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| 2. |
- Grolig, Jan Gustav, 1986
(författare)
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Coated Ferritic Stainless Steels as Interconnects in Solid Oxide Fuel Cells - Material Development and Electrical Properties
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Solid oxide fuel cells (SOFCs) are attracting increasing interest as devices with potentialuses in decentralized and clean electricity and heat production. Several challengeswith respect to materials have to be overcome to achieve efficiencies and life-spansthat are sufficient for long-term applications.An important element of an SOFC stack is the interconnect component, which connectstwo adjacent fuel cell elements. Interconnects, which are commonly composedof ferritic stainless steels, have to be corrosion-resistant, mechanically stable and costoptimized.This work aimed to investigate economic solutions for interconnect materials and tounderstand the underlying mechanisms of degradation and electrical conduction ofthese materials. Mainly two substrates, a commercially available steel (AISI 441) anda ferritic stainless steel that was optimized for an SOFC application (Sandvik SanergyHT) were combined with different barrier coatings and exposed to a cathode-sideatmosphere. A method was developed that allows for the electrical characterizationof promising material systems and model alloys, thereby facilitating a fundamentalunderstanding of the dominant electrical conduction processes linked to the oxidescales that grow on interconnects. The AISI 441 steel coated with reactive elementsand cobalt showed good corrosion and chromium evaporation profiles, while AISI 441coated with cerium and cobalt also had promising electrical properties. The SanergyHT steel was examined with coatings of copper and iron and copper and manganese,respectively. The corrosion and chromium evaporation profiles of Sanergy HT wereimproved by coating with copper and iron. The copper and iron-coated Sanergy HTshowed lower area specific resistance values than cobalt-coated Sanergy HT. Chromia,which is the main constituent of oxide scales, was synthesized using differentmethods. The electrical properties of chromia were found to be sensitive to not onlyimpurities, but also heat treatment. Finally the electrical properties of cobalt- andcobalt cerium-coated Sanergy HT steels were investigated. It was revealed that theaddition of cerium improved the conductivity of the interconnect by both slowingdown chromia growth and preventing the outward diffusion of iron into the spinel.
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| 3. |
- Goel, Sneha, 1993-, et al.
(författare)
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The Effect of Location and Post-treatment on the Microstructure of EBM-Built Alloy 718
- 2018
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Ingår i: Proceedings of the 9th International Symposium on Superalloy 718 & Derivatives. - Cham : Springer. - 2367-1696 .- 2367-1181. - 9783319894799 - 9783319894805 ; , s. 115-129
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Konferensbidrag (refereegranskat)abstract
- Additive manufacturing (AM) of Ni-based superalloys such as Alloy 718 may obviate the need for difficult machining and welding operations associated with geometrically intricate parts, thus potentially expanding design possibilities and facilitating cost-effective manufacture of complex components. However, processing AM builds completely free from defects, which may impair mechanical properties such as fatigue and ductility, is challenging. Anisotropic properties, microstructural heterogeneities and local formation of undesired phases are additional concerns that have motivated post-treatment of AM builds. This work investigates the microstructural changes associated with post-treatment of Alloy 718 specimens produced by Electron Beam Melting (EBM) for as-built microstructures at 3 build heights: near base plate, in the middle of build and near the top of the build. Two different post-treatment conditions, hot isostatic pressing (HIP) alone and a combined HIP with solutionising and two-step aging were examined and compared to the results for the as-built condition. The influence of various post-treatments on minor phase distributions (δ, γ″, carbides), overall porosity, longitudinal grain widths and Vickers microhardness was considered. The HIP treatment led to significant reduction in overall porosity and dissolution of δ phase, which led to appreciable grain growth for both post-treatment conditions. The variation in hardness noted as a function of build height for the as-built specimens was eliminated after post-treatment. Overall, the hardness was found to decrease after HIP and increase after the full HIP, solutionising and aging treatment, which was attributed to dissolution of γ″ during HIP and its re-precipitation in subsequent heat treatment steps.
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| 4. |
- Vilardell, A. M., et al.
