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Publications (10 of 133) Show all publications
Zhang, H., Hedman, D., Feng, P., Han, G. & Akhtar, F. (2019). A high-entropy B4(HfMo2TaTi)C and SiC ceramic composite. Dalton Transactions
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 1477-9234Article in journal (Refereed) Epub ahead of print
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.

National Category
Materials Engineering Ceramics Composite Science and Engineering
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-72953 (URN)10.1039/C8DT04555K (DOI)30778490 (PubMedID)
Available from: 2019-02-20 Created: 2019-02-20 Last updated: 2019-03-14
Saeidi, K., Alvi, S., Lofaj, F., Petkov, V. I. & Akhtar, F. (2019). Advanced Mechanical Strength in Post Heat Treated SLM 2507 at Room and High Temperature Promoted by Hard/Ductile Sigma Precipitates. Metals, 9(2), Article ID 199.
Open this publication in new window or tab >>Advanced Mechanical Strength in Post Heat Treated SLM 2507 at Room and High Temperature Promoted by Hard/Ductile Sigma Precipitates
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2019 (English)In: Metals, E-ISSN 2075-4701, Vol. 9, no 2, article id 199Article in journal (Refereed) Published
Abstract [en]

Duplex stainless steel, 71 wt.% austenite, 13 wt.% ferrite and 16 wt.% sigma, was made upon heat treating of fully ferritic as-built selective laser melted (SLM) 2507 stainless steel at 1200 °C. Formation of sigma phase in the heat treated SLM 2507 was investigated using optical microscopy and scanning electron microscopy (SEM). The heat treated SLM 2507 demonstrated a yield strength of 686 MPa, ultimate tensile strength of 920 MPa and an elongation of 1.8% at room temperature with a brittle fracture morphology. Precipitation of sigma phase during heat treatment and slow cooling improved the mechanical and wear properties at high temperatures (1200 °C and 800 °C, respectively). The tensile strength and elongation of the heat treated SLM 2507 was measured 400 MPa and 20% as compared to casted duplex steel with 19 MPa and 30% elongation at 1200 °C. The 20 times higher mechanical strength as compared to casted duplex steel was attributed to sigma precipitates. Tribological behaviour of heat treated duplex SLM 2507 containing sigma at 800 °C showed very low wear rate of 4.5 × 10−5 mm3/mN compared to casted duplex steel with 1.6 × 10−4 mm3/mN.

Place, publisher, year, edition, pages
MDPI, 2019
Keywords
selective laser melting, duplex stainless steel, heat treatment, mechanical properties
National Category
Other Materials Engineering
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-73183 (URN)10.3390/met9020199 (DOI)000460764700090 ()2-s2.0-85062367956 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-03-13 (johcin)

Available from: 2019-03-13 Created: 2019-03-13 Last updated: 2019-04-12Bibliographically 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. Advanced Engineering Materials
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 1527-2648Article in journal (Refereed) Epub ahead of print
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)
Available from: 2019-02-01 Created: 2019-02-01 Last updated: 2019-02-15
Alvi, S. & Akhtar, F. (2019). High temperature tribology of CuMoTaWV high entropy alloy. In: Wear of Materials: . Paper presented at 22nd International Conference on Wear of Materials, April 14-18 2019, Miami, USA (pp. 412-419). , 426-427
Open this publication in new window or tab >>High temperature tribology of CuMoTaWV high entropy alloy
2019 (English)In: Wear of Materials, 2019, Vol. 426-427, p. 412-419Conference paper, Published paper (Refereed)
Abstract [en]

