| 1. |
- Goel, Sneha, 1993-, et al.
(författare)
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Residual stress determination by neutron diffraction in powder bed fusion-built Alloy 718: Influence of process parameters and post-treatment
- 2020
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Ingår i: Materials and Design. - : Elsevier BV. - 1873-4197 .- 0264-1275. ; 195
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Tidskriftsartikel (refereegranskat)abstract
- Alloy 718 is a nickel-based superalloy that is widely used as a structural material for high-temperature applications. One concern that arises when Alloy 718 is manufactured using powder bed fusion (PBF) is that residual stresses appear due to the high thermal gradients. These residual stresses can be detrimental as they can degrade mechanical properties and distort components. In this work, residual stresses in PBF built Alloy 718, using both electron and laser energy sources, were measured by neutron diffraction. The effects of process parameters and thermal post-treatments were studied. The results show that thermal post-treatments effectively reduce the residual stresses present in the material. Moreover, the material built with laser based PBF showed a higher residual stress compared to the material built with electron-beam based PBF. The scanning strategy with the lower amount of residual stresses in case of laser based PBF was the chessboard strategy compared to the bi-directional raster strategy. In addition, the influence of measured and calculated lattice spacing (d0) on the evaluated residual stresses was investigated.
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| 2. |
- Neikter, Magnus, 1988-, et al.
(författare)
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Fatigue Crack Growth of Electron Beam Melted Ti-6Al-4V in High-Pressure Hydrogen
- 2020
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Ingår i: Materials. - : MDPI. - 1996-1944. ; 13:6
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Tidskriftsartikel (refereegranskat)abstract
- Titanium-based alloys are susceptible to hydrogen embrittlement (HE), a phenomenon that deteriorates fatigue properties. Ti-6Al-4V is the most widely used titanium alloy and the effect of hydrogen embrittlement on fatigue crack growth (FCG) was investigated by carrying out crack propagation tests in air and high-pressure H2 environment. The FCG test in hydrogen environment resulted in a drastic increase in crack growth rate at a certain Δ K, with crack propagation rates up to 13 times higher than those observed in air. Possible reasons for such behavior were discussed in this paper. The relationship between FCG results in high-pressure H2 environment and microstructure was investigated by comparison with already published results of cast and forged Ti-6Al-4V. Coarser microstructure was found to be more sensitive to HE. Moreover, the electron beam melting (EBM) materials experienced a crack growth acceleration in-between that of cast and wrought Ti-6Al-4V.
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| 3. |
- Segerstark, Andreas, 1988-, et al.
(författare)
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Processing of high-performance materials by laser-directed energy deposition with powders
- 2023. - 1.
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Ingår i: Additive Manufacturing of High-Performance metallic Materials. - : Elsevier. - 9780323918855 - 9780323913829 ; , s. 230-259
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Bokkapitel (refereegranskat)abstract
- Processing of high-performance materials by Directed Energy Deposition with Powders (L-DED-P) is frequently utilized in repair as well as remanufacturing apart from manufacturing. One benefit of the process is the low heat input in comparison to, i.e., L-DED with wire which is preferable regarding residual stresses and distortion. However, care must be taken to minimize defects that are at stake in forming if process parameters are not adequately adapted to the specific application. There is a strong correlation between the process parameters and metallurgical behavior which in turn give rise to potential defects and the final performance of the part to be produced. This chapter gives an overview of the processmicrostructure-defect relations that are of importance in L- DED-P processing.
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| 4. |
- Alvi, Sajid, et al.
(författare)
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Tribological performance of Ti6Al4V at elevated temperatures fabricated by electron beam powder bed fusion
- 2021
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Ingår i: Tribology International. - : Elsevier. - 0301-679X .- 1879-2464. ; 153
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Tidskriftsartikel (refereegranskat)abstract
- Electron beam powder bed fusion (EBPBF) is a beneficial processing route to fabricate Ti6Al4V alloy for aerospace applications due to its relatively low lead time and the possibility of topology optimization. The dry sliding wear behavior of EBPBF-Ti6Al4V against steel and alumina counterballs from room temperature (RT) to 500 °C was investigated to evaluate the influence of EBPBF processing and microstructure on the wear properties for broadening the application criteria of this lightweight alloy. The wear tests revealed that the wear rate decreased with increasing temperature due to formation of stable oxide glaze layer. This study reveals elevated temperature sliding wear behavior, wear mechanisms and microstructural changes below the wear track of EBPBF Ti6Al4V alloy against steel and alumina counterbodies.
