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Zhang, H. & Akhtar, F. (2021). Refractory multicomponent boron-carbide high entropy oxidation-protective coating for carbon-carbon composites. Surface & Coatings Technology, 425, Article ID 127697.
Open this publication in new window or tab >>Refractory multicomponent boron-carbide high entropy oxidation-protective coating for carbon-carbon composites
2021 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 425, article id 127697Article in journal (Refereed) Published
Abstract [en]

A novel refractory multicomponent boron-carbide coating of 300 nm thickness, HfMoTaTi-BC, was deposited on carbon-carbon composites (CCC). The coating showed a face-centred cubic (FCC) structure of lattice parameter of 0.4429 nm with an average crystallite size of 5 nm. The FCC coating transformed from single-phase solid solution into multiple ceramic carbides and boride phases at 900°C during long-term thermal stability test. The exposure of HEC coated CCC to the flame (2000°C) of liquefied petroleum gas (LPG) torch for 5 minutes revealed that the film had excellent resistance to oxidation and protected the CCC material under extreme aerothermal heating.

Place, publisher, year, edition, pages
Elsevier, 2021
Keywords
High-entropy ceramic, Magnetron sputtering, Carbon-carbon composite, Oxidation
National Category
Ceramics and Powder Metallurgical Materials Composite Science and Engineering
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-87099 (URN)10.1016/j.surfcoat.2021.127697 (DOI)000704240100003 ()2-s2.0-85118755788 (Scopus ID)
Funder
Swedish Foundation for Strategic Research , RIF14-0083
Note

Validerad;2021;Nivå 2;2021-10-01 (alebob)

Available from: 2021-09-16 Created: 2021-09-16 Last updated: 2025-02-09Bibliographically approved
Zhang, H. & Akhtar, F. (2020). Effect of SiC on Microstructure, Phase Evolution, and Mechanical Properties of Spark-Plasma-Sintered High-Entropy Ceramic Composite. Ceramics, 3(3), 359-371
Open this publication in new window or tab >>Effect of SiC on Microstructure, Phase Evolution, and Mechanical Properties of Spark-Plasma-Sintered High-Entropy Ceramic Composite
2020 (English)In: Ceramics, ISSN 2571-6131, Vol. 3, no 3, p. 359-371Article in journal (Refereed) Published
Abstract [en]

Ultra-high temperature ceramic composites have been widely investigated due to their improved sinterability and superior mechanical properties compared to monolithic ceramics. In this work, high-entropy boron-carbide ceramic/SiC composites with different SiC content were synthesized from multicomponent carbides HfC, Mo2C, TaC, TiC, B4C, and SiC in spark plasma sintering (SPS) from 1600 °C to 2000 °C. It was found that the SiC addition tailors the phase formation and mechanical properties of the high-entropy ceramic (HEC) composites. The microhardness and fracture toughness of the HEC composites sintered at 2000 °C were improved from 20.3 GPa and 3.14 MPa·m1/2 to 26.9 GPa and 5.95 MPa·m1/2, with increasing SiC content from HEC-(SiC)0 (0 vol. %) to HEC-(SiC)3.0 (37 vol. %). The addition of SiC (37 vol. %) to the carbide precursors resulted in the formation of two high-entropy ceramic phases with two different crystal structures, face-centered cubic (FCC) structure, and hexagonal structure. The volume fraction ratio between the hexagonal and FCC high-entropy phases increased from 0.36 to 0.76 when SiC volume fraction was increased in the composites from HEC-(SiC)0 to HEC-(SiC)3.0, suggesting the stabilization of the hexagonal high-entropy phase over the FCC phase with SiC addition.

Place, publisher, year, edition, pages
MDPI, 2020
Keywords
high-entropy ceramic, SiC composite, spark plasma sintering, phase transformation, mechanical properties
National Category
Materials Engineering Other Materials Engineering
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-80847 (URN)10.3390/ceramics3030032 (DOI)000722240000001 ()2-s2.0-85117791996 (Scopus ID)
Funder
Swedish Foundation for Strategic Research
Note

Validerad;2020;Nivå 1;2020-10-08 (alebob)

