DON26BZ01-NV028 TITLE: Overlay/Bond Coatings that Resist Hot Corrosion in Navy Gas Turbines
OUSW (R&E) CRITICAL TECHNOLOGY AREA(S): Contested Logistics Technologies (LOG)
COMPONENT TECHNOLOGY PRIORITY AREA(S): Advanced Materials;Sustainment
PROJECTED CMMC LEVEL REQUIREMENT: Level 2 (Self)
OBJECTIVE: Develop overlay or bond coatings 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 various temperature combinations via integrated computational material engineering (ICME), which will foster creation of new coatings resistant to these degradation modes.
DESCRIPTION: Marine gas turbine engines serve as primary and auxiliary power sources for several current classes of ships in the U.S. Navy. It is desirable for marine gas turbine engines to have a mean time between removals of 20,000 hours. While some engines have approached this goal, others have fallen significantly short. The main reason for this shortfall is various forms of hot corrosion (Type I and Type II) damage in the hot section turbine hardware due to intrusion of salts from the marine air and/or from sulfur in the gas turbine combustion fuels.
The synergistic effect of stress- and deposit-induced high temperature corrosion can lead to other corrosion mechanisms. Corrosion fatigue as well as fatigue often initiates at stress risers. Metallurgical examination of several failed marine gas turbine blades that had operated between 5,000 and 10,000 hours was performed and compared to "unfailed" blades with 18,000 operating hours from a similar marine engine. Deposition occurring at sites under the platform of unfailed turbine blades revealed pitting at those sites.
Further examination revealed poor coating quality (i.e., high porosity and variable thickness) under the platform of first stage turbine blades that allowed salts to permeate through the coating to the alloy surface and initiate hot corrosion. Further coating examination under the platform showed highly variable coating thicknesses (0-40 µm) in the curved area of transition between the under platform and the blade stem. In a few cases, coatings were non-existent on the "unfailed" blades. The Cobalt Chromium Aluminum Yttrium (CoCrAlY) coating, when present, usually was porous or the available coating under the platform was highly contaminated due to lack of adequate spray deposition in these non-line-of-sight areas. CoCrAlY coating thicknesses at other sites along the blade stem were 35 µm to 105 µm (1.4 to 4.1 mils) and devoid of porosity. The corrosion that was observed under the platform in all cases was caused by Type II, low-temperature hot corrosion, which occurs in the temperature range of 649°-732°C (1,200°-1,350°F). Corrosion penetrated the porous coating and caused further undercutting of the coating along the coating/alloy substrate interface, Type II hot corrosion caused pitting at these locations under the platform, which caused stress risers where corrosion fatigue cracks initiated. These pits advanced through the blade stems to varying degrees.
The synergistic effect of stress- and deposit-induced high temperature corrosion leads to the premature failure of aero turbine blades reportedly due to stress corrosion cracking. The lower shank of aero gas turbine blades, which operates below 600°C is susceptible to this mode of failure. Two important factors that lead to stress corrosion cracking of single crystal nickel-based superalloys are the type of deposits that form on components (these include alkali chlorides and sulfates which are introduced through the environment) and the concentration of SOx in the environment. Therefore, it is important to understand the synergistic role of deposits and sulfur containing gases on the stress corrosion cracking susceptibility of single crystal nickel-based superalloys below 600°C.
PHASE I: Demonstrate an understanding of what differences and influences exist between aviation and marine propulsion. Determine the mechanism for the observed corrosion at 500°-550°C. if stress corrosion cracking (SCC) is the prevalent corrosion mechanism, determine the interplay with NaCl, Na2SO4, SOx, and stress. For a given concentration of the chemical compounds, determine at what stress initiates SCC. Initiate correlations that should begin to formulate the ICME model framework to create a coating that would avoid reactions leading to SCC. (Note: For shipboard operations this would be either an overlay or diffusion coatings. For aero applications, this would lead to creation of a bond coat that would also promote long thermal barrier coating (TBC) life (goal: > 5K hours) and assist in maximizing corrosion and oxidation resistance by changes in coating chemistry and structure while not impacting fatigue, SCC, 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. Collaboration with coating and engine gas turbine original equipment manufacturers (OEMs) is encouraged for advice and direction for further developments of the ICME models and strategies. 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 the 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 coating corrosion resistance to SCC for a given set of alloys and (2) an ICME-derived model that would predict and assist in the development of future overlay or bond coats to minimize SCC in gas turbine 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 bond coat/overlay coat chemistry and structure with the selected strategies to mitigate salt interaction that could lead to SCC. TBCs are permeable so the bond coat must form an impermeable barrier to avoid salt interaction with the alloy substrate that would tend to cause SCC. Engage with a gas turbine engine OEM to have an appropriate bond coat-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 SCC in the marine environment, and (3) an ICME-derived model that would predict and assist in the development of future TBC systems (i.e., alloy, bond coat, TBC, TBC strategy to minimize SCC with marine aero engine operational environment). Engage with a marine engine OEM to further develop the TBC technology for incorporation into current and future Navy ship engines.
Development of long-lived TBC systems able to withstand hot corrosion and subsequent SCC at temperatures below 600°C 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:
KEYWORDS: Hot Corrosion, Stress Corrosion Cracking, Environmental-Induced Cracking, Corrosion Fatigue, Gas Turbines, Superalloys
TPOC 1
David Shifler
david.a.shifler.civ@us.navy.milTPOC 2
Calvin Faucett
david.c.faucett.civ@us.navy.mil
** TOPIC NOTICE ** |
The Navy Topic above is an "unofficial" copy from the Navy Topics in the DoW FY-26 Release 1 SBIR BAA. Please see the official DoW Topic website at www.dodsbirsttr.mil/submissions/solicitation-documents/active-solicitations for any updates. The DoW issued its Navy FY-26 Release 1 SBIR Topics pre-release on April 13, 2026 which opens to receive proposals on May 6, 2026, and closes June 3, 2026 (12:00pm ET). Direct Contact with Topic Authors: During the pre-release period (April 13, through May 5, 2026) proposing firms have an opportunity to directly contact the Technical Point of Contact (TPOC) to ask technical questions about the specific BAA topic. The TPOC contact information is listed in each topic description. Once DoW begins accepting proposals on May 6, 2026 no further direct contact between proposers and topic authors is allowed unless the Topic Author is responding to a question submitted during the Pre-release period. DoD On-line Q&A System: After the pre-release period, until May 20, 2026, at 12:00 PM ET, proposers may submit written questions through the DoW On-line Topic Q&A at https://www.dodsbirsttr.mil/submissions/login/ by logging in and following instructions. In the Topic Q&A system, the questioner and respondent remain anonymous but all questions and answers are posted for general viewing. DoW Topics Search Tool: Visit the DoW Topic Search Tool at www.dodsbirsttr.mil/topics-app/ to find topics by keyword across all DoW Components participating in this BAA.
|