| 1. |
- Åkerfeldt, Pia, et al.
(author)
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Electron backscatter diffraction characterization of fatigue crack growth in laser metal wire deposited Ti-6Al-4V
- 2018
-
In: Materials Characterization. - : Elsevier BV. - 1044-5803 .- 1873-4189. ; 135, s. 245-256
-
Journal article (peer-reviewed)abstract
- By additive manufacturing (AM) there is a feasibility of producing near net shape components in basically one step from 3D CAD model to final product. The interest for AM is high and during the past decade a lot of research has been carried out in order to understand the influence from process parameters on the microstructure and furthermore on the mechanical properties. In the present study laser metal wire deposition of Ti-6Al-4V has been studied in detail with regard to its fatigue crack propagation characteristics. Two specimen orientations, parallel and perpendicular to the deposition direction, have been evaluated at room temperature and at 250 °C. No difference in the fatigue crack growth rate could be confirmed for the two specimen orientations. However, in the fractographic study it was observed that the tortuosity varied between certain regions on the fracture surface. The local crack path characteristic could be related to the alpha colony size and/or the crystallographic orientation. Moreover, large areas exhibiting similar crystallographic orientation were observed along the prior beta grain boundaries, which were attributed to the wide alpha colonies frequently observed along the prior beta grain boundaries. © 2017 Elsevier Inc.
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| 2. |
- Grolig, Jan Gustav, 1986
(author)
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Coated Ferritic Stainless Steels as Interconnects in Solid Oxide Fuel Cells - Material Development and Electrical Properties
- 2015
-
Doctoral thesis (other academic/artistic)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. |
- Krakhmalev, Pavel, 1973-, et al.
(author)
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Microstructure, solidification texture, and thermal stability of 316 L stainless steel manufactured by laser powder bed fusion
- 2018
-
In: Metals. - : MDPI AG. - 2075-4701. ; 8:8, s. 1-18
-
Journal article (peer-reviewed)abstract
- This article overviews the scientific results of the microstructural features observed in 316 L stainless steel manufactured by the laser powder bed fusion (LPBF) method obtained by the authors, and discusses the results with respect to the recently published literature. Microscopic features of the LPBF microstructure, i.e., epitaxial nucleation, cellular structure, microsegregation, porosity, competitive colony growth, and solidification texture, were experimentally studied by scanning and transmission electron microscopy, diffraction methods, and atom probe tomography. The influence of laser power and laser scanning speed on the microstructure was discussed in the perspective of governing the microstructure by controlling the process parameters. It was shown that the three-dimensional (3D) zig-zag solidification texture observed in the LPBF 316 L was related to the laser scanning strategy. The thermal stability of the microstructure was investigated under isothermal annealing conditions. It was shown that the cells formed at solidification started to disappear at about 800 °C, and that this process leads to a substantial decrease in hardness. Colony boundaries, nevertheless, were quite stable, and no significant grain growth was observed after heat treatment at 1050 °C. The observed experimental results are discussed with respect to the fundamental knowledge of the solidification processes, and compared with the existing literature data.
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| 4. |
- Goel, Sneha, 1993-, et al.
(author)
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Effect of post-treatments under hot isostatic pressure on microstructural characteristics of EBM-built Alloy 718
- 2019
-
In: Additive Manufacturing. - : Elsevier BV. - 2214-8604 .- 2214-7810. ; 28, s. 727-737
-
Journal article (peer-reviewed)abstract
- Electron beam melting (EBM) has emerged as an important additive manufacturing technique. In this study, Alloy 718 produced by EBM was investigated in as-built and post-treated conditions for microstructural characteristics and hardness. The post-treatments investigated were hot isostatic pressing (HIP) and combined HIP + heat treatment (HIP + HT) carried out as a single cycle inside the HIP vessel. Both the post-treatments resulted in significant decrease in defects inevitably present in the as-built material. The columnar grain structure of the as-built material was found to be maintained after post-treatment, with some sporadic localized grain coarsening noted. Although HIP led to complete dissolution of δ and γ′′ phase, stable NbC and TiN (occasionally present) particles were observed in the post-treated specimens. Significant precipitation of γ′′ phase was observed after HIP + HT, which was attributed to the two-step aging heat treatment carried out during HIP + HT. The presence of γ′′ phase or otherwise was correlated to the hardness of the material. While the HIP treatment resulted in drop in hardness, HIP + HT led to ‘recovery’ of the hardness to values exceeding those exhibited by the as-built material.
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| 5. |
- Goel, Sneha, 1993-, et al.
(author)
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The Effect of Location and Post-treatment on the Microstructure of EBM-Built Alloy 718
- 2018
-
In: Proceedings of the 9th International Symposium on Superalloy 718 & Derivatives. - Cham : Springer. - 2367-1696 .- 2367-1181. - 9783319894799 - 9783319894805 ; , s. 115-129
-
Conference paper (peer-reviewed)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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| 6. |
- Wärmefjord, Kristina, 1976, et al.
(author)
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Welding of non-nominal geometries : physical tests
- 2016
-
In: Procedia CIRP. - : Elsevier BV. - 2212-8271 .- 2212-8271. ; 43, s. 136-141
-
Journal article (peer-reviewed)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. |
- Charles Murgau, Corinne, et al.
(author)
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Temperature and Microstructure Evolution in Gas Tungsten Arc Welding Wire Feed Additive Manufacturing of Ti-6Al-4V
- 2019
-
In: Materials. - : MDPI. - 1996-1944. ; 12:21
-
Journal article (peer-reviewed)abstract
- In the present study, the gas tungsten arc welding wire feed additive manufacturing process is simulated and its final microstructure predicted by microstructural modelling, which is validated by microstructural characterization. The Finite Element Method is used to solve the temperature field and microstructural evolution during a gas tungsten arc welding wire feed additive manufacturing process. The microstructure of titanium alloy Ti-6Al-4V is computed based on the temperature evolution in a density-based approach and coupled to a model that predicts the thickness of the α lath morphology. The work presented herein includes the first coupling of the process simulation and microstructural modelling, which have been studied separately in previous work by the authors. In addition, the results from simulations are presented and validated with qualitative and quantitative microstructural analyses. The coupling of the process simulation and microstructural modeling indicate promising results, since the microstructural analysis shows good agreement with the predicted alpha lath size.
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| 8. |
- Fargas, G., et al.
(author)
-
Influence of cyclic thermal treatments on the oxidation behavior of Ti-6Al-2Sn-4Zr-2Mo alloy
- 2018
-
In: Materials Characterization. - : Elsevier BV. - 1044-5803 .- 1873-4189. ; 145, s. 218-224
-
Journal article (peer-reviewed)abstract
- Ti-6Al-2Sn-4Zr-2Mo is one of the most common titanium alloys for aerospace industry. This alloy experiences oxidation phenomenon at elevated temperatures. In the present study, cyclic thermal treatments were performed in air at 500, 593 and 700 °C, up to 500 cycles, in order to determine the oxidation kinetics and to analyze the oxide scale and alpha-case formation. Moreover, results were compared to those achieved under isothermal conditions to elucidate differences between both thermal conditions. In this sense, metallographic techniques and X-ray diffraction, together with a detailed advanced characterization of the microstructure by Field Emission Scanning Electron Microscopy and Focus Ions Beam, were used to analyze surface oxidation evolution. Results pointed out that cyclic treatments induced a strong increase of the weight gain compared to isothermal treatments. The analysis of the oxide scale revealed the formation of not only rutile, as isothermal treatments, but also anatase. Thickness of the oxide scale was higher for cyclic conditions, while alpha case did not exceed values reached by isothermal treatments and even became lower at 500 °C.
