N151-070 TITLE: Development of Marinized Protective Coatings for Higher Temperature Operations of Marine Gas Turbine Engines

TECHNOLOGY AREAS: Ground/Sea Vehicles, Materials/Processes, Battlespace

ACQUISITION PROGRAM: EPE FY15-02 Gas Turbine Development for Reduced Total Ownership Cost (TOC)

OBJECTIVE: Develop an Integrated Computational Materials (Science) and Engineering (ICME) related methodology to predict and develop compatible marinized materials/coatings upgrades for Navy surface ship propulsion or auxiliary power gas turbines that will maintain long hot section life at sustained higher operating temperatures leading to reduced maintenance and repair budgets.

DESCRIPTION: It is the Navy�s goal to increase the operational capabilities of its gas turbine engines that are used in Surface Fleet propulsion and auxiliary electrical power generation. Operational changes and future needs will require increased gas turbine operating temperatures and change the associated operating environment to one where Type I and Type II hot corrosion AND oxidation will be prevalent in newly anticipated operational profiles. The U.S. Navy (USN) shipboard environment (the marine environment) is high in salt-laden air and water, which coupled with air and fuel sulfur species, causes aggressive Type I and Type II hot corrosion in gas turbine hot sections. Higher temperatures and environmental changes will increase engine corrosion and oxidation rates thereby shortening engine life and increasing engine maintenance and repair costs. Current USN Hot Section Materials were designed for Low Temperature Hot Corrosion (~700�C), but new USN operations may require engine materials to withstand higher sustained temperatures (950-1050�C) and cycle more often reducing engine life severely. Current coating development has been empirically based and has not been linked on computational/ scientific/ experimental data where predictive models could lessen time and cost for the development of corrosion-resistant and oxidation-resistant robust coatings capable of higher temperature service. This program would incorporate a computational and an experimental base to develop predictive models that will guide creation and development of coatings that are resistive to high temperature corrosion (including hot corrosion) and oxidation in the Navy's higher temperature operational profile.

PHASE I: Explore the coating literature as related to marine propulsion and develop coatings that would indicate the ability to perform at higher temperatures. Then perform short-term (~200 hours) high temperature experiments to correlate coating chemistry with hot corrosion and oxidation performance. The correlations should begin to form the ICME framework to assist in maximizing corrosion and oxidation resistance by changes in coating chemistry while not impacting fatigue, creep, or substrate strength of the substrate alloys.

PHASE II: The ICME framework shall be further expanded to include compatibility of the coating to different alloy substrates as well as further development, modification, and maturation of the ICME models. Coating and engine original gas turbine equipment manufacturers (OEMs) should be consulted for advice and direction for further developments of the ICME models. 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. Coatings shall be applied onto alloy substrates by at least one recognized commercial coating process (line-of-sight and/or non-line-of-sight).

PHASE III: The ICME model will be further developed and matured through the expansion of coating chemistry and hot corrosion and oxidation resistance testing results. 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 coatings that are compatible to other alloy substrates. In Phase III, the performer shall correlate the interaction of the substrate alloy to the coatings� ability to form chromia or alumina scales, especially when the substrate is a single crystal versus a polycrystalline alloy. A partnership between the small business and an engine OEM would be encouraged in order to further improve chances of transition.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Development of more robust coatings able to withstand hot corrosion and oxidation at higher temperatures for U.S. Navy applications will also enable more efficient service for commercial applications. 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 if the business case justifies the results.

REFERENCES:
1. D.A. Shifler, D. Hoffman, J. Hartranft, C. Grala, D. Groghan, L. Aprigliano, "USN Marine Gas Turbine Development Initiatives Part I: Advanced High Temperature Materials", Paper GT2010-23596, TurboExpo 2010, IGTI, Glasgow, Scotland (June 2010).

2. D.A. Shifler, "Substrate-Coating Interactions and Their Effects on Hot Corrosion Resistance", Symposium on High Temperature Corrosion and Materials Chemistry V, PV2004-16, E.Opila, J.Fergus, T. Maruyama, J. Mizusaki, T. Narita, D. Shifler, E. Wuchina, Eds., The Electrochemical Society, Pennington, NJ, 294 (2005).

3. B. Gleeson, "Thermodynamics and Theory of External and Internal Oxidation of Alloys", Shreir�s Corrosion, Vol. 1 Basic Concepts, High Temperature Corrosion, T. Richardson et al. (eds), Elsevier, (2010) pp. 180.

4. B. Gleeson, "High Temperature Corrosion of Metallic Alloys and Coatings," chapter in Corrosion and Environmental Degradation of Materials, edited by M. Schütze, Vol. 19 of the Series: Materials Science and Technology, R.W. Cahn, P. Haasen, E.J. Kramer (Series Editors) (Wiley-VCH, Germany, 2000), 173.

KEYWORDS: Hot corrosion; oxidation; coatings; gas turbines; marinization; marinized alloys, interdiffusion

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