A perspective on investigating transition metal high-entropy alloys for high-temperature applications. (November 2022)

• Record Type: Journal Article
• Authors: Li, Meifeng; Zhang, Hao; Zeng, Yimin; Liu, Jing
• Is Part Of: Acta materialia. Volume 240(2022)
• Publication Date: 2022-11
• Subjects: TM HEAs -- Oxidation -- High temperature -- Diffusion coefficient -- DFT; Materials -- Periodicals; Materials science -- Periodicals; Materials -- Mechanical properties -- Periodicals; Metallurgy -- Periodicals; Chemistry, Inorganic -- Periodicals; 620.112
• DOI: 10.1016/j.actamat.2022.118313
• Languages: English
• ISSNs: 1359-6454

Abstract

Abstract: Transition metal high-entropy alloys (TM HEAs) are currently considered as promising structural materials for high-temperature (HT) applications. However, their HT oxidation is a critical issue and must be addressed for hot-end components. This work presents a feasible strategy to identify the HT oxidation behaviors of TM HEAs through experimental investigation and density-functional theory (DFT) calculation. Fe20 Co20 Ni20 Cr20 Cu20 (H4Cu20 ) is chosen as the starting model alloy to investigate the HT oxidation behavior of TM HEAs in the ambient atmosphere at the temperature range of 700–900 °C, followed by gradually replacing 5 and 10 at.% Cu with Al, i.e., Fe20 Co20 Ni20 Cr20 Cu15 Al5 (H4Cu15 Al5 ) and Fe20 Co20 Ni20 Cr20 Cu10 Al10 (H4Cu10 Al10 ). Oxide scales grown on the TM HEAs at HT show a strong temperature and composition dependence and follow a three-stage oxidation growth law. Results show that H4Cu20 in general suffers from severe localized and internal oxidation, particularly in a secondary phase (FCC2) with low mixing entropy ( Δ S m i x ) and highly positive enthalpy ( Δ H m i x ). The gradual replacement of Cu with Al facilitates the formation of a protective pure or Al2 O3 -rich scale, and significantly reduces the oxidation rate of the TM HEAs. A theoretical investigation is performed from a comprehensive thermodynamics and kinetics perspectives. DFT calculation on the individual constituent phase is conducted to examine the diffusion kinetics of three TM HEAs, and to clarify the postulate of "sluggish diffusion" in high entropy (HE) systems. The diffusivity of constituent elements in each phase follows the empirical "compensation rule", and diffusion in HE systems shows a strong elemental dependency. Finally, recommendations for selecting alloying elements are given in designing and tailoring TM HEAs for HT applications. Graphical abstract: Elemental effects on the microstructure and oxidation behavior of Fe20 Co20 Ni20 Cr20 Cu20 (H4Cu20 ) TM HEA by replacing 10 at.% Cu with Al, i.e., H4Cu10 Al10 . (HE, ME and LE represent for high-, middle- and low-mixing entropy, respectively) Image, graphical abstract