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| 9. |
- Maimaitiyili, Tuerdi, et al.
(author)
-
Residual Lattice Strain and Phase Distribution in Ti-6Al-4V Produced by Electron Beam Melting
- 2019
-
In: Materials. - : MDPI. - 1996-1944. ; 12:4
-
Journal article (peer-reviewed)abstract
- Residual stress/strain and microstructure used in additively manufactured material are strongly dependent on process parameter combination. With the aim to better understand and correlate process parameters used in electron beam melting (EBM) of Ti-6Al-4V with resulting phase distributions and residual stress/strains, extensive experimental work has been performed. A large number of polycrystalline Ti-6Al-4V specimens were produced with different optimized EBM process parameter combinations. These specimens were post-sequentially studied by using high-energy X-ray and neutron diffraction. In addition, visible light microscopy, scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD) studies were performed and linked to the other findings. Results show that the influence of scan speed and offset focus on resulting residual strain in a fully dense sample was not significant. In contrast to some previous literature, a uniform α- and β-Ti phase distribution was found in all investigated specimens. Furthermore, no strong strain variations along the build direction with respect to the deposition were found. The magnitude of strain in α and β phase show some variations both in the build plane and along the build direction, which seemed to correlate with the size of the primary β grains. However, no relation was found between measured residual strains in α and β phase. Large primary β grains and texture appear to have a strong effect on X-ray based stress results with relatively small beam size, therefore it is suggested to use a large beam for representative bulk measurements and also to consider the prior β grain size in experimental planning, as well as for mathematical modelling.
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| 10. |
- Neikter, Magnus, 1988-, et al.
(author)
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Alpha texture variations in additive manufactured Ti-6Al-4V investigated with neutron diffraction
- 2018
-
In: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 23, s. 225-234
-
Journal article (peer-reviewed)abstract
- Variation of texture in Ti-6Al-4V samples produced by three different additive manufacturing (AM) processes has been studied by neutron time-of-flight (TOF) diffraction. The investigated AM processes were electron beam melting (EBM), selective laser melting (SLM) and laser metal wire deposition (LMwD). Additionally, for the LMwD material separate measurements were done on samples from the top and bottom pieces in order to detect potential texture variations between areas close to and distant from the supporting substrate in the manufacturing process. Electron backscattered diffraction (EBSD) was also performed on material parallel and perpendicular to the build direction to characterize the microstructure. Understanding the context of texture for AM processes is of significant relevance as texture can be linked to anisotropic mechanical behavior. It was found that LMwD had the strongest texture while the two powder bed fusion (PBF) processes EBM and SLM displayed comparatively weaker texture. The texture of EBM and SLM was of the same order of magnitude. These results correlate well with previous microstructural studies. Additionally, texture variations were found in the LMwD sample, where the part closest to the substrate featured stronger texture than the corresponding top part. The crystal direction of the α phase with the strongest texture component was [112¯3]. © 2018 Elsevier B.V.
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| 11. |
- Gaska, Karolina, 1986, et al.
(author)
-
Gas Barrier, Thermal, Mechanical and Rheological Properties of Highly Aligned Graphene-LDPE Nanocomposites
- 2017
-
In: Polymers. - : MDPI AG. - 2073-4360. ; 9:7, s. 294-
-
Journal article (peer-reviewed)abstract
- This contribution reports on properties of low-density polyethylene-based composites filled with different amounts of graphene nanoplatelets. The studied samples were prepared in the form of films by means of the precoating technique and single screw melt-extrusion, which yields a highly ordered arrangement of graphene flakes and results in a strong anisotropy of composites morphology. The performed tests of gas permeability reveal a drastic decrease of this property with increasing filler content. A clear correlation is found between permeability and free volume fraction in the material, the latter evaluated by means of positron annihilation spectroscopy. A strong anisotropy of the thermal conductivity is also achieved and the thermal conductivity along the extrusion direction for samples filled with 7.5 wt % of GnP (graphene nanoplatelets) reached 2.2 W/m·K. At the same time, when measured through a plane, a slight decrease of thermal conductivity is found. The use of GnP filler leads also to improvements of mechanical properties. The increase of Young’s modulus and tensile strength are reached as the composites become more brittle.
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| 12. |
- Hanning, Fabian, 1988, et al.
(author)
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Investigation of the Effect of Short Exposure in the Temperature Range of 750-950 degrees C on the Ductility of Haynes (R) 282 (R) by Advanced Microstructural Characterization
- 2019
-
In: Metals. - : MDPI. - 2075-4701. ; 9:12
-
Journal article (peer-reviewed)abstract
- A Gleeble-based test method has been developed to study the change in the ductility signature of Haynes (R) 282 (R) during isothermal exposure from 5 s to 1800 s. A temperature range of 750 to 950 degrees C has been used to investigate the effect of age-hardening reactions. Microstructural constituents have been analyzed and quantified using scanning and transmission electron microscopy. Carbides present in the material are identified as primary MC-type TiC carbides, Mo-rich M6C secondary carbides, and Cr-rich M23C6 secondary carbides. Gamma prime (gamma’) precipitates are present in all the material conditions with particle sizes ranging from 2.5 nm to 58 nm. Isothermal exposure causes the growth of gamma’ and development of a grain boundary carbide network. A ductility minimum is observed at 800-850 degrees C. The fracture mode is found to be dependent on the stroke rate, where a transition toward intergranular fracture is observed for stroke rates below 0.055 mm/s. Intergranular fracture is characterized by microvoids present on grain facets, while ductility did not change during ongoing age-hardening reactions for intergranularly fractured Haynes (R) 282 (R).
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| 13. |
- Jacobsson, Jonny, et al.
(author)
-
Weldability of superalloys alloy 718 and ATI® 718Plus™ : A study performed by Varestraint testing
- 2017
-
In: Materialprüfung (München). - : Walter de Gruyter GmbH. - 0025-5300 .- 2195-8572. ; 59:9, s. 769-773
-
Journal article (peer-reviewed)abstract
- In this study, the old and well-known alloy 718 is compared with the newly developed ATI® 718Plus™ from the weldability point of view. This is done in order to gain new information that have not been documented and established yet among the high-temperature materials with high strength, oxidation resistance, thermal stability and sufficient weldability, yet. ATI® 718Plus™ shows a lower sensitivity to hot cracking than alloy 718 with approximately 10 mm total crack length (TCL) difference in Varestraint testing. In the solution-annealed condition at 982°C for 4.5 h followed by air cooling, the crack sensitivity is decreased as compared to the mill-annealed condition. Along the crack path and also ahead of the crack tip, γ-Laves eutectic is present in both alloys. The microhardness measurements showed similar hardness level of 250 HV in the weld metal of both alloys and even in the parent material of alloy 718. ATI® 718Plus™ parent metal had hardness of 380 HV and a small increase of less than 50 HV was observed for both studied alloys in the heat affected zone (HAZ). For the same grain size of ATI® 718Plus™ (8.3 μm) and alloy 718 (15.6 μm), the susceptibility to liquation cracking may increase with increasing grain size. With a small grain size, there is a possibility to accommodate more trace elements (B, S, P) due to the larger grain boundary area. The impurity elements were found in relatively small precipitates, typically borides (0.2 μm), phosphides (0.1 to 0.5 μm) and carbo-sulphides. The solidification sequence of alloy 718 and ATI® 718Plus™ is relatively similar, where the liquid starts to solidify as γ-phase followed by γ/MC reaction at about 1260 °C and then final γ/Laves eutectic reaction at around 1150 °C. Detailed knowledge about weldability of alloy 718 and ATI® 718Plus™ can be used for material selection.
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| 14. |
- Cantatore, Valentina, 1986, et al.
