| 1. |
- Mahade, Satyapal, 1987-, et al.
(författare)
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Incorporation of graphene nano platelets in suspension plasma sprayed alumina coatings for improved tribological properties
- 2021
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 570
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Tidskriftsartikel (refereegranskat)abstract
- Graphene possesses high fracture toughness and excellent lubrication properties, which can be exploited to enhance tribological performance of coating systems utilized to combat wear. In this work, suspension plasma spray (SPS) process was employed to deposit a composite, graphene nano-platelets (GNP) incorporated alumina coating. For comparison, monolithic alumina was also deposited utilizing identical spray conditions. The as-deposited coatings were characterized in detail for their microstructure, porosity content, hardness, fracture toughness and phase composition. Raman analysis of the as-deposited composite coating confirmed retention of GNP. The composite coating also showed good microstructural integrity, comparable porosity, higher fracture toughness and similar alumina phase composition as the monolithic alumina coating. The as-deposited coatings were subjected to dry sliding wear tests. The GNP incorporated composite coating showed lower CoF and lower specific wear rate than the pure alumina coating. Additionally, the counter surface also showed a lower wear rate in case of the composite coating. Post-wear analysis performed by SEM/EDS showed differences in the coating wear track and in the ball wear track of monolithic and composite coatings. Furthermore, Raman analysis in the wear track of composite coating confirmed the presence of GNP. The micro-indentation and wear test results indicate that the presence of GNP in the composite coating aided in improving fracture toughness, lowering CoF and specific wear rate compared to the monolithic coating. Results from this work demonstrated retention of GNP in an SPS processed coating, which can be further exploited to design superior wear-resistant coatings.
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| 2. |
- Johansen, Marcus, 1994, et al.
(författare)
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Mapping nitrogen heteroatoms in carbon fibres using atom probe tomography and photoelectron spectroscopy
- 2021
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Ingår i: Carbon. - : Elsevier BV. - 0008-6223. ; 179, s. 20-27
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Tidskriftsartikel (refereegranskat)abstract
- Carbon fibres show great potential as multifunctional negative electrode for novel structural battery composites – a rechargeable electrochemical cell with structural function. The electrochemical performance of carbon materials can be enhanced with nitrogen heteroatoms, which conveniently are inherent in polyacrylonitrile (PAN)-based carbon fibres. However, it is not fully understood how the electrochemical performance is governed by microstructure and composition of the carbon fibres, particularly the distribution and chemical states of nitrogen heteroatoms. Here we reveal the atom-by-atom three-dimensional spatial distribution and the chemical states of nitrogen in three PAN-carbon fibre types (M60J, T800 and IMS65), using atom probe tomography (APT) and synchrotron hard X-ray photoelectron spectroscopy (HAXPES), and correlate the results to electrochemical performance. The findings pave the way for future tailoring of carbon fibre microstructure for multifunctional applications.
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| 3. |
- Johansen, Marcus, 1994
(författare)
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Microstructure of Carbon Fibres for Multifunctional Composites: 3D Distribution and Configuration of Atoms
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lightweight energy storage is a must for increased driving range of electric vehicles. “Mass-less” energy storage can be achieved by directly storing energy in structural components. In such multifunctional devices called structural composite batteries, carbon fibres carry mechanical load and simultaneously act as negative battery electrode by hosting lithium ions in its microstructure. Little is known of how the microstructure of carbon fibres is optimised for multifunctionality, and deeper understanding of the configuration and the distribution of atoms in carbon fibres is needed. Here synchrotron hard X-ray photoelectron spectroscopy and atom probe tomography are used to reveal the chemical states and three-dimensional distribution of atoms in commercial carbon fibres. This thesis presents the first ever guide for how to perform atom probe tomography on carbon fibres, and the first ever three-dimensional atomic reconstruction of a carbon fibre. The results show that the chemical states and distribution of nitrogen heteroatoms in carbon fibres affect the electrochemical performance of the fibres. Carbon fibres performed electrochemically better with higher amount of nitrogen with pyridinic and pyrrolic configurations. Additionally, the nitrogen concentration varies throughout the carbon fibre, which may suggest that the electrochemical properties also vary throughout the carbon fibre. The knowledge provided by this thesis can lead to future carbon fibre designs with enhanced electrochemical performance for multifunctional applications.