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| 5. |
- Andersson, Joel, 1981-, et al.
(författare)
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Welding of special alloys
- 2023
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Ingår i: Welding of Metallic Materials. - : Elsevier. - 9780323906708 - 9780323905527 ; , s. 279-316
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Specialty alloys are a broad group of materials providing superior properties to common materials and are therefore used for more demanding applications. Specialty alloys require sophisticated manufacturing routes, e.g., vacuum metallurgy, to account for all the alloying elements needed to finalize the specific alloy for its intended purpose. The alloys of Duplex stainless steels, superalloys, and Titanium alloys are examples of so-called specialty alloys where aerospace, chemical, and petrochemical industries are just a few areas mentioned where these specialty alloys are frequently used. Duplex stainless steel, had superior mechanical properties and corrosion resistance, making them a sustainable choice for a wide variety of applications i.e., petrochemical industries. The superalloys, and especially the precipitation hardening ones belong to a unique plethora of alloys commonly used in aerospace as well as land-based gas turbines which possess superb mechanical performance at elevated temperatures. However, the superalloys are unfortunately very challenging to process, not at least regarding weld cracking. With their high specific strength and corrosion resistance, titanium alloys are favorable for numerous applications. However, they react readily with oxygen at elevated temperatures and therefore inert atmosphere must be used during welding.
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| 6. |
- Edin, Emil, et al.
(författare)
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Stress relief heat treatment and mechanical properties of laser powder bed fusion built 21-6-9 stainless steel
- 2023
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Ingår i: Materials Science and Engineering A. - : Elsevier. - 0921-5093 .- 1873-4936. ; 868
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Tidskriftsartikel (refereegranskat)abstract
- In this work, the effectiveness of residual stress relief annealing on a laser powder bed fusion (L-PBF) manufactured austenitic stainless steel, alloy 21-6-9 was investigated. Residual stress levels were gauged using geometrical distortion and relaxation testing results. In the investigated temperature interval (600–850 °C), shape stability was reached after subjecting the as-built material to an annealing temperature of 850 °C for 1 h. Microstructural characterization and tensile testing were also performed for each annealing temperature to evaluate the alloy's thermal stability and the resulting tensile properties. In the as-built state, a yield strength (YS) of 640 MPa, ultimate tensile strength (UTS) of 810 MPa and 4D elongation of 47% were measured. Annealing at 850 °C for 1 h had little measurable effect on ductility (48% 4D elongation) while still having a softening effect (UTS = 775 MPa, YS = 540 MPa). From the microstructural characterization, cell-like features were observed sporadically in the annealed condition and appeared stable up until 800 °C after which gradual dissolution began, with the last remnants disappearing after subjecting the material to 900 °C for 1 h.
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| 7. |
- Heidarzadeh, Akbar, et al.
(författare)
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Post-treatment of additively manufactured Fe-Cr-Ni stainless steels by high pressure torsion : TRIP effect
- 2021
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Ingår i: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 811
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Tidskriftsartikel (refereegranskat)abstract
- High pressure torsion (HPT) at room temperature was used for post-treatment of additively manufactured Fe-Cr-Ni stainless steel with 12.9 wt. % Ni as a very strong austenite stabilizer. The results showed that HPT caused a considerable increase in nanohardness of the additively manufactured samples. In contrast with thermodynamic equilibrium-state modeling, a phase transformation from FCC to HCP structure occurred, leading to the formation of ε-martensite during HPT on high angle boundaries, low angle boundaries, and dislocation cells with no detection of deformation twins. It was demonstrated that the combination of additive manufacturing thanks to the high density of dislocations after solidification and HPT process expands the opportunities of both methods to control deformation mechanisms in stainless steels leading to different phase and microstructural features. Thus, the outcome of this study provides a fundamental basis to design advanced structural materials.