(author)
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Towards multifunctional coating in the boron-doped graphene/copper system
- 2017
-
In: Carbon. - : Elsevier BV. - 0008-6223. ; 115, s. 375-379
-
Journal article (peer-reviewed)abstract
- A route to achieve multi-functional graphene coating is explored. Chemical bonding between copper substrate and coating results if the graphene is a priori boron doped. After pair-wise binding of boron sites to the Cu(111) surface, co-existence of pseudo-gap property in the graphene subsystem and a metallic density of states in the Cu subsystem at the common Fermi energy emerges. Apparently a paradox is that the two subsystems preserve and even recover their individual integrities upon formation of surface chemical bonds. Sensor capabilities are inferred. Employing pyridine as test molecule, conditioned ability of a nucleophile to offer competitive dative bonding, with the sub-strate, for boron sites is demonstrated. It is shown to occur for the case of half coverage and for adsorption to boron atoms originally bound to the on-top site on Cu(111). The ability of complementary boron sites to compensate for loss of binding between on-top site and boron, resulting from said bonding to the incoming nucleophile, is emphasized. Multifunctional substrate-coating system for catalysis as well as enhanced sensitization is inferred.
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| 15. |
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| 16. |
- Angseryd, Jenny, 1979, et al.
(author)
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Nanostructure of a cubic BN cutting tool material
- 2015
-
In: International Journal of Refractory Metals and Hard Materials. - : Elsevier BV. - 0263-4368 .- 2213-3917. ; 49:1, s. 283-287
-
Journal article (peer-reviewed)abstract
- Advanced microscopy techniques, laser assisted atom probe tomography and electron energy loss spectroscopy in transmission electron microscopy are used to investigate in detail the microstructure of a polycrystalline cubic boron nitride tool material. During sintering at high pressure superhard cubic boron nitride combines with hard ceramic Ti(C,N) to form a dense material. Diffusion in Ti(C,N) and reactions between Ti(C,N), cBN and additives result in the formation of several nitride, oxide and boride phases in a complex mixed microcrystalline and nano- crystalline microstructure.
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| 17. |
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| 18. |
- Jafari, Reza, et al.
(author)
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KCl-Induced High Temperature Corrosion Behavior of HVAF-Sprayed Ni-Based Coatings in Ambient Air
- 2018
-
In: Journal of thermal spray technology (Print). - : Springer Science and Business Media LLC. - 1059-9630 .- 1544-1016. ; 27:3, s. 500-511
-
Journal article (peer-reviewed)abstract
- KCl-induced high temperature corrosion behavior of four HVAF-sprayed Ni-based coatings (Ni21Cr, Ni5Al, Ni21Cr7Al1Y, and Ni21Cr9Mo) under KCl deposit has been investigated in ambient air at 600°C up to 168h. The coatings were deposited onto 16Mo3 steel - a widely used boiler tube material.Uncoated substrate, 304L and Sanicro25 were used as reference materials in the test environment.SEM/EDS and XRD techniques were utilized to characterize the as-sprayed and exposed samples.The results showed that the small addition of KCl significantly accelerated degradation to the coatings. All coatings provided better corrosion resistance compared to the reference materials. The alumina-forming Ni5Al coating under KCl deposit was capable of forming a more protective oxide scale compared to the chromia-forming coatings as penetration of Cl through diffusion paths was hindered. Both active corrosion and chromate formation mechanisms were found to be responsible for Page 1 of 23ASM the corrosion damages. The corrosion resistance of the coatings based on the microstructure analysis and kinetics had the following ranking (from the best to worst): Ni5Al >Ni21Cr> Ni21Cr7Al1Y>Ni21Cr9Mo.
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| 19. |
- Sadeghimeresht, Esmaeil, 1985-, et al.
(author)
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Chlorine-induced high temperature corrosion of HVAF-sprayed Ni-based alumina and chromia forming coatings
- 2018
-
In: Corrosion Science. - : Elsevier BV. - 0010-938X .- 1879-0496. ; 132:March, s. 170-184
-
Journal article (peer-reviewed)abstract
- Chlorine-induced corrosion of HVAF-sprayed Ni21Cr and Ni5Al coatings was investigated in 5 vol.% O2 + 500vppm HCl + N2 with and without KCl at 600 °C up to 168 h. Both coatings were protective in the absence of KCl. With KCl, Ni21Cr degraded through a two-stage mechanism: 1) formation of K2CrO4 followed by diffusion of Cl− through the oxide grain boundaries to yield chlorine and a non-protective oxide, and 2) inward diffusion of chlorine though defects in the non-protective oxide, leading to breakaway oxidation. Cl−/Cl2 could not diffuse through the protective alumina scale formed on Ni5Al, hence the corrosion resistance increased.
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| 20. |
- Vilardell, Anna M., et al.
(author)
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Cold spray as an emerging technology for biocompatible and antibacterial coatings : State of art
- 2015
-
In: Journal of Materials Science. - New York : Springer. - 0022-2461 .- 1573-4803. ; 50:13, s. 4441-4462
-
Research review (peer-reviewed)abstract
- The use of coatings in biomaterials has been fundamental on the applicability of many medical devices and has helped improve mechanical properties such as wear and fatigue and biological properties such as biocompatibility and bioactivity of implant prosthesis, thus, in essence, ameliorating human quality life. The aim of the present paper is to give a review on cold spray (CS) coating systems that are emerging in orthopedics industry (internal fixation systems and prosthesis) as well as those for antibacterial purposes (in body and touch external surfaces). These studies are very new, the oldest dating from the half of last decade and most deal with the improvement of biocompatibility and bioactivity of hard tissue replacement; therefore, research on biocoatings is in constant development with the aim to produce implant surfaces that provide a balance between cell adhesion and low cytotoxicity, mechanical properties, and functionalization. CS offers many advantages over conventional high-temperature processes and seems to be able to become competitive in front of the low-temperature techniques. It is mainly cost effective, appropriate for oxygen-sensitive materials, and environmentally green. It basically involves the use of feedstock material in powder form, which is supersonically sprayed onto the appropriate substrate but without any melting as it occurs in conventional thermal spray processes. Biocompatible metallic materials and polymers have been successfully deposited by this method because it is based on the plasticity of the coating material; pure ceramic deposits, for example of hydroxyapatite, are still a challenge.
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| 21. |
- Cruz-Crespo, Amado, et al.
(author)
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Flux for Hardfacing by Submerged Arc Welding from Ferrochrome-manganese and Slag from the Simultaneous Reduction of Chromite and Pyrolusite
- 2019
-
In: Soldagem & Inspeção. - 0104-9224 .- 1980-6973. ; 24
-
Journal article (peer-reviewed)abstract
- The obtaining of a flux for hardfacing by Submerged Arc Welding (SAW), using ferrochrome-manganese and slag obtained from the simultaneous carbothermal reduction of chromite and pyrolusite is addressed. The ferrochrome-manganese and the slag were obtained, conceiving that both products satisfy the requirements of the components (alloy system and matrix) of an agglomerated flux for hardfacing. The fusion-reduction process to obtain the alloy and the slag was carried out in a direct current electric arc furnace. The pouring was carried out into water to facilitate the separation and grinding of the cast products. An experimental flux was manufactured, using the obtained alloy and slag. Deposits were obtained by SAW, which were characterized in terms of: chemical composition, microstructure and hardness. It was concluded that the flux obtained from ferrochrome-manganese and slag from the simultaneous carbothermal reduction of chromite and pyrolusite, allows to deposit an appropriate metal for work under abrasion conditions, characterized by significant carbon and chromium contents and a martensitic microstructure predominantly, with hardness of 63 HRc.
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| 22. |
- Draxler, Joar, et al.
