| 1. |
- Alzati, L., et al.
(författare)
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PM parts sintered state improvement achieved by carbon source selection
- 2013
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Ingår i: 2013 International Conference on Powder Metallurgy and Particulate Materials, PowderMet 2013. - 9780985339739 ; , s. 516-524
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Konferensbidrag (refereegranskat)abstract
- In this work primary synthetic graphite, natural graphite and carbon black as carbon sources for PM parts sintering are compared. In order to highlight the different behaviour in demanding applications, special focus is on Cr-alloyed PM steels. Interrupted sintering trials have been run on specimens that were analysed both by advanced techniques (HR SEM, EDX) and Light Optical Microscopy, highlighting how sintering process rate can be positively affected by carbon source selection. Confirmation from tests run on Iron-Copper-Carbon is also presented. Implications for production of different typologies of PM parts is are also discussed. Test results on Key properties like Dimensional Stability (within one lot and lot-to-lot), Mechanical Performance (in terms of macro-Hardness, Tensile Rupture Strength) and solid-state Lubrication are also displayed.
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| 2. |
- Ananthanarayanan, Durga, et al.
(författare)
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Grain refinement in additively manufactured ferritic stainless steel by in situ inoculation using pre-alloyed powder
- 2021
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Ingår i: Scripta Materialia. - : Elsevier BV. - 1359-6462 .- 1872-8456. ; 194
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Tidskriftsartikel (refereegranskat)abstract
- For ferritic stainless steels, TiN has effectively been used as an inoculant to produce equiaxed grain structures in casting and welding. However, it is not established whether TiN would be an effective inoculant in additive manufacturing. In this study, the effectiveness of TiN as an inoculant in a ferritic stainless steel processed by laser powder-bed fusion is studied. An alloy without Ti is fabricated and compared to an alloy designed to form a high amount of TiN early during solidification. The work shows that the presence of TiN provides general grain refinement and that TiN-covered oxide particles are effective in enabling columnar-to-equiaxed transition in certain regions of the meltpool. The applied approach of pre-alloying powders with inoculant-forming elements offers a straightforward route to achieving fine, equiaxed grain structures in additively manufactured metallic materials. It also shows how oxygen present during the process can be utilized to nucleate effective inoculating phases.
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| 3. |
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| 4. |
- Bengtsson, S., et al.
(författare)
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New Aluminium Alloy Tailored For Powder Bed Fusion - Laser Beam Process
- 2022
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Ingår i: World PM 2022 Congress Proceedings.
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Konferensbidrag (refereegranskat)abstract
- The powder bed fusion - laser beam (PBF-LB) process can produce parts with complex geometry. Light weight designs can be created and by using light alloys further weight savings can be achieved. However, minimizing printing defects using standard aluminium alloys, such as 2000, 6000 and 7000 series alloys, have proved to be difficult since they are all prone to solidification cracking. In the present study, two aluminium alloys are addressed: The first alloy is the AlSi10Mg alloy known for easy printing and consistent quality in PBF-LB printing process. The second material is a novel alloy from self-developed Al-Mn-Cr-Zr family of alloys designed to inherently resist solidification cracking, while also providing strong ageing response. The quality of printing and the resulting mechanical properties are compared. The results show that the new material prints in a robust way and that the mechanical properties are superior to those of AlSi10Mg.
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| 5. |
- Bergman, Ola, et al.
(författare)
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Analysis of oxide reduction during sintering of Cr-alloyed steel powder through photoacoustic spectroscopy measurements
- 2009
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Ingår i: Proceedings of the Euro International Powder Metallurgy Congress and Exhibition, Euro PM 2009. - : European Powder Metallurgy Association (EPMA). - 9781899072088 ; 3
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Konferensbidrag (refereegranskat)abstract
- The usage of steel powders prealloyed with chromium in PM components for high performance applications is steadily increasing. Excellent mechanical properties are achieved with these powder grades, provided that the processing into components is accurately done. Photoacoustic spectroscopy (PAS) technique has been used here to study oxide reduction during sintering in 90N2/10H2 atmosphere of test specimens based on 3%Cr-0.5%Mo prealloyed powders with 0.5% C added. Results from performed reduction trials show that Fe oxides on the powder surfaces are removed by H2 reduction early in the heating stage of the process. Carbothermal reduction is the main mechanism for reduction of stable Cr-containing oxides from 900°C and above. Efficient Cr oxide reduction requires a sintering temperature of at least around 1200°C. Therefore, small oxide particles remain in the material after sintering at 1120°C for 30 minutes. However, such oxides have earlier been shown to have no significant influence on mechanical properties.
