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| 2. |
- Åsberg, Mikael, et al.
(author)
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Influence of post treatment on microstructure, porosity and mechanical properties of additive manufactured H13 tool steel
- 2019
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In: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 742, s. 584-589
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Journal article (peer-reviewed)abstract
- Additive manufacturing (AM) is an attractive manufacturing technology in tooling applications. It provides unique opportunities to manufacture tools with complex shapes, containing inner channels for conformal cooling. In this investigation, H13, a widely used tool steel, was manufactured using a laser powder bed fusion method. Microstructure, tensile mechanical properties, hardness, and porosity of the AM H13 after stress relieve (SR), standard hardening and tempering (SR + HT), and hot isostatic pressing (SR + HIP + HT) were investigated. It was found that the microstructure of directly solidified colonies of prior austenite, which is typical for AM, disappeared after austenitizing at the hardening heat treatment. In specimens SR + HT and SR + HIP + HT, a microstructure similar to the conventional but finer was observed. Electron microscopy showed that SR and SR + HT specimens contained lack of fusion, and spherical gas porosity, which resulted in remarkable scatter in the observed elongation to break values. Application of HIP resulted in the highest strength values, higher than those observed for conventional H13 heat treated in the same way. The conclusion is that HIP promotes reduction of porosity and lack of fusion defects and can be efficiently used to improve the mechanical properties of AM H13 tool steel.
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| 6. |
- Bergström, Jens, et al.
(author)
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Fatigue of cold work tool steel
- 1999
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In: Matériaux & Techniques. - : EDP Sciences. - 0032-6895 .- 1778-3771. ; 87:1-2, s. 9-14
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Journal article (peer-reviewed)abstract
- One important surface property of forming tools is their resistance to cracking due to fatigue loading. The wide variety of steel grades, material handling, machining operations and surface treatments will give very different fatigue properties. The present article gives examples on the influence of steel grades, EDM machining and surface coating. Initial cracks may be introduced in the tool during the processing to its final shape and surface finish, why a particular interest is given to small cracks introduced by the EDM process.
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| 15. |
- Fredriksson, Gunnel
(author)
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Influence of EDM : Post treatments and coatings on mechanical porperties of cold work steels
- 1999
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Reports (other academic/artistic)abstract
- This report is a presentation of results from the laboratory tests of the project Electrical Discharge Machining of Tools in Cold Work Applications. Two high speed steels, two cold work ingot cast and forged steels, and one powder metallurgical cold work steel at hardness from 51 to 66 HRc were included in the study. In the first part of the report differences between the various tool steels in how they respond to electrical discharge machining (EDM) are discussed. Surface alterations, defect distributions, static and fatigue strength are included as well as wire and die sinking EDM, both rough and fine. In the second part some post EDM treatments are examined. The effect of tempering and shot peening after EDM on mechanical properties of the tool steel is shown and a comparison of mechanical polishing and electrochemical polishing (ECP) is given. Since cold work tool steels are being used at increasing hardness, the third part is a study where the hardness of two tool steels has been varied in order to see how important this is to the effect of EDM on mechanical properties of the steel. In the last part the combination of EDM, mechanical or electrochemical polishing and thin ceramic surface coatings are studied, one CVD and one PVD coating
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| 19. |
- Fredriksson, Matilda
(author)
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Fostran till anställningsbarhet : Ungas berättelser inifrån den kommunala arbetsmarknadspolitiken
- 2022
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Doctoral thesis (other academic/artistic)abstract