(author)
-
Modeling and simulation of weld solidification cracking part II : A model for estimation of grain boundary liquid pressure in a columnar dendritic microstructure
- 2019
-
In: Welding in the World. - : Springer Science and Business Media LLC. - 0043-2288 .- 1878-6669. ; 63:5, s. 1503-1519
-
Journal article (peer-reviewed)abstract
- Several advanced alloy systems are susceptible to weld solidification cracking. One example is nickel-based superalloys, which are commonly used in critical applications such as aerospace engines and nuclear power plants. Weld solidification cracking is often expensive to repair, and if not repaired, can lead to catastrophic failure. This study, presented in three papers, presents an approach for simulating weld solidification cracking applicable to large-scale components. The results from finite element simulation of welding are post-processed and combined with models of metallurgy, as well as the behavior of the liquid film between the grain boundaries, in order to estimate the risk of crack initiation. The first paper in this study describes the crack criterion for crack initiation in a grain boundary liquid film. The second paper describes the model for computing the pressure and the thickness of the grain boundary liquid film, which are required to evaluate the crack criterion in paper 1. The third and final paper describes the application of the model to Varestraint tests of Alloy 718. The derived model can fairly well predict crack locations, crack orientations, and crack widths for the Varestraint tests. The importance of liquid permeability and strain localization for the predicted crack susceptibility in Varestraint tests is shown. © 2019, The Author(s).
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| 23. |
- Gruber, Hans, 1983, et al.
(author)
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Effect of Powder Recycling on the Fracture Behavior of Electron Beam Melted Alloy 718
- 2018
-
In: Powder Metallurgy Progress. - : de Gruyter. - 1335-8987 .- 1339-4533. ; 18:1, s. 40-48
-
Journal article (other academic/artistic)abstract
- Understanding the effect of powder feedstock alterations during multicycle additive manufacturing on the quality of built components is crucial to meet the requirements on critical parts for aerospace engine applications. In this study, powder recycling of Alloy 718 during electron beam melting was studied to understand its influence on fracture behavior of Charpy impact test bars. High resolution scanning electron microscopy was employed for fracture surface analysis on test bars produced from virgin and recycled powder. For all investigated samples, an intergranular type of fracture, initiated by non-metallic phases and bonding defects, was typically observed in the regions close to or within the contour zone. The fracture mode in the bulk of the samples was mainly moderately ductile dimple fracture. The results show a clear correlation between powder degradation during multi-cycle powder reuse and the amount of damage relevant defects observed on the fracture surfaces. In particular, samples produced from recycled powder show a significant amount of aluminum-rich oxide defects, originating from aluminum-rich oxide particulates on the surface of the recycled powder. © 2018 H. Gruber et al., published by Sciendo.
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| 24. |
- Hanning, Fabian, et al.
(author)
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Measurement of the thermal cycle in the base metal heat affected zone of cast ATI ® 718Plus TM during manual multi-pass TIG welding
- 2018
-
In: Procedia Manufacturing. - : Elsevier BV. - 2351-9789. ; 25, s. 443-449
-
Journal article (peer-reviewed)abstract
- This paper presents a method to acquire thermal data in the base metal heat affected zone (HAZ) during manual multi-pass TIG welding of ATI ® 718Plus TM , representing conditions close to an actual repair welding operation. Thermocouples were mounted in different locations along side walls of linear grooves to record temperature data. The thermal cycling was found to be largely independent of location within the HAZ. The recorded temperatures were below the incipient laves melting temperature, indicating that the current test setup requires optimisation to study HAZ liquation. Based on the results of this study, a modified thermocouple mounting technique is proposed. © 2018 Elsevier B.V. All rights reserved.
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| 25. |
- Hanning, Fabian, 1988, et al.
(author)
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The Influence of Base Metal Microstructure on Weld Cracking in Manually GTA Repair Welded Cast ATI 718Plus®
- 2018
-
In: Proceedings of the 9th International Symposium on Superalloy 718 & Derivatives. - Cham : Springer International Publishing. - 2367-1696 .- 2367-1181. - 9783319894799 - 9783319894805 ; , s. 917-928
-
Conference paper (peer-reviewed)abstract
- The effect of base metal conditions on the weld cracking response of cast ATI 718Plus® was investigated in this study, comparing as cast microstructure with pseudo hot isostatic pressing (HIP) heat treatments at 1120, 1160 and 1190 °C for dwell times of 4 and 24 h. Linear grooves have been filled using multipass manual gas tungsten arc welding (GTAW) to simulate repair welding conditions. Metallographic investigation revealed cracks in both base metal heat affected zone and fusion zone layers. The heat treatment temperatures chosen below, at and above incipient laves melting temperature of ATI 718Plus® were found to have an effect on weld cracking behaviour, with an increased average total crack length in the base metal heat affected zone for both 1160 and 1190 °C as compared to the as cast condition and the 1120 °C homogenization treatment. The increase in cracking susceptibility shows a correlation with the amount of Nb-rich secondary phases, with lower amounts leading to crack concentration to solidification grain boundaries present from the casting process, increasing the average crack length.
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| 26. |
- Holmberg, Jonas, et al.
(author)
-
Grit Blasting for Removal of Recast Layer from EDM Process on Inconel 718 Shaft : An Evaluation of Surface Integrity
- 2016
-
In: Journal of materials engineering and performance (Print). - : Springer Science and Business Media LLC. - 1059-9495 .- 1544-1024. ; 25:12, s. 5540-5550
-
Journal article (peer-reviewed)abstract
- The heat generated during EDM melts the work material and thereby allows large amounts to be removed,but an unfavorable surface of a recast layer (RCL) will also be created. This layer has entirely different properties compared to the bulk. Hence, it is of great interest to efficiently remove this layer and to verify that it has been removed. The main objective of this work has been to study the efficiency of grit blasting forremoval of RCL on an EDM aero space shaft. Additionally, x-ray fluorescence (XRF) has been evaluated asa nondestructive measurement to determine RCL presence. The results show that the grit-blasting processing parameters have strong influence on the ability to remove RCL and at the same time introduce beneficial compressive stresses even after short exposure time. Longer exposure will remove the RCL fromthe surface but also increase the risk that a larger amount of the blasting medium will get stuck into the surface. This investigation shows that a short exposure time in combination with a short grit-blasting nozzle distance is the most preferable process setting. It was further found that handheld XRF equipment can be used as a nondestructive measurement in order to evaluate the amount of RCL present on an EDM surface.This was realized by analyzing the residual elements from the EDM wire.
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| 27. |
- Jaladurgam, Nitesh Raj, 1993
(author)
-
Heterogeneous deformation of multi-phase engineering materials - an in-situ neutron diffraction study
- 2019
-
Licentiate thesis (other academic/artistic)abstract
- Gas turbines are complex power generation systems used in aerospace or land-based-power stations. Materials such as Ni-base superalloys are involved in the combustion zone of these machines, which continuously experiences harsh environments with loading at high temperatures. Moreover, the continuous demand for increasing operating temperature to achieve higher efficiencies and reduced emission levels opens the scene to new heat resistant materials like the state-of-the-art high entropy alloys (HEAs), which require a thorough understanding of the structure-process-property relationships. The microstructures of these advanced multi-phase, multi-component alloys are complex, and the deformation is generally heterogeneous both with respect to the different phases and to the crystallographic orientation within each phase. Hence, it is important to understand their behavior and performance during processing and service. In-situ neutron diffraction is a unique technique to probe the deformation behaviour during service/processing-like conditions, including plastic deformation at various temperatures, in order to provide insights into the structure-property relations. In the first part of this work the deformation mechanisms of a newly developed Ni-base superalloy was investigated using in-situ neutron diffraction and electron microscopy at room temperature. In addition, elasto-plastic self-consistent (EPSC) crystal plasticity simulations are used to obtain insights into the operating deformation mechanisms. In the second part, the as-cast eutectic high entropy alloy AlCoCrFeNi2.1 was studied using in-situ neutron diffraction at temperatures from 77 to 673 K. These investigations provide unique insights into the complex heterogeneous deformation behavior of these high-performance multi-phase engineering materials.
