DoD weapon systems often experience significant corrosion problems, especially with magnesium alloys used to fabricate components for rotary- and fixed-wing aircraft. Magnesium provides superior mechanical properties given its low-density and high strength-to-weight characteristics. Despite these advantages, magnesium remains electrochemically active and is anodic to all other structural metals; meaning that it will corrode more quickly when coupled with any other metal.
To limit this electrochemical activity, component surfaces are treated with acids, conversion coatings, sealants, and primers – all of which increase the use of chromates (a known occupational health hazard) as well as replacement costs for repair. Corpus Christi Army Depot (CCAD) has over $250-million-dollars in magnesium parts removed from service due to excess corrosion and wear. A significant cost to the DoD supply-chain will be mitigated with the introduction of the Cold Spray process. [1]
Magnesium and magnesium alloy parts are employed across 341 specific weapon systems and 1,925 individual NSN items. Table 1 lists the number of references to related specifications across multiple DoD organizations by weapon system (WS) type.[2]
U.S. Army Research Laboratory (ARL), with support from the Environmental Security Technology Certification Program (WP-200620), has developed a Cold Spray technology to reclaim and repair a variety of these components, eliminating the need for hexavalent chromium and this process utilizes no volatile organic compounds (VOCs) or hazardous air pollutants (HAPs). Cold Spray has been demonstrated to be suitable for a wide variety of common military parts and substrates, at high-production volume, and is adaptable to field application – requiring only an air compressor and electric power. The process is able to deposit coatings with deposition rates exceeding 20 pounds per hour, at thicknesses of 0.030 inches in a matter of seconds, with localized control that eliminates the necessity of masking. A recent benefit-to-cost study provides conservative estimates of cost savings based only on currently approved repair processes.
Cold Spray works by accelerating powdered metal, polymeric or cermet particles to supersonic velocities within a nozzle and deposits them upon impact onto a substrate. Without melting, these particles do not experience the microstructural changes associated with thermal processes (solid-state). Required consumables include the powder and gas (Nitrogen, Air, or Helium). Cold Spray has successfully coated magnesium alloys and a variety of other substrates –titanium, steel alloys, aluminum alloys, nickel super alloys and even ceramics with varied coating, i.e. stainless steel, tungsten carbide-cobalt (WC-Co), chromium carbide (CrC)-nichrome (NiCr), aluminum, titanium, tantalum, even elemental chrome or nickel, as well as with mixed metals such as tantalum and tungsten. In some cases, repaired components have been shown to exceed the properties of their base material’s ultimate tensile strength (50 ksi as compared to 35 ksi for ZE41A magnesium) and increase in ductility (10% as compared to 3%).
The Aviation and Missile Research Development and Engineering Center (AMRDEC), has requested the use of Cold Spray for the Apache Intermediate Gear Support as part of an on-going effort toward technology transition. Annual savings are expected to exceed $100-Million dollars for only this single magnesium part for the UH-60 aircraft. These components are being salvaged from the Storage, Analysis, Failure Evaluation and Reclamation (SAFR) Program Office at CCAD, and reclaimed for use; a 10-to-1 return on investment.
Technology Transfer: Based on the success of the ESTCP demonstration, the project team transitioned the work to a Defense-wide Manufacturing Science & Technology (DMS&T) Manufacturing Technology (MaTech) Program. MOOG, Inc. has successfully established a dedicated turnkey repair station, which has resulted in the development of the world’s first efficient cold spray helium recovery system that will be unveiled at the facility during the Cold Spray Action Team (CSAT) meeting at Worcester Polytechnic Institute on 21 June 2016. in Webster, Massachusetts.
ARL has collaborated with various companies to transfer cold spray technology throughout the industrial base; including major Original Equipment Manufacturers (OEM’s) such as Sikorsky, Westinghouse, United Technology and Boeing. MOOG has worked with ARL, the Navy and the Air Force under various programs to transition cold spray, and together have developed repair processes for over 241 aerospace components for DoD rotorcraft and fixed wing aircraft; including the B-1 Bomber, Apache and Blackhawk helicopters and also fighters such as the F-15 and F-18 saving tens of millions of dollars in replacement costs.
Through partnership with the Repair, Refurbish and Return to Service (R3S) Center at the South Dakota School of Mines & Technology, the VRC Gen III Cold Spray System has been commercialized through the ARL Technology Transfer Office with a Joint Ownership Agreement (JOA) and represents the world’s most versatile and powerful system that can be used manually in the field or automated for production.
What’s Next: A new start project funded by the Strategic Environmental Research and Development Program (WP-2607) is focused toward the synthesis of cold spray powders, nozzle design, and optimization of process parameters needed to replace electrolytic chromium and nickel plating for larger applications that meet or exceed the performance of electroplated hard chrome.
Approval for the use of Cold Spray Technology has been granted to Sikorsky Aircraft, and other OEMs, through Overhaul Repair Instruction (ORI) SS8491 and by AMRDEC/PM–UH-60, through Maintenance Engineering Order (MEO) T7631. This technology meets the needs posed by Executive Order 13148, addresses high-priority Army Environmental requirements and Technology Assessment (AERTA) PP-2-02-04, DoD Strategic Sustainability Performance Plan, DoD Emerging Contaminants, and Minimizing the Use of Hexavalent Chromium memo.
For more information, visit the ARL Center for Cold Spray.
[1] Victor Champagne. Cost and Performance Report: Cold Spray for Repair of Magnesium Components. Department of Defense, Environmental Security Technology Certification Program. November 2011.
[2] Defense Logistics Agency – Weapon System Impact Tool (WSIT); Referenced 13-May-2015.