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| 4. |
- al-Karawi, Hassan, 1993, et al.
(författare)
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The efficiency of HFMI treatment and TIG remelting for extending the fatigue life of existing welded structures
- 2021
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Ingår i: Steel Construction. - : Wiley. - 1867-0520 .- 1867-0539. ; 14:2, s. 95-106
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Tidskriftsartikel (refereegranskat)abstract
- Different post‐weld treatment methods have been developed to enhance the fatigue strength of welded steel structures and extend the service lives of their components. High‐frequency mechanical impact (HFMI) treatment and tungsten inert gas (TIG) remelting are two methods that have attracted considerable interest in recent decades. This paper presents the results of a study of fatigue life extension for pre‐fatigued welded steel details which can be achieved using HFMI treatment and TIG remelting. More than 250 fatigue test results were collected – including different details such as butt welds, longitudinal attachments, transverse attachments and cover plate attachments. HFMI treatment was found to extend the life considerably when the specimens treated were free from cracks or when existing cracks were < 2.25 mm deep. TIG remelting could extend fatigue lives even with cracks > 4 mm deep. In comparison to TIG remelting, HFMI treatment results in a longer fatigue life extension for pre‐fatigued details, provided existing cracks are < 2.25 mm deep. Regarding TIG remelting, the depth of possible remaining cracks was found to be a substantial parameter when assessing the degree of life extension.
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| 5. |
- Fazi, Andrea, 1992
(författare)
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Cold spray Cr-coated Optimized ZIRLO claddings: an option for accident tolerant fuels
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Accident tolerant fuel development has started with the aim of providing nuclear fuels able to endure severe accident conditions. Research in this field has also sparked a wave of material renewal in the nuclear industry that had being delayed for the last few decades. Climate change is an ever-growing public concern, and policies about greenhouse gas emissions are becoming more stringent both at the national and international level. Nuclear energy produces very low carbon emissions and the successful development of new accident tolerant materials might play a role in making this technology a viable solution to this global issue. Cr-coated zirconium claddings are one of the most promising candidates as near-term response to the need for accident tolerant materials. These coatings can be produced via a range of different technologies, but the two main designs being currently developed are obtained with physical vapour deposition or cold spray (CS) deposition. In cold spray, high pressure gas is fed through a nozzle together with Cr powder. The Cr particles are accelerated up to 1200 m/s and directed to the substrate, in this case cladding tubes made of Optimized ZIRLO™ alloy. The resulting Cr-coated zirconium cladding is the subject of this work. As-fabricated samples and autoclave tested material are characterized with atom probe tomography and a range of electron microscopy techniques. The scope of the investigation is to evaluate the performances of Cr-coated claddings under operating conditions. Additionally, the nature of the adhesion in cold spray coating and the effects of this deposition method on the substrate are explored. A 10-20 nm thick intermixed bonding region was observed at the Cr/Zr interface of the as-fabricated cladding. This region is deemed to play an important role in the strong adhesion of CS coatings. When exposed to operating conditions, ZrCr2-Laves phase was found to nucleate in the intermixed bonding region. CS deposition involves severe plastic deformation of both coating and substrate. As a result, a 1-2 μm thick nanocrystalline layer can be found in the substrate adjacent to the Cr/Zr interface. After autoclave exposure, a Zr-Cr-Fe phase was discovered precipitating in this nanocrystalline layer at the Zr grain boundaries.
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| 6. |
- Ganvir, Ashish, 1991-, et al.