Available from: 2020-09-20 Created: 2020-09-20 Last updated: 2021-12-13Bibliographically approved
Zhang, H. (2020). High-entropy boron-carbide and its composites. (Doctoral dissertation). Luleå: Luleå University of Technology
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
Alvi, S., Zhang, H. & Akhtar, F. (2020). High-Entropy Ceramics. In: Ashutosh Sharma; Sanjeev Kumar; Zoia Duriagina (Ed.), Engineering Steels and High Entropy-Alloys: . INTECH
Open this publication in new window or tab >>High-Entropy Ceramics
2020 (English)In: Engineering Steels and High Entropy-Alloys / [ed] Ashutosh Sharma; Sanjeev Kumar; Zoia Duriagina, INTECH, 2020Chapter in book (Refereed)
Abstract [en]

High-entropy ceramics is an emerging class of high-entropy materials with properties superior to conventional ceramics. Recent research has been focused on the development of new high-entropy ceramic compositions. High-entropy oxides, carbides, borides, silicides, and boron carbides had been reported with superior mechanical, oxidation, corrosion, and wear properties. The research work on the processing and characterization of bulk high-entropy ceramics and coating systems has been summarized in this chapter. The composition design, structure, chemistry, composite processing of bulk high-entropy ceramics, and evolution of microstructure and properties are reported. The literature on the deposition of high-entropy ceramic coating and the influence of coating parameters have been discussed to produce high-entropy ceramic coatings with superior mechanical, oxidation, and wear properties. 

Place, publisher, year, edition, pages
INTECH, 2020
Keywords
ceramics, spark plasma sintering, coatings, high temperature properties
National Category
Materials Engineering
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-78144 (URN)10.5772/intechopen.89527 (DOI)
Note

ISBN för värdpublikation: 978-1-78985-948-5; 978-1-78985-947-8; 978-1-83880-556-2

Available from: 2020-03-23 Created: 2020-03-23 Last updated: 2021-09-01Bibliographically approved
Zhang, H., Hedman, D., Feng, P., Han, G. & Akhtar, F. (2019). A high-entropy B4(HfMo2TaTi)C and SiC ceramic composite. Dalton Transactions, 48(16), 5161-5167
Open this publication in new window or tab >>A high-entropy B4(HfMo2TaTi)C and SiC ceramic composite
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2019 (English)In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 48, no 16, p. 5161-5167Article in journal (Refereed) Published
Abstract [en]

A multicomponent composite of refractory carbides, B4C, HfC, Mo2C, TaC, TiC and SiC, of rhombohedral, face-centered cubic (FCC) and hexagonal crystal structures is reported to form a single phase B4(HfMo2TaTi)C ceramic with SiC. The independent diffusion of the metal and nonmetal atoms led to a unique hexagonal lattice structure of the B4(HfMo2TaTi)C ceramic with alternating layers of metal atoms and C/B atoms. In addition, the classical differences in the crystal structures and lattice parameters among the utilized carbides were overcome. Electron microscopy, X-ray diffraction and calculations using density functional theory (DFT) confirmed the formation of a single phase B4(HfMo2TaTi)C ceramic with a hexagonal close-packed (HCP) crystal structure. The DFT based crystal structure prediction suggests that the metal atoms of Hf, Mo, Ta and Ti are distributed on the (0001) plane in the HCP lattice, while the carbon/boron atoms form hexagonal 2D grids on the (0002) plane in the HCP unit cell. The nanoindentation of the high-entropy phase showed hardness values of 35 GPa compared to the theoretical hardness value estimated based on the rule of mixtures (23 GPa). The higher hardness was contributed by the solid solution strengthening effect in the multicomponent hexagonal structure. The addition of SiC as the secondary phase in the sintered material tailored the microstructure of the composite and offered oxidation resistance to the high-entropy ceramic composite at high temperatures.

Place, publisher, year, edition, pages
Royal Society of Medicine Press, 2019
National Category
Materials Engineering Ceramics and Powder Metallurgical Materials Composite Science and Engineering Other Physics Topics
Research subject
Engineering Materials; Applied Physics
Identifiers
urn:nbn:se:ltu:diva-72953 (URN)10.1039/C8DT04555K (DOI)000465328200037 ()30778490 (PubMedID)2-s2.0-85064521555 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-08-20 (johcin);

For correction, see: Dalton Trans., 2019,48, 6647-6647. DOI:10.1039/C9DT90099C

Available from: 2019-02-20 Created: 2019-02-20 Last updated: 2025-02-09Bibliographically approved
Liu, Y., Cai, X., Sun, Z., Zhang, H., Akhtar, F., Czujko, T. & Feng, P. (2019). Fabrication and Characterization of Highly Porous FeAl‐Based Intermetallics by Thermal Explosion Reaction. Paper presented at 2nd International Conference and Exhibition on Light Materials − Science and Technology(LightMAT2017), September 8-10, 2017, Bremen, Germany. Advanced Engineering Materials, 21(4), Article ID 1801110.
Open this publication in new window or tab >>Fabrication and Characterization of Highly Porous FeAl‐Based Intermetallics by Thermal Explosion Reaction
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2019 (English)In: Advanced Engineering Materials, ISSN 1438-1656, E-ISSN 1527-2648, Vol. 21, no 4, article id 1801110Article in journal (Refereed) Published
Abstract [en]

