Thermal Barrier Coatings for Long Life in Marine Gas Turbine Engines
Navy STTR 2016.A - Topic N16A-T019
ONR - Ms. Dusty Lang - dusty.lang@navy.mil
Opens: January 11, 2016 - Closes: February 17, 2016

N16A-T019 TITLE: Thermal Barrier Coatings for Long Life in Marine Gas Turbine Engines

TECHNOLOGY AREA(S): Battlespace, Ground/Sea Vehicles, Materials/Processes

ACQUISITION PROGRAM: FNC EPE FY15-02 Gas Turbine Developments for Reduced Total Ownership Cost a

OBJECTIVE: To develop thermal barrier coatings (TBCs) and a coating model that enables longer service and prediction of corrosion, oxidation and overall degradation when exposed to marine Naval environments as a function of corrosivity, stress, and higher temperature combinations via integrated computational material engineering.

DESCRIPTION: Materials for current marine gas turbine engines were developed and testing during 1960-1990s to resist degradation from Type I hot corrosion (1600-1700F) and Type II hot corrosion (1250-1350F). This development for USN marine gas turbines produced the highly reliable marine gas turbines that exist today where engines are not operated at full power where there may be only occasional spikes to 1700F. Navy engines operating at less than full power mode allowed these hot section materials to exist for 20k hours or more before repair or replacement was required.

Navy gas turbine operations that typically run at less than full power are inefficient compared to engines that are operated much closer to full power (and higher engine temperatures). The increased temperatures for marine gas turbine engines will permit greater engine efficiencies and the potential for greater power that will be needed in the future for weapon systems such as laser and electromagnetic rail gun. The greater power provided by ship engines, along with energy storage devices, will enable less supplemental power sources such as fuel cells and batteries that will add weight to the ship.

However, higher operational temperatures in marine engines may accelerate alloy and coating diffusion and interdiffusion interactions that may negatively affect the protective capabilities of overlay and diffusion coatings. The average engine temperatures are estimated to rise about 150-250F with occasional excursions to approximately 1850F. At these upper operating temperatures, oxidation rather than hot corrosion will be the prevailing reaction on coatings and alloys. Thus, The USN is entering a new region of marine gas turbine operations that will involve both corrosion and oxidation attacks materials on gas turbine engine hot sections. These are two totally different types of attack mechanisms. In addition, the USN shipboard environment (the marine environment) is high in salt laden air and water, coupled with air and fuel sulfur species that cause aggressive corrosion in gas turbine hot sections.

There is evidence that engine materials operating at these higher temperatures will dramatically experience shorter life (<10k hours) before the engine needs to be replaced. Thermal barrier coatings (TBCs) are regularly used in aero engines and have the potential to lower the substrate temperatures about 200-300F. Thermal Barrier coatings applied over the overlay or diffusion coatings could preserve the coating chemistry and structure and consequently maintain hot corrosion and oxidation resistance. Because of fuel and air contaminants, reactions have occurred that have shorted TBC life well below 20K hours because of spallation. Research must be performed to avoid spallation. There have been earlier efforts to evaluate TBCs in a simulated marine engine test environment, but spallation by salt intrusion into the TBC and subsequent salt solidification in the TBC has led to spallation. Increased understanding derived from aviation engine research and the utilization of computational methods will develop TBCs that will be resistant to spallation. This research would develop the understanding and processing of TBCs for sustained service for up to 20K hours marine gas turbine environments that will be experienced in the future.

PHASE I: Demonstrate an understanding of what differences exist between aviation and marine propulsion and what influences TBC spallation. Initiate correlations that should begin to formulate the ICME (integrated computational material engineering) model framework to promote long TBC life (goal: > 20K hours) and assist in maximizing corrosion and oxidation resistance by changes in coating chemistry and structure while not impacting fatigue, creep, or substrate strength of the substrate alloys. It is suggested that the starting TBC be yttria-stabilized zirconia. Lastly, perform a short-term (~200 hours) high temperature test to validate the feasibility of the ICME model.