- The issue of unemployment has become individualised. In recent decades, Swedish social- and labour market policies have changed towards an emphasis on activation, which places greater demands on the job seeker to actively seek work, participate in employment initiatives and improve their employability. This thesis studies how these requirements are expressed in the municipal activation of young people (18-29 years of age). The purpose of the study is to highlight and problematise the activation’s creation of employable individuals and its consequences for young people’s identity work.The study is based on ethnographic field work in an activation programme. The data consists of field notes, interviews and audio recordings from the programme’s daily activities and the young people’s tripartite meetings with public employment officers, which are also attended by staff from the activation programme. Based on Goffman’s perspective on total institutions and an interactionist, discursive and narrative approach, the study illustrates activation from the point of view of the programme participants’ own perspectives and narratives.The analysis shows how the programme screens young people from their environment and at the same time monitors and controls them. A daily schedule has to be followed, which means that all the young people do the same activity at the same time. The analysis identifies the prominent discourses that set the framework for the design of the activation and the everyday activities, as well as how the young people’s situations and needs are understood. The participants are categorised as “problem young people” with faults and failings. Included in the activation is a desire to change them into employable and capable individuals who can fit into the adult world. However, it is the young people who are responsible for working on themselves in accordance with the prevailing ideals. Thus, it is not primarily about reinforcing their competences in aspects like education and experience of working life. Rather, the young people are encouraged to adopt new ways of thinking and characteristics, such as being active, flexible, reflexive, well-behaved and accepting responsibility. They are challenged to show motivation, self-confidence and social and communicative skills. By encouraging the young people to change themselves and adopt certain personal characteristics, the activation conveys the image of unemployment as a personal problem that requires a personal solution, rather than a social problem. In the young people’s narratives, the activation is depicted as meaningless in that the programme does not lead to employment. At the same time, the young people say that the programme has given them new values and ways of seeing themselves. The activation can therefore be understood as a practice of normalisation as well as a semi-total institution that disciplines and changes the participants.
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| 20. |
- Hentschel, Oliver, et al.
(author)
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Influence of the in-situ heat treatment during manufacturing on the microstructure and properties of DED-LB/M manufactured maraging tool steel
- 2023
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In: Journal of Materials Processing Technology. - : Elsevier. - 0924-0136 .- 1873-4774. ; 315
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Journal article (peer-reviewed)abstract
- Due to high productivity, additive manufacturing (AM), and especially Directed Energy Deposition using laser and metallic powder (DED-LB/M) is attractive for manufacturing tools with integrated functionalities. This investigation was dedicated to DED-LB/M manufacturing of experimental maraging tool steel, characterization of the build microstructure with advanced electron microscopy and evaluation of hardness properties. High printability and low porosity of the final builds were observed, relative density was not lower than 99.5% for specimens manufactured with 600 W and 800 W, but microstructure and properties of the build had a gradient along the height. The characteristic hardness profile and microstructure, which were dependent on the manufacturing parameters, were observed. The top layers of manufactured maraging steel samples had a structure of martensite with precipitates presumably formed during solidification. The top layers were therefore softer to the depth of the austenitization isotherm. The higher hardness was measured in the inner regions which was a result of an in-situ heat treatment that the manufactured material was subjected to during layer-by-layer manufacturing. Thermal cycles during manufacturing resulted in precipitation hardening effect in the inner regions. Scanning and transmission electron microscopy confirmed the formation film-like and round particles in the as-build material, in top and inner regions. However, the quasicrystalline nano-sized R′-phase precipitates were observed only in the inner regions. The formation of the R′-phase precipitated during manufacturing as a result of the in-situ heat treatment was discussed as a reason for higher hardness (440 – 450 HV1) measured in the inner regions.
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| 22. |
- Kazantseva, Natalia, et al.
(author)
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Twins in SLM Ti alloy
- 2017
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In: Titan. - : Mezhgosudarstvennaya Assotsyatsiya Titan. - 2075-2903. ; :2, s. 8-15
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Journal article (peer-reviewed)
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| 23. |
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| 26. |
- Krakhmalev, Pavel, 1973-, et al.