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| 8. |
- Karimi Neghlani, Paria, 1986-, et al.
(författare)
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Processing of high-performance materials by electron beam-powder bed fusion
- 2023. - 1.
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Ingår i: Additive Manufacturing of High-Performance Metallic Materials. - : Elsevier. - 9780323918855 - 9780323913829 ; , s. 103-181
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Bokkapitel (refereegranskat)abstract
- Electron beam-powder bed fusion (EB-PBF) is a process that uses a highly intense electron beam to melt metallic powders to create parts. In comparison to a conventional process, EB-PBF is more efficient at producing customized and specific parts in industries such as aerospace, space, and medical. Additionally, the EB-PBF process is used to manufacture highly complex parts for which other technologies would be prohibitively expensive or difficult to apply; increased geometric complexity does not necessarily imply increased cost. However, because the interaction of the electron beam with the powder and substrate material is complex, a high level of knowledge is required to master the skill of producing structurally sound components. This chapter discusses crucial features of the process parametermicrostructure-defect relationship that must be taken into Electron beam-powder bed fusion (EB-PBF) is a process that uses a highly intense electron beam to melt metallic powders to create parts. In comparison to a conventional process, EB-PBF is more efficient at producing customized and specific parts in industries such as aerospace, space, and medical. Additionally, the EB-PBF process is used to manufacture highly complex parts for which other technologies would be prohibitively expensive or difficult to apply; increased geometric complexity does not necessarily imply increased cost. However, because the interaction of the electron beam with the powder and substrate material is complex, a high level of knowledge is required to master the skill of producing structurally sound components. This chapter discusses crucial features of the process parametermicrostructure-defect relationship that must be taken into account in order to generate sufficiently sound builds of highperformance materials employing EB-PBF.
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| 9. |
- Mahade, Satyapal, et al.
(författare)
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Processing of high-performance materials by laser directed energy deposition with wire
- 2023. - 1.
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Ingår i: Additive Manufacturing of High-Performance metallic Materials. - : Elsevier. - 9780323918855 - 9780323913829 ; , s. 260-305
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Bokkapitel (refereegranskat)abstract
- Processing of metallic materials by Laser Directed Energy Deposition (LDED), with Wire (w) as the feedstock, enables the manufacturing of high precision, near-net shape components that require minimal postmachining, without compromising the performance. L-DEDw has also shown the capability to add intricate features on large structures, which makes it an attractive fabrication technique for aerospace application. The key merits of wire as the feedstock when compared to powder include; higher deposition rates, low porosity in the deposited material, excellent surface finish, and, ∼ 100% utilization of the feedstock. However, despite the attractive merits, the difference in solidification rates during L-DEDw processing when compared to other fabrication routes could induce high residual stresses, which can be detrimental to the integrity of cracksensitive alloys. Additionally, there exists an inherent challenge during L-DEDw fabrication, where controlling the process variables to ensure stable deposition conditions becomes essential to achieve repeatable, and desired results. The recent advancements in the area of monitoring and control systems, and their integration with L-DEDw processing, have enabled to overcome the processing instability related challenges. Furthermore, different L-DEDw processing strategies for alleviating residual stresses (tensile) accumulation in the deposits are discussed, which could enable defectfree, high-performance component fabrication. Although the utilization of L-DEDw for processing diverse alloy systems has been explored in the literature, the current chapter's scope is restricted to L-DEDw processing of Nickel-based and Titanium-based alloys, which are often utilized in the aeroengine. This work aims to provide a holistic perspective and shed light on the state-of-the-art, recent developments, sustainability aspects and future directions for L-DEDw processed, highperformance Ni-based and Ti-based alloys.
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| 10. |
- Maimaitiyili, Tuerdi, et al.
(författare)
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Residual Lattice Strain and Phase Distribution in Ti-6Al-4V Produced by Electron Beam Melting
- 2019
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Ingår i: Materials. - : MDPI. - 1996-1944. ; 12:4
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Tidskriftsartikel (refereegranskat)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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