Investigation of microstructure and oxidation properties of amorphous and nanocrystalline HfNbTaTiZr high-entropy alloy thin films

• Published in: Surface & coatings technology Vol. 496; p. 131642
• Main Authors: Hruška, Petr, Eijt, Stephan W.H., Schut, Henk, Lukáč, František, Čížek, Jakub, Chevalier, Joris More, Cichoň, Stanislav, Vondráček, Martin, Fekete, Ladislav, Prokop, Dejan, Lančok, Ján
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.01.2025
• Subjects: Defects; High-entropy alloys; Positron annihilation spectroscopy; Thin films; X-ray photoelectron spectroscopy; Thin films; High-entropy alloys; X-ray photoelectron spectroscopy; Positron annihilation spectroscopy; Defects
• ISSN: 0257-8972
• DOI: 10.1016/j.surfcoat.2024.131642

In this study, the deposition, annealing process, and oxidation properties of HfNbTaTiZr high-entropy alloy thin films were thoroughly investigated. The films, approximately 250 nm thick, were deposited on MgO substrates by DC magnetron sputtering using a single target. The preparation temperature was identified as a key factor influencing the resulting structure. Amorphous films formed at room temperature, whereas nanocrystalline films, characterized by multiple intermetallic phases, were obtained either by deposition at elevated temperatures (600 °C – 750 °C) or through in situ annealing of amorphous films (600 °C – 700 °C). Positron annihilation spectroscopy revealed that nanocrystalline films predominantly contain vacancy-like misfit defects, with concentration decreasing as the preparation temperature increases. Additionally, amorphous films exhibited a high concentration of large vacancy clusters. X-ray photoelectron spectroscopy showed greater oxygen absorption in amorphous films due to their defective structure, with preferential oxidation of Zr and Hf. Further annealing of naturally oxidized films in a vacuum at temperatures up to 1400 °C led to films' recrystallization and eventually the formation of complex oxides, including ZrO2, HfO2, and various Mg-containing oxides, indicating a reaction with the MgO substrate. This work demonstrates the ability to fine-tune the microstructure and defect characteristics of high-entropy alloy films and highlights their direct correlation with oxidation properties. [Display omitted] •Amorphous and multiple-phase nanocrystalline HfNbTaTiZr films deposited by magnetron sputtering•Defect structures tuned by deposition temperature or post-deposition annealing•Vacancy clusters enhance natural oxidation in the ambient atmosphere•High-temperature annealing induces hydrogen desorption, recrystallization and complex oxide formation