| 1. |
- Moritz, Juliane, et al.
(författare)
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Electron beam powder bed fusion of γ‐titanium aluminide : Effect of processing parameters on part density, surface characteristics and aluminum content
- 2021
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Ingår i: Metals. - : MDPI. - 2075-4701. ; 11:7
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Tidskriftsartikel (refereegranskat)abstract
- Gamma titanium aluminides are very interesting for their use in high‐performance applications such as aircraft engines due to their low density, high stiffness and favorable hightemperature properties. However, the pronounced brittleness of these intermetallic alloys is a major challenge for their processing through conventional fabrication methods. Additive manufacturing by means of electron beam powder bed fusion (EB‐PBF) significantly improves the processability of titanium aluminides due to the high preheating temperatures and facilitates complex components. The objective of this study was to determine a suitable processing window for EB‐PBF of the TNM‐B1 alloy (Ti‐43.5Al‐4Nb‐1Mo‐0.1B), using an increased aluminum content in the powder raw material to compensate for evaporation losses during the process. Design of experiments was used to evaluate the effect of beam current, scan speed, focus offset, line offset and layer thickness on porosity. Top surface roughness was assessed through laser scanning confocal microscopy. Scanning electron microscopy, electron backscatter diffraction (EBSD) and energydispersive X‐ray spectroscopy (EDX) were used for microstructural investigation and to analyze aluminum loss depending on the volumetric energy density used in EB‐PBF. An optimized process parameter set for achieving part densities of 99.9% and smooth top surfaces was derived. The results regarding microstructures and aluminum evaporation suggest a solidification via the β‐phase.
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| 2. |
- Moritz, Juliane, et al.
(författare)
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Influence of Electron Beam Powder Bed Fusion Process Parameters at Constant Volumetric Energy Density on Surface Topography and Microstructural Homogeneity of a Titanium Aluminide Alloy
- 2023
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Ingår i: Advanced Engineering Materials. - : John Wiley & Sons. - 1438-1656 .- 1527-2648. ; 25:15
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Tidskriftsartikel (refereegranskat)abstract
- In powder bed fusion additive manufacturing, the volumetric energy density E V is a commonly used parameter to quantify process energy input. However, recent results question the suitability of E V as a design parameter, as varying the contributing parameters may yield different part properties. Herein, beam current, scan velocity, and line offset in electron beam powder bed fusion (PBF-EB) of the titanium aluminide alloy TNM–B1 are systematically varied while maintaining an overall constant E V. The samples are evaluated regarding surface morphology, relative density, microstructure, hardness, and aluminum loss due to evaporation. Moreover, the specimens are subjected to two different heat treatments to obtain fully lamellar (FL) and nearly lamellar (NLγ) microstructures, respectively. With a combination of low beam currents, low-to-intermediate scan velocities, and low line offsets, parts with even surfaces, relative densities above 99.9%, and homogeneous microstructures are achieved. On the other hand, especially high beam currents promote the formation of surface bulges and pronounced aluminum evaporation, resulting in inhomogeneous banded microstructures after heat treatment. The results demonstrate the importance of considering the individual parameters instead of E V in process optimization for PBF-EB.
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| 3. |
- Moritz, Juliane, et al.
(författare)
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Influence of Two-Step Heat Treatments on Microstructure and Mechanical Properties of a β-Solidifying Titanium Aluminide Alloy Fabricated via Electron Beam Powder Bed Fusion
- 2023
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Ingår i: Advanced Engineering Materials. - : John Wiley & Sons. - 1438-1656 .- 1527-2648. ; 25:2
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Tidskriftsartikel (refereegranskat)abstract
- Additive manufacturing technologies, particularly electron beam powder bed fusion (PBF-EB/M), are becoming increasingly important for the processing of intermetallic titanium aluminides. This study presents the effects of hot isostatic pressing (HIP) and subsequent two-step heat treatments on the microstructure and mechanical properties of the TNM-B1 alloy (Ti–43.5Al–4Nb–1Mo–0.1B) fabricated via PBF-EB/M. Adequate solution heat treatment temperatures allow the adjustment of fully lamellar (FL) and nearly lamellar (NL-β) microstructures. The specimens are characterized by optical microscopy and scanning electron microscopy (SEM), X-ray computed tomography (CT), X-ray diffraction (XRD), and electron backscatter diffraction (EBSD). The mechanical properties at ambient temperatures are evaluated via tensile testing and subsequent fractography. While lack-of-fusion defects are the main causes of failure in the as-built condition, the mechanical properties in the heat-treated conditions are predominantly controlled by the microstructure. The highest ultimate tensile strength is achieved after HIP due to the elimination of lack-of-fusion defects. The results reveal challenges originating from the PBF-EB/M process, for example, local variations in chemical composition due to aluminum evaporation, which in turn affect the microstructures after heat treatment. For designing suitable heat treatment strategies, particular attention should therefore be paid to the microstructural characteristics associated with additive manufacturing.