(författare)
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B2-structured Fe3Al alloy manufactured by laser powder bed fusion : Processing, microstructure and mechanical performance
- 2023
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Ingår i: Intermetallics (Barking). - : Elsevier. - 0966-9795 .- 1879-0216. ; 156
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Tidskriftsartikel (refereegranskat)abstract
- Prealloyed Fe3Al was successfully manufactured by laser powder bed fusion. The best set of process parameters led to parts with a relative density of 99.5 %, a surface roughness, Sa, of 31.5 ± 5.6 μm and a hardness of 319 ± 14 HV0.1. Its microstructure as well as its mechanical properties at room and high temperatures were analyzed. The results of the chemical composition showed minor variations in aluminum content oscillating between 21 and 28 at.% along the melt pool. Additionally, elongated grains were observed to grow parallel to the building direction, as well as the development of a weak 001 texture along the building direction. The mechanical properties were influenced by the temperature. Compression tests showed a loss in strength with the increase in temperature, from a yield strength of 621 ± 40 MPa at room temperature to 89 ± 20 MPa at 650 °C. Reciprocating sliding wear tests showed that fragmentation of the intermetallic at room temperature occurs, whereas plastic deformation dominated at higher temperatures. For all temperatures, tribochemical wear was also present due to the oxidation of wear debris.
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| 5. |
- Balachandramurthi, Arun Ramanathan, et al.
(författare)
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Influence of defects and as-built surface roughness on fatigue properties of additively manufactured Alloy 718
- 2018
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Ingår i: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 735, s. 463-474
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Tidskriftsartikel (refereegranskat)abstract
- Electron beam melting (EBM) and Selective Laser Melting (SLM) are powder bed based additive manufacturing (AM) processes. These, relatively new, processes offer advantages such as near net shaping, manufacturing complex geometries with a design space that was previously not accessible with conventional manufacturing processes, part consolidation to reduce number of assemblies, shorter time to market etc. The aerospace and gas turbine industries have shown interest in the EBM and the SLM processes to enable topology-optimized designs, parts with lattice structures and part consolidation. However, to realize such advantages, factors affecting the mechanical properties must be well understood – especially the fatigue properties. In the context of fatigue performance, apart from the effect of different phases in the material, the effect of defects in terms of both the amount and distribution and the effect of “rough†as-built surface must be studied in detail. Fatigue properties of Alloy 718, a Ni-Fe based superalloy widely used in the aerospace engines is investigated in this study. Four point bending fatigue tests have been performed at 20 Hz in room temperature at different stress ranges to compare the performance of the EBM and the SLM material to the wrought material. The experiment aims to assess the differences in fatigue properties between the two powder bed AM processes as well as assess the effect of two post-treatment methods namely – machining and hot isostatic pressing (HIP). Fractography and metallography have been performed to explain the observed properties. Both HIPing and machining improve the fatigue performance; however, a large scatter is observed for machined specimens. Fatigue properties of SLM material approach that of wrought material while in EBM material defects severely affect the fatigue life. © 2018 Elsevier B.V.
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| 6. |
- Wärmefjord, Kristina, 1976, et al.
(författare)
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Welding of non-nominal geometries : physical tests
- 2016
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Ingår i: Procedia CIRP. - : Elsevier BV. - 2212-8271. ; 43, s. 136-141
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Tidskriftsartikel (refereegranskat)abstract
- The geometrical quality of a welded assembly is to some extent depending part positions before welding. Here, a design of experiment is set up in order to investigate this relation using physical tests in a controlled environment. Based on the experimental results it can be concluded that the influence of part position before welding is significant for geometrical deviation after welding. Furthermore, a working procedure for a completely virtual geometry assurance process for welded assemblies is outlined. In this process, part variations, assembly fixture variations and welding induced variations are important inputs when predicting the capability of the final assembly.
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| 7. |
- Karimi Neghlani, Paria, 1986-, et al.
