| 1. |
- Aydin, Gökçe, et al.
(författare)
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Influence of laser metal deposition process parameters on a precipitation hardening stainless steel
- 2023
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Ingår i: Welding in the World. - : Springer. - 0043-2288 .- 1878-6669. ; 67:4, s. 1067-1080
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Tidskriftsartikel (refereegranskat)abstract
- The combination of corrosion resistance and mechanical properties of martensitic precipitation hardening stainless steels (MPHSS) makes them well suited for demanding applications in aerospace, high-pressure gas bottles, or in injection molding of corrosive plastics. Directed energy deposition methods and specifically the laser metal deposition process with powder as feedstock (LMDp) have the potential to be applied in the production of such components. It is well-known that the geometrical features of the deposited beads such as aspect ratio and dilution are crucial for process efficiency and deposition quality. Therefore, this work aims at understanding the influence of the process parameters and the resulting microstructure of a MPHSS modified PH 13-8Mo alloy when using LMDp. Design of experiment (DoE) was used to plan and analyze the influence and interaction of the different LMDp process variables in the geometry of the deposits. It was found that height, width, and depth were statistically significantly influenced by speed, while height was also considerably influenced by the powder feeding rate. In terms of laser power, it was the most significant factor for the width and the depth, but it did not significantly affect the height of the beads. The results showed that the as-deposited microstructure of the modified PH 13-8Mo under the LMDp conditions investigated in this work consists of a martensitic matrix with some amount of primary δ ferrite. The presence of a low amount of retained austenite and aluminum-enriched inclusions was confirmed. This work enhances the fundamental process and material understanding of LMDp of the modified PH 13-8Mo alloy as a first stage in the fabrication of additively manufactured components.
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| 2. |
- Chou, Chia-Ying, et al.
(författare)
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Influence of solidification structure on austenite to martensite transformation in additively manufactured hot-work tool steels
- 2021
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Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 215
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Tidskriftsartikel (refereegranskat)abstract
- The microstructure of a hot-work tool steel additively manufactured using laser powder-bed fusion (L-PBF), and its response to post heat treatment, is studied in detail by microstructure characterization and computational thermodynamics and kinetics. The high solidification and cooling rates during the L-PBF process lead to suppression of delta-ferrite and instead solidification of an austenite phase directly containing a cellular substructure where the alloying elements have segregated to the inter-cellular regions and where solidification carbides have formed in the cell junctions. The austenite is then partly decomposed into martensite at lower temperatures. The micro-segregation can be predicted by reducing the complex solidification behavior to a diffusion problem in one dimension enabling detailed comparisons with the measured segregation profiles quantified at a nanometer scale. Martensite start temperature (M-s) calculations along the spatially varying composition show that the M-s temperature decreases in the inter-cellular regions where austenite is observed. The network of austenite in the as-built microstructure can be understood from the combined influence of the composition dependence of the M-s temperature in relation to the build plate temperature and the mechanical stabilization of the small-sized austenite regions. This work demonstrates the power of computational tools based on computational thermodynamics and kinetics for designing tool steels for additive manufacturing by predictions of the steel's response to the L-PBF process and post heat treatments.
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| 3. |
- Karlsson, Patrik, 1973-, et al.
(författare)
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Factors Influencing Mechanical Properties of Additive Manufactured Thin-Walled Parts
- 2017
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Ingår i: Euro PM2017 Congress Proceedings. - : European Powder Metallurgy Association (EPMA).
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Konferensbidrag (refereegranskat)abstract
- By using the Additive Manufacturing (AM) method it is possible to manufacture components with thin-walled sections and complex geometry. However, it is not clear when the surface becomes the strength limiting factor on thin-walled sections in the components or if the thickness of the components is reduced. Also, the microstructure of AM produced specimens may be heterogeneous and it is not clear how the build direction influence the strength of thin section components. In the present study, the influence of component thickness, surface roughness and build direction on the strength of AM produced components were investigated. Test specimens were manufactured using EOS M290 3D-printer and EN 1.2709 maraging steel powder. To investigate when the part thickness, surface and built orientation becomes the strength limiting factors tensile testing using thin samples built in both horizontal and vertical build orientation with thicknesses ranging from 0.2 mm to 4 mm was performed. Results on strength limiting factors are discussed.
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| 4. |
- Klement, Uta, 1962, et al.