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| 4. |
- Moritz, Juliane, et al.
(författare)
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Locally Adapted Microstructures in an Additively Manufactured Titanium Aluminide Alloy Through Process Parameter Variation and Heat Treatment
- 2023
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Ingår i: Advanced Engineering Materials. - : John Wiley & Sons. - 1438-1656 .- 1527-2648. ; 25:2
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Tidskriftsartikel (refereegranskat)abstract
- Electron beam powder bed fusion (PBF-EB/M) has been attracting great research interest as a promising technology for additive manufacturing of titanium aluminide alloys. However, challenges often arise from the process-induced evaporation of aluminum, which is linked to the PBF-EB/M process parameters. This study applies different volumetric energy densities during PBF-EB/M processing to deliberately adjust the aluminum contents in additively manufactured Ti–43.5Al–4Nb–1Mo–0.1B (TNM-B1) samples. The specimens are subsequently subjected to hot isostatic pressing (HIP) and a two-step heat treatment. The influence of process parameter variation and heat treatments on microstructure and defect distribution are investigated using optical and scanning electron microscopy, as well as X-ray computed tomography (CT). Depending on the aluminum content, shifts in the phase transition temperatures can be identified via differential scanning calorimetry (DSC). It is confirmed that the microstructure after heat treatment is strongly linked to the PBF-EB/M parameters and the associated aluminum evaporation. The feasibility of producing locally adapted microstructures within one component through process parameter variation and subsequent heat treatment can be demonstrated. Thus, fully lamellar and nearly lamellar microstructures in two adjacent component areas can be adjusted, respectively.
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| 5. |
- Schwitter, Juerg, et al.
(författare)
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MR-IMPACT : comparison of perfusion-cardiac magnetic resonance with single-photon emission computed tomography for the detection of coronary artery disease in a multicentre, multivendor, randomized trial
- 2008
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Ingår i: European Heart Journal. - : Oxford University Press (OUP). - 0195-668X .- 1522-9645. ; 29:4, s. 480-9
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Tidskriftsartikel (refereegranskat)abstract
- AIMS: To determine in a multicentre, multivendor trial the diagnostic performance for perfusion-cardiac magnetic resonance (perfusion-CMR) in comparison with coronary X-ray angiography (CXA) and single-photon emission computed tomography (SPECT). METHODS AND RESULTS: Of 241 eligible patients from 18 centres, 234 were randomly dosed with 0.01, 0.025, 0.05, 0.075, or 0.1 mmol/kg Gd-DTPA-BMA (Omniscantrade mark, GE-Healthcare) per stress (0.42 mg/kg adenosine) and rest perfusion study. Coronary artery disease (CAD) was defined as diameter stenosis > or =50% on quantitative CXA. Five CMR and eight SPECT studies (of 225 complete studies) were excluded from analyses due to inadequate quality (three blinded readers scored per modality). The comparison of CMR vs. SPECT was based on receiver operating characteristic (ROC) analysis. Perfusion-CMR at the optimal CM dose (0.1 mmol/kg) had similar performance as SPECT, if only the SPECT studies of the 42 patients with this dose were considered [area under ROC curve (AUC): 0.86 +/- 0.06 vs. 0.75 +/- 0.09 for SPECT, P = 0.12]; however, diagnostic performance of perfusion-CMR was better vs. the entire SPECT population (AUC: 0.67 +/- 0.05, n = 212, P = 0.013). CONCLUSIONS: In this multicentre, multivendor trial, ROC analyses suggest perfusion-CMR as a valuable alternative to SPECT for CAD detection showing equal performance in the head-to-head comparison. Comparing perfusion-CMR with the entire SPECT population suggests CMR superiority over SPECT, which warrants further evaluation in larger trials.