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| 28. |
- Kumara, Chamara, et al.
(author)
-
Microstructure modelling of laser metal powder directed energy deposition of alloy 718
- 2019
-
In: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 25, s. 357-364
-
Journal article (peer-reviewed)abstract
- A multi-component and multi-phase-field modelling approach, combined with transformation kinetics modelling, was used to model microstructure evolution during laser metal powder directed energy deposition of Alloy 718 and subsequent heat treatments. Experimental temperature measurements were utilised to predict microstructural evolution during successive addition of layers. Segregation of alloying elements as well as formation of Laves and δ phase was specifically modelled. The predicted elemental concentrations were then used in transformation kinetics to estimate changes in Continuous Cooling Transformation (CCT) and Time Temperature Transformation (TTT) diagrams for Alloy 718. Modelling results showed good agreement with experimentally observed phase evolution within the microstructure. The results indicate that the approach can be a valuable tool, both for improving process understanding and for process development including subsequent heat treatment.
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| 29. |
- Singh, Sukhdeep, 1988, et al.
(author)
-
Investigation on effect of welding parameters on solidification cracking of austenitic stainless steel 314
- 2018
-
In: Procedia Manufacturing. - : Elsevier BV. - 2351-9789. ; , s. 351-357
-
Journal article (other academic/artistic)abstract
- This study investigates the solidification cracking susceptibility of the austenitic stainless steel 314. Longitudinal Varestraint testing was used with three different set of welding test parameters. Weld speed, current and voltage values were selected so that the same heat input resulted in all the test conditions. From the crack measurements it was seen that the test condition with the lowest current and welding speed value also produced the least amount of cracking with very good repeatability.
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| 30. |
- Singh, Sukhdeep, 1988, et al.
(author)
-
Varestraint Weldability Testing of ATI 718Plus® : Influence of Eta Phase
- 2018
-
In: Proceedings of the 9th International Symposium on Superalloy 718 & Derivatives. - Cham : Springer. - 9783319894799 - 9783319894805 ; , s. 929-937, s. 929-937
-
Conference paper (peer-reviewed)abstract
- This study investigates the effect of eta phase on hot cracking susceptibility of ATI 718Plus®. Two heat treatment conditions of 950 °C/1 h and 950 °C/15 h having different amounts of eta phase were tested by longitudinal Varestraint testing method. The heat treatment at 950 °C/15 h exhibited the highest amount of cracking. This was related to the higher amount of eta phase precipitation during the long dwell heat treatment which aided to extensive liquation during welding.
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| 31. |
- Tolvanen, Sakari, 1984, et al.
(author)
-
Microstructure and Porosity of Laser Welds in Cast Ti-6Al-4V with Addition of Boron
- 2018
-
In: Metallurgical and Materials Transactions. A. - : Springer Science and Business Media LLC. - 1073-5623 .- 1543-1940. ; 49A:5, s. 1683-1691
-
Journal article (peer-reviewed)abstract
- Addition of small amounts of boron to cast Ti-6Al-4V alloy has shown to render a finer microstructure and improved mechanical properties. For such an improved alloy to be widely applicable for large aerospace structural components, successful welding of such castings is essential. In the present work, the microstructure and porosity of laser welds in a standard grade cast Ti-6Al-4V alloy as well as two modified alloy versions with different boron concentrations have been investigated. Prior-β grain reconstruction revealed the prior-β grain structure in the weld zones. In fusion zones of the welds, boron was found to refine the grain size significantly and rendered narrow elongated grains. TiB particles in the prior-β grain boundaries in the cast base material restricted grain growth in the heat-affected zone. The TiB particles that existed in the as cast alloys decreased in size in the fusion zones of welds. The hardness in the weld zones was higher than in the base material and boron did not have a significant effect on hardness of the weld zones. The fusion zones were smaller in the boron-modified alloys as compared with Ti-6Al-4V without boron. Computed tomography X-ray investigations of the laser welds showed that pores in the FZ of the boron modified alloys were confined to the lower part of the welds, suggesting that boron addition influences melt pool flow. © 2018 The Author(s)
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| 32. |
- Holmberg, Jonas, 1976-
(author)
-
Surface integrity on post processed alloy 718 after nonconventional machining
- 2018
-
Licentiate thesis (other academic/artistic)abstract
- There is a strong industrial driving force to find alternative production technologies in order to make the production of aero engine components of superalloys even more efficient than it is today. Introducing new and nonconventional machining technologies allows taking a giant leap to increase the material removal rate and thereby drastically increase the productivity. However, the end result is to meet the requirements set for today's machined surfaces.The present work has been dedicated to improving the knowledge of how the non-conventional machining methods Abrasive Water Jet Machining, AWJM, Laser Beam Machining, LBM, and Electrical Discharge Machining, EDM, affect the surface integrity. The aim has been to understand how the surface integrity could be altered to an acceptable level. The results of this work have shown that both EDM and AWJM are two possible candidates but EDM is the better alternative; mainly due to the method's ability to machine complex geometries. It has further been shown that both methods require post processing in order to clean the surface and to improve the topography and for the case of EDM ageneration of compressive residual stresses are also needed.Three cold working post processes have been evaluated in order to attain this: shot peening, grit blasting and high pressure water jet cleaning, HPWJC. There sults showed that a combination of two post processes is required in order to reach the specified level of surface integrity in terms of cleaning and generating compressive residual stresses and low surface roughness. The method of high pressure water jet cleaning was the most effective method for removing the EDM wire residuals, and shot peening generated the highest compressive residual stresses as well as improved the surface topography.To summarise: the most promising production flow alternative using nonconventional machining would be EDM followed by post processing using HPWJC and shot peening.
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| 33. |
- Ahlström, Johan, 1969, et al.
(author)
-
Effect of strain gradient on the microstructure and mechanical properties of pearlitic steel
- 2019
-
In: IOP Conference Series: Materials Science and Engineering. - 1757-8981 .- 1757-899X. ; 580:1
-
Conference paper (peer-reviewed)abstract
- Pearlitic steels, with a combination of good strength and wear properties, are commonly used for railway rails. The passage of trains creates large shear strain gradients in the surface layer of rails. Knowledge of the microstructural evolution and material properties as related to the shear strain in this layer is therefore important for prediction both of crack evolution and fatigue life. A bi-axial torsion-compression machine was used to deform fully pearlitic R260 rail steel test bars to create a similar gradient structure. Uniaxial tension and compression tests were performed on these pre-deformed test bars to evaluate the mechanical properties of the material. The local microstructural parameters, such as thickness of the ferrite and cementite lamellae, the dislocation density in the ferrite lamellae, the interlamellar spacing and eth local hardness at different places across the diameter of the bars, as well as microstructural evolution across the radius, were characterized. An attempt to set up a correlation between the local microstructural parameters, hardness and the macro mechanical properties is made and discussed in the present study.
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| 34. |
- Bueno, Moises, et al.
