Release Date
August 23rd, 2023
Open Date
September 20th, 2023
Due Date(s)
October 18th, 2023
Close Date
October 18th, 2023
Topic No.


Functional Gradient Coatings for Landing Gear


Department of DefenseN/A


Type: SBIRPhase: BOTHYear: 2023


The Department of Defense (DoD) is seeking proposals for the development of functional gradient coatings for landing gear. The objective is to develop coatings that allow for greater dimensional restoration of work surfaces on landing gear, reducing or eliminating the use of hexavalent chrome and reducing production time. The current process involves the use of Engineering Hard Chrome, which is being replaced by High Velocity Oxygen Fuel (HVOF) deposited Tungsten Carbide Cobalt. However, excessive build of this coating can lead to stress cracks and coating separation. The proposed solution is a Functional Gradient Coating (FGC) that consists of a build layer, an intermediary transition layer, and a wear coating layer. This FGC will provide greater dimensional restoration while still applying a replaceable wear-resistant layer. The project will be conducted in three phases: Phase I involves feasibility documentation, Phase II includes spraying the FGC on multiple candidate aircraft parts and conducting flight worthiness testing, and Phase III focuses on upgrading machinery and implementing the FGC process. The project is restricted under the International Traffic in Arms Regulation (ITAR) and the Export Administration Regulation (EAR). The solicitation is closed, and more information can be found on the DoD SBIR website.


OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Hypersonics;Microelectronics;Advanced Materials


The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws.


OBJECTIVE: Develop and activate coatings that will allow for greater dimensional restoration of work surfaces on landing gear. As compared to the current process, this will reduce or eliminate Hexavelant Chrome on many aircraft part surfaces. The new process will reduce production time by a quicker deposition process and elimination of an 8 hour relief bake of production parts.


DESCRIPTION: Aircraft components wear down over time. To prolong the service life of parts, wear resistant coatings are applied to the working surface of the parts. Previously, this was done with Engineering Hard Chrome (also known as hexavalent chromium / hex-chrome). This coating is replaced by High Velocity Oxygen Fuel (HVOF) deposited Tungsten Carbide Cobalt, a metal/ceramic blend that has a very long functional life without the health hazards of hex-chrome   Tungsten Carbide Cobalt, as applied per AF DWG 200310641, has a maximum thickness before the coating develops stress cracks. Excessive build can lead to the coating removing itself from the part’s surface. This exposes the underlying part to wear, and the shards of the coating can damage seals. A careful balance of proper coating thickness must be maintained for part functionality and preventing the part from rusting as well.  A Functional Gradient Coating (FGC), consisting of a build layer, then an intermediary transition layer, then the wear coating layer, allows for much greater dimensional restoration while still applying a replaceable wear resistant layer on top. The coating’s intermediary transition layer absorbs and dissipates much of the stresses that would normally cause a two-part coating system to fail under stress, eliminating or severely reducing the problem of stress cracks and coating separation.   This process will reduce our condemnation rate, which will help maintain functional supply of available assets reduce aircraft part replacement delivery times, allowing faster asset readiness to deploy or fight.


PHASE I: As this is a Direct-to-Phase-II (D2P2) topic, no Phase I awards will be made as a result of this topic. To qualify for this D2P2 topic, the Government expects the applicant to demonstrate feasibility by means of a prior “Phase I-type” effort that does not constitute work undertaken as part of a prior SBIR/STTR funding agreement.   FEASABILITY DOCUMENTATION.  For this Direct-to-Phase II topic, evaluators are expecting that the submittal firm demonstrate the ability to spraying of representative samples and candidate aircraft parts with the FGC and examining the cross-sectional properties, bend strength, adhesive strength, and fatigue characteristics.    Submittal Firm shall demonstrate on a representative sample, a functionally graded coating comprising of a thickness build/bond layer graded into a wear resistant layer. This functionally graded coating shall demonstrate a wear layer with FGM that satisfies performance criteria as identified in AF DWG 200310641.


PHASE II: Spraying the FGC on multiple candidate aircraft parts. Destructive testing would be done on the first item to confirm characteristics between representative samples and actual aircraft parts. Surface would then be ground to operational dimensions, then flight worthiness testing would commence. Addendums or supplements to AF DWG 200310641 would then be supplied to the 417 SCMS/GUEA for adaptation.


PHASE III DUAL USE APPLICATIONS: Once flight worthiness is established, upgrading Hill AFB machinery to be able to apply FGC’s to aircraft parts. First article acceptance procedures would be carried out, then workload activation begins. Addendums or supplements to AF DWG 200310641 would then be supplied to the 417 SCMS/GUEA for adaptation. Coordination with 417 SCMS/GUEA to update applicable technical orders to use this process across the various assets as needed.



L. Prchlik, S. Sampath, J. Gutleber, G. Bancke, A.W. Ruff , Friction and wear properties of WC-Co and Mo-Mo2C based functionally graded materials, Wear 249 (2001) Elsevier, 3 May 2001   
Giovanni Bolelli, Valeria Cannillo, Luca Lusvarghi, Roberto Rosa, Alfredo Valarezo, Wanhuk B. Choi, Ravi Dey, Christopher Weyant, Sanjay Sampath, Functionally graded WC–Co/NiAl HVOF coatings for damage tolerance, wear and corrosion protection, Surface & Coatings Technology 206 (2012) 2585-2601, 20 July 2021  
M. Hasan, J. Stokes, L. Looney, M.S.J. Hashmi, Surf. Coat. Technol. 202 (2008) 4006.


KEYWORDS: Thermal Spray, High Velocity Oxygen Fuel, HVOF, Functional Gradient Coating, Wear Surface, Landing Gear, Dimensional Restoration