(författare)
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Influence of additives on texture development of submicro- and nanocrystalline Nickel
- 2012
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Ingår i: Materials Science Forum. - 1662-9752 .- 0255-5476. ; 702-703, s. 928-931
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Konferensbidrag (refereegranskat)abstract
- Organic additives such as saccharin have been frequently used in electroplatingoperations to moderate deposit growth rates and to control film quality. In this study, texturedevelopment upon annealing of pulse-electroplated Nickel produced without additives is analyzedby use of electron backscatter diffraction technique.Plating without additives results in a microstructure with slightly elongated grains and a fibre texture in growth direction and this texture is conserved upon annealing up to 600°C.Structural units in form of groups of elongated grains possessing a common zone axis ingrowth direction and twin relationships between themselves are found in the microstructure. Forrevealing the influence of additives, the observations are compared with results obtained for Ni andNi-Fe plated in the presence of additives where during abnormal grain growth the initial fibre texture changes to an energetically more favourable texture by twinning. The lack ofadditives is assumed to be responsible for the observed differences in texture and microstructuredevelopment.
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| 5. |
- König, Hans-Henrik, et al.
(författare)
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Solidification modes during additive manufacturing of steel revealed by high-speed X-ray diffraction
- 2023
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Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 246, s. 118713-
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Tidskriftsartikel (refereegranskat)abstract
- Solidification during fusion-based additive manufacturing (AM) is characterized by high solidification velocities and large thermal gradients, two factors that control the solidification mode of metals and alloys. Using two synchrotron-based, in situ setups, we perform high-speed X-ray diffraction measurements to investigate the impact of the solidification velocities and thermal gradients on the solidification mode of a hot-work tool steel over a wide range of thermal conditions of relevance to AM of metals. The solidification mode of primary delta-ferrite is observed at a cooling rate of 2.12 x 104 K/s, and at a higher cooling rate of 1.5 x 106 K/s, delta-ferrite is sup-pressed, and primary austenite is observed. The experimental thermal conditions are evaluated and linked to a Kurz-Giovanola-Trivedi (KGT) based solidification model. The modelling results show that the predictions from the multicomponent KGT model agree with the experimental observations. This work highlights the role of in situ XRD measurements for a fundamental understanding of the microstructure evolution during AM and for vali-dation of computational thermodynamics and kinetics models, facilitating parameter and alloy development for AM processes.
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| 6. |
- Magnusson, Hans, et al.
(författare)
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Atmosphere control during hot isostatic pressing of capsule-free materials
- 2019
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Ingår i: Euro PM 2019 Congress and Exhibition.
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Konferensbidrag (refereegranskat)abstract
- Producing components via powder yields a final product with few process steps. In order to get improved mechanical properties, final consolidation using hot isostatic pressing (HIP) is often performed. In this work, the aim is to include atmosphere control for HIP of capsule-free materials, e.g., additively manufactured components or conventionally pressed and sintered materials. Atmosphere control is applied for various purposes, such as carburising, e.g., traditional case hardening, or introducing an inert furnace atmosphere for HIP of sensitive materials. Carburisation experiments have been performed in a HIP-unit using methane as carbon source. The material response has been evaluated based on varying ratios of methane, time for carburising, ingoing densities, and alloy composition. The results show that porosity has a strong influence on carbon uptake, and lower density yields more carbon. As expected, a strong relation between added methane content and carbon uptake is also seen. Carburisation times of a few minutes gave little effect, however, 60 minutes gave approximately 500µm carburisation depth.
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| 7. |
- Magnusson, Hans, et al.
(författare)
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Atmosphere control during hot isostatic pressing of capsule free materials
- 2020
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Ingår i: Proceedings - Euro PM2020 Congress and Exhibition.
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Konferensbidrag (refereegranskat)abstract
- Producing components via powder metallurgy yields a final product with few process steps. In order to get improved mechanical properties, a final compaction using hot isostatic pressing (HIP) is often made. Capsule free HIP can be used for components produced via consolidation processes that yield a closed porosity at the surface, such as additive manufacturing (AM) or press and sinter methods that achieve high density. Without capsule, the compacted material is exposed to the atmosphere during HIP and it is, therefore possible to adjust the surface properties by carburising or nitriding before gas quenching, similar to conventional case hardening processes. The potential of this process has been evaluated in this work. More than 20 different HIP trials have been performed with variations of atmosphere, time, and temperature. Sinter steels and tool steels have been included in the trials. The materials are characterised and evaluated, and thereafter used to optimise this new process.
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| 8. |
- Maistro, Giulio, 1987, et al.
