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Aerospace

The aerospace industry is a major user of Cr⁶⁺ generating processes as well as materials that are not RoHS-compliant (Cd, Cr⁶⁺, Pb).  At this point RoHS-compliance is not as issue since aircraft are exempt from ELV, WEEE and RoHS.  However, we cannot be sure how long this exemption will last.  Industries that are not exempt are driving the development of better and better alternatives to the corrosion and wear treatments most commonly used in the aircraft industry today, which will eventually undermine the case for the aerospace exemption.  In addition, the costs associated with continuing to use chrome plating, chromates and cadmium are rising, while the performance of alternatives is improving, leading customers to demand the use of clean alternatives to reduce their maintenance costs.  The coming OSHA Cr⁶⁺ PEL is likely to further accelerate this process.

Fortunately many of the best new clean coating and surface treating processes have been developed specifically for the aerospace.  The primary clean alternatives include:

• Chrome plating alternatives

  • HVOF using WC-CoCr and other materials are replacing hard chrome for wear resistance and for rebuilding worn or corroded components.  This is especially true for landing gear, which are now specified for HVOF rather than hard chrome on all new programs.

  • For internal surfaces (hydraulic outer cylinder, for example) there are various electroless and electroplated Ni coatings, as well as a new Co-based electroplate currently in validation

• Cadmium plating alternatives

  • Zn-Ni has become the most widely used Cd alternative coating

  • Electroplated Al has proved to have excellent corrosion resistance and its use in military aircraft is growing

  • The aircraft hydraulics industry has largely moved to 15-5PH stainless steel in place of Cd-plated 4340, while stainless fasteners are becoming standard in engines.  New high strength stainless steels are new becoming available for landing gear.

• Chromate alternatives

  • Trivalent chrome conversion coatings (often with additional inhibitors) are becoming used increasingly in the aircraft industry, in addition to a variety of other inhibitor packages

  • Rare earth  based primers are proving to be more effective than chromated primers.

Click on the DoD & Aerospace button for access to details aerospace alternatives to hard chrome, Cd and chromates.  A very large amount of information is available is from the HCAT data sharing web site (click on Teams & Workgroups/Hard Chrome Alternatives Team).  A usernames and passwords are available to aerospace industry users – contact rowan@rowantechnology.com.  The data on the HCAT site are so extensive that if you are a new user you may wish to call Keith Legg at Rowan Technology Group (847.680.9420) for a quick guided tour or to be pointed in the direction of the most important information to answer your immediate questions.

Industry Solutions

Aerospace

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