Systems Design Approach to Low-Cost Coinage Materials

Abstract

A systems approach within an integrated computational materials engineering framework was used to design three new low-cost seamless replacement coinage alloys to reduce the raw material cost of the current US coinage alloys. Maintaining compatibility with current coinage materials required matching the currently used alloy properties of yield strength, work-hardening behavior, electrical conductivity, color, corrosion resistance, and wear resistance. In addition, the designed alloys were required to use current production processes. CALPHAD-based models for electrical conductivity and color were developed to integrate into the system design. Three prototype alloys were designed, produced, and characterized. The design process highlighted the trade-off between minimizing the raw material costs and achieving the desired color properties. Characterization of the three prototype alloys showed good agreement with the design goals.

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Notes

  1. 1.

    The “±” symbol represents one standard deviation.

  2. 2.

    CALPHAD originally stood for CALulation for PHAse Diagrams. The method is now used as phase-based modeling for a variety of phase-based material properties.

  3. 3.

    All alloy compositions provided are given in mass percent unless otherwise noted.

  4. 4.

    Certain commercial entities, equipment, or materials may be identified in this document to describe an experimental procedure or concept adequately. Such identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the entities, materials, or equipment are necessarily the best available for the purpose.

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Acknowledgments

Funding for this work was provided by an Interagency Agreement between the United States Mint and the National Institute of Standards and Technology, HQ14RA-38 NISTMOD. 001 (IA# 1404-642-01). The authors gratefully acknowledge Tony Ying of the United State Mint for providing stamping, vending machine testing, and additional color and electrical conductivity measurements.

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Correspondence to Eric A. Lass.

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Lass, E.A., Stoudt, M.R. & Campbell, C.E. Systems Design Approach to Low-Cost Coinage Materials. Integr Mater Manuf Innov 7, 52–69 (2018). https://doi.org/10.1007/s40192-018-0110-2

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Keywords

  • CALPHAD
  • ICME
  • Materials design
  • Coinage alloy