An equiatomic high entropy alloy (HEA) CuMoTaWV was designed for room temperature to high temperature wear applications using spark plasma sintering of elemental powder mixture at 1400 °C. The sintered solid solution showed uniform distribution of elements in a BCC high entropy alloy phase along with V rich solid solution phase with an average hardness of 600 Hv and 900 Hv, respectively. Room temperature (RT) dry sliding wear tests, against alloy steel (700–880 Hv) for 200 m sliding distance at 5 N normal load, showed negligible wear of 5 × 10−7 mm/N m and a coefficient of friction (COF) of 0.5. Sliding wear characterization of sintered CuMoTaWV alloy against Si3N4 (1550 Hv) counter body from RT to 600 °C showed an increasing average COF of 0.45–0.67 from RT to 400 °C and then reducing to 0.54 at 600 °C. The wear rate was found to be lower at RT (4 × 10−3 mm3/N m) and 400 °C (5 × 10−3 mm3/N m), and slightly higher at 200 °C (2.3 × 10−2 mm3/N m) and 600 °C (4.5 × 10−2 mm3/N m). The CuMoTaWV alloy showed wear mechanisms specific to the test temperatures. The wear of CuMoTaWV alloy was governed by adhesive wear at RT and 200 °C and oxidative wear at 400 °C and 600 °C. The analyses of wear surfaces showed that the low wear rate at RT was due to the high hardness of the HEA, presence of V rich zones and formation of W and Ta tribofilm. At 400 °C, the formation of CuO tribolayer reduced the wear and hindered oxidation of wear track. At 600 °C, the wear rate increased due to oxidation of Cu, Ta and W. Moreover, the formation of lubricating elongated magneli phase V2O5 in V rich regions of CuMoTaWV alloy reduced the COF to 0.54.

Keywords
Sliding wear, High temperature wear, Adaptive wear, High, Entropy alloy (HEA, ) Refractory, Tribology, Spark plasma sintering (SPS)
National Category
Other Materials Engineering
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-73687 (URN)10.1016/j.wear.2018.12.085 (DOI)
Conference
22nd International Conference on Wear of Materials, April 14-18 2019, Miami, USA
Available from: 2019-04-17 Created: 2019-04-17 Last updated: 2019-04-17Bibliographically approved
Nikjoo, D., Perrot, V. & Akhtar, F. (2019). Laminated Porous Diatomite Monoliths for Adsorption of Dyes From Water. Environmental Progress & Sustainable Energy, 38(s1), 377-385
Open this publication in new window or tab >>Laminated Porous Diatomite Monoliths for Adsorption of Dyes From Water
2019 (English)In: Environmental Progress & Sustainable Energy, ISSN 1944-7442, E-ISSN 1944-7450, Vol. 38, no s1, p. 377-385Article in journal (Refereed) Published
Abstract [en]

Structured laminated diatomite monoliths with superior mechanical properties were prepared by controlled freeze-casting of the aqueous suspensions of diatomite powders for wastewater treatment. The directional freezing of suspensions with solids loading of 25, 30, and 37 wt % at cooling from 0.5 to 5 K/min resulted in the formation of lamellar pores and solid walls with the thickness of 12–30 and 14–39 μm, respectively. The increase in solid loading and freezing rate resulted in refinement of the porous structure. Durable monoliths with the mechanical strength of 5.3 MPa were obtained by thermal treatment of the freeze-dried green bodies at 1,373 K. Diatomite monoliths with a pore size of 29.6 μm showed the removal of model dye pollutant Rhodamine B from water by adsorption and long-term water stability. The dye uptake capacity of monolith changed from 1.38 to 17.04 mg/g for the initial dye concentrations between 1.0 and 12.5 mg/L at 298 K and pH = 6, respectively. The adsorption data analysis using Lagergren's pseudo-first-order, pseudo-second-order, and intra-particle diffusion models revealed that diatomite monoliths offered efficient mass transfer in the porous laminated scaffold and to the adsorption sites and bulk diffusion of dye molecules in water was the rate-limiting mechanism for dye removal. © 2018 American Institute of Chemical Engineers Environ Prog, 2018.

Place, publisher, year, edition, pages
John Wiley & Sons, 2019
Keywords
porous ceramic, diatomite, freeze‐casting, adsorption, dye uptake
National Category
Other Materials Engineering
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-71352 (URN)10.1002/ep.13064 (DOI)000460576900040 ()2-s2.0-85054712187 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-03-08 (johcin)

Available from: 2018-10-26 Created: 2018-10-26 Last updated: 2019-04-12Bibliographically approved
Lal, G., Derakhshandeh, M., Akhtar, F., Spasyuk, D. M., Lin, J.-B., Trifkovic, M. & Shimizu, G. K. H. (2019). Mechanical Properties of a Metal−Organic Framework formed by Covalent Cross-Linking of Metal−Organic Polyhedra. Journal of the American Chemical Society, 141(2), 1045-1053
Open this publication in new window or tab >>Mechanical Properties of a Metal−Organic Framework formed by Covalent Cross-Linking of Metal−Organic Polyhedra
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2019 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 141, no 2, p. 1045-1053Article in journal (Refereed) Published
Abstract [en]