(author)
-
Modification of asphalt mixtures for cold regions using microencapsulated phase change materials
- 2019
-
In: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 9:1
-
Journal article (peer-reviewed)abstract
- Phase change materials (PCMs) may be used to regulate the temperature of road surfaces to avoid low-temperature damages when asphalt materials become brittle and prone to cracking. With this in mind, different asphalt mixtures were modified with microencapsulated phase change materials (i.e. tetradecane) to assess their thermal benefits during the phase change process. Likewise, the effect on the mechanical performance of PCMs as a replacement of mineral filler was assessed. Special attention was paid to dry and wet modification processes for incorporating the PCMs into the mixtures. The results showed that PCM modifications are indeed able to slow down cooling and affect temperatures below zero. Approximately, a maximum of 2.5 °C offset was achieved under the tested cooling conditions compared to the unmodified reference specimens. Regarding the mechanical response at 0 °C and 10 °C, the results indicated that the PCM modification significantly reduces the stiffness of the material in comparison with the values obtained for the reference mixture.
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| 35. |
- Holmberg, Jonas, et al.
(author)
-
Experimental and PFEM-simulations of residual stresses from turning tests of a cylindrical Ti-6Al-4V shaft
- 2018
-
In: Procedia CIRP. - : Elsevier. - 2212-8271 .- 2212-8271. ; 71, s. 144-149
-
Journal article (peer-reviewed)abstract
- Alloy Ti-6Al-4V is a frequently used material in aero space applications due the high strength and low weight. This material is however often considered as a difficult to machine alloy due to several material properties such as the inherent characteristics of high hot hardness and strength which is causing an increased deformation of the cutting tool during machining. The thermal properties also cause a low thermal diffusion from locally high temperatures in the cutting zone that allows for reaction to the tool material resulting in increased tool wear.Predicting the behavior of machining of this alloy is therefore essential when selecting machining tools or machining strategies. If the surface integrity is predicted, the influence of different machining parameters could be studied using Particle Finite Element (PFEM)-simulations. In this investigation the influence from cutting speed and feed during turning on the residual stresses has been measured using x-ray diffraction and compared to PFEM-simulations.The results showed that cutting speed and feed have great impact on the residual stress state. The measured cutting force showed a strong correlation especially to the cutting feed. The microstructure, observed in SEM, showed highly deformed grains at the surface from the impact of the turning operation and the full width half maximum from the XDR measurements distinguish a clear impact from different cutting speed and feed which differed most for the higher feed rate.The experimental measurements of the residual stresses and the PFEM simulations did however not correlate. The surface stresses as well as the sign of the residuals stresses differed which might be due to the material model used and the assumption of using a Coulomb friction model that might not represent the cutting conditions in the investigated case.
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| 36. |
- Kahlin, Magnus
(author)
-
Fatigue Performance of Additive Manufactured Ti6Al4V in Aerospace Applications
- 2017
-
Licentiate thesis (other academic/artistic)abstract
- Additive Manufacturing (AM) for metals includes is a group of production methodst hat use a layer-by-layer approach to directly manufacture final parts. In recent years, the production rate and material quality of additive manufactured materials have improved rapidly which has gained increased interest from the industry to use AM not only for prototyping, but for serial production. AM offers a greater design freedom, compared to conventional production methods, which allows for parts with new innovative design. This is very attractive to the aerospace industry, in which parts could be designed to have reduced weight and improved performance contributing to reduced fuel consumption, increased payload and extended flight range. There are, however, challenges yet to solve before the potential of AM could be fully utilized in aerospace applications. One of the major challenges is how to deal with the poor fatigue behaviour of AM material with rough as-built surface.The aim of this thesis is to increase the knowledge of how AM can be used for high performance industrial parts by investigating the fatigue behaviour of the titanium alloy Ti6Al4V produced with different AM processes. Foremost, the intention is to improve the understanding of how rough as-built AM surfaces in combination with AM built geometrical notches affects the fatigue properties.This was done by performing constant amplitude fatigue testing to compare different combinations of AM material produced by Electron Beam Melting(EBM) and Laser Sintering (LS) with machined or rough as-built surfaces with or without geometrical notches and Hot Isostatic Pressing (HIP) treatment. Furthermore, the material response can be different between constant amplitude and variable amplitude fatigue loading due to effects of overloads and local plastic deformations. The results from constant amplitude testing were used to predict the fatigue life for variable amplitude loading by cumulative damage approach and these predictions were then verified by experimental variable amplitude testing.The constant amplitude fatigue strength of material with rough as-built surfaces was found to be 65-75 % lower, compared to conventional wrought bar, in which HIP treatments had neglectable influence on the fatigue strength. Furthermore, the fatigue life predictions with cumulative damage calculations showed good agreement with the experimental results which indicates that a cumulative damage approach can be used, at least for a tensile dominated load sequences, to predict the fatigue behaviour of additive manufactured Ti6Al4V.
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| 37. |
- Khalilitehrani, Mohammad, 1984, et al.
(author)
-
The morphology of the deposited particles after a wet agglomerate normal surface impact
- 2019
-
In: Powder Technology. - : Elsevier BV. - 1873-328X .- 0032-5910. ; 345, s. 796-803
-
Journal article (peer-reviewed)abstract
- Through discrete element modeling, we investigate the breakage, deposition and attachment of wet dust agglomerates during normal surface impacts. The morphology and structure of the deposited dirt layer is studied through statistical analysis of the height profiles. It is found that the deposited layer is influenced by both the structural properties of the primary agglomerates and the impact conditions. The roughness of the deposited dirt layer shows a positive correlation to impact velocity and a negative correlation to the agglomerate moisture content. Within the pendular liquid regime the structural strength of the agglomerates shows a strong correlation to the moisture content while at higher moisture content the correlation becomes weaker. It is also observed that for a given impact velocity agglomerates of various sizes show similar deposition patterns. To unify the results for different agglomerate sizes, a dimensionless surface density is introduced.
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| 38. |
- Kuzmenko, Volodymyr, 1987, et al.
(author)
-
Sustainable carbon nanofibers/nanotubes composites from cellulose as electrodes for supercapacitors
- 2015
-
In: Energy. - : Elsevier BV. - 0360-5442 .- 1873-6785. ; 90:2, s. 1490-1496
-
Journal article (peer-reviewed)abstract
- Supercapacitors are efficient energy storage devices with long lifetime and safe service. Their effectiveness,to a big extent, is dependent on electrode materials used for accumulation of energy in form ofelectrostatic charges. Over the last decades, variety of carbonaceous electrode materials has been used insupercapacitors. Mostly the production of such electrodes is still oriented on unsustainable fossil fuels asprecursors instead of sustainable renewable resources. In this study, freestanding carbonaceous electrodematerials for supercapacitors were derived from cellulose, the most abundant renewable resource. Theywere synthesized via carbonization of fibrillar cellulose impregnated with CNTs (carbon nanotubes). Theensuing composite materials consisted of a CNF (carbon nanofiber) scaffold (fiber diameter in the rangeof 50-250 nm) covered with layers of CNTs (tube diameter in the range of 1-20 nm). Moreover, thesecomposites were tested as electrode materials for supercapacitors. Incorporation of the CNTs into theCNFs improved electrical conductivity and also increased the surface area of the produced compositematerials, which led to high specific capacitance values (up to 241 F/g), cyclic stability, and powerdensity of these materials in electrochemical measurements. These results suggest that cellulose-derivedoriginal CNF/CNT composites are sustainable and efficient carbonaceous electrodes for supercapacitors.
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| 39. |
- Mishra, Pragya, 1989-, et al.
