| 1. |
- Adegoke, Olutayo, 1979-, et al.
(författare)
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Influence of laser powder bed fusion process parameters on the microstructure and cracking susceptibility of nickel-based superalloy Alloy 247LC
- 2022
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Ingår i: Results in Materials. - : Elsevier. - 2590-048X. ; 13
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Tidskriftsartikel (refereegranskat)abstract
- Microstructures of material conditions of nickel-based superalloy Alloy 247LC fabricated using laser powder bed fusion (L-PBF) were investigated. Experiments designed in a prior study revealed the L-PBF process parameters for which the material conditions displayed a reduced susceptibility to cracking. Certain process parameters produced material conditions with an increased susceptibility to cracking. In this study, the material conditions were investigated in detail to reveal their microstructure and to determine the cause of cracking. The reason for the transition between a reduced to an increased susceptibility to cracking was examined. The results revealed solidification cracking occurred at high-angle grain boundaries. Solidification cracking may have been promoted at high-angle grain boundaries because of the undercooling contribution of the grain boundary energy. Furthermore, Si segregation was observed in the cracks. Thus, the presence of Si most likely promoted solidification cracking. It was observed that a high crack density, which occurred in the high energy density material condition, was associated with a large average grain size. The fact that certain combination of process parameters produced microstructures with a low susceptibility to cracking, indicates that reliable Alloy 247LC material may be printed using L-PBF by employing improved process parameters. © 2022
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| 2. |
- Adegoke, Olutayo, 1979-, et al.
(författare)
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Influence of laser powder bed fusion process parameters on the microstructure of solution heat-treated nickel-based superalloy Alloy 247LC
- 2022
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Ingår i: Materials Characterization. - : Elsevier. - 1044-5803 .- 1873-4189. ; 183
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Tidskriftsartikel (refereegranskat)abstract
- In this study, Alloy 247LC samples were built with different laser powder bed fusion (L-PBF) process parameters. The samples were then subjected to solution heat treatment at 1260 °C for 2 h. The grain size of all the samples increased significantly after the heat treatment. The relationship between the process parameters and grain size of the samples was investigated by performing a design of experiment analysis. The results indicated that the laser power was the most significant process parameter that influenced the grain height and aspect ratio. The laser power also significantly influenced the grain width. The as-built and as-built + heat-treated samples with high, medium, and low energy densities were characterized using a field emission gun scanning electron microscope equipped with an electron backscatter diffraction detector. The micrographs revealed that the cells present in the as-built samples disappeared after the heat treatment. Isolated cases of twinning were observed in the grains of the as-built + heat-treated samples. The disappearance of cells, increase in the grain size, and appearance of twins suggested that recrystallization occurred in the alloy after the heat treatment. The occurrence of recrystallization was confirmed by analyzing the grain orientation spread of the alloy, which was lower and more predominantly <1° in the as-built + heat-treated conditions than in the as-built conditions. The microhardness of the as-built + heat-treated samples were high which was plausible because γ’ precipitates were observed in the samples. However, the L-PBF process parameters had a very low correlation with the microhardness of the as-built + heat-treated samples.
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| 3. |
- Adegoke, Olutayo, et al.
