Projects were sought to demonstrate and validate alternative materials and processes to hexavalent chromium (Cr6+) containing primers that are currently used on a variety of weapons systems. Proposals were required to address non-chromated primers as well as accelerated aging protocols that could shorten decision times. Alternative conversion coatings could also have been considered as part of a systems approach.
The materials and processes to be demonstrated/validated should have already been developed to at least a Technology Readiness Level (TRL) of 4, and the proposed project should bring it to TRL 7 or higher. The primary concern was coatings that provide corrosion protection and equivalent or better performance. Proposals should have provided information on previous laboratory testing and field testing, if available, shown performance of the alternative material, as well as information on existing use, if any. Additional materials testing could have been proposed (and would be required in the absence of publicly-available, high-quality performance data). In addition, projects must have developed a Joint Test Protocol* and Demonstration Plan involving stakeholder input and approval from the Original Equipment Manufacturer and/or Department of Defense (DoD) organizations.
Alternative Cr6+ free formulations should have been in production level materials rather than laboratory batch level samples. Projects were required to demonstrate producibility, which is defined as the ability to be used in production for the application specified under relevant production conditions. This includes the ability to scale-up the process to accommodate high-volume production of small items or the application of coatings to large surface areas. Field testing or accelerated aging of coated items should have been included in the proposed project.
Proposed materials and processes should have taken into account compatibility of the alternative material with the matrix material or with the adjacent coating materials in the paint stack-up.
Proposals should have included an assessment of the human health and environmental impacts of proposed ingredients, formulations, and byproducts. These proposals should have established a baseline lifecycle framework and identify the elements of a life cycle inventory that were already known, those that would be investigated during the course of the project, and those that were beyond the scope of the proposed work.
All projects required the involvement of at least one DoD organization as a funded co-performer that was considered a stakeholder for the intended application. Proposals should have indicated the involvement of other DoD stakeholders at least at the consultant level. Unless the technology was already included in existing specifications, proposed projects were asked to include support for the development of a new specification, or modification of an existing specification, to include the alternative material.
Funded projects will appear below as project overviews are posted to the website.
Hexavalent chromium is a known carcinogen, with the major route of exposure through inhalation of vapors or dust. The primary health risk from exposure to Cr6+ is an increased likelihood of developing lung cancer. Other potential health risks include asthma, nasal septa ulcerations and perforations, and dermatitis. In 2006, the Occupational Safety and Health Administration lowered the permissible exposure limit ten-fold from 52 to 5 micrograms-per-cubic-meter, making it among the most stringently regulated materials used in manufacturing and maintenance operations.
Within the DoD, chromated primers are applied primarily to the outer mold line (OML) of aircraft, interior areas of aircraft (non-OML), and steel and aluminum aircraft components within ventilated paint booths. Spray painting operations using chromated primers and paints can generate elevated airborne concentrations of Cr6+. Based on past personnel monitoring, there exists a high risk potential to exceed regulatory limits.
A primer or undercoat is a preparatory coating product applied to improve the adhesion of topcoat or finishing paint and, in many cases, provides additional environmental corrosion resistance. Primers are designed to adhere to surfaces and to form a binding layer that is better prepared to receive the paint. Because primers do not need to be engineered to have durable, finished surfaces, they can instead be engineered to have improved filling and binding properties with the substrate. Chromated primers contain hexavalent chrome compounds (e.g., zinc chromate, strontium chromate, magnesium chromate) as the primary pigment and corrosion inhibitor.
Chromate conversion is used to form an amorphous protective coating for enhanced corrosion protection and adhesion of subsequently applied sealants and topcoats on various metal surfaces. The process serves to inhibit corrosion and improve the adhesion of both paint and powder finishes and provides an added degree of protection. When the protective coating or paint is scratched, chromates from the conversion coating deposit on the bare metal recreating a corrosion-resistant layer at the exposed surface. Chromate conversion coatings are produced by chemical treatment with hexavalent chromium compounds and other activators. These coatings can be applied through immersion, spray, or wipe-on techniques.
Laboratory accelerated corrosion test protocols have historically been used as an indicator or quality control for known and proven coatings technologies, such as those containing chromates. These test requirements were based upon already established coating performance on operational aircraft. Military specifications were derived from laboratory testing results to ensure that new product chemistries performed similarly to legacy chromate treatments/coatings. Non-chromate primers rely more on the pre-paint surface preparation performance than do chromate primers. This variation is not reflected in specification testing and poses an increased technical risk when the non-chromate primer may potentially be combined with non-chromate conversion coatings, anodize/seals, or non-cadmium/non-chromate sacrificial coatings.
Topcoats are generally urethane or epoxy and compatibility with the primer in terms of adhesion is of paramount importance.