Porous FeAl-based intermetallics with different nominal compositions ranging from Fe–40 at% Al to Fe–60 at% Al are prepared by a novel process of thermal explosion (TE) mode. The results show that the Al content significantly affects the combustion behavior of the specimens, the ignition temperature of the Fe–Al intermetallics varies from 641 to 633 °C and the combustion temperature from 978 to 1179 °C. The porous materials exhibit uniform pore structures with porosities and average pore sizes of 52–61% and 20–25 µm, respectively. The TE reaction is the dominant pore formation mechanism regardless of the alloy composition. However, differences in the porosity and average pore size are observed depending on the Al content. The compressive strength of porous Fe–Al intermetallics is in the range of 23–34 MPa, duly applied as filters. Additionally, a surface alumina layer is formed at the early stage and both of the oxidation process and the sulfidation process follows the familiar parabolic rate law in the given atmosphere, exhibiting excellent resistance to oxidation and sulfidation. These results suggest that the porous Fe–Al intermetallics are promising materials for applications in harsh environments with a high-temperature sulfide-bearing atmosphere, such as in the coal chemical industry.

Place, publisher, year, edition, pages
John Wiley & Sons, 2019
Keywords
FeAl intermetallics, microstructure, porous material, properties, thermal explosion
National Category
Materials Engineering
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-72765 (URN)10.1002/adem.201801110 (DOI)000468000300020 ()2-s2.0-85060210181 (Scopus ID)
Conference
2nd International Conference and Exhibition on Light Materials − Science and Technology(LightMAT2017), September 8-10, 2017, Bremen, Germany
Note

Konferensartikel i tidskrift

Available from: 2019-02-01 Created: 2019-02-01 Last updated: 2020-08-26Bibliographically approved
Zhang, H., Hedman, D., Feng, P., Han, G. & Akhtar, F. (2019). High Entropy B2(HfMoTaTi)C and SiC Ceramic Composite. In: XVI Conference and Exhibition of the European Ceramic Society: Book of Abstracts. Paper presented at XVI Conference and Exhibition of the European Ceramic Society (ECerS 2019), Torino, Italy, June 16-19, 2019 (pp. 338-338). European Ceramic Society (ECerS)
Open this publication in new window or tab >>High Entropy B2(HfMoTaTi)C and SiC Ceramic Composite
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2019 (English)In: XVI Conference and Exhibition of the European Ceramic Society: Book of Abstracts, European Ceramic Society (ECerS) , 2019, p. 338-338Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

Refractory carbides HfC, Mo2C, TiC, TaC, B4C, and SiC were mixed with a molar ratio of 2:1:2:2:1:2 to fabricate multicomponent ceramic composite by pulsed current processing (PCP). From the starting materials that consist of face-centered cubic (FCC), hexagonal and rhombohedral crystal structures, the investigated carbide system is reported to form a single phase B2(HfMoTaTi)C high-entropy ceramic (HEC) with SiC. The HEC phase contains uniform distribution of constitutional elements Hf, Mo, Ta, Ti, B and C, according to Energy dispersive X-ray spectroscopy (EDS) and wavelength dispersive X-ray spectroscopy (WDS) results.

The fabricated HEC phase displays a hexagonal close-packed (HCP) crystal structure, with a high average lattice distortion of 8.26% (see Figure). The HCP structure was observed by X-ray diffraction and selected area diffraction in transmission electron microscopy (TEM). Density-functional theory (DFT) optimization suggested that the hexagonal close-packed (HCP) crystal structure has alternating layers of metal atoms and carbon/boron atoms, i.e. metal atoms of Hf, Mo, Ta and Ti were distributed on the (0001) plane in the HCP lattice, while the carbon/boron atoms formed hexagonal 2D grids on the (0002) plane in the HCP unit cell. Despite of the vast differences in the crystal structures and lattice parameters among the utilized carbides, the formation of the unique hexagonal lattice structure of B2(HfMoTaTi)C can be a result of independent diffusion of the metal and nonmetal atoms. The sintered HEC ceramic composite exhibits excellent oxidation resistance at mediate temperature, 900 ºC for 50h, and elevated temperature, 2000 ºC for 20 s. Nanoindentation test shows that the HEC phase has a high hardness of 35 GPa. The remarkable improvement compared to the theoretical hardness value estimated based on the rule of mixtures (23 GPa) was contributed by the severe lattice distortion in the HCP structure. 

