On the Dependence of Durability of Thermal Barrier Coatings on the Oxidation Resistance of Composite Substrate Systems P
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JMEPEG https://doi.org/10.1007/s11665-019-04222-9
On the Dependence of Durability of Thermal Barrier Coatings on the Oxidation Resistance of Composite Substrate Systems Produced by Diffusing Platinum into Selected Ni-Based Superalloys H.M. Tawancy (Submitted February 3, 2019; in revised form June 3, 2019) Platinum is diffused into the single-crystal superalloys CMSX-4 and CMSX-10 to integrate a surface protection layer consisting of a mixture of c¢- and c-phases. It is shown that the Pt/CMSX-10 system is characterized by higher thermal stability and resistance to oxidation in comparison with the Pt/CMSX-4 system. Such difference is correlated with the initial microstructure and composition of the two systems and is reflected on their performance in thermal barrier coatings utilizing yttria-stabilized zirconia as top coating. Based upon cyclic oxidation tests, the Pt/CMSX-10 system is found to provide about threefold increase in useful life. However, both coatings are found to fail by spallation of the top coating due to decohesion of the thermally grown oxide developed by each system. It is concluded that the higher performance provided by the Pt/CMSX-10 stems from decelerated kinetics of interdiffusion and oxidation. Keywords
bond coatings, electron microscopy, microstructure, oxidation, superalloys, thermal barrier coatings
1. Introduction Modern gas turbine engines are required to operate at extreme temperatures to achieve the highest possible energy conversion efficiency for more power/thrust output which reduces fuel consumption and maintains cleaner environments. This can only be met by an engineering process comprising the best in design concepts utilizing the most advanced structural materials as well as manufacturing technologies. Since blades of the turbine section experience the highest temperature, a great deal of emphasis is placed on modifying their surfaces to allow the turbine entry temperature to exceed the melting point of the superalloys used to manufacture the blades. Current technology relies upon the use of state-of-the-art thermal barrier coatings (TBCs) which utilize an outermost thermal insulating layer (top coating) made of zirconia stabilized by 6-8 wt.% yttria deposited on an intermediate layer of metallic coating usually referred to as bond coating (Ref 1). Bond coatings used in aeroengine applications are commonly of the diffusion type in contrast to land-based engines which rely more on overlays of the MCrAlY type due to the difference in service conditions. Diffusion-type bond coatings are developed by diffusing elements into the superalloy such as Al, Pt or a combination of both to integrate a surface layer capable of developing a protective layer of Al2O3. It has long H.M. Tawancy, Center for Engineering Research, Research Institute, King Fahd University of Petroleum and Minerals, P.O. Box 1639, Dhahran 31261, Saudi Arabia. Contact e-mail: [email protected].
Journal of Materials Engineering and Performance
been an industry practice to view surface treatments as remedies for e
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