Cast Al-Ce based Eutectic Alloys with High Creep Resistance

Tiffany Wu ,*Yang Liu, and *Daniel Ng,

co-advised with Dr. Alex Plotkowski, Dr.Amit Shyam, and Dr. Ryan Dehoff, Oak Ridge National Laboratory

Previous studies on Al-Ce-Mg alloys have demonstrated thermal stability of Ce-rich eutectic strengthening phases up to 540°C. These results show promise for the development of Al-Ce alloys which maintain their strength at elevated temperatures. Our work involves microstructural investigations and compression creep testing of Al-Ce binary alloys, with the goal of studying how Ce additions may be utilized to develop alloys with enhanced creep resistance. Initial microstructural investigations have revealed a coarse grain structure with millimeter-scale grains expected to be resistant to diffusional creep. In addition, we observe a fine dispersion of eutectic Ce-rich phases which provide strength to the alloy. During compression creep testing at 300°C, we have observed creep deformation at lower rates and higher stresses than those of Er-free L12 -strengthened alloys extensively studied in our group, suggesting that Ce-additions may be used in developing the next generation of creep-resistant aluminum alloys.

With promising creep- and coarsening resistance, the two binary eutectic systems, Al-Ni and Al-Ce, are combined into a ternary Al-Ce-Ni eutectics. Microhardness and microstructure evolution demonstrate excellent coarsening up to 425°C, with a gradual decrease in microhardness over long times. The sub-micron eutectic Al11Ce3 phase shows superior thermal stability and maintain its submicron fiber morphology, whereas the sub-micron eutectic Al3Ni rods coarsen faster into equiaxed micron-size precipitates. Creep resistance of as-cast eutectic Al-Ce-Ni at 300°C is comparable with binary eutectic Al-Ni and higher than binary eutectic Al-Ce. Overaged samples show higher creep rates than as-cast states due to their coarsened microstructures, but retains significant creep resistance, implying that load transfer is an important strengthening mechanism.

SEM image of Al-16Ce alloy, showing the euctic region

Double-logarithmic plot of minimum creep strain rate vs. stress, with best-fit lines drawn, at 300°C, for as-cast Eut (Al-10Ce-Ni) and Eut overaged at 590 °C for 24 h prior to creep.

BSE micrographs of cast Al-10Ce-5Ni aged at 400 °C for 1050 h showing phases (dark: Al, grey: Al3Ni and white: Al11Ce3). (a) hypoeutectic region, with coarsened Al3Ni and Al11Ce3 in eutectic colonies and, in a more pronounced manner, at interface between primary Al dendrites and eutectic regions (arrows). Higher-magnification insert highlights with arrow an example of Al3Ni engulfing Al11Ce3; (b) eutectic region, showing clearly coarsened Al3Ni precipitates and barely coarsened Al11Ce3 fibers (see higher magnification insert)

Related Publications

  1. T. Wu, A. Plotkowski, A. Shyam, D.C. Dunand, Microstructure and creep properties of cast near-eutectic Al-Ce-Ni alloys, Materials Science and Engineering: A. 833 (2022) 142551.
  2. Y. Liu, R. A. Michi, and D. C. Dunand, "Cast near-eutectic Al-12.5 wt.% Ce alloy with high coarsening and creep resistance," Materials Science and Engineering: A, vol. 767, p. 138440, Nov. 2019, doi: 10.1016/j.msea.2019.138440.
  3. D. S. Ng and D. C. Dunand, "Coarsening- and Creep-Resistant Cast Hypoeutectic Al-Ce-Mg Alloy," SSRN Journal, 2019, doi: 10.2139/ssrn.3485043.
  4. Sims, Z. C., Rios, O. R., Weiss, D., Turchi, P. E., Perron, A., Lee, J. R., ... & An, K. (2017). High performance aluminum–cerium alloys for high-temperature applications. Materials Horizons, 4(6), 1070-1078.

Funding support

  1. Oak Ridge National Laboratory