(författare)
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Scanning electron microscopy and atom probe tomography characterization of laser powder bed fusion precipitation strengthening nickel-based superalloy
- 2023
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Ingår i: Micron. - 0968-4328 .- 1878-4291. ; 171
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Tidskriftsartikel (refereegranskat)abstract
- Atom probe tomography (APT) was utilized to supplement scanning electron microscopy (SEM) characterizationof a precipitation strengthening nickel-based superalloy, Alloy 247LC, processed by laser powder bed fusion (LPBF). It was observed that the material in the as-built condition had a relatively high strength. Using both SEMand APT, it was concluded that the high strength was not attributed to the typical precipitation strengtheningeffect of γ’. In the absence of γ’ it could be reasonably inferred that the numerous black dots observed in thecells/grains with SEM were dislocations and as such should be contributing significantly to the strengthening.Thus, the current investigation demonstrated that relatively high strengthening can be attained in L-PBF even inthe absence of precipitated γ’. Even though γ’ was not precipitated, the APT analysis displayed a nanometer scalepartitioning of Cr that could be contributing to the strengthening. After heat-treatment, γ’ was precipitated and itdemonstrated the expected high strengthening behavior. Al, Ta and Ti partitioned to γ’. The strong partitioningof Ta in γ’ is indicative that the element, together with Al and Ti, was contributing to the strain-age crackingoccurring during heat-treatment. Cr, Mo and Co partitioned to the matrix γ phase. Hf, Ta, Ti and W were found inthe carbides corroborating previous reports that they are MC.
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| 4. |
- Harlin, Peter, 1974-
(författare)
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Metal powders for additive manufacturing of superalloys and titanium alloys
- 2023. - 1
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Ingår i: Additive Manufacturing of High-Performance metallic Materials. - : Elsevier. - 9780323918855 - 9780323913829 ; , s. 41-82
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Bokkapitel (refereegranskat)abstract
- This chapter explores the fundamentals of powders for metaladditive manufacturing and includes descriptions of powdermanufacturing processes, powder properties, and how theproperties affect the powder performance in metal additivemanufacturing processes. The powder manufacturing processeswill be restricted to processes used for titanium alloys andsuperalloys. Related to the powder properties, the reader will beintroduced to both characteristics of discrete particles and as avolume of a larger amount of powder particles and some of themost used standards.
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| 5. |
- Harlin, Peter, 1974
(författare)
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On the processing of starch consolidated high speed steel - Microstructure and tribological properties
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis focuses on processing of high speed steel (HSS) powder into components using starch consolidation (SC) and supersolidus liquid phase sintering (SLPS). The work consists of four parts. First, the possibilities and constrains of the SC process are investigated and the role of starch in the green body fabrication clarified. Secondly, the possibility to sinter green bodies to full density using SLPS is investigated and the influence of sintering temperature on the as-sintered microstructures evaluated. Further, the mechanical and tribological properties of the as-sintered microstructures were evaluated using hardness indentation, scratch testing and three different wear tests. Finally, the use of physical vapour deposited (PVD) coatings, TiN and WC/C, for improved tribological performance of HSS components in sliding contacts was investigated and the importance of pre- and post-surface treatment illuminated. Also, the mechanisms of material transfer and tribo film formation and how these influences the tribo contact was investigated.The results show that it is possible to combine SC and SLPS in order to produce HSS components with fully dense microstructure and retained green body geometry from coarser HSS powder. The strength of the green bodies is mainly controlled by the morphology and distribution of starch and green bodies easy to handle can be obtained. The sintering temperature has a strong impact on the resulting microstructures, i.e. microstructures sintered at low temperatures show a porous microstructure while microstructures sintered at high temperatures show a coarser more inhomogeneous microstructure. The mechanical and tribological properties of SC HSS are in different extent controlled by the microstructure. The presence of a residual porosity will result in lower hardness but also in increased cracking tendency if porous areas are loaded. In contrast, microstructures sintered at high temperatures result in lower hardness and a more plastic behaviour. The abrasive wear resistance is, as compared with HIPed HSS, surprisingly good both under low and high stress abrasion conditions and the influence of any residual porosity is relatively small. Under sliding wear conditions a porous microstructure should be avoided since it will increase the wear of a softer counter surface. However, the deposition of a PVD coating will significantly improve the performance also of a porous microstructure.Evaluation of the sliding wear characteristics of PVD coated HSS shows that, besides a correct choice of the coating material, the control of surface structure topography is of outmost importance in order to obtain low friction and stable contact conditions.In summary, the obtained results are positive regarding the near net shape manufacturing (based on SC and SLPS) of PVD-coated HSS components for tribological applications.