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| 6. |
- Bojestig, Eric, 1991, et al.
(författare)
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Laser powder bed fusion of bronze - Process optimization and influence on microstructure and mechanical properties
- 2019
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Ingår i: Euro PM 2019 Congress and Exhibition.
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Konferensbidrag (refereegranskat)abstract
- As the interest in additive manufacturing increases, so does the demand for new materials. Among these are the copper alloys due to their good bearing properties, corrosion resistance and electrical conductivity. When attempting to print Cu-base materials with laser powder bed fusion, their low laser absorption and high thermal conductivity restricts the attainable local heat absorption in the material and hence the manufacturability with respect full density processing, especially for pure Cu. Alloyed Cu constitutes, however, less challenge in this respect. Hence, spherical gas atomized bronze (Cu-11Sn) powder was used and all printing was performed in an EOS M100 machine in argon atmosphere. Design of experiment method was used to determine optimized process parameters with respect to laser power, scan speed and hatch distance. Full density (99.9%) parts were successfully fabricated with UTS>400 MPa and the fine cellular microstructure was displayed. Furthermore, thin wall capacity of 150 µm was demonstrated.
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| 7. |
- Bojestig, Eric, 1991, et al.
(författare)
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Surface chemical analysis of copper powder used in additive manufacturing
- 2020
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Ingår i: Surface and Interface Analysis. - : Wiley. - 1096-9918 .- 0142-2421. ; 52:12, s. 1104-1110
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Tidskriftsartikel (refereegranskat)abstract
- Additive manufacturing (AM) has during years gained significant interest owing to its endless component design possibilities. One of the most popular AM techniques is laser powder bed fusion (LPBF), which selectively melts metal powder layer-by-layer in a chamber with protective argon atmosphere. This technique is attractive for realizing Cu-based products in which the high electrical conductivity of Cu is combined with component design possibilities. The successful use of Cu powder not only poses challenges owing to the high reflectivity and thermal conductivity of Cu but also involves the important concern of controlling the powder surface chemistry since the powder surface constitutes the main source of oxygen. It is of crucial importance to control the oxygen level in order to maintain good electrical conductivity and brazing ability of the AM-fabricated Cu-part. In LPBF, fine spherical powder with size of 10-60 mu m is used, providing significant specific surface area, and this powder is also usually recycled several times, and hence, the role of powder surface chemistry is evident. Two kinds of copper powder with purities 99.70 and 99.95 wt% were analysed in both virgin and in used conditions after numerous printing cycles using LPBF. The powder was analysed by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). A clear difference between the two powder grades in terms of surface chemistry was observed. The oxide thickness and bulk oxygen content increased for both powder grades after recycling. The surface oxides under different conditions are identified and the effect of powder purity on the oxide formed is discussed.
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| 8. |
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| 9. |
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| 10. |
- Borgström, Henrik, 1975, et al.
(författare)
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Optimising grey iron powder compacts
- 2009
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Ingår i: Powder Metallurgy. - 0032-5899 .- 1743-2901. ; 52:4, s. 291-297
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Tidskriftsartikel (refereegranskat)abstract
- The grey iron microstructure Fe–2C–2Si powder based compact is tailored by different kinds of in situ and post sintering processing. This has been achieved by combining thermodynamic and kinetics modelling of microstructure development with sintering and controlled heat treatment experiments of tensile test specimens die compacted at 600 MPa. Applying optimised sintering conditions led to a grey iron like microstructure with 95% relative sintered density. Sinter hardening the compacts led to 500 MPa in yield strength and 600 MPa in ultimate tensile strength in combination with ductile fracture. Quenched and tempered condition showed the same strength values, but combined with brittle fracture due to martensitic structure. Pore rounding and partial pore filling by graphite were obtained by austenising isothermal hold during the cooling of the sintering cycle.
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