N14A-T014 TITLE: Surface Modification Process to Limit Cathodic Current Density

TECHNOLOGY AREAS: Air Platform, Materials/Processes

ACQUISITION PROGRAM: F/A-18, T-45

OBJECTIVE: Develop a novel surface modification process, to limit or control high current densities on cathodic structural materials like fasteners, pins, attachment points, and interfaces; commonly constructed from materials like copper-beryllium, stainless (CRES) steel, or titanium, without reducing the mechanical properties or function of the fastener substrate.

DESCRIPTION: Open circuit potential (OCP) is used as a proxy for corrosion driving force; however, OCP is a steady-state, uncoupled bulk material property, and structural materials are not uncoupled. OCP is not accurate in assessing corrosion rates or cracking. Recent research has shown that surface chemistry, residual stress, and current density are key. Specifically, this work has shown the acceleration factor to be linked with cathodic current density. Bushings, fasteners, and other structural attachment materials are usually CRES, Ti, or Ni-based alloys, all cathodic to the standard airframe metals. Corrosion at holes and other interfaces drives crack initiation and propagation; since these areas are stress intensity risers, and therefore at a higher energy state. A surface modification process is required to suppress cathode current density without affecting the mechanical properties of the fastener/bushing materials.

PHASE I: Demonstrate the process and concept for modifying the chemical or physical structure of the alloy surface to effect electrical and ionic conductivity, polarization response and/or coupled current density.

PHASE II: Validate the process(es) for ability to modify surfaces or substrate alloy with respect to cathodic current density when coupled to anodic substrates such as aluminum, magnesium, or steel. Validate the mechanical properties, such as strength, toughness, stiffness, etc. are not negatively impacted by the changes to electrochemical properties. Demonstrate the mechanism(s) of limiting cathodic current, via insulation, conductivity, etc. Demonstrate the scalability to bulk, high rate fastener or bushing manufacturing process incorporation.

PHASE III: Scale up and transition the process to a validated commercial surface finishing product. Coordinate with the Naval Air Warfare Center Materials and Structures engineering competencies for approval and transition to FRC or approved OEM vendor applications.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Commercial aviation, automotive, maritime/ships, and facility/infrastructure applications are all viable transition of this technology into dual-DoD/private sector applications.

REFERENCES:
1. "Galvanic Test Panels for Accelerated Corrosion Testing of Coated Al Alloys, Part I: Concept", Corrosion: The Journal of Science and Engineering 10.5006.0905, C.A. Matzdorf, W.C. Nickerson, B.C. Rincon Troconis, G.S. Frankel, Longfei Li, and R.G. Buchheit.

2. "Galvanic Test Panels for Accelerated Corrosion Testing of Coated Al Alloys, Part II: Measurement of Galvanic Interaction", Corrosion: The Journal of Science and Engineering 10.5006.0907, C.A. Matzdorf, W.C. Nickerson, B.C. Rincon Troconis, G.S. Frankel, Longfei Li, and R.G. Buchheit.

3. "Atmospheric Pitting and Galvanic Corrosion of High Strength Al Alloys", Abstract #1748, 224th ECS Meeting, © 2013 The Electrochemical Society, Z. Feng, S.C. Morton, M.S. Thomson, and G.S. Frankel.