(författare)
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Novel utilization of liquid feedstock in high velocity air fuel (HVAF) spraying to deposit solid lubricant reinforced wear resistant coatings
- 2021
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Ingår i: Journal of Materials Processing Technology. - : Elsevier BV. - 0924-0136 .- 1873-4774. ; 295
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Tidskriftsartikel (refereegranskat)abstract
- The ability to axially inject liquid feedstock has encouraged the thermal spray research community to explore this concept to deposit coatings for various next generation functional applications. The current study explores the utilization of liquid feedstock in high velocity air fuel (HVAF) spraying to deposit solid lubricant reinforced wear resistant coatings for the first time. The study successfully demonstrates the use of a powder-suspension hybrid processing approach to incorporate a solid lubricant Boron Nitride (as suspension) in a wear resistant Cr3C2–NiCr (as powder) cermet matrix. Coatings were characterized using Scanning Electron Microscopy and Raman Spectroscopy to analyze their microstructure and phase constitution. The results show that the tribological performance of the hexagonal boron nitride (hBN)-incorporated composite coating was significantly better than the traditional powder-derived Cr3C2–NiCr coating. Such hBN-incorporated composite coatings are needed to improve the mechanical properties and enhance the overall tribological performance of metallic components used in various applications, especially at high temperature such as cylinder bore, pistons, deformation tools, etc. The limitations of liquid based lubricants at high temperature motivates the use of hBN reinforced composite coatings as it can form a protective solid lubrication tribo-film. The study concludes that the emerging HVAF technology can accommodate liquid feedstock and be successfully utilized to deposit hybrid powder-suspension composite coatings to create multi length scale microstructures which can be attractive for combining different tribological attributes in the same coatings system.
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| 7. |
- Jaladurgam, Nitesh Raj, 1993, et al.
(författare)
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Macro- and micro-mechanical behaviour of a γ′ strengthened Ni-based superalloy at cryogenic temperatures
- 2021
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Ingår i: Materials and Design. - : Elsevier BV. - 1873-4197 .- 0264-1275. ; 209
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Tidskriftsartikel (refereegranskat)abstract
- In-situ neutron diffraction was performed during tensile deformation of Ni-base superalloy, Haynes 282, at 20, 100 and 300 K. Two distinct uni-modal microstructures with fine (20 nm) and coarse (200 nm) \(\gamma^\prime\) particles were investigated. On the macro-scale yield strength increased and ductility decreased with decreasing temperature, although most significant decrease in ductility occurred between 100 and 20 K. The work hardening differed between the two microstructures, but was independent of temperature for each microstructure. On the micro-scale intergranular elastic interactions mainly lead to a transfer of the load to grains with the $\left<200\right>$ parallel to the tensile axis. No further load re-distribution between matrix and particles occurred in the microstructure with fine \(\gamma^\prime\), where shearing of precipitates lead to co-deformation at all temperatures. In the coarse \(\gamma^\prime\) microstructure, the load was transferred intragranularly from matrix to particles, in addition to the intergranular load transfer. The particles initially behaved elastically while the matrix deformed plastically, but at higher stresses a change in load partitioning indicated that also the \(\gamma^\prime\) phase underwent plastic deformation as a result of the elastic stress build-up from the load partitioning. The tendency for, and effect of, plastic deformation of \(\gamma^\prime\) increased with decreasing temperature.
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| 8. |
- Lozinko, Adrianna, 1992
(författare)
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Microstructure development and mechanical properties of cast and thermo-mechanically treated eutectic high-entropy alloys
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The recently emerging high-entropy alloys (HEAs) present a novel alloying strategy, significantly expanding the scope of metal alloy design. Single-phase HEAs, nevertheless, suffer from the strength-ductility trade off as seen in conventional metallic materials. A possible solution is found in the recently developed eutectic HEAs (EHEAs), which borrow the concept of using lamellar structures as in-situ composites to balance mechanical properties. The first such alloy, AlCoCrFeNi2.1, with an FCC(L12) + BCC(B2) lamellar microstructure, remains the most studied EHEA. Despite much work put into its characterization, much remains to be understood. For example, more efforts have been given to optimize the mechanical properties while less are given to quantitatively describe the microstructure. Various thermo-mechanical treatments have been used to modify the mechanical properties of the AlCoCrFeNi2.1 alloy, however, previous studies mainly focused on the fully recrystallized materials, while a clear understanding of the recrystallization process is still missing, and the potential of partial recrystallization remains to be explored. The first part of this thesis work focuses on the as-cast microstructures of the eutectic and near-eutectic compositions of the AlCoCrFeNi2.1 system. Quantification of the phase volume and lamellar spacing is performed as a function of the Ni content. Orientation relationship and misorientation angle-axis changes in the five investigated alloys are also studied, with the previously unknown dependency of misorientation angle on the Ni content revealed. Some attention is also given to irregular microstructures in eutectic and near-eutectic compositions, which have not been discussed in previous studies. In the second part of this thesis work, a systematic study of the recrystallization process and the correlation between microstructure and mechanical properties in the thermo-mechanically treated AlCoCrFeNi2.1 alloy is undertaken. Distinctive behavior of the constituent phases during recrystallization, with varying rates of recrystallization and grain growth are observed, providing new insights to the recrystallization process in this alloy. Furthermore, it is shown that by controlling the annealing temperature and time, hetero-deformation induced hardening could lead to abnormal hardening in the as-rolled alloy, providing a new strategy to achieve high-strength with acceptable ductility in EHEAs.