(author)
-
Energy efficiency contributions and losses during selective laser melting
- 2018
-
In: Journal of laser applications. - : American Institute of Physics (AIP). - 1042-346X .- 1938-1387. ; 30:3
-
Journal article (peer-reviewed)abstract
- Selective Laser Melting technique, SLM, requires remelting of adjacent tracks to avoid cavities and other imperfections. Usually, very conservative process parameters are chosen to avoid imperfections, resulting in a low building rate. The process efficiency relates the energy required for the generation of a new track to the laser beam power. For SLM this efficiency is determined by the process parameters, specifically hatch distance, layer depth and scanning speed, independent of the resulting process mechanisms. For SLM the process efficiency often very low, typically 2‑20%. Apart from beam reflection losses of normally 50-60%, significant energy losses result from the remelting of surrounding layers. Some areas can even experience multiple remelting cycles. Further losses originate inevitably from substrate heating. A simplified mathematical model of the track cross section and the corresponding layer overlap geometry has been developed, to analyze the different loss contributions from remelting with respect to the process parameters. The model explains why increasing the hatch distance or the layer depth proportionally increases the process efficiency. However, these increases are limited by cavity formation. The cross section of the overlapping tracks generated by SLM can be regarded as an experimental fingerprint linked to the process conditions. The track cross section geometries can significantly fluctuate, in terms of area and coordinate position. The fluctuations require additional reduction of the hatch distance or layer depth, to ensure robust, cavity-free processing. Examples are presented for stainless steel where a 180 W laser beam has led to a process efficiency of 5-11%, proportional to a hatch distance that was increased from 50 to 110 µm, for 40 µm powder layer depth, at a speed of 50 m/min.
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| 40. |
- Neikter, Magnus, et al.
(author)
-
Microstructural characterization and comparison of Ti-6Al-4V manufactured with different additive manufacturing processes
- 2018
-
In: Materials Characterization. - : Elsevier. - 1044-5803 .- 1873-4189. ; 143:SI, s. 68-75
-
Journal article (peer-reviewed)abstract
- In this work, the microstructures of Ti-6Al-4V manufactured by different additive manufacturing (AM) processes have been characterized and compared. The microstructural features that were characterized are the α lath thickness, grain boundary α (GB-α) thickness, prior β grain size and α colony size. In addition, the microhardnesses were also measured and compared. The microstructure of shaped metal deposited (SMD) Ti-6Al-4V material showed the smallest variations in α lath size, whereas the material manufactured with laser metal wire deposition-0 (LMwD-0) showed the largest variation. The prior β grain size was found to be smaller in material manufactured with powder bed fusion (PBF) as compared with corresponding material manufactured with the directed energy deposition (DED) processes. Parallel bands were only observed in materials manufactured with DED processes while being non-present in material manufactured with PBF processes.
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| 41. |
- Vega, Alberto, 1984, et al.
(author)
-
Degradation mechanisms in PUR foam of district heating pipes after accelerated ageing
- 2017
-
Conference paper (other academic/artistic)abstract
- Modern societies demand the use of non-fossil and sustainable energy resources. In this sense, district heating (DH) systems have been playing an important role in the last years. However, some questions still remains unanswered such as technical life time prediction, heat losses challenge or status assessment. These questions are the driving force of DH system development, especially for the DH pipe manufacturers. Pre-insulated heating pipes include a HDPE jacket, rigid polyurethane (PUR) foam and steel service pipe, and are used to transport the heat from a central point out to the customers and then back again for reuse. These pipes must withstand axial mechanical loads and have good long-term thermal properties. Therefore, it is important to have reliable methods to evaluate the current status of a DH system at any time. The main aim of the project is to determine the degradation mechanisms during natural and accelerated aging of DH pipes. In this project, the pipes have been aged using an accelerated thermal ageing and both mechanical and thermal properties were investigated. Mechanical property was evaluated using the SP plug method, which determined the remaining adhesion force between the PUR and the steel service pipe [1]. This method has also been designed for application in field for a quick status check. At the same time, the thermal property has also been measured in real-time using a transient plane source (TPS) technique instead of a steady-state method [2]. Characterization of the PUR material has been performed using a three-point flexural test, Fourier transform infra-red spectroscopy (FTIR) and gas chromatography-mass spectrometry (GC-MS) analysis [3]. Preliminary results suggest three different phases where the degradation of DH pipes is a combination of physical and chemical phenomena. In the early aging period, the changes in both mechanical and thermal properties are caused by physical effects. After that, an upturn is observed due to changes in the PUR chemical structure observed in the FTIR analysis. Finally, the chemical degradation takes over which is an effect of thermo-oxidation. At the end a better model comprising all three phases for the entire degradation process is needed and will be proposed in order to determine the real technical life time of DH pipes.
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| 42. |
- Hagqvist, Petter
(author)
-
Non-intrusive instrumentation and estimation : Applications for control of an additive manufacturing process
- 2015
-
Doctoral thesis (other academic/artistic)abstract
- For integration of additive manufacturing into industrial production, there is a need for capable yet robust automation solutions. Such solutions are to ensure consistent process outputs, both with regard to deposit geometry and material properties. In this thesis, instrumentation and control solutions have been investigated for the laser metal wire deposition additive manufacturing process. This particular process is promising with regard to e.g. high deposition rates and negligible material waste. However, due to its inherent dynamics, it requires automatic control in order to prove competitive. A large number of process parameters affect the resulting quality of the deposit. Successful control of these parameters is crucial for turning laser metal wire deposition into an industrially tractable process. This requires relevant and reliable process information such as the temperature of the deposit and the positioning of the tool relative to the workpiece. Due to the particular requirements of instrumenting the process, only non-intrusive measurement methods are viable. In this thesis, such measurement solutions are presented that advance automatic control of the laser metal wire deposition. In response to the need for accurate temperature measurements for the process, a new temperature measurement method has been developed. By adopting the novel concept of temporal, rather than spectral, constraints for solving the multispectral pyrometry problem, it opens up for temperature measurements which compensates for e.g. an oxidising deposit. For maintaining a good deposition process in laser metal wire deposition, control of tool position and wire feed rate is required. Based on measurements of resistance through the weld pool, a simple yet well performing control system is presented in this thesis. The control system obtains geometrical input information from resistance measurements made in-situ, and feeds this information to an iterative learning controller. This results in a robust, cheap and practical control solution for laser metal wire deposition, which is suitable for industrial use and that can easily be retrofitted to existing equipment.
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| 43. |
- Svenman, Edvard, 1969-, et al.
(author)
-
Model based compensation of systematic errors in an inductive gap measurement method
- 2017
-
In: Measurement : Journal of the International Measurement Confederation. - : Elsevier. - 0263-2241 .- 1873-412X. ; 105, s. 17-24
-
Journal article (peer-reviewed)abstract
- This paper presents an improvement to a recently presented inductive gap measurement method, using a model to reduce systematic errors. Gap measurement is important in laser keyhole welding, where the laser beam and the resulting weld seam are very narrow, requiring high precision in alignment and gap preparation. The previously reported method for gap measurement uses one inductive coil on each side of the gap, each measuring distance to the gap and lift off above a plate, to estimate the position, width and alignment of the gap in a square butt joint. The method can detect zero width gap and shows position error less than 0.1 mm, but gap width and alignment measurement suffer from systematic errors. The improvement is based on a model that is designed to describe these systematic errors as functions of the gap dimensions. The model relies on observations of experimental data, and is calibrated to a small set of measurements. Using the model with the initial estimate of the gap dimensions to compensate the coil measurements, an improved estimate of the gap dimensions can be calculated. The errors in the compensated results are within 0.1 mm except for gap width, which still suffers from the effect of combined gap width and misalignment.
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| 44. |
- Saarimäki, Jonas, et al.