(author)
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Influence of heat treatment under hot isostatic pressing (HIP) on microstructure of intermetallic-reinforced tool steel manufactured by laser powder bed fusion
- 2020
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In: Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 772
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Journal article (peer-reviewed)abstract
- Microstructure and properties of as-built laser powder bed fusion (LPBF) steels differ from the conventional ones, and they may contain some porosity and lack of fusion. Therefore, post-treatments, including hot isostatic pressing (HIP), are used to density the material, and tailor the properties of the final product. Usually, HIP is performed as an operation separate from heat treatment. In the present investigation a new approach was used, in which the whole cycle of the heat treatment was carried out in HIP under pressure, and the influence of HIP on microstructure of an advanced stainless maraging tool steel manufactured by LPBF was investigated. For a comparison, a conventional steel grade of the same chemical composition, after a heat treatment at the same temperature-time conditions, was also characterized. The microstructure of the steel was investigated by means of advanced microscopy and atom probe tomography. The influence of the manufacturing route, heat treatment and HIP on microstructure, austenitic phase fraction and size distribution of precipitates was investigated, and the role of high pressure in stabilization of austenite in the microstructure was discussed. It was concluded that since HIP influences phase transformations, a fundamental understanding of the influence of HIP on microstructure is nececcary, and development of new post processing regimes guaranteeing the best performance of the material is required.
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| 27. |
- Krakhmalev, Pavel, 1973-, et al.
(author)
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Microstructural and thermal stability of selective laser melted 316L stainless steel single tracks
- 2017
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In: South African Journal of Industrial Engineering. - : Stellenbosch University. - 1012-277X .- 2224-7890. ; 28:1, s. 12-19
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Journal article (peer-reviewed)abstract
- To remove residual stresses, an as-built SLM object is usually posttreated. This treatment can affect the microstructure, changing the final mechanical characteristics. This investigation is focused on the microstructural characterisation of 316L austenitic stainless steel in as-built and annealed conditions. The SLM microstructure was relatively stable up to 900°C, when cell boundaries start to disappear. At higher temperatures, an insignificant grain coarsening was detected. These microstructural changes caused a gradual drop in the hardness. The obtained result is background for the future development of post-treatment regimens to achieve a high level in the final mechanical properties of SLM objects.
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| 28. |
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| 29. |
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| 30. |
- Krakhmalev, Pavel, 1973-, et al.
(author)
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Microstructure, solidification texture, and thermal stability of 316 L stainless steel manufactured by laser powder bed fusion
- 2018
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In: Metals. - : MDPI AG. - 2075-4701. ; 8:8, s. 1-18
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Journal article (peer-reviewed)abstract
- This article overviews the scientific results of the microstructural features observed in 316 L stainless steel manufactured by the laser powder bed fusion (LPBF) method obtained by the authors, and discusses the results with respect to the recently published literature. Microscopic features of the LPBF microstructure, i.e., epitaxial nucleation, cellular structure, microsegregation, porosity, competitive colony growth, and solidification texture, were experimentally studied by scanning and transmission electron microscopy, diffraction methods, and atom probe tomography. The influence of laser power and laser scanning speed on the microstructure was discussed in the perspective of governing the microstructure by controlling the process parameters. It was shown that the three-dimensional (3D) zig-zag solidification texture observed in the LPBF 316 L was related to the laser scanning strategy. The thermal stability of the microstructure was investigated under isothermal annealing conditions. It was shown that the cells formed at solidification started to disappear at about 800 °C, and that this process leads to a substantial decrease in hardness. Colony boundaries, nevertheless, were quite stable, and no significant grain growth was observed after heat treatment at 1050 °C. The observed experimental results are discussed with respect to the fundamental knowledge of the solidification processes, and compared with the existing literature data.
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| 31. |
- Vilardell, Anna M., et al.
(author)
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Fracture mechanisms in the as-built and stress-relieved laser powder bed fusion Ti6Al4V ELI alloy
- 2019
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In: Optics and Laser Technology. - : Elsevier. - 0030-3992 .- 1879-2545. ; 109, s. 608-615
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Journal article (peer-reviewed)abstract
- The influence of a stress-relief treatment on impact and fatigue properties of Ti6Al4V ELI samples manufactured by laser powder bed fusion was analyzed. The heat treatment resulted in removal of residual stresses, coarsening of needles and formation of precipitations between needles. In both, impact and fatigue tests, crack development was correlated to microstructural features. Fracture analysis was carried out by means of optical and electron microscopy to reveal the influence of microstructure on crack development. Ductile fracture was the dominating fracture mode at impact testing. Pore formation and coalescence were the main crack formation mechanisms. The microstructural changes led to a decrease in impact toughness after heat treatment. Presumably, this was a result of the precipitations between needles. Fatigue results showed multiple crack nucleation at the surface in both, as-built and stress-relieved material. The crack propagation rate was slightly higher and the crack was less deflected in the stress-relieved material due to the stress relief and coarsening of the microstructure.
