| 41. |
- Adegoke, Olutayo
(author)
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Processability of Laser Powder Bed Fusion of Alloy 247LC : Influence of process parameters on microstructure and defects
- 2020
-
Licentiate thesis (other academic/artistic)abstract
- This thesis is about laser powder bed fusion (L-PBF) of the nickel-based superalloy: Alloy 247LC. Alloy 247LC is used mainly in gas turbine blades and processing the blades with L-PBF confers performance advantage over the blades manufactured with conventional methods. This is mainly because L-PBF is more suitable, than conventional methods, for manufacturing the complex cooling holes in the blades. The research was motivated by the need for academia and industry to gain knowledge about the processability of the alloy using L-PBF. The knowledge is essential in order to eventually solve the problem of cracking which is a major problem when manufacturing the alloy. In addition, dense parts with low void content should be manufactured and the parts should meet the required performance. Thus, the thesis answered some of the important questions related to process parameter-microstructure-defect relationships.The thesis presented an introduction in chapter 1. A literature review was made in chapter 2 to 4. In chapter 2, the topic of additive manufacturing was introduced followed by an overview of laser powder bed fusion. Chapter 3 focused on superalloys. Here, a review was made from the broader perspective of superalloys but was eventually narrowed down to the characteristics of nickelbased superalloys and finally Alloy 247LC. Chapter 4 reviewed the main research on L-PBF of Alloy 247LC. The methodology applied in the thesis was discussed in chapter 5. The thesis applied statistical design of experiments to show the influence of process parameters on the defects and microstructure, so a detail description of the method was warranted. This was given at the beginning of chapter 5 and followed by the description of the L-PBF manufacturing and the characterization methods. The main results and discussions, in chapter 6, included a preliminary investigation on how the process parameters influenced the amount of discontinuity in single track samples. This was followed by the results and discussions on the investigation of voids, cracks and microhardness in cube samples (detail presentation was given in the attached paper B). Finally, the thesis presented results of the microstructure obtainable in L-PBF manufactured Alloy 247LC. The initial results of the microstructure investigation were presented in paper A.
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| 42. |
- Adegoke, Olutayo, 1979-
(author)
-
Processability of Laser Powder Bed Fusion of Alloy 247LC-Influence of process parameters on microstructure and defects
- 2021
-
Doctoral thesis (other academic/artistic)abstract
- This thesis is about laser powder bed fusion (L-PBF) of the nickel-basedsuperalloy Alloy 247LC. Alloy 247LC is mainly used in gas turbine blades and processing the blades with L-PBF may confer performance advantage over the blades manufactured with conventional methods. This is mainly because L-PBFis more suitable, than conventional methods, for manufacturing the complex cooling holes in the blades. The research was motivated by the need for academia and industry to gain knowledge about the processability of the alloy using L-PBF. The knowledge is essential to eventually solve the problem of cracking encountered when processing the alloy. In addition, dense parts with low void content should be processed and the microstructure and properties should meett he required performance. Heat-treatment is usually performed to acquire final properties, so it is also of interest to study this aspect. Thus, the thesis answered some of the important questions related to process parameter-microstructure- property relationships.
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| 43. |
- Adegoke, Olutayo, et al.
(author)
-
Review of laser powder bed fusion of gamma-prime-strengthened nickel-based superalloys
- 2020
-
In: Metals. - : MDPI AG. - 2075-4701. ; 10:8
-
Journal article (peer-reviewed)abstract
- This paper reviews state of the art laser powder bed fusion (L-PBF) manufacturing of γ′ nickel-based superalloys. L-PBF resembles welding; therefore, weld-cracking mechanisms, such as solidification, liquation, strain age, and ductility-dip cracking, may occur during L-PBF manufacturing. Spherical pores and lack-of-fusion voids are other defects that may occur in γ′-strengthened nickel-based superalloys manufactured with L-PBF. There is a correlation between defect formation and the process parameters used in the L-PBF process. Prerequisites for solidification cracking include nonequilibrium solidification due to segregating elements, the presence of liquid film between cells, a wide critical temperature range, and the presence of thermal or residual stress. These prerequisites are present in L-PBF processes. The phases found in L-PBF-manufactured γ′-strengthened superalloys closely resemble those of the equivalent cast materials, where γ, γ′, and γ/γ′ eutectic and carbides are typically present in the microstructure. Additionally, the sizes of the γ′ particles are small in as-built L-PBF materials because of the high cooling rate. Furthermore, the creep performance of L-PBF-manufactured materials is inferior to that of cast material because of the presence of defects and the small grain size in the L-PBF materials; however, some vertically built L-PBF materials have demonstrated creep properties that are close to those of cast materials.© 2020 by the authors. Licensee MDPI, Basel, Switzerland.
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| 44. |
- Adegoke, Olutayo, et al.
(author)
-
Scanning electron microscopy and atom probe tomography characterization of laser powder bed fusion precipitation strengthening nickel-based superalloy
- 2023
-
In: Micron. - 0968-4328 .- 1878-4291. ; 171
-
Journal article (peer-reviewed)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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| 45. |
- Adli, Erik, et al.
(author)
-
Progress Of The Ess Proton Beam Imaging Systems
- 2022
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In: LINAC2022. - : ACoW Publishing. ; , s. 395-398
-
Conference paper (peer-reviewed)abstract
- The ESS Target Proton Beam Imaging Systems has the objective to image the 5 MW ESS proton beam as it entersthe spallation target. The imaging systems has to operate in a harsh radiation environment, leading to a number of challenges : development of radiation hard photon sources, long and aperture-restricted optical paths and fast electronics required to provide rapid information in case of beam anomalies. This paper outlines how main challenges of the imaging systems have been addressed, and the status of deployment as ESS gets closer to beam.