Place, publisher, year, edition, pages
European Ceramic Society (ECerS), 2019
Keywords
High-entropy ceramic, Ceramic composite
National Category
Other Materials Engineering
Research subject
Applied Physics; Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-74894 (URN)
Conference
XVI Conference and Exhibition of the European Ceramic Society (ECerS 2019), Torino, Italy, June 16-19, 2019
Available from: 2019-06-24 Created: 2019-06-24 Last updated: 2021-04-23Bibliographically approved
Zhang, H. & Akhtar, F. (2019). Processing and Characterization of Refractory Quaternary and Quinary High-Entropy Carbide Composite. Entropy, 21(5), Article ID 474.
Open this publication in new window or tab >>Processing and Characterization of Refractory Quaternary and Quinary High-Entropy Carbide Composite
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
Keywords
high-entropy ceramic, solid-state diffusion, microstructure, phase evolution, hardness
National Category
Other Materials Engineering
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-73885 (URN)10.3390/e21050474 (DOI)000472675900038 ()33267188 (PubMedID)2-s2.0-85066624692 (Scopus ID)
Note

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

Available from: 2019-05-09 Created: 2019-05-09 Last updated: 2023-03-28Bibliographically approved
Jiang, Z., Feng, P., Wang, X., Zhang, H. & Liu, Y. (2018). Combustion synthesis and mechanical properties of MoSi2­-ZrB2­-SiC ceramics. Journal of the Ceramic Society of Japan, 126(7), 504-509
Open this publication in new window or tab >>Combustion synthesis and mechanical properties of MoSi2­-ZrB2­-SiC ceramics
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2018 (English)In: Journal of the Ceramic Society of Japan, ISSN 1882-0743, Vol. 126, no 7, p. 504-509Article in journal (Refereed) Published
Abstract [en]

MoSi2ZrB2SiC ceramics were synthesized using Mo, Zr, Si and B4C powders by self-propagating high-temperature synthesis and densifying by spark plasma sintering. The effects of MoSi2 content on the combustion synthesis process, microstructure, and mechanical properties of the ceramics were investigated. The results showed that combustion synthesis is an unstable mode, spiral combustion. The Gibbs calculations and combustion temperature curves indicate there are two reactions occurring at the same time. The volume fraction of the four different phases and their relative densities were also measured and calculated. Compared to pure MoSi2, the 1.0MoSi20.2ZrB20.1SiC (M10) ceramic exhibits excellent mechanical properties with its maximum Vickers hardness and fracture toughness being 14.0 GPa and of 5.5 MPa m1/2, respectively. The hardness is in agreement with the rule of mixture. The morphology of indentation cracks reveals that the fracture toughness improves as a result of toughening mechanisms such as crack bridge, crack deflection, and microcracks.

Place, publisher, year, edition, pages
Ceramic Society of Japan, 2018
Keywords
Combustion synthesis, In situ, Spark plasma sintering, Mechanical properties, MoSi2
National Category
Ceramics and Powder Metallurgical Materials Other Materials Engineering
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-70244 (URN)10.2109/jcersj2.17261 (DOI)000437358200002 ()2-s2.0-85049330174 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-08-09 (andbra)

Available from: 2018-08-07 Created: 2018-08-07 Last updated: 2025-02-09Bibliographically approved
Zhang, H. (2018). Synthesis of metallic/high entropy ceramic composite and a study of the phase transformation mechanism. (Licentiate dissertation). Luleå: Luleå University of Technology
Open this publication in new window or tab >>Synthesis of metallic/high entropy ceramic composite and a study of the phase transformation mechanism
2018 (English)Licentiate thesis, comprehensive summary (Other academic)
Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2018
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
National Category
Materials Engineering Other Materials Engineering
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-71600 (URN)978-91-7790-270-6 (ISBN)978-91-7790-271-3 (ISBN)
Presentation
2018-12-20, E231, Luleå University of Technology, Luleå, 09:00 (English)
Opponent
Supervisors
Available from: 2018-11-19 Created: 2018-11-15 Last updated: 2018-12-08Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-0111-4558

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