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| 32. |
- Vilardell, A. M., et al.
(author)
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Influence of surface topography on fatigue behavior of Ti6Al4V alloy by laser powder bed fusion
- 2018
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In: Procedia CIRP. - : Elsevier. ; , s. 49-52
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Conference paper (peer-reviewed)abstract
- This article deals with the understanding of the influence of surface topography on fatigue behavior of Ti6Al4V alloy specimens produced by laser powder bed fusion (LPBF). The same laser parameters and scan strategy were used for all specimens, giving a sample density higher than 99.5 %. Two different surface topographies were obtained by using the top and side surfaces of the specimens. The surface topography and morphology were investigated by optical surface profilometry and focus variation microscopy. Four-point bending fatigue test was performed on specimens with top and side surfaces as the highest stressed surface respectively. Machined specimens were used as reference. The features of the fracture surface, such as crack initiation and propagation, were analyzed by focus variation and scanning electron microscopy (SEM). Both, fatigue results and fracture surface investigations, were correlated and discussed in relation to surface topography and microstructure, as well as manufacturing parameters.
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| 33. |
- Vilardell, Anna M., et al.
(author)
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Surface integrity factors influencing fatigue crack nucleation of laser powder bed fusion Ti6Al4V alloy
- 2020
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In: Procedia CIRP. - : Elsevier. - 2212-8271. ; , s. 222-226
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Conference paper (peer-reviewed)abstract
- The quality of the surface influences remarkably the fatigue life of additive manufactured components. This work proposes to study the influence of surface integrity on the bending fatigue life of Ti6Al4V manufactured by laser powder bed fusion. Rectangular specimens were manufactured horizontally and the last printed layer had laser track scanning directions (α=30°,60°,90°) in relation to the specimen length. The top surface 3D-roughness average was similar for all the specimens. The specimens were studied under as-built and heat-treated conditions. A correlation between laser track scanning direction, 2D-roughness parameters, and fatigue life for as-built specimens was found. The as-built specimens with 90° and 30° direction showed the shortest and the longest fatigue life, respectively. Heat-treated specimens showed a shorter fatigue life independently of the surface roughness. This could be explained by other surface integrity factors influencing fatigue performance of the material, such as the presence of subsurface porosity and surface oxygen enrichment. © 2020 The Authors. Published by Elsevier B.V.
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| 34. |
- Wingren, Maria, 1976-, et al.
(author)
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A more active parenting after attending Let's Get Organized - Experiences of parents with ADHD
- 2023
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In: Scandinavian Journal of Occupational Therapy. - : Taylor & Francis. - 1103-8128 .- 1651-2014. ; 30:8, s. 1267-1279
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Journal article (peer-reviewed)abstract
- Background: Parenting demands a high degree of attention, planning, and problem-solving, including time management, demands that can be challenging for parents with ADHD. Let's Get Organized (LGO) is an occupational therapy group intervention aiming at developing skills in time management, organisation and planning. There is a need to investigate if LGO may have an impact also on parenting.Aim: To describe how parents with ADHD experienced the intervention, their time management strategies, parenting and family life after the occupational therapy group intervention LGO.Method: Interviews were performed with 15 parents with ADHD, after completing LGO. Data were analysed using qualitative content analysis.Results: The findings are described in one overarching main category, Active parenting and better relations within and outside the family through daily time management with three underlying generic categories: Let's Get Organized facilitates empowerment in daily life; The individual and family - both facilitators of and obstacles to implementation of time management strategies; and A changed parenting and family life.Conclusions and significance: Participants experienced a positive impact on time management skills after LGO, which generated more active parenting and better predictability in the whole family. LGO can be a valuable intervention for parents with ADHD.
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