Purpose:

Electrolytic hard chrome (EHC) plating is used extensively by helicopter original equipment manufacturers (OEMs) to impart wear and/or corrosion resistance to many components such as pistons and piston rings. Hard chrome plating utilizes chromium in the hexavalent state (hex-Cr) which is a known carcinogen. As a result, the Environmental Protection Agency has issued air and water emission standards for chromium, and Occupational Safety and Health Administration has established a permissible exposure limit (PEL) for hex-Cr in the workplace. Recent epidemiological studies appear to support a substantial lowering of the PEL, perhaps by as much as two orders of magnitude, which would greatly increase the cost of chrome plating to OEMs and Department of Defense (DoD) facilities.

Description:

A tri-service/OEM/private-sector group, designated the Hard Chrome Alternatives Team (HCAT), has been formed to demonstrate and validate thermal spray coatings as an environmentally-acceptable, superior-performance alternative to EHC on many different types of aircraft components. A detailed technology assessment concluded that the optimum coatings for replacing EHC plating on helicopter dynamic components were high-velocity oxygen-fuel (HVOF) Tribaloy 400 (a cobalt-based alloy), WC(83%)/Co(17%), and WC(86%)/Co(10%)Cr(4%). It is expected that the Joint Test Protocol (JTP) will be divided into two main parts, with the first part addressing materials testing on coupons, including extensive fatigue, fretting and sliding wear, and corrosion testing. The second part of the JTP includes evaluating the performance of the HVOF coatings sliding against seal materials and rig and flight testing on actual coated components. It is anticipated that both utility and flight-control actuators will be evaluated. In addition, producibility testing and assessments will be conducted which will include optimum methods for stripping and grinding of the HVOF coatings.

Benefits:

This new technology will result in the elimination of hexavalent chromium emissions, leading to reduced toxic waste disposal and a safer working environment. The anticipated superior performance of the HVOF coatings will lead to decreased component repair frequency, reduced process turnaround time, and increased readiness. Taken together, these benefits should result in reduced life-cycle costs on DoD aircraft.
(Anticipated Project Completion - 2005)

Contact:

Mr. Bruce Sartwell
Naval Research Laboratory
Code 6176
4555 Overlook Avenue, SW
Washington, DC 20375
Phone: (202) 767-0722
Fax: (202) 767-3321
E-mail: sartwell@nrl.navy.mil