Durable Hybrid Coatings for Aircraft

Sponsor: Air Force Research Laboratory

Background. Due to their desirable mechanical properties and relatively light weight, aluminum alloys have been widely used for the construction of aircraft. While these aluminum alloys exhibit good mechanical properties, they are very prone to environmentally-induced corrosion. To date, the corrosion protection of aluminum alloys for aircraft has relied extensively on the use of hexavalent-chromium compounds as corrosion inhibitors in pretreatments and paints. Due to the toxicity and carcinogenic properties of chromium, federal agencies, in particular the Environmental Protection Agency, have imposed severe restrictions on hexavalent-chromium use. As a result, there is an urgent need for an environmentally-benign replacement for hexavalent-chromium-based materials for corrosion inhibition of aluminum alloys.

Recently, Professor Gordon P. Bierwagen of the NDSU Department of Coatings and Polymeric Materials at NDSU developed a new primer system for the corrosion inhibition of aluminum alloys that relies on the use of surface passivated magnesium (Mg) particles to cathodically protect the substrate. The surface passivated Mg particles are formulated into a coating by simply dispersing the particles in a binder system using a particle to binder ratio that enables physical contact between Mg-particles in the cured coating. Physical contact between Mg particles and the substrate is necessary to enable electron transfer from the Mg particles to the aluminum alloy substrate.

The current (2005-2010) research program includes continued studies of the Mg-based primer and corrosion sensor work performed primarily in the Department of Coatings and Polymeric Materials. The emphases of research performed at CNSE are described below.

Program Objectives. CNSE objectives in the current program are to:

  1. Develop new high-throughput methods for enabling the application of a combinatorial approach to the development of new primers for corrosion protection.
  2. Develop new Mg-rich primers for corrosion protection of aluminum alloys.
  3. Investigate hard coatings for several applications: (1) pretreatment of the aluminum alloys prior to priming; (2) coatings for titanium alloys; and (3) in-field repair of aircraft canopy conducting coatings with indium tin oxide (ITO).

Progress. Through multiple phases of funding, many significant milestones have been achieved:

  1. A fully functional combinatorial workflow was developed that enables the application of a combinatorial approach to the development of primers for corrosion protection.
  2. A novel electrochemical measurement system (parallel EIS) was developed that enables high-throughput characterization of corrosion protection.
  3. Novel Mg-rich primers based on a hybrid organic-inorganic binder system were developed.
  4. Several publications based on both novel high-throughput methods and new coating compositions have been produced.
  5. SiC pre-primer treatment and ITO canopy coatings have been successfully demonstrated. Early work with plasma spray technologies has had promising results.

Contacts
Greg McCarthy (program manager) – Greg.McCarthy@ndsu.edu
Bret Chisholm (combinatorial science) – Bret.Chisholm@ndsu.edu
Doug Schulz (hard coatings) – Doug.Schulz@ndsu.edu

This material is based on research sponsored by the Air Force Research Laboratory under agreement number FA8650-04-1-5045, and prior agreements.