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- Allard, Christina, et al.
(författare)
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Rasbiologiskt språkbruk i statens rättsprocess mot sameby : DN Debatt 2015-06-11
- 2015
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Annan publikation (populärvet., debatt m.m.)abstract
- Statens hantering av forskningsresultat i rättsprocessen med Girjas sameby utgör ett hot mot Sverige som rättsstat och kunskapsnation. Åratal av svensk och internationell forskning underkänns och man använder ett språkbruk som skulle kunna vara hämtat från rasbiologins tid. Nu måste staten ta sitt ansvar och börja agera som en demokratisk rättsstat, skriver 59 forskare.
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| 7. |
- Nilsson Åhman, Hanna, et al.
(författare)
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An Enhanced Understanding of the Powder Bed Fusion-Laser Beam Processing of Mg-Y-3.9wt%-Nd-3wt%-Zr-0.5wt% (WE43) Alloy through Thermodynamic Modeling and Experimental Characterization
- 2022
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Ingår i: Materials. - : MDPI AG. - 1996-1944. ; 15:2
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Tidskriftsartikel (refereegranskat)abstract
- Powder Bed Fusion-Laser Beam (PBF-LB) processing of magnesium (Mg) alloys is gaining increasing attention due to the possibility of producing complex biodegradable implants for improved healing of large bone defects. However, the understanding of the correlation between the PBF-LB process parameters and the microstructure formed in Mg alloys remains limited. Thus, the purpose of this study was to enhance the understanding of the effect of the PBF-LB process parameters on the microstructure of Mg alloys by investigating the applicability of computational thermodynamic modelling and verifying the results experimentally. Thus, PBF-LB process parameters were optimized for a Mg WE43 alloy (Mg-Y-3.(9wt%)-Nd-3wt%-Zr-0.5wt%) on a commercially available machine. Two sets of process parameters successfully produced sample densities >99.4%. Thermodynamic computations based on the Calphad method were employed to predict the phases present in the processed material. Phases experimentally established for both processing parameters included alpha-Mg, Y2O3, Mg3Nd, Mg24Y5 and hcp-Zr. Phases alpha-Mg, Mg24Y5 and hcp-Zr were also predicted by the calculations. In conclusion, the extent of the applicability of thermodynamic modeling was shown, and the understanding of the correlation between the PBF-LB process parameters and the formed microstructure was enhanced, thus increasing the viability of the PBF-LB process for Mg alloys.
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| 8. |
- Nilsson Åhman, Hanna, et al.
(författare)
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Computational and Experimental Microstructural Characterization of A Magnesium WE43 Alloy Processed on A Commercially Available PBF-LB Machine
- 2020
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Ingår i: Proceedings - Euro PM2020 Congress and Exhibition. - : European Powder Metallurgy Association (EPMA).
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Konferensbidrag (refereegranskat)abstract
- Magnesium (Mg) has gained a lot of attention for its biodegradable properties. Additive manufacturing of Mg would further provide an opportunity to manufacture optimized structures for implants. However, much work remains to ensure stable processes and to understand the correlation between processing parameters, microstructure and related properties. The aim of this study was to process gas-atomized WE43 powder by Powder Bed Fusion-Laser Beam (PBF-LB) in a commercially available machine (EOS M290). The built material was characterized in terms of microstructure and composition and compared with the virgin powder. Thermodynamic computations based on the Calphad-method were for the first time employed to an additively manufactured Mg-alloy to predict phases present. Samples with above 99% density were successfully manufactured. The phases predicted using computational thermodynamics partly overlapped with phases observed experimentally. The study confirms the feasibility of using commercial PBF-LB systems for processing Mg-alloys, and the applicability of thermodynamic modelling to this system.
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| 9. |
- Nilsson Åhman, Hanna, et al.
(författare)
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Higher Laser power improves strength but reduces corrosion resistance of Mg WE43 processed by powder bed fusion
- 2024
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Ingår i: Materials Today Communications. - : Elsevier. - 2352-4928. ; 39
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Tidskriftsartikel (refereegranskat)abstract
- Powder bed fusion – laser beam (PBF-LB) of Mg alloys provides new possibilities for the production of complex structures with optimized designs, both for weight reduction in aerospace applications, as well as for patient-specific implants in orthopedic applications. However, even though numerous studies have been carried out on the topic, the influence of the individual PBF-LB process parameters on the microstructure and resulting material properties of Mg alloys remains ambiguous. Thus, this study aims to investigate the influence of laser power on the surface roughness, microstructure and resulting key material properties, namely corrosion resistance and mechanical performance. Samples were produced by PBF-LB from gas atomized Mg-4%Y-3%Nd-0.5%Zr (WE43) alloy powder, using three different laser powers: 60 W, 80 W, and 90 W. Contrary to expectation, the 90 W samples exhibited the highest degradation rate, while 60 W samples had the lowest, despite the latter having highest surface roughness and large internal pores. The higher degradation rate for the 90 W samples was instead found to stem from the near-surface microstructure. The higher energy input and subsequently reduced grain size, resulted in an increased amount of second phase precipitates than for the 60 W samples, thereby increasing the tendency for pitting via microgalvanic corrosion. For the tensile strength and elongation at break, the opposite trend was observed. Here, a reduction in grain size and an increase in precipitates for the 90 W samples were found to be beneficial. In conclusion, a definite influence of laser power on the formation of microstructure was observed, ultimately impacting the resulting corrosion and tensile properties of WE43. Future work should investigate the influence of other PBF-LB process parameters, with the aim of establishing an optimum balance between corrosion resistance and mechanical properties.