PHASE II: The ICME framework shall be further expanded to include compatibility of the TBC to different bond coats as well as further development, modification, and maturation of the ICME model. Coating and engine original gas turbine equipment manufacturers (OEMs) is encouraged for advice and direction for further developments of the ICME models and strategies to enhance TBC life in marine shipboard engine applications. The performer shall correlate into the ICME-derived model the interaction of chromium and aluminum content in a coating that leads to the formation of chromia or alumina scales. Coatings on several alloys shall be tested to determine coating compatibility and assess impact of coatings on alloy substrate properties in a burner-rig or similar test environment that includes salt ingestion. Coatings shall be applied onto alloy substrates by at least one recognized commercial coating process (line-of-sight and/or non-line-of-sight). The expected deliverables will be: (1) optimized corrosion and oxidation-resistant coatings for a given set of alloys and (2) an ICME-derived model that would predict and assist in the development of future TBC systems (alloy, bond coat, TBC, TBC strategy to minimize spallation with Marine engine operational environment) that are compatible with multiple alloy substrates.

PHASE III DUAL USE APPLICATIONS: The ICME model will be further developed and matured through the expansion of TBC chemistry and structure with the selected strategies to mitigate salt intrusion into the TBCs that tend to cause premature cracking. Coating developed under the ONR FNC program (FNC EPE FY15-02 Gas Turbine Developments for Reduced Total Ownership Cost (TOC) and Improved Ship Impact) should be tested in a burner-rig or similar test environment that includes salt ingestion. The small business should engage with a marine engine OEM to have an appropriate TBC system applied on select static and/or rotating engine components of a current Navy engine and testing in cycling temperature test. The expected deliverables will be: (1) a TBC(s) compatible to corrosion and hot corrosion-resistant bond coat substrates, (2) TBC(s) resistant to spallation in the marine environment, and (3) an ICME-derived model that would predict and assist in the development of future TBC systems (alloy, bond coat, TBC, TBC strategy to minimize spallation with marine engine operational environment) The bond coat and salt intrusion into TBC behavior should be understood to minimize long-term interactions with TBCs that will promote long-term TBC life. The small business needs to engage with a marine engine OEM to further develop the TBC technology for incorporation in the current and future Navy ship engines. Development of long-lived TBC systems able to withstand hot corrosion, oxidation, and spallation at higher temperatures for U.S. Navy applications will also enable more efficient service for commercial applications that employ industrial gas turbines. Marine gas turbine engines are industrial gas turbines that are intended for Naval use. Successful development of better coatings for the current alloys, capable of extended service in the highly corrosive Naval operating environment, should enable subsequent use in commercial applications such as cargo ships, cruise ships, ferries, and tankers if the business case justifies the results.

REFERENCES:

1. T.A. Taylor, Thermal barrier coating for substrates and process for producing it, U.S. Patent 5,073,433 (1991).

2. D.M. Gray, Y.C. Lau, C.A. Johnson, M.P. Borom, W.A. Nelson, Thermal barrier coatings having an improved columnar microstructure, U.S. Patent 6,180,184 B1 (2001).

3. C.G. Levi, "Emerging Materials and Processes for Thermal Barrier Systems," Current Opinion in Solid State and Materials Science, 8 [1] 77-91 (2004).

4. P.K. Wright and A.G. Evans, "Mechanisms governing the performance of thermal barrier coatings," Current Opinion in Solid State and Materials Science, 4, 255-265 (1999).

5. A.G. Evans, D.R. Mumm, J.W. Hutchinson, G.H. Meier, and F.S. Pettit, "Mechanisms controlling the durability of thermal barrier coatings," Progress in Materials Science, 46 [5] 505-553 (2001).

6. M.P. Borom, C.A. Johnson, and L.A. Peluso, "Role of environmental deposits and operating surface temperature in spallation of air plasma sprayed thermal barrier coatings," Surface and Coatings Technology, 86-87, 116-126 (1996).

KEYWORDS: Thermal Barrier Coatings, spallation, bond coats, TBC failure, environmental deposits, marine engines

TPOC-1: David Shifler

Email: david.shifler@navy.mil

TPOC-2: Donald Hoffman

Email: donald.hoffman@navy.mil

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