Overcoming the brittleness of metal-organic frameworks (MOFs) is a challenge for industrial applications. To increase the mechanical strength, MOFs have been blended with polymers to form composites. However, this also brings challenges, such as integration and integrity of MOF in the composite, which can hamper the selectivity of gas separations. In this report, an "all MOF" material with mechanical flexibility has been prepared by covalent cross-linking of metal-organic polyhedra (MOPs). The ubiquitous Cu 24 isophthalate MOP has been decorated with a long alkyl chain having terminal alkene functionalities so that MOPs can be cross-linked via olefin metathesis using Grubbs second generation catalyst. Different degrees of cross-linked MOP materials have been obtained by varying the amount of catalyst in the reaction. Rheology of these structures with varying number of cross-links was performed to assess the cross-link density and its homogeneity throughout the sample. The mechanical properties were further investigated by the nanoindentation method, which showed increasing hardness with higher cross-link density. Thus, this strategy of cross-linking MOPs with covalent flexible units allows us to create MOFs of increasing mechanical strength while retaining the MOP cavities.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2019
National Category
Other Materials Engineering
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-73213 (URN)10.1021/jacs.8b11527 (DOI)000456350300045 ()30582892 (PubMedID)2-s2.0-85059781426 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-03-15 (svasva)

Available from: 2019-03-15 Created: 2019-03-15 Last updated: 2019-03-25Bibliographically approved
Liu, Y., Cai, X., Sun, Z., Jiao, X., Akhtar, F., Wang, J. & Feng, P. (2018). A novel fabrication strategy for highly porous FeAl/Al2O3 composite by thermal explosion in vacuum. Vacuum, 149, 225-230
Open this publication in new window or tab >>A novel fabrication strategy for highly porous FeAl/Al2O3 composite by thermal explosion in vacuum
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2018 (English)In: Vacuum, ISSN 0042-207X, Vol. 149, p. 225-230Article in journal (Refereed) Published
Abstract [en]

The high porosity of FeAl/Al2O3 composites was successfully prepared via a low-energy consumption method of thermal explosion (TE) in vacuum from reactant mixtures of Fe, Al and Fe2O3. The temperature profiles, phase compositions, microstructure, porosity and pore size of the products were investigated. The TE reactions were ignited between 639 and 648 °C and maximum combustion temperatures reached to 1196–1867 °C. XRD patterns showed that FeAl, Fe2Al5 and Al2O3 were formed via TE reaction, and FeAl and Al2O3 were evolved as dominant phase after the final sintering at 1100 °C. The FeAl/Al2O3 composites exhibited an interconnected pore structure with porosities and pore size of 52–61% and 27–32 μm, respectively.

Place, publisher, year, edition, pages
Elsevier, 2018
National Category
Other Materials Engineering
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-67230 (URN)10.1016/j.vacuum.2017.12.043 (DOI)000425576100038 ()2-s2.0-85039993183 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-01-11 (andbra)

Available from: 2018-01-11 Created: 2018-01-11 Last updated: 2018-03-15Bibliographically approved
Cai, X., Liu, Y., Wang, X., Jiao, X., Feng, P. & Akhtar, F. (2018). Fabrication of Highly Porous CuAl Intermetallic by Thermal Explosion Using NaCl Space Holder. JOM: The Member Journal of TMS, 70(10), 2173-2178
Open this publication in new window or tab >>Fabrication of Highly Porous CuAl Intermetallic by Thermal Explosion Using NaCl Space Holder
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2018 (English)In: JOM: The Member Journal of TMS, ISSN 1047-4838, E-ISSN 1543-1851, Vol. 70, no 10, p. 2173-2178Article in journal (Refereed) Published
Abstract [en]

A high-porosity CuAl-based intermetallic compound with composition Cu-50 at.% Al has been successfully prepared by thermal explosion (TE) using NaCl as space holder. The results showed that the NaCl particles were completely removed from the green compact by water leaching. The temperature of the specimen during the TE and the evolution of the porous microstructure were investigated. The TE was ignited at 560°C, and the specimen temperature increased to 775°C in 3 s, resulting in formation of intermetallic CuAl and CuAl2 phases in the final product. A porous CuAl-based intermetallic compound with up to 62 vol.% open porosity was produced when adding 60 vol.% NaCl. The compound exhibited a bimodal pore size structure, including large pores (200 μm to 300 μm) that replicated the NaCl particles and small pores (5 μm to 10 μm) interspersed in the pore walls. Moreover, the large pores were interconnected by channels and formed an open CuAl-based intermetallic cellular structure, having great potential for use in heat exchange and filtration applications.