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- Nilsson Åhman, Hanna, et al.
(författare)
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Influence of Hot Isostatic Pressing on the corrosion resistance of Mg-4wt%Y-3wt%Nd processed by Laser - Powder Bed Fusion
- 2021
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Magnesium alloys have recently gained increased attention as a biodegradable metal implant. They can be biocompatible and have superior mechanical properties compared to the biodegradable polymeric implants used today. However, poor formability and excessive corrosion rates have limited the clinical implementation of Mg alloys to an extruded Mg-Y-Nd alloy .Additive manufacturing through Laser - Powder Bed Fusion (L-PBF) allows for the production of patient specific implant designs. Hot Isostatic Pressing (HIP) is a common method applied after printing to obtain fully dense materials for improved mechanical and corrosion properties. However, the amount of work done on L-PBF of Mg alloys remains limited. Esmaily et al found an improved corrosion resistance after HIP of a Mg-Y-Nd alloy processed by L-PBF, as evidenced by surface activity and H2 evolution over 24h. However, the influence of HIP on the long term corrosion properties and the part morphology after corrosion have not been evaluated. Herein we show that HIP can be highly detrimental to the long-term corrosion properties of a Mg alloy processed by L-PBF.
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| 12. |
- Nilsson Åhman, Hanna, et al.
(författare)
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Microstructural Origins of the Corrosion Resistance of a Mg-Y-Nd-Zr Alloy Processed by Powder Bed Fusion - Laser Beam
- 2022
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Ingår i: Frontiers in Bioengineering and Biotechnology. - : Frontiers Media S.A.. - 2296-4185. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- Magnesium alloys are biocompatible, biodegradable and have the ability to promote bone ingrowth, making them ideal candidate materials for replacing auto- and allografts in future treatments of large bone defects. Powder bed fusion-laser beam (PBF-LB) additive manufacturing of these alloys would further allow for the production of complex structures, optimized for bone grafting. However, the corrosion rates of structures processed by PBF-LB remain too high. An improved understanding of the influence of the microstructure generated during PBF-LB on the corrosion properties is considered key to their future implementation in implants. In this study, the effect of PBF-LB processing and subsequent hot isostatic pressing (HIP) on the microstructure and texture in different sample directions was studied and related to the corrosion behavior of a Mg-Y-Nd-Zr alloy. The results were compared with an extruded Mg-Y-Nd-Zr alloy. A higher amount of secondary phases resulted in a higher rate of localized corrosion for the PBF-LB processed material compared to that for the extruded one. Due to growth of the secondary phases, the corrosion rate was further increased after HIP. Moreover, a strong texture was observed in the PBF-LB material, and it was also enhanced in the HIP material. While this affected the electrochemical activity as measured by potentiodynamic polarization tests, any texture effect appeared to be masked by the contribution of the secondary phases in the longer-term mass change and hydrogen evolution tests. Future work should look further into the influence of individual process parameters on the microstructure and the resulting corrosion behavior of the material, to further clarify its interdependence.
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| 13. |
- Nilsson Åhman, Hanna
(författare)
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Powder Bed Fusion – Laser Beam of Mg alloy WE43 : Establishing the process – structure – properties relationship
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Powder bed fusion - laser beam (PBF-LB) of Mg alloy WE43 (Mg-4wt%Y-3wt%RE-Zr) has great potential for the development of future biodegradable metal implants, as well as aerospace lightweight materials. However, the work published thus far has mainly focused on obtaining a fully dense material, and the understanding of the relationship among the PBF-LB process parameters, structure and the resulting material properties remains limited. Thus, the aim of the thesis was to relate the main PBF-LB processing parameters to the formation of key microstructural features in WE43, and their effect on corrosion and tensile test properties. The work was carried out on PBF-LB processing units EOS M100 and EOS M290, and the investigated process parameters included laser power, laser scanning speed, hatch distance and sample wall thickness. Depending on the resulting thermal conditions, two main microstructural regions were observed. For process parameters resulting in warmer processes, such as higher laser powers and shorter scan lengths, mainly equiaxed dendritic grains were observed. The grains measured up to 10 µm in maximum diameter and exhibited a weak texture, with the inter-dendritic regions rich in Mg-RE intermetallic compunds. For process parameters resulting in conductive mode melting, mainly a lamellar structure was observed. The lamellar structure consisted in large grains with basal texture, and an intragranular structure where lines of Mg-RE intermetallic compunds precipitated parallel to the melt pool boundary. The larger grains had a maximum diameter of around 60 µm to 100 µm in the build direction, and up to 250 µm in the transverse direction, with a preferential growth along the melt pool.A larger number of dendritic grains was detrimental to the corrosion properties but resulted in higher tensile strength. The result was ascribed to the higher amount of Mg-RE intermetallics and the smaller grains, strengthening the material, but also causing microgalvanic corrosion. Hot isostatic pressing also resulted in growth of the secondary phases and was thus also detrimental to corrosion properties. While a change in hatch distance (40-60 mm) did not cause any dendritic structure to form, a higher hatch distance resulted in improved corrosion properties, but had minor effect on tensile properties, showing the possibilities of applying hatch distance variations to balance corrosion and tensile properties.In conclusion, the findings presented here show the possibilities of controlling the microstructure and thus the material properties by changing some of the key PBF-LB process parameters, and the major importance of understanding the relationship among process, structure and material properties of PBF-LB processed WE43.
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