The objective of this Statement of Need (SON) is to develop a suitable, flexible, chromium-free, low-volatile organic compound (VOC) primer coating that is compatible with the basic materials systems on the inner and outer mold line (IML and OML) of legacy, fifth generation, and future platforms.

A fully chromium-free, VOC compliant, highly flexible primer coating should have the following characteristics, although proposed concepts towards development of novel flexible systems compatible with the below requirements are also acceptable:

• Prevent coating failure during installation of fasteners and high structural loading scenarios during aircraft operation.
• Have significantly improved moisture barrier properties relative to MIL-PRF-23377, leading to increased resistance to general corrosion and galvanic corrosion.
• Must be compatible with composite, aerospace aluminum, titanium, magnesium, and other typical alloys.
• Must have comparable performance to MIL-PRF-32239 Class 2 (High flexibility coating systems), MIL-PRF-81733 Type III Grade B (Sealing and Coating Compound, Corrosion Inhibitive), and/or TT-P-2760 Class N (Primer coating: polyurethane, Elastomeric, High-solids).
• Suitable pretreatments should be anodized (without chromate seal) on 2000 and 7000 series aluminum, inhibitive and non-inhibitive pretreatments for aerospace metals (see above), and compatible with Zn-Ni plated fasteners/components, titanium fasteners/components, and typical OML sealants.
• Should be removable using standard depainting technologies.
• Should reduce or eliminate the use of chemicals with risk evaluations under TSCA.¹
• The proposed primer should reduce or eliminate the use of emerging chemicals of concern² or other chemicals or materials that have been the subject of extensive replacement and/or cleanup efforts.

Proposals should develop fundamental means to enable primer coating flexibility; propose methods to assess flexibility, barrier properties, and corrosion resistance; and propose and assess primer coating formulation solutions that would result in improved flexible primer coating solutions.

Proposals must include a plan to conduct a Sustainability Analysis³ of appropriate proportion to the proposed research. Proposals should establish a lifecycle framework that can mature as the technology or process advances through the acquisition process. This tiered approach aims to develop and document a minimum data set at each stage of research and development that can be used to make informed decisions and streamline transition to an acquisition program. The Sustainability Analysis may include varying depths of data and information that can inform: the goal and scope of an analysis; the identity and quantity of relevant inputs and outputs to the system; and the estimation of life cycle impacts and costs.

Implementing new primer coatings will lead to improved material sustainability as well as provide improved corrosion protection and enhanced coating life. The prolonged primer coating life will reduce the number of primer coatings used to repair damaged primer coatings and maintenance person-hours associated with treating and repairing corrosion around fastener locations and other flexibility prone areas. Being VOC compliant and chromate free will expand the usage of a more durable, highly performing primer coating systems. Program Managers, installations, and Warfighters across all services would benefit from new, innovative and improved weapons systems advanced coating resins. These would improve asset operational performance and readiness and application/removal production and field throughput characteristics.

Large aircraft expand and flex from pressurization and the normal process of flight, landing and takeoffs. Since the aircraft is expanding and flexing, the primer coating system must have similar adhesion properties. The current primer coating systems are good barriers; corrosion is rarely observed occurring in the center of a panel. Typically, primer coating systems fail around seams and fasteners due to a paint bridge that forms across the gaps of the seams and fasteners. Since the paint bridge does not have backing support across these gaps, the expansion and flexing of the aircraft concentrate forces on these paint bridges. If the primer coating system does not possess superior flexibility properties, the primer coating system adhesion will fail, accelerating corrosion at the fastener location.

Polysulfide sealant possesses unusual flexibility properties that allow it to blunt cracks that initiate in the topcoat preventing the cracks from propagating to the substrate. However, these coatings have relatively high VOC content and are difficult to remove. As a result, their use is limited and only allowed on the OML of aircraft; they are not currently used on the IML. Improved flexible primer coatings could increase their usage on OML, thereby reducing corrosion and the use of regulated corrosion inhibitors.

The DLA ASSIST Tool can be used to download relevant specifications: https://assist.dla.mil/online/start/ 

The cost and time to meet the requirements of this SON are at the discretion of the proposer. The two options are as follows:

Standard Proposals: These proposals describe a complete research effort. The proposer should incorporate the appropriate time, schedule, and cost requirements to accomplish the scope of work proposed. SERDP projects normally run from two to five years in length and vary considerably in cost consistent with the scope of the effort. It is expected that most proposals will fall into this category.

Limited Scope Proposals: Proposers with innovative approaches to the SON that entail high technical risk or have minimal supporting data may submit a Limited Scope Proposal for funding up to $250,000 and approximately one year in duration. Such proposals may be eligible for follow-on funding if they result in a successful initial project. The objective of these proposals should be to acquire the data necessary to demonstrate proof-of-concept or reduction of risk that will lead to development of a future Standard Proposal. Proposers should submit Limited Scope Proposals in accordance with the SERDP Core Solicitation instructions and deadlines.