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| 6. |
- Seidel, André, et al.
(författare)
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Hybrid Additive Manufacturing of Gamma Titanium Aluminide Space Hardware
- 2018
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Ingår i: Contributed Papers from Materials Science and Technology 2018 (MS&T18). - : Association for Iron and Steel Technology (AISTECH). ; , s. 13-21
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Konferensbidrag (refereegranskat)abstract
- A major part of laser additive manufacturing focuses on the fabrication of metallic parts for applications in the space and aerospace sector. Especially the processing of the very brittle titanium aluminides can be particularly challenging [1-2].In the present paper a gamma titanium aluminide (γ-TiAl) nozzle, manufactured via Electron Beam Melting (EBM), is extended and adapted via hybrid Laser Metal Deposition (LMD). The presented approach considers critical impacts like processing temperatures, temperature gradients and solidification conditions with particular regard to crucial material properties like the phenomena of lamellar interface cracking [3-6]. Furthermore, the potential of microstructural tailoring is going to be addressed by the process-specific manipulation of the composition and/or microstructure.In addition to this, selected destructive and non-destructive testing is performed in order to prove the material properties. Finally, post manufacturing and surface modification are briefly addressed.
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| 7. |
- Seidel, André, et al.
(författare)
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Intrinsic Heat Treatment Within Additive Manufacturing of Gamma Titanium Aluminide Space Hardware
- 2019
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Ingår i: JOM. - : Springer. - 1047-4838 .- 1543-1851. ; 71:4, s. 1513-1519
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Tidskriftsartikel (refereegranskat)abstract
- A major part of laser additive manufacturing focuses on the fabrication of metallic parts for applications in the space and aerospace sectors. Especially, the processing of the very brittle titanium aluminides can be particularly challenging because of their distinct tendency to lamellar interface cracking. In the present paper, a gamma titanium aluminide (γ-TiAl) nozzle, manufactured via electron beam melting, is extended and adapted via hybrid laser metal deposition. The presented example considers a new field of application for this class of materials and approaches the process-specific manipulation of the composition and/or microstructure via the adjustment of processing temperatures, temperature gradients and solidification conditions. Furthermore, intrinsic heat treatment is investigated for electron beam melting and laser metal deposition with powder, and the resulting influence is releated to conventional processing.
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| 8. |
- Seidel, A., et al.
(författare)
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Surface modification of additively manufactured gamma titanium aluminide hardware
- 2019
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Ingår i: Journal of laser applications. - : Laser Institute of America. - 1042-346X .- 1938-1387. ; 31:2
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Tidskriftsartikel (refereegranskat)abstract
- A major part of additive manufacturing focuses on the fabrication of metallic parts in different fields of applications. Examples include components for jet engines and turbines and also implants in the medical sector. Titanium alloys represent a material group which is used cross-sectoral in a large number of applications. The present paper addresses the titanium aluminides in particular. These materials have a low density in combination with a comparatively high-temperature resistance [G. Sauthoff, Intermetallics (Wiley-VCH Verlag, Weinheim, Germany, 2008)]. Nevertheless, the laser material processing is rather challenging because of their distinct tendency to lamellar interface cracking. This requires tailored processing strategies and equipment [C. Leyens et al., in Ti-2015: The 13th World Conference on Titanium, Symposium 5. Intermetallics and MMCs, 16–20 August 2015, San Diego, CA (The Minerals, Metals & Materials Society, Pittsburgh, PA, 2016)]. This work focusses on tailored processing of titanium aluminides with focus on the process-dependent surface characteristics. This includes the as-built status for powder bed processing and direct laser metal deposition but also the surface modification via post and/or advanced machining. Finally, comprehensive characterization is performed using destructive as well as nondestructive testing methods. The latter includes 3D scanning, computed tomography, microscopic analysis, and, in particular, surface roughness measurements.
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