N101-041 TITLE: High Temperature Survivability Coating Materials with Innovative Application Processes

TECHNOLOGY AREAS: Air Platform, Materials/Processes, Weapons

ACQUISITION PROGRAM: PMA-201, Precision Strike Weapons; PMA-266; Joint Strike Fighter

RESTRICTION ON PERFORMANCE BY FOREIGN CITIZENS (i.e., those holding non-U.S. Passports): This topic is "ITAR Restricted." The information and materials provided pursuant to or resulting from this topic are restricted under the International Traffic in Arms Regulations (ITAR), 22 CFR Parts 120 - 130, which control the export of defense-related material and services, including the export of sensitive technical data. Foreign Citizens may perform work under an award resulting from this topic only if they hold the "Permanent Resident Card", or are designated as "Protected Individuals" as defined by 8 U.S.C. 1324b(a)(3). If a proposal for this topic contains participation by a foreign citizen who is not in one of the above two categories, the proposal will be rejected.

OBJECTIVE: Develop high temperature survivability coating concepts with corresponding vulcanization and co-cure bonding application processes for airframe component integration. The coating concepts should be loadable with fillers with properties for either electromagnetic interference/radio frequency (EMI/RF) control or thermal insulation.

DESCRIPTION: Many high temperature elastomers operate at temperatures of 350 to 500 degrees Farenheit. There is a need for innovation and expansion of material options and processes to address challenging high temperature coating applications from 600 through 1300 degrees Farenheit. EMI/RF coatings tend to be thick and, for spray applications, require repetitive and lengthy build-up processes at several mils per coating pass. Elastomeric sheet materials can be formed to necessary thicknesses with compression forming or calendaring but the sheet material must still be applied to components with adhesives. Innovative methods are sought to apply the coating(s) to components by vulcanization for metal substrates or by co-cure for composite structures without thick adhesive layers. It is desired that coating materials pursued not contain methylenedianiline (MDA) polyimide and should minimize the use of other highly volatile compounds where possible. The coating materials should be able to withstand both subsonic and supersonic airflow conditions when used externally on airframe components. A sprayable variant of the molding material or other alternative is also desired but not required.

Future system airframe substrates and components will continue to be made from aluminum and steel, complex composite structures, and plastics. Vehicle areas exposed to high temperatures may include engine exhausts, motor combustion sections, inlet ducts and faces, wings and fins, nose tips, and other protruding surfaces such as fairings and pitot probes. Developing reliable, vulcanization processes for formation bonding elastomeric sheet material to airframe components with minimal priming and without the additional steps of adhesive layers would yield a cost and labor benefit for sheet materials over spray coating applications. Vulcanization and composite pre-preg processes employ elevated temperatures and are a good match for research into high temperature elastomers and fillers. The high temperature materials developed would likely also serve well as very durable coatings for applications encountering only low and moderate temperatures.

Material candidates should at a minimum withstand in-service sustained operation at 500 degrees F for 1 hour and long term use at lower 450 degrees F temperatures. Long term operation at 650 degrees F is desired. Reliable one-time use temperature operation at 680 degrees F for 10 minutes without degradation is required as a primary project objective, while the goal would be capability for one-time operation at 800 degrees F for 10 minutes without any significant degradation. A solution is also sought for one time operation at temperatures approaching close to 1300 degrees F for 10 minutes. If necessary this 1300 degrees F need can be addressed by a different material though a common material would be ideal. In addition to protection from these temperature exposures, the coating should survive in supersonic airflow at low or high altitude. If materials considered have ablative properties, temperature of intumescence should be at least above 700 degrees F and ideally above 1300 degrees F. It is a goal that manufacturing cure processes to apply the coatings do not require elevated temperatures above 400 degrees F.

The goal of this effort is to demonstrate sheet material EMI/RF shielding performance prior to vulcanization or co-cure. Investigate potential methods for verification of installed EMI/RF performance or quality assurance after part assembly. Demonstrate adhesion performance of samples with respect to MIL-SPEC standards including tensile and shear strength performance at room temperature and elevated temperatures to the extent possible. Research any potential issues with molding contaminants and develop processes to minimize or remove them. Investigate methods to minimize and assess bonding issues such as void content. Materials should be resilient against micro-cracking issues while in service. Demonstrate final material performance to MIL-STD 810 environmental standards.

PHASE I: Demonstrate the technical feasibility of developing the coating material and corresponding application process technologies. In Phase I, develop detailed Phase II research and prototype plans that include definition of success criteria, manufacturing demonstration, and test verification. Plans should include test verification of material durability, stability, EMI/RF control performance for samples and installed performance for prototypes with testing at elevated temperatures.

PHASE II: Develop, prototype, optimize, and validate a high temperature elastomer material with a filler formulation for electromagnetic shielding/RF control and a secondary formulation for thermal insulation. If possible demonstrate proof-of-concept durability of the coatings in subsonic airflow and high temperature supersonic airflow. Prototype a vulcanization process for applying the loaded elastomer to notional parts to include a steel and aluminum control fin and an aluminum wing without the use of adhesive layers. Prototype a co-cure process for coating application within a multi-layer composite structure such as an inlet duct. Investigate co-cure onto an external plastic structure such as a nylon inlet and inlet face edges. Document the research, theory, and materials and manufacturing process steps and technologies developed. Develop cost information and manufacturing specifications for producing and processing the loaded elastomer materials.

PHASE III: Transition coating technology for military and commercial applications.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Private sector commercial dual use applications include airframe and component thermal insulation, rain and sand erosion boots for leading edges, and high temperature EMI gaskets and seals. Air platforms supported could be supersonic transport aircraft, space launch systems, civil aviation aircraft, helicopters, and UAVs. Ground and sea systems may also benefit. Rubber, coating, and composites manufacturing industries will benefit.

REFERENCES:
1. Todd, Robert H., Dell, Allen K., Alting, Leo, "Manufacturing processes Reference Guide", New York, 1993.

2. Peterson, Charles W., Ehnert, G., Liebold, R., Kühfusz, R., "Compression Molding, ASM Handbook 2001, Volume 21 Composites", ISBN 0-817170-703.

3. Dow Corning Tech Bulletin, "Moulding of Silastic Silicone Rubber", http://www.dowcorning.com/content/sitech/

4. Dow Corning Tech Bulletin, "Fabricating with Silastic High Consistency Silicone Rubber", http://www.dowcorning.com/content/sitech/

5. Dow Corning Tech Bulletin, "Some Like It Hot", http://www.dowcorning.com/content/sitech/

6. NASA Spinoff, "Elastomers That Endure", 2001, http://www.nasatech.com/Spinoff/spinoff2001/ip1.html

KEYWORDS: high temperature; elastomer; coating; vulcanization; co-cure; shielding

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