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| 46. |
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| 47. |
- Adolphs, Svenja, et al.
(author)
-
Digital innovations in L2 motivation : Harnessing the power of the Ideal L2 Self
- 2018
-
In: System (Linköping). - : Elsevier BV. - 0346-251X .- 1879-3282. ; 78, s. 173-185
-
Journal article (peer-reviewed)abstract
- Sustained motivation is crucial to learning a second language (L2), and one way to support this can be through the mental visualisation of ideal L2 selves (Dörnyei & Kubanyiova, 2014). This paper reports on an exploratory study which investigated the possibility of using technology to create representations of language learners' ideal L2 selves digitally. Nine Chinese learners of L2 English were invited to three semi-structured interviews to discuss their ideal L2 selves and their future language goals, as well as their opinions on several different technological approaches to representing their ideal L2 selves. Three approaches were shown to participants: (a) 2D and 3D animations, (b) Facial Overlay, and (c) Facial Mask. Within these, several iterations were also included (e.g. with/without background or context). Results indicate that 3D animation currently offers the best approach in terms of realism and animation of facial features, and improvements to Facial Overlay could lead to beneficial results in the future. Approaches using the 2D animations and the Facial Mask approach appeared to have little future potential. The descriptive details of learners' ideal L2 selves also provide preliminary directions for the development of content that might be included in future technology-based interventions.
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| 48. |
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| 49. |
- Aggestam, Lena, et al.
(author)
-
How to Apply and Manage Critical Success Factors in Healthcare Information Systems Development?
- 2023
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In: Systems. - : MDPI. - 2079-8954. ; 11:9
-
Journal article (peer-reviewed)abstract
- Studies on Critical Success Factors (CSFs) in Healthcare Information Systems (HIS) development projects have traditionally often been limited to retrospectively identifying CSFs in a finished project. In this paper, we focus on how to prospectively apply and manage CSFs in HIS projects. Based on a holistic perspective and systems thinking, an inductive research strategy was applied and a single in-depth case study was conducted. The findings include detailed descriptions that contribute to further understanding of how to prospectively apply and manage CSFs in HIS projects. The analysis reveals that CSFs must be applied differently and managed on various system levels. Furthermore, it shows how interactions exist between different system levels, both in the case of a specific CSF and between different CSFs on various system levels. Our analysis framework and findings indicate new directions for future research: how to prospectively apply and manage CSFs in HIS development projects can now be investigated both in a more holistic way and more in detail. Finally, healthcare practitioners can use the descriptions as practical checklists for guiding them in how to realize situational adaptation of CSFs in HIS projects across different system levels.
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| 50. |
- Aggestam, Lena, et al.
(author)
-
LEARNING AND QUALITY ASSURANCE IN THE SAME PACKAGE
- 2024
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In: INTED2024 Proceedings. - : IATED. - 9788409592159 ; , s. 2006-2011
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Conference paper (other academic/artistic)abstract
- The critical need for organizations to learn and change is well known. “The ability to learn faster than your competitors is your only lasting competitive advantage” as put by a HR manager. Thus, knowledge is vital, both as a resource and a competitive advantage. The importance of life-long learning and distance education is clear, just as the role of higher education. The aim of this paper is to share academic experiences and lessons learnt concerning performing high quality assessment on-line and at the same time offering a learning opportunity for both teachers and students. This is a big challenge.We performed a case study in an on-going hybrid course. There were 10 students on the course, all professionals and employed and hence performing the course and working at the same time. We used the final course assessment as a case unit, which was performed as structured on-line dialogues between each student individual and the examiner. Data were collected by observations of three students performing and a deep follow-up interview with the examiner responsible. Each dialogue lasted about one hour. To be eligible to participate the student must have prepared a task based on two books and questions aiming to put the literature in comparison as well as in the context of their own employment. The examiner leads the dialogue based on graduate assessment criteria, developed by the examiner. The collected data were inductively analyzed.The analysis reveals advantages that oral individual assessments have concerning quality assurance and at the same time enable learning. The examiner has natural opportunities to ask follow-up questions to stimulate reflections and further learning. The examiner also has opportunities to ask questions that reveal the students’ knowledge and understanding related to the assessment criteria and the syllabus learning outcomes, which is a critical aspect not at least from the perspective of AI and chat-GPT. Since the dialogues are individual, the time perspective is a matter of fact that is often lift as an argument against this type of examination. According to the examiner, this is not a problem if you take all the steps in the examination process into consideration. The total time is more or less equal compared to traditional written examinations. Furthermore, the examiner emphasizes that this form of examination is much more fun.To achieve both quality assessment assurance and learning, the analysis also reveals the importance of a holistic approach, as for example putting the matter of course in the students´ reality as well as the critical interface between the task and the assessment dialogue. It also strengthens the importance of preparing for both the examiner and the student and emphasizes the importance of having a system for continuous follow-up and improvements. Finally, the follow-up interview with the examiner reveals the learning it means by having someone externally observing the performance and then asking relevant questions and having a dialogue afterwards. “It forced me to think and reflect on the work from new perspectives, which is critical for future improvements” as put by the examiner. One piece of advice from the examiner is to include this type of work in the quality assurance system for course development. To reflect on the work was an important input to further increase and develop the course.
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