Place, publisher, year, edition, pages
The Minerals, Metals, and Materials Society, 2018
National Category
Other Materials Engineering
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-70257 (URN)10.1007/s11837-018-3035-5 (DOI)000445161500036 ()2-s2.0-85050195385 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-10-09 (inah)

Available from: 2018-08-07 Created: 2018-08-07 Last updated: 2018-10-09Bibliographically approved
Alvi, S. & Akhtar, F. (2018). High temperature tribology of polymer derived ceramic composite coatings. Scientific Reports, 8, Article ID 15105.
Open this publication in new window or tab >>High temperature tribology of polymer derived ceramic composite coatings
2018 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 15105Article in journal (Refereed) Published
Abstract [en]

Polymer derived ceramic (PDC) composite coatings were deposited on AISI 304 substrates using siloxane based preceramic polymer polymethlysilsquioxane (PMS) and ZrSi2 as active filler or Ag as passive filler. The tribological performance of the composite coatings was evaluated at room temperature and moderately high temperatures (150 °C, 200 °C, 300 °C and 400 °C). The composite coatings showed low coefficient of friction (COF), µ, from 0.08 to 0.2 for SiOC-ZrSi2 composite coatings, and from 0.02 to 0.3 for SiOC-Ag composite coatings, at room temperature with increasing normal load from 1 to 5 N. High temperature tribology tests showed high COF values from 0.4 to 1 but low wear for SiOC-ZrSi2 coating, and low COF from 0.2 to 0.3 for SiOC-Ag coatings at lower temperature ranges. Low load friction tests at room temperature showed negligible wear in SiOC-ZrSi2 coatings, suggesting good wear resistant and lubricating properties due to formation of t-ZrO2 and carbon. Low COF and high amount of wear was observed in SiOC-Ag composite coatings at room temperature due to high ductility of Ag and smearing of wear debris in the wear track. The coatings and wear tracks were characterized to evaluate the lubrication and wear behavior.

Place, publisher, year, edition, pages
Nature Publishing Group, 2018
National Category
Other Materials Engineering
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-71176 (URN)10.1038/s41598-018-33441-8 (DOI)000446856000052 ()30305660 (PubMedID)2-s2.0-85054667754 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-10-12 (johcin)

Available from: 2018-10-12 Created: 2018-10-12 Last updated: 2018-12-07Bibliographically approved
Jiang, Z., Zhu, G., Feng, P. & Akhtar, F. (2018). In Situ Fabrication and Properties of 0.4MoB-0.1SiC-xMoSi2 Composites by Self-propagating Synthesis and Hot-press sintering. Ceramics International, 44(1), 51-56
Open this publication in new window or tab >>In Situ Fabrication and Properties of 0.4MoB-0.1SiC-xMoSi2 Composites by Self-propagating Synthesis and Hot-press sintering
2018 (English)In: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 44, no 1, p. 51-56Article in journal (Refereed) Published
Abstract [en]

Mo, Si and B4C powders were used to fabricate 0.4MoB-0.1SiC-xMoSi2 composites by self-propagating high-temperature synthesis (SHS) and hot pressing (HP). The effects of MoSi2 content (x=1, 0.75, 0.5 and 0.25) on phase composition, microstructure and properties of the composites were investigated. The results showed that the 0.4MoB-0.1SiC-xMoSi2 composite exhibited Vickers hardness of 10.7–15.2 GPa, bending strength of 337–827 MPa and fracture toughness of 4.9–7.0 MPa∙m1/2. The fracture toughness increased with the increasing volume fraction of MoB and SiC particles which were promoted by the toughening mechanisms, such as crack bridging, cracks deflection and crack branching. Moreover, the electrical resistivity showed an increasing trend with decreasing volume fraction of MoSi2.

Place, publisher, year, edition, pages
Elsevier, 2018
National Category
Other Materials Engineering
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-66006 (URN)10.1016/j.ceramint.2017.08.207 (DOI)000416877900007 ()
Note

Validerad;2017;Nivå 2;2017-11-09 (andbra)

Available from: 2017-10-09 Created: 2017-10-09 Last updated: 2017-12-21Bibliographically approved
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