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| 6. |
- Isoaho, Jerry, et al.
(författare)
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Applications of additive manufacturing : Selected case studies and future prospects
- 2023. - 1
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Ingår i: Additive Manufacturing of High-Performance metallic Materials. - : Elsevier. - 9780323918855 - 9780323913829 ; , s. 676-716
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Bokkapitel (refereegranskat)abstract
- From an industrial standpoint, cost is of one of the most important drivers for utilizing new technologies such as additive manufacturing (AM). Other important drivers for why AM can be an advantageous technology for component manufacturing is decreased manufacturing lead time, rapid demonstration capability, freedom of design/geometry, advancing technology development, and not least sustainability in terms of both material utilization and improved part/system performance. In this chapter, six selected “case studies” are compiled, in which AM techniques have been used to manufacture components for actual applications. In some case studies, a comparison between the additive manufacturing route and the corresponding conventional manufacturing route is also included.
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| 7. |
- Squillaci, Linda, et al.
(författare)
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Extending powder particle size distribution of laser powder bed fusion Ti-6Al-4V : investigation of single tracks and multilayer experiments
- 2023
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This paper explores the effects of varying process parameters (i.e., laser power, laser scanning speed, hatch distance) on the characteristics of single tracks, triple tracks and cubes, in order to provide answers to Research Question 1. A full factorial DoE approach was adopted to produce the experiments. Data was extracted from different sources to find correlations between tracks and multilayer geometries. A digital microscope was used to obtain height profiles, whilst polished/etched cross sections cut parallel to the build direction were imaged using a LOM to obtain measurements of track height, width, melt pool depth, subsurface porosity and residual defect content in cubes. Track height was found to exceed the recoated value of 70μm for both single and triple tracks. The width of single tracks showed a clear upward trend when displayed against VED, showing a lateral expansion as energy input increased. It was also revealed that single tracks expand laterally as they grow above the substrate, indicating swelling. The melt pool depth showed a steady upward trend when plotted against LED, though less systematic than track width. A martensitic microstructure was detected, with hierarchical α’ needles growing at prescribed crystallographic directions within vertical prior-β grains. A large portion of spatter particles and unmelted powder granules were detected on the substrate and tracks, with many accumulating on the side of the tracks forming a denudation zone.
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| 8. |
- Swaminathan, Kameshwaran, et al.
(författare)
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Characterization of Laser Powder Bed Fusion of Nickel-Based Superalloy Haynes 282
- 2023
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Ingår i: Proceedings of the 10th International Symposium on Superalloy 718 and Derivatives. - : Springer. - 9783031274466 - 9783031274473 ; , s. 553-570
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Konferensbidrag (refereegranskat)abstract
- Nickel-based superalloy Haynes 282 specimens were manufactured using the Laser Powder Bed Fusion process with a powder layer thickness of 60 and 90 microns to study the effect of laser power, laser scan speed, and hatch distance on the melt pool dimensions and porosity. The melt pool dimensions and porosity were measured at the center of the cubes parallel to the build direction. Variation of melt pool depth and overlap exist within the same sample signifying the scatter present in the process. Laser scan speed was found to be the most significant parameter for porosity and hatch distance was found to be the most significant parameter affecting the average melt pool overlap depth in the cubes built with 60 microns layer thickness. Interaction of speed and hatch distance was found to be the most significant parameter for porosity and Laser scan speed was the most significant parameter for average melt pool overlap depth in cubes built with 90 microns layer thickness. Comparison of measured responses with individual parameters provides partial trends of melt pool dimensions and porosity. As the heat input is captured better in line energy and area energy density, a better trend of the melt pool dimensions data and marginal trend of porosity in comparison with energy densities is discussed. The ratio of maximum length to minimum length of defects such as porosity and lack of fusion is measured to determine the shape of the defects and averaged to provide insight into the dominant shape of defect for a given set of parameters.
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