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Characterization of Continuous and Discontinuous Precipitation Phases in Pd-Rich Precious Metal Alloys

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Abstract

Aberration-corrected scanning transmission electron microscopy (AC-STEM), X-ray diffraction (XRD), electron backscatter diffraction, and electron probe microanalysis were applied to characterize continuous and discontinuous phase formation in precious metal alloys used in electrical contacts. The Pd-rich Paliney® (®Paliney is tradename of Deringer-Ney Inc., Bloomfield, CT) alloys contain Pd, Ag, Cu, Au, Pt (and Zn or Ni). With aging at 755 K (482 °C), nanometer-scale chemistry modulation was observed indicating spinodal decomposition. An ordered body-centered tetragonal (bct) structure was also observed with AC-STEM after the 755 K (482 °C) aging treatment and another phase, tentatively identified as β-Cu3Pd4Zn, was found by microscopy and XRD after prolonged holds at higher temperatures. During slow cooling or isothermal holds at high temperature [755 K to 973 K (482 °C to 700 °C)], a two-phase lamellar structure develops along grain boundaries by discontinuous precipitation. XRD and AC-STEM showed that the lamellar structure was comprised of Ag-rich and Cu-rich fcc phases (α 1 and α 2). The phases are discussed in relation to a pseudo-ternary diagram based on Ag-Cu-Pd, which provides a simplified representation of the discontinuous phase compositions in the multi-component alloy system.

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Acknowledgments

The authors would like to express appreciation to Dr. P.T. Vianco for careful review of the manuscript and to others who supported this work at Sandia National Laboratories: Dr. C.V. Robino, Dr. D. Hirschfeld, M. Reece, A.C. Kilgo, B.B. McKenzie, and M.F. Hosking.

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Authors and Affiliations

  1. Sandia National Laboratories, Albuquerque, NM, USA

    Donald F. Susan (Principal Member of Technical Staff), Paul G. Kotula (Principal Member of Technical Staff), Joseph R. Michael (Senior Scientist) & Mark A. Rodriguez (Principal Member of Technical Staff)

  2. Colorado School of Mines, Golden, CO, USA

    Zahra Ghanbari (Graduate Student)

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  1. Donald F. Susan
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  2. Zahra Ghanbari
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  3. Paul G. Kotula
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  4. Joseph R. Michael
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Correspondence to Donald F. Susan.

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Sandia is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.

Manuscript submitted October 14, 2013.

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Susan, D.F., Ghanbari, Z., Kotula, P.G. et al. Characterization of Continuous and Discontinuous Precipitation Phases in Pd-Rich Precious Metal Alloys. Metall Mater Trans A 45, 3755–3766 (2014). https://doi.org/10.1007/s11661-014-2334-x

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  • DOI: https://doi.org/10.1007/s11661-014-2334-x

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