In situ synchrotron X-ray diffraction revealing competition between A1 and B2 phases in AlCoCrFeNi high-entropy alloys

Acta Materialia, vol. 309, pp. 122097

Abstract

Phase competition in AlCoCrFeNi x high-entropy alloys ( x = 2.0, 2.1, 2.2, and 2.4) was investigated using synchrotron X-ray diffraction combined with electromagnetic levitation. In undercooled melts with x = 2.0, 2.1, and 2.2, the ordered B2 phase forms first via the transformation L → B2, marking the initial stage of solidification. This observation aligns well with the double recalescence phenomenon, where B2 crystallizes directly from the liquid, followed by the formation of a B2/A1 eutectic structure from the mushy zone, as captured in high-speed video recordings of the AlCoCrFeNi 2.1 sample. In contrast, the AlCoCrFeNi 2.4 alloy solidifies initially with the primary A1 phase via L → A1. The delay time (Δ t ) between nucleation of the primary phase and onset of eutectic transformation is strongly influenced by the nickel concentration. Moreover, the dissolution temperature of the ordered L1 2 phase during solid-state heating increases steadily with rising nickel content. These experimental findings show strong agreement with phase evolution predictions obtained through thermodynamic modeling of the AlCoCrFeNi system using Thermo-Calc software. Overall, this study provides a comprehensive picture of the phase formation and stability, solidification kinetics, and microstructural development of AlCoCrFeNi x high-entropy alloys.

Authors 4

1. Shilei Liu corresponding

   Leibniz Institute for Solid State and Materials Research

   Affiliation as printed

   Leibniz Institute for Solid State and Materials Research Dresden, Helmholtzstr. 20, 01069, Dresden, Germany

2. Victoria Kaban

   Leibniz Institute for Solid State and Materials Research

   Affiliation as printed

   Leibniz Institute for Solid State and Materials Research Dresden, Helmholtzstr. 20, 01069, Dresden, Germany

3. Victor Timofey Witusiewicz Aachen Access e.V

   Access

   Affiliation as printed

   ACCESS e.V., Inzestraße 5, 52072, Aachen, Germany

4. Ivan G. Kaban corresponding

   Leibniz Institute for Solid State and Materials Research

   Affiliation as printed

   Leibniz Institute for Solid State and Materials Research Dresden, Helmholtzstr. 20, 01069, Dresden, Germany