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Pressureless synthesis and consolidation of the entropy-stabilized (Hf0.25Zr0.25Ti0.25V0.25)B2-B4C composite by ultra-fast high-temperature sintering (UHS)
Department of Industrial Engineering, University of Trento, Via Sommarive 9, Trento 38123, Italy.
Department of Industrial Engineering, University of Trento, Via Sommarive 9, Trento 38123, Italy; Department of Materials Science and Engineering, Izmir Institute of Technology, İzmir 35430, Turkey.
Department of Industrial Engineering, University of Trento, Via Sommarive 9, Trento 38123, Italy.
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2025 (English)In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 45, no 5, article id 117132Article in journal (Refereed) Published
Abstract [en]

Entropy-stabilized Ultra High-Temperature Ceramics (UHTC) offer a groundbreaking solution to the challenges of extreme environments, showcasing enhanced mechanical properties, thermal stability, and resistance to oxidation at high temperatures. The consolidation of UHTC by ultra-fast high-temperature sintering (UHS) significantly reduces processing times and temperature and can produce dense high-performance ceramics with superior mechanical properties. This study reports the pressureless synthesis and consolidation of the entropy-stabilized (Hf0.25Zr0.25Ti0.25V0.25)B2-B4C composite through UHS within 1 minute, starting from transition metal diboride powders. B4C acts as an effective sintering aid, promoting the densification of the system and the formation of a nearly single-phase hexagonal diboride with a diboride-eutectic phase. Furthermore, a secondary minor hexagonal phase rich in V and Zr is formed close to the eutectic regions. Sintering currents of 40 A were necessary to reach densities higher than 90 % under pressureless conditions, achieving nano hardness higher than 27.3 GPa, comparable with high-entropy diborides produced by Spark Plasma Sintering. The study highlights the entropy-stabilized phase formation, diffusion, densification, and grain growth mechanisms involved during UHS. The work contributes to the understanding of entropy-stabilized ceramics produced by UHS as a faster and less energy-consuming process than conventional sintering methods.

Place, publisher, year, edition, pages
Elsevier, 2025. Vol. 45, no 5, article id 117132
Keywords [en]
Entropy-stabilization, Ultra-high-temperature ceramics, Ultra-fast high-temperature sintering
National Category
Materials Chemistry Ceramics and Powder Metallurgical Materials
Research subject
Engineering Materials
Identifiers
URN: urn:nbn:se:ltu:diva-111159DOI: 10.1016/j.jeurceramsoc.2024.117132Scopus ID: 2-s2.0-85211967959OAI: oai:DiVA.org:ltu-111159DiVA, id: diva2:1925455
Funder
Swedish Foundation for Strategic Research, RIF14–0083
Note

Validerad;2025;Nivå 2;2025-01-08 (signyg);

Fulltext license: CC BY

Available from: 2025-01-08 Created: 2025-01-08 Last updated: 2025-02-09Bibliographically approved
In thesis
1. Entropy-stabilized transition metal diborides for high-temperature applications
Open this publication in new window or tab >>Entropy-stabilized transition metal diborides for high-temperature applications
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Ultra-high temperature ceramics (UHTCs) are on the cutting edge as structural or protective materials that can withstand extreme environments such as hypersonic vehicles, nuclear reactors, and advanced turbine engines. These materials stand out for their melting temperatures above 2500 °C, high chemical stability, and retained mechanical resistance at temperatures higher than 1650 °C. Introducing entropy-stabilization into multicomponent ceramics has attracted interest in their properties over a broad range of UHTC compositions. Entropy plays a dominant role in stabilizing single-phase multicomponent materials, offering new pathways for synthesis and enabling the tailoring of properties. The promising properties are mainly attributed to their compositional complexity, lattice distortion and atomic-level disorder.

In this thesis, by screening potential high-entropy ceramic candidates via ab initio calculations, we identified six potential high-entropy ceramics compositions containing Li, Ti, V, Zr, Nb, and Hf. Subsequently, we have focused on and covered the design, synthesis, and high-temperature oxidation and ablation properties of the entropy-stabilized (Ti0.25V0.25Zr0.25Hf0.25)B2

The diboride synthesis using Spark Plasma Sintering (SPS) resulted in a dual-phase (Ti0.25V0.25Zr0.25Hf0.25)B2, composed of Hf-Zr-rich and Ti-V-rich hexagonal phases. Upon thermal annealing, the dual-phase diboride transformed into a single-phase entropy-stabilized diboride, exhibiting superior mechanical properties compared to the dual-phase diboride. The oxidation mechanisms were the same for the dual- and single-phase diborides; however, the entropy-stabilized diboride outperformed the dual-phase diboride in terms of oxidation resistance. The improved mechanical and oxidation properties were attributed to the lattice distortion, high-entropy, and sluggish diffusion effects. 

UHTC coatings are usually applied in carbon materials to improve their service life in harsh environments. Due to the improved oxidation performance of the entropy-stabilized diboride, single-phase (Ti0.25V0.25Zr0.25Hf0.25)B2 was produced as a coating on graphite by Spark Plasma Sintering (SPS) and its resistance to ablation was evaluated. The mechanical resistance of the entropy-stabilized coating at high temperatures was attributed to its low thermal conductivity and the efficient heat dissipation of the coating-substrate pair. The (Ti0.25V0.25Zr0.25Hf0.25)B2 coating was considered an efficient thermal barrier with high resistance to intense heat fluxes. 

Furthermore, manufacturing of the (Hf0.25Zr0.25Ti0.25V0.25)B2-B4C by pressureless and less energy intensive Ultra-fast High-temperature Sintering (UHS) method was investigated for entropy-stabilization. Single-phase formation happened before the full densification of the composite, and the B4C sintering aid promoted the densification of the (Hf0.25Zr0.25Ti0.25V0.25)B2 with a minor eutectic phase. 

Overall, the results obtained by this work contribute to the growing body of knowledge surrounding entropy-stabilized ceramics, their design and fabrication through computational and experimental methods, and their potential applications in engineering components at high temperatures. These findings pave the way for new paths to be followed in the entropy-stabilized materials realm.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2024
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
National Category
Other Materials Engineering
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-104567 (URN)978-91-8048-497-8 (ISBN)978-91-8048-498-5 (ISBN)
Public defence
2024-05-06, A109, Luleå University of Technology, Luleå, 10:00 (English)
Opponent
Supervisors
Available from: 2024-03-13 Created: 2024-03-12 Last updated: 2025-01-31Bibliographically approved

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Feltrin, Ana C.Akhtar, Farid

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