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Phase Stability and Precipitation in L12-Strengthened CoCrNi Medium-Entropy Alloys at Intermediate Temperatures


Understanding phase stability and precipitation at intermediate temperatures is crucial for tailoring microstructures and mechanical properties of L12-strengthened multicomponent alloys. In this study, the precipitate type, morphology, and distribution of (CoCrNi)100−2x(AlTi)x (x = 3, 5, and 7 at.%) medium-entropy alloys (MEAs) at 600-900 °C were systematically investigated through a combination of scanning electron microscopy, energy dispersive x-ray spectroscopy, x-ray diffraction, electron backscatter diffraction, and thermodynamic calculations. Our results reveal that the Al and Ti additions promote the destabilization of supersaturated fcc into L12 and σ phases, and the dominating phases of the MEAs change from fcc + L12 to fcc + L12 + σ and to L12 + σ + L21 phases as the Al and Ti concentrations increase. In addition, increasing the temperature leads to a change of precipitate morphology from lamellar to granular microstructures. The effects of alloying additions and aging temperature on the phase stability, precipitation behavior, and mechanical properties of the MEAs were discussed from the thermodynamic and kinetic points of view.

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This research was supported by the Early Career Scheme from the Research Grants Council of Hong Kong (25202719), State Key Laboratory for Advanced Metals and Materials Open Fund (2021-ZD04), Guangzhou International Science & Technology Cooperation Program (201907010026), and PolyU internal funds (P0009738, P0000538, and P0013994).

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Correspondence to Z. B. Jiao.

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This article is part of a special topical focus in the Journal of Phase Equilibria and Diffusion on the Thermodynamics and Kinetics of High-Entropy Alloys. This issue was organized by Dr. Michael Gao, National Energy Technology Laboratory; Dr. Ursula Kattner, NIST; Prof. Raymundo Arroyave, Texas A&M University; and the late Dr. John Morral, The Ohio State University.

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Fang, J.Y.C., Liu, W.H., Luan, J.H. et al. Phase Stability and Precipitation in L12-Strengthened CoCrNi Medium-Entropy Alloys at Intermediate Temperatures. J. Phase Equilib. Diffus. (2021).

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  • medium entropy alloy
  • precipitation
  • phase relation
  • precipitate microstructure