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<p>In this paper, we studied the microstructure, microhardness and phase composition of CoCrFeNiTa<sub>0.3</sub> eutectic high-entropy alloy (HEA) in the as-cast state and after 50-h isothermal oxidation at 1000 and 1100&#xa0;°C in air atmosphere. A eutectic microstructure consisting of a FCC solid solution and a secondary Co<sub>2</sub>Ta-type intermetallic was formed in the as-cast state, in which the Co<sub>2</sub>Ta Laves phase evolved to (Co,Cr)<sub>2</sub>Ta phase after isothermal oxidation. The specific weight change and oxidation rate constant at each temperature were determined, and the activation energy of the oxidation process was calculated. The parabolic oxidation rate constants of <i>k</i><sub>p</sub> = 39.16 (g<sup>2</sup>/cm<sup>4</sup>s) at 1000&#xa0;°C and <i>k</i><sub>p</sub> = 92.22 (g<sup>2</sup>/cm<sup>4</sup>s) at 1100&#xa0;°C indicate fairly good resistance of CoCrFeNiTa<sub>0.3</sub> HEA to high-temperature oxidation. The oxidation resistance of CoCrFeNiTa<sub>0.3</sub> is highly determined by the presence of an inner CrTaO<sub>4</sub> oxide layer formed between the Cr<sub>2</sub>O<sub>3</sub> outer layer and the metallic alloy surface.</p>

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Microstructure, Microhardness and High-Temperature Oxidation Behavior of Ta-substituted CoCrFeNiTa0.3 Eutectic High-Entropy Alloy

  • 期刊论文

  • 发表日期：

    2025年7月19日

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  • Olga Samoilova,
  • Ilsiya Suleymanova,
  • Nataliya Shaburova,
  • Ahmad Ostovari Moghaddam,
  • Evgeny Trofimov

摘要

In this paper, we studied the microstructure, microhardness and phase composition of CoCrFeNiTa0.3 eutectic high-entropy alloy (HEA) in the as-cast state and after 50-h isothermal oxidation at 1000 and 1100 °C in air atmosphere. A eutectic microstructure consisting of a FCC solid solution and a secondary Co2Ta-type intermetallic was formed in the as-cast state, in which the Co2Ta Laves phase evolved to (Co,Cr)2Ta phase after isothermal oxidation. The specific weight change and oxidation rate constant at each temperature were determined, and the activation energy of the oxidation process was calculated. The parabolic oxidation rate constants of kp = 39.16 (g2/cm4s) at 1000 °C and kp = 92.22 (g2/cm4s) at 1100 °C indicate fairly good resistance of CoCrFeNiTa0.3 HEA to high-temperature oxidation. The oxidation resistance of CoCrFeNiTa0.3 is highly determined by the presence of an inner CrTaO4 oxide layer formed between the Cr2O3 outer layer and the metallic alloy surface.