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| 9. |
- Townsend, Philip, 1991, et al.
(författare)
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Tessellation-based stochastic modelling of 3D coating structures imaged with FIB-SEM tomography
- 2021
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Ingår i: Computational Materials Science. - : Elsevier BV. - 0927-0256 .- 1879-0801. ; 197
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Tidskriftsartikel (refereegranskat)abstract
- To facilitate printing, coatings are typically applied to paperboard used for packaging to provide a good surface for application. To optimise the performance of the coating, it is important to understand the relationship between the microstructure of the material and its mass transport properties. In this work, three samples of paperboard coating are imaged using combined focused ion beam and scanning electron microscope (FIB-SEM) tomography data appropriately segmented to characterise the internal microstructure. These images are used to inform a parametric, tessellation-based stochastic three-dimensional model intended to mimic the irregular geometry of the particles that can be seen in the coating. Parameters for the model are estimated from the FIBSEM image data, and we demonstrate good agreement between the real and virtual structures both in terms of geometrical measures and mass transport properties. The development of this model facilitates exploration of the relationship between the structure and its properties.
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| 10. |
- Manchili, Swathi Kiranmayee, 1987, et al.
(författare)
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Comparative study on the densification of chromium pre-alloyed powder metallurgy steel through nanopowder addition using design of experiments
- 2021
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Ingår i: Results in Materials. - : Elsevier BV. - 2590-048X. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- There is a constant demand for high density press and sinter powder metallurgical components for automotiveapplications. Steel powder pre-alloyed with chromium is an attractive material for such applications, but newways to further increase the sinter density are required for successful processing of these powders to high density.Nanopowder could be used as a potential sintering aid in order to boost the densification of the steel powdercompact. In this study, steel powder pre-alloyed with chromium, without and with admixed nickel, is used as basepowder, to which nanopowder was added. Surface oxide removal, crucial for successful sintering of such mate-rials, was studied by thermogravimetry analysis in order to understand the influence of nanopowder addition onthe oxide reduction. Powder compacts containing nanopowder showed higher mass loss in comparison to the oneswithout nanopowder. Linear shrinkage obtained from dilatometric curves increased with the addition of nano-powder. To depict the influence of the critical parameters; sintering temperature, powder size, addition ofnanopowder and composition (with or without nickel), a design of experiment approach was applied. The criticalparameters were then adjusted at 2 different values (categorical parameters) and a‘full factorial design model’was used involving 16 experiments, with sinter density and hardness as output measures of the experimentsdetermined. The results were analyzed using polynomialfit to determine which of the parameter exerts themaximum influence. Presence of nickel increased the hardness whereas sintering temperature and presence ofnanopowder enhanced the sinter density. This led to the tentative design of optimum conditions that resulted inincrease in sinter density from 7.25 g/cm3(92.5% of the theoretical density) to 7.4 g/cm3(94% of the theoreticaldensity) with an addition of 5% nanopowder to Ni-containing grade when sintered at 1350 °C instead of 1250 °C.
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