Synthesis and Characterization of Mixed Rare Earth Zirconia, Zirconate and Silicate Radiative Barrier Coatings
Abstract
The thermal barrier coatings (TBCs) and environmental barrier coatings (EBCs) currently used to protect superalloy and silicon-based ceramic matric composites (CMCs) in the high-pressure turbine of gas turbine engines are transparent to the near infra-red wavelength radiation emitted by combustion gas at temperatures of 1200-1800 oC. As engine temperatures continue to rise, the thermal flux that is radiatively transported through these coatings increases as the fourth power of absolute temperature. This heat must be removed by increased gas cooling, which adversely effects the overall efficiency of the efficiency of the engine. This project seeks to select, synthesize, deposit and demonstrate that dopant ion combinations can be substituted into the crystal structure of t stabilized ZrO2, and gadolinium zirconate (GZO) type thermal barrier coatings, and into rare earth disilicate type EBCs enabling them all tofunction as radiation barrier coatings at typical use temperatures, while meeting the thermal expansion coefficient, thermal conductivity and other requirements of the engine application. The research is to be performed in a collaborative manner with selection ofdopants guided via collaborations with Clarke (Harvard), and computational simulations by Balachandran (UVA), with by measurements of optical and thermal conductivity properties conducted by Clarke and Hopkins (UVA) who are each independently supported. Combinatorial synthesis methods will be used to accelerate the screening of the many candidate materials. Measurement of their CTE via high temperature X-ray diffraction measurement of lattice parameters will be used in conjunction with thermomechanical modeling and high intensity CO2 laser thermal gradient testing to ensure thermomechanical compatibility with substrates. The CTE data is also intended to support the development of Balachandrans beyond DFT modeling capability that will used to guide the design of the most promisingRBC systems. The year 3-program objective is a demonstration of the capability to achieve a 50 % drop in radiative heat flux through modified YSZ and GZO coatings applied to superalloy test coupons compared with standard 7YSZ and GZO coatings. These new coatingswill be shown to achieve this while meeting or exceeding the CTE, thermal conductivity, steam volatility, oxidizer diffusivity and steam/molten silicate resistance of the baseline systems. An optional Year 4 program will identify and similarly demonstrate a radiation barrier dopant system for rare earth disilicate EBCs. It will demonstrate the ability to coat CMC substrates with a disilicate-based RBC. The RBC will be deposited on bond coated SiC substrates, and exposed to oxidizing conditions similar to those of the application environment. The diffusivity of the oxidizers through the coatings will be determined by comparison of the growth rate of the thermally grown oxide on these bond coats with those on samples with un-doped coatings. UVA test facilities will be used to demonstrate the ability of the coatings to block radiative thermal shock, and to measure the improved coating performance on a coated CMCheated to a surface temperature of 1500 oC. Comprehensive annual reports describing the technical progress of the research program will be provided as well as copies of fundamental research papers published by the RBC team. A final report of the program will be provided within 30 days of program completion. Approved for Public Release.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- May 05, 2021
- Source ID
- N000142112460
Entities
People
- H.N.G. Wadley
Organizations
- Office of Naval Research
- United States Navy
- University of Virginia