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Processing and Characterization of Refractory Quaternary and Quinary High-Entropy Carbide Composite
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.ORCID iD: 0000-0002-0111-4558
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.ORCID iD: 0000-0003-4888-6237
2019 (English)In: Entropy, E-ISSN 1099-4300, Vol. 21, no 5, article id 474Article in journal (Refereed) Published
Abstract [en]

Quaternary high-entropy ceramic (HEC) composite was synthesized from HfC, Mo2C, TaC, and TiC in pulsed current processing. A high-entropy solid solution that contained all principal elements along with a minor amount of a Ta-rich phase was observed in the microstructure. The high entropy phase and Ta-rich phase displayed a face-centered cubic (FCC) crystal structure with similar lattice parameters, suggesting that TaC acted as a solvent carbide during phase evolution. The addition of B4C to the quaternary carbide system induced the formation of two high-entropy solid solutions with different elemental compositions. With the increase in the number of principal elements, on the addition of B4C, the crystal structure of the HEC phase transformed from FCC to a hexagonal structure. The study on the effect of starting particle sizes on the phase composition and properties of the HEC composites showed that reducing the size of solute carbide components HfC, Mo2C, and TiC could effectively promote the interdiffusion process, resulting in a higher fraction of a hexagonal structured HEC phase in the material. On the other hand, tuning the particle size of solvent carbide, TaC, showed a negligible effect on the composition of the final product. However, reducing the TaC size from −325 mesh down to <1 µm resulted in an improvement of the nanohardness of the HEC composite from 21 GPa to 23 GPa. These findings suggested the possibility of forming a high-entropy ceramic phase despite the vast difference in the precursor crystal structures, provided a clearer understanding of the phase transformation process which could be applied for the designing of HEC materials.

Place, publisher, year, edition, pages
MDPI, 2019. Vol. 21, no 5, article id 474
Keywords [en]
high-entropy ceramic, solid-state diffusion, microstructure, phase evolution, hardness
National Category
Other Materials Engineering
Research subject
Engineering Materials
Identifiers
URN: urn:nbn:se:ltu:diva-73885DOI: 10.3390/e21050474ISI: 000472675900038PubMedID: 33267188Scopus ID: 2-s2.0-85066624692OAI: oai:DiVA.org:ltu-73885DiVA, id: diva2:1314607
Note

Validerad;2019;Nivå 2;2019-06-05 (oliekm)

Available from: 2019-05-09 Created: 2019-05-09 Last updated: 2023-03-28Bibliographically approved
In thesis
1. High-entropy boron-carbide and its composites
Open this publication in new window or tab >>High-entropy boron-carbide and its composites
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

High-entropy alloy (HEA) is a multicomponent alloy material that contains five or more principal elements in equi- or near equi-atomic ratios. The entropy stabilisation leads to the formation of a crystalline solid solution accommodating the principal elements. The HEA solid solution has characteristic features such as lattice distortion, sluggish diffusion and cocktail effect that contribute to the superior properties of HEA including high strength, high hardness, excellent thermal and chemical stability, etc. The concept of HEA has been extended to ceramic materials to process high-entropy ceramic (HEC) that consists of multiple ceramic compounds such as metallic oxides, nitrides or carbides. The HECs have shown entropy stabilisation and formed single-phase ceramic solid solutions. However, the formation mechanism of high-entropic phase in HECs remains unclear and unpredictable. Generally, in order to maximise the probability of forming a high-entropy solid solution in a ceramic system, ceramic compounds with least difference in the crystal structure, preferably with only one anionic constituent element, are favoured when designing HECs, which limits the potential of discovering and developing new HECs. In this project, a multicomponent ceramic system containing six ultra-high temperature ceramics (UHTCs), B4C, HfC, Mo2C, TaC, TiC and SiC, was used to investigate the formation of high-entropy ceramics, UHTC composites, as well as the microstructure evolution, properties and high temperature applications. A ceramic composite composed of SiC and a high-entropy boron-carbide with hexagonal crystal structure was successfully processed from the carbide system in spite of the difference in the crystal structures of precursors (face-centred cubic, hexagonal and rhombohedral). The hexagonal HEC solid solution exhibited a unique AlB2 structure with alternating layers of metal and non-metal C/B atoms according to the experimental and simulation investigations. The HEC/SiC composite showed superior mechanical properties such as ultra-high hardness, excellent wear and oxidation resistance. The addition of B4C was discovered to be the key factor in the formation of the hexagonal high-entropy boron-carbide solid solution, while the final phase composition was tailored by utilising precursors of different particle size. Additionally, SiC as the reinforcement component in the HEC/SiC composite was used to tailor the microstructure, phase evolution and mechanical properties of the high-entropy boron-carbide composite. Higher content of SiC resulted in enhanced mechanical properties such as hardness and fracture toughness, as well as promoted the formation of the hexagonal high-entropy boron-carbide solid solution. To extend the investigation on the high-entropy boron-carbide composite to application, B4C, HfC, Mo2C, TaC and TiC were consolidated into a target for magnetron sputtering. The target was used to deposit oxidation-resistant high-entropy coatings using magnetron sputtering on carbon-carbon composites. The coatings showed superior mechanical performance and high temperature oxidation resistance at 2000 °C on carbon-carbon composite, suggesting potential applications of high-entropy boron-carbide ceramics as a protective coating material against oxidation at elevated temperature. This work pointed out the possibilities of synthesising high-performance HECs with superior properties from components with vast elemental and structure diversity, and thereby advanced the design criteria of HECs and provided more potential research directions for the new high-performance ceramic materials.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2020
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
National Category
Materials Engineering Other Materials Engineering
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-78339 (URN)978-91-7790-571-4 (ISBN)978-91-7790-572-1 (ISBN)
Public defence
2020-05-29, A109, Luleå, 09:00 (English)
Opponent
Supervisors
Available from: 2020-04-06 Created: 2020-04-03 Last updated: 2023-09-07Bibliographically approved

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Zhang, HanzhuAkhtar, Farid

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