(författare)
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Influence of successive thermal cycling on microstructure evolution of EBM-manufactured alloy 718 in track-by-track and layer-by-layer design
- 2018
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Ingår i: Materials & design. - : Elsevier BV. - 0264-1275 .- 1873-4197. ; 160, s. 427-441
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Tidskriftsartikel (refereegranskat)abstract
- Successive thermal cycling (STC) during multi-track and multi-layer manufacturing of Alloy 718 using electron beam melting (EBM) process leads to a microstructure with a high degree of complexity. In the present study, a detailed microstructural study of EBM-manufactured Alloy 718 was conducted by producing samples in shapes from one single track and single wall to 3D samples with maximum 10 longitudinal tracks and 50 vertical layers. The relationship between STC, solidification microstructure, interdendritic segregation, phase precipitation (MC, δ-phase), and hardness was investigated. Cooling rates (liquid-to-solid and solid-to-solid state) was estimated by measuring primary dendrite arm spacing (PDAS) and showed an increased cooling rate at the bottom compared to the top of the multi-layer samples. Thus, microstructure gradient was identified along the build direction. Moreover, extensive formation of solidification micro-constituents including MC-type carbides, induced by micro-segregation, was observed in all the samples. The electron backscatter diffraction (EBSD) technique showed a high textured structure in 〈001〉 direction with a few grains misoriented at the surface of all samples. Finer microstructure and possibility of more γ″ phase precipitation at the bottom of the samples resulted in slightly higher (~11%) hardness values compared to top of the samples.
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| 8. |
- Lyphout, Christophe, 1981-, et al.
(författare)
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Characterization of adhesion strenght of HVOF sprayed IN718 coatings
- 2009
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Ingår i: Proceedings of th 22nd Internationa Conference on Surface Modification technolgies - SMT22. Trollhättan, Sweden. - : VALAR Docs. - 9780981706511 ; , s. 11-18
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Konferensbidrag (refereegranskat)abstract
- The tensile adhesion strength of thermally sprayed coating is conventionally evaluated via the ASTM C633-69 standard. The maximum measurable adhesion is then limited by the adhesion strength of the polymer media. High velocity oxy-fuel (HVOF) spraying can exhibit very high bonding strength and thus it is essential to develop an alternative method to evaluate coating adhesion strength. In this work a Modified Tensile Adhesion Test (MTAT) is proposed replacing gluing with induction brazing. The method was evaluated for HVOF sprayed Inconel 718 coatings deposited on Inconel 718 substrates. The effect of induction brazing process and the characteristics of the braze-coating interface was given particular interest. The results indicate that the method is superior to the ASTM C633-69 for characterisation of adhesion of coatings with high bond strength.
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| 9. |
- Hosseini, Seyedehsan, 1994
(författare)
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Additive-Driven Improvements in Interfacial Properties and Processing of TMP-Polymer Composites
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Efforts to address environmental concerns have resulted in new regulations designed to plan the reduction of plastic and synthetic polymer usage, necessitating the search for sustainable natural alternatives with comparable cost-effectiveness and mechanical performance. Thermomechanical pulp (TMP) fibres are one of the most affordable natural fibres that have no chemical refining in production, production have a high yield of 90-98% and TMP fibres have been demonstrated to improve the mechanical characteristics (strength, stiffness and toughness) of wood-polymer composites (WPCs) compared to the pure polymer. The integration of TMP fibres with non-polar synthetic polymers remains a challenge due to surface polarity differences. This PhD thesis aims to ease the processing of TMP fibre composites through the incorporation of additives. The hypothesis posits that incorporating magnesium stearate (MgSt), molybdenum disulfide (MoS2) and alkyl ketene dimer (AKD) as additives in TMP composites will enhance interfacial properties, resulting in improved processability and flow behaviour at high temperatures. MoS2 is known for its interaction with lignin, which exists in TMP and MgSt is recognised for its ability to improve flow in pharmaceutical processing when combined with cellulose, also a component of TMP. AKD modifies the hydrophilic properties of lignocellulosic surfaces. The experimental work explores the effect of these additives on the properties of TMP composites of ethylene acrylic acid copolymer (EAA) and polypropylene (PP) matrices. The dynamic mechanical analysis (DMA) and mechanical analysis results reveal that MoS2 exhibits superior interaction with TMP fibres, yielding enhanced interfacial properties compared to MgSt in between EAA and TMP fibres. Rheological studies elucidate the transition from a fluid-like state to a network-like structure upon the incorporation of TMP into the PP matrix. The incorporation of AKD with C18 reduces the viscosity of TMP-PP composites and PP itself, and, as determined through theoretical Hansen solubility parameter (HSP) calculations, increases compatibility between cellulose in TMP fibres and PP. The addition of AKD influences both the colour (lighter) and shape (smoother surface) of the extrudate filaments in the TMP-PP composites, indicative of improved processing. In addition, frictional analysis demonstrates the reduction of the coefficient of friction (COF) between metal and TMP fibre by MgSt and AKD treatments.
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| 10. |
- 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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