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Electrochemical Deposition of Metals Using Ionic Liquids

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Background / Problem Statement

Acceptable alternatives to hard-chrome plating from hexavalent chromium (Cr VI) containing plating baths as tribological and corrosion-resisting surface treatments have been elusive for decades. Environmental mandates call for elimination of Cr (VI) plating baths and other Cr (VI)-contaning surface treatment chemistries. New plating technologies, predicated on the use of ionic liquids (ILs), provide a more environmentally- friendly approach to forming metallic chromium layers from trivalent precursors, offering the potential to approach the characteristics of traditional hard chrome, albeit with certain compromises in plating efficiency and cost. Developments are required to both optimize the plating processes from ILs, as well as the performance of the resulting surface layers for their intended applications. Ionic-liquid baths have also been employed for deposition of aluminum, again principally for tribological and corrosion-resisting applications involving such articles as fasteners and base-metal (typically high-strength steel) protection. A suitable and environmentally-friendly alternative to aluminizing with physical vapor deposition processes or the incumbent Sigal (AlumiPlate®) process (employing hazardous organometallic precursors and organic solvents, e.g. toluene) is desired. Early indications are that plating of aluminum metal from ionic solutions may be advanced to a point where it can offer an alternative to the existing technologies. This project seeks to advance both plating of chromium and aluminum metallic layers from selected ionic liquids for tribological (e.g. hard-chrome replacement) and corrosion resisting layers (aluminizing), and validate performance of such coatings in advancement of MRL levels assessed.

Objectives

The project is structured so as to address the following coatings and applications:

Hard chrome replacement – this aspect of the project addresses the use of metallic chromium plated from ILs as a replacement for the Cr(VI) hard chrome tribological coatings as presently employed for such applications as engine valve stems, hydraulic rods and other tribological applications requiring a degree of corrosion resistance. Notre Dame and U. Texas are responsible for basic plating parameter development. The principal target applications will be defined by Eaton Corp.

Aluminum coatings for corrosion resistance:

Aluminum substrates – The objective here is a surface layer intended for overcoat coverage of alloyed and tempered aluminum substrates with a focus on novel Al-Li alloys are being developed by Pratt & Whitney Division of United Technologies for aircraft engine application. The envisioned performance is seen as a parallel to the Alclad family of high-purity aluminum overlays on 2000 series substrates. The primary development responsibility is with Xtalic, with performance appraisal by United Technologies.

High-strength steel substrates – In this instance, aluminizing from ionic liquids is intended to replace cadmium plating on steel for tribological and corrosion resisting applications and also offer an alternative to aluminum coating by physical vapor deposition (e.g. IVAD) or the Sigal process, producing aluminum layers by electroplating from organometallic salts of aluminum dissolved in toluene. High-strength steel fasteners and components such as landing-gear axles are the intended applications. Reduction in tendency for hydrogen embrittlement of hardened steel components is a secondary objective,

While the physical objectives of the project are in the form of prototype coated components as indicated above, the determination of performance attributes relative to the current baseline processes are a part of the broader systems engineering approach. This approach to the evolution of MRL advancement follows the following process:

  • Definition of the system-level performance attributes for the subject coatings applied to components of interest. (e.g. tribological demands, corrosion performance)
  • Validation and optimiziation of the coating processes for the components or surrogates of interest
  • Production of prototype component or its surrogate (in the event actual component pieces prove unreasonable to obtain)
  • Validation of component performance using metrics provided by the relevant OEMs
  • Development of parameters and metrics for the scale-up process to pilot scale production

Participants

Industry Partners

  • United Technologies Research Center
  • Xtalic
  • DNV GL
  • Eaton
  • Materion
  • Lockheed Martin

Research Partners

  • Case Western Reserve University
  • University of Notre Dame
  • University of Texas