alloys on the existing wide range of turbine disk components (Figure 1) sets the stage for this program. The objective of the program is to develop a scalable cost effective process to produce coatings that can enhance high temperature reliability and corrosion/oxidation resistance. We have designed, installed, and demonstrated the potential of scalable system to produce high quality electrolytic codeposits of NiCoCrAlY. The potential of the system to maintain the particle suspension of a large volume of solution has also been demonstrated. Additionally, we evaluated the potential of designing new state of the art coatings, based on our scalable approach, to further improve resistance to operating temperatures in excess of 760°C. This program resulted in a manufacturing pathway to produce these high value coatings for turbine disk materials and provide a pathway to identify better alloys systems for higher temperature operations.

Acknowledgement

This material is based upon work supported by an SBIR from NASA the under Grant No. NNX17CP44P

References:

[1] Zhang, Y. JOM, 67 (2015) 2599,

[2] Goward, G.W. Surf. Coat. Technol. 73 (1998) 108.

[3] Wride, V. M., et. al., “Gas Turbine Blades”, US. Patent 5,076,897 Dec. 31 1991

[4] Taheri, M., et. al., Surf. Eng, 28 (2012) 266.

[5] Zhang, L.Z., et al.. Surf. Eng., (2016) 1743.

[6] Foster, J., et. al., Trans. Inst. Met. Finish, 63 (1985) 115

[7] Lu, X., et al.. Oxid. Met., 43 (1995) 353.

[8] Bacos, M.P., et al., Surf. Coat. Technol., 162 (2003) 248.

[9] Foster, J., et. al. “Metallic Protective Coatings and Method of Making” US. Patent 4,789,441 Dec 6 1988.