(author)
-
3D Residual Stresses in Selective Laser Melted Hastelloy X
- 2017
-
In: Residual Stresses 2016: ICRS-10, Materials Research Proceedings 2 (2016). - : Materials Research Forum LLC. ; , s. 73-78
-
Conference paper (peer-reviewed)abstract
- 3D residual stresses in as manufactured EOS NickelAlloy HX, produced by laser powder bed additive manufacturing, are analysed on the surface closest to the build-plate. Due to the severe thermal gradient produced during the melting and solidification process, profound amounts of thermal strains are generated. Which can result in unwanted geometrical distortion and effect the mechanical properties of the manufactured component. Measurements were performed using a four-circle goniometer Seifert X-ray machine, equipped with a linear sensitive detector and a Cr-tube. Evaluation of the residual stresses was conducted using sin2ψ method of the Ni {220} diffraction peak, together with material removal technique to obtain in-depth profiles. An analysis of the material is reported. The analysis reveals unwanted residual stresses, and a complicated non-uniform grain structure containing large grains with multiple low angle grain boundaries together with nano-sized grains. Grains are to a large extent, not equiaxed, but rather elongated.
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| 45. |
- Ahmad, Maqsood, et al.
(author)
-
Bending Fatigue Behavior of Blast Cleaned Grey Cast Iron
- 2017
-
In: Residual Stresses 2016: ICRS-10, Materials Research Proceedings 2 (2016). - : Materials Research Forum LLC. - 9781945291166 ; , s. 193-198
-
Conference paper (peer-reviewed)abstract
- This paper presents a detailed study on the effect of an industrial blast cleaning process on the fatigue behavior of a grey cast iron with regard to the residual stresses and microstructural changes induced by the process. A comparison was also made to the effect of a machining operation which removed the casting skin layer. The blast cleaning process was found to greatly improve the fatigue resistance in both the low and high cycle regimes with a 75% increase in the fatigue limit. Xray diffraction measurements and scanning electron microscopic analyses showed that the improvement was mainly attributed to compressive residual stresses in a surface layer up to 800 μm in thickness in the blast cleaned specimens. The machining also gave better fatigue performance with a 30% increase in the fatigue limit, which was ascribed to the removal of the weaker casting skin layer.
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| 46. |
- Hanning, Fabian, 1988, et al.
(author)
-
Weldability of wrought Haynes 282 repair welded using manual gas tungsten arc welding
- 2018
-
In: Welding in the World. - : Springer Science and Business Media LLC. - 0043-2288 .- 1878-6669. ; 62:1, s. 39-45
-
Journal article (peer-reviewed)abstract
- The ability of the precipitation hardening superalloy Haynes® 282® to be repaired by multi-pass gas tungsten arc welding is investigated in this study. The repair welding has been carried out on forged discs having four pre weld heat treatments, resulting in different grain sizes and precipitate structures of the base material. Another set of discs has additionally been put through a post weld heat treatment. The tendency to form cracks in the heat-affected zone and the fusion zone has been investigated metallographically. No cracks in the base metal heat-affected zone were found,whereas solidification cracks were present in the weld fusion zone of all tested conditions. While high heat input during welding increased cracking by a factor of 1.5, none of the heat treatments had a measurable influence on the cracking behaviour. Voids with solid state crack-like appearance turned out tobe aluminium-rich oxides being present from the deposition of previous weld deposit layers.
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| 47. |
- Tofeldt, Oskar, et al.
(author)
-
Guided wave evaluation techniques for testing of plate-like concrete structures
- 2018
-
Conference paper (other academic/artistic)abstract
- There is a growing need for non-destructive techniques capable of investigating civilengineering structures of concrete material. The Impact-Echo (IE) method is one suchtechnique based on the study of a resonant and stationary mode. This mode corresponds to a Lamb mode. In turn, this accentuates that the IE method can easily be extended to include the analysis of propagating Lamb modes as well. Thereby a quantitative evaluation of the elastic plate properties and thickness is possible. Moreover, the use of Lamb waves lay the foundations for extended analysis which makes measurements based on an extension of the IE method an attractive complement to current ultrasonic techniques for plate-like concrete structures.
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| 48. |
- Karlsson, Dennis, et al.
(author)
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Binder jetting of the AlCoCrFeNi alloy
- 2019
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In: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 27, s. 72-79
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Journal article (peer-reviewed)abstract
- High density components of an AlCoCrFeNi alloy, often described as a high-entropy alloy, were manufactured by binder jetting followed by sintering. Thermodynamic calculations using the CALPHAD approach show that the high-entropy alloy is only stable as a single phase in a narrow temperature range below the melting point. At all other temperatures, the alloy will form a mixture of phases, including a sigma phase, which can strongly influence the mechanical properties. The phase stabilities in built AlCoCrFeNi components were investigated by comparing the as-sintered samples with the post-sintering annealed samples at temperatures between 900 °C and 1300 °C. The as-sintered material shows a dominant B2/bcc structure with additional fcc phase in the grain boundaries and sigma phase precipitating in the grain interior. Annealing experiments between 1000 °C and 1100 °C inhibit the sigma phase and only a B2/bcc phase with a fcc phase is observed. Increasing the temperature further suppresses the fcc phase in favor for the B2/bcc phases. The mechanical properties are, as expected, dependent on the annealing temperature, with the higher annealing temperature giving an increase in yield strength from 1203 MPa to 1461 MPa and fracture strength from 1996 MPa to 2272 MPa. This can be explained by a hierarchical microstructure with nano-sized precipitates at higher annealing temperatures. The results enlighten the importance of microstructure control, which can be utilized in order to tune the mechanical properties of these alloys. Furthermore, an excellent oxidation resistance was observed with oxide layers with a thickness of less than 5 μm after 20 h annealing at 1200 °C, which would be of great importance for industrial applications.
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| 49. |
- Kanhed, Satish, et al.
(author)
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Microporous Hydroxyapatite Ceramic Composites as Tissue Engineering Scaffolds : An Experimental and Computational Study
- 2018
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In: Advanced Engineering Materials. - : Wiley. - 1438-1656 .- 1527-2648. ; 20:7
-
Journal article (peer-reviewed)abstract
- Bone‐tissue engineering mandates the development of multi‐functional bioactive porous hydroxyapatite (HAp) scaffolds. Herein, microwave sintered HAp/ZnO and HAp/Ag composite scaffolds with ≈5–19% porosity are developed using 0–30 vol% graphite as a porogen. The mechanical properties of the porous scaffold are analyzed in detail, revealing that even being more porous, the reinforcement of ZnO (9% porosity, hardness of 2.8 GPa, and toughness of 3.5 MPa.m1/2) has shown to have better hardness and fracture toughness when compared to Ag (5% porosity, hardness of 1.6 GPa, and toughness of 2.6 MPa.m1/2). The flexural strength obtained experimentally are complemented with a finite‐element technique that adopts microstructural features in visualizing the effect of porosity on stress distribution. The antibacterial efficacy and cytocompatibility of these composites are validated by increased metabolic activity and conspicuous cell‐matrix interactions. The anticipation of the results reveal that HAp/ZnO (9% porosity) and HAp/Ag (5% porosity) composites can be used as a potential multi‐functional bone implant scaffolds.
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| 50. |
- Agic, Adnan, 1967-, et al.
(author)
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Influence of cutting edge geometry on force build-up process in intermittent turning
- 2016
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In: Procedia CIRP. - : Elsevier BV. - 2212-8271 .- 2212-8271. ; 46, s. 364-367
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Journal article (peer-reviewed)abstract
- In the intermittent turning and milling processes, during the entry phase the cutting edges are subjected to high impact loads that can give rise to dynamical and strength issues which in general cause tool life reduction. In this study the effect of geometrical features of the cutting tool on the force generation during the entry phase is investigated. Cutting forces are measured by a stiff dynamometer at a high sampling frequency. In addition, the chip load area is analyzed and related to the measured cutting force. The results show that micro-geometrical features, in particular the protection chamfer, significantly affect the force generation during the entry phase.
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