(författare)
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Understanding the microstructure-properties relationship of low-temperature carburized austenitic stainless steels through EBSD analysis
- 2017
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Ingår i: Surface and Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 322:322, s. 141-151
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Tidskriftsartikel (refereegranskat)abstract
- The present article is dedicated to the microstructural characterization of the surface layer of two different austenitic stainless steels, 304L and 904L, subjected to a low-temperature carburizing process (Kolsterising®,Bodycote) and a subsequent annealing at high-temperature. The carburizing treatment forms a hard expanded austenite in both materials. However, thermal decomposition occurs at high temperatures through precipitation of chromium-carbides, hence compromising the surface hardness of the treated materials.The purpose of this paper is to explore the potential applicability of electron backscatter diffraction (EBSD) technique to reveal the correlation between phase transformation and hardness. First of all, EBSD was used to create kernel average misorientation (KAM) maps of the modified surface layers to identify the internal strains. Moreover,the preferential sites for precipitation of chromium-compound during annealing were identified. We provehere that EBSD can provide useful information to distinguish the main hardening mechanisms within modifiedsurface layers at different annealing conditions. When combined with nano-indentation, X-ray diffraction(XRD) and glow discharge optical emission spectrometry (GDOES), an effective bridge between macro and microanalysis can be obtained. Solid solution hardening was found to be the dominant mechanismin as-carburized materials, with pre-existing strain promoting a higher supersaturation. In the annealed materials, the alloy composition and surface finish can also dictate the preferential sites of precipitation and can therefore affect the residual hardening.
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| 9. |
- Mellin, P., et al.
(författare)
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Environmental and safety aspects of AM metal powder recycling
- 2019
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Ingår i: Euro PM 2019 Congress and Exhibition.
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Konferensbidrag (refereegranskat)abstract
- Repeated recirculation of powder in AM processes ultimately results in a powder with degraded properties. We firstly discuss this topic and describe an experiment designed to understand the mechanisms behind the degradation. Secondly, we perform yield analysis for build jobs on a SLM 125 at RISE IVF. Further on, we consider the required resources and estimate the emitted carbon dioxide equivalents (kgCO2eq) during production of the PBF-LB fraction of two gas atomized powders. The first powder is a tool steel alloy that emits 3.1 kgCO2eq/kg; the second powder is Hastelloy X (HX) that emits 24.2 kgCO2eq/kg. The HX powder, if degraded, is hence very desirable to recycle. Producing 1 kg of PBF-LB fraction from recycled HX material causes 5.7 kgCO2eq vs 24.2 from virgin sources. Finally, we review the health and safety aspects of recirculation and recycling of powder.
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| 10. |
- Oikonomou, Christos, 1980, et al.
(författare)
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An XPS investigation on the thermal stability of the insulating surface layer of soft magnetic composite powder
- 2016
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Ingår i: Surface and Interface Analysis. - : Wiley. - 1096-9918 .- 0142-2421. ; 48:7, s. 445-450
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Tidskriftsartikel (refereegranskat)abstract
- Ferromagnetic powder particles coated with electrical insulating inorganic layers constitute composite materials used as powdered iron cores in electromagnetic applications. The aforementioned surface layers of these soft magnetic composites (SMC) are responsible for their high electrical resistivity. The perseverance of the coating through annealing processing step is crucial to the performance of finalized SMC products. In the present study, the thermal stability and microstructure of an iron phosphate based surface layer from a commercially available SMC powder were investigated by coupling various analytical techniques. The material was annealed at different temperature regimes, both in oxidizing (air) and inert (N-2) conditions in order to isolate the effect of temperature from the atmosphere composition on the chemical state of the coating. X-ray photoelectron spectroscopy (XPS) was utilized to assess the composition of the surface layer at all conditions. Moreover, phosphate-based chemical standards were processed and analyzed in a similar manner so as to facilitate the interpretation of the observed XPS spectra from the SMC powder. High resolution scanning electron microscopy, energy-dispersive X-ray spectrometry and X-ray diffraction were implemented in order to fully characterize the material under question. The results indicated the transition of the insulating layer from an amorphous state to fully crystalline under annealing in inert atmospheric conditions. Moreover, it was observed that phosphates are still present in the coating in mixture of valance states. Conversely, a thick iron oxide scale was formed under treatment in air, and no phosphorus signal was detected, indicating a total decomposition of the layer. Copyright (c) 2016 John Wiley & Sons, Ltd.
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