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  • 1. Amin Yavari, S.
    et al.
    Croes, M.
    Akhavan, B.
    Jahanmard, F.
    Eigenhuis, C. C.
    Dadbakhsh, Sasan
    KTH, School of Industrial Engineering and Management (ITM).
    Vogely, H. C.
    Bilek, M. M.
    Fluit, A. C.
    Boel, C. H. E.
    van der Wal, B. C. H.
    Vermonden, T.
    Weinans, H.
    Zadpoor, A. A.
    Layer by layer coating for bio-functionalization of additively manufactured meta-biomaterials2020In: Additive Manufacturing, ISSN 2214-8604, E-ISSN 2214-7810, Vol. 32Article in journal (Refereed)
    Abstract [en]

    Additive manufacturing has facilitated fabrication of complex and patient-specific metallic meta-biomaterials that offer an unprecedented collection of mechanical, mass transport, and biological properties as well as a fully interconnected porous structure. However, applying meta-biomaterials for addressing unmet clinical needs in orthopedic surgery requires additional surface functionalities that should be induced through tailor-made coatings. Here, we developed multi-functional layer-by-layer coatings to simultaneously prevent implant-associated infections and stimulate bone tissue regeneration. We applied multiple layers of gelatin- and chitosan-based coatings containing either bone morphogenetic protein (BMP)-2 or vancomycin on the surface of selective laser melted porous structures made from commercial pure Titanium (CP Ti) and designed using a triply periodic minimal surface (i.e., sheet gyroid). The additive manufacturing process resulted in a porous structure and met the the design values comparatively. X-ray photoelectron spectroscopy spectra confirmed the presence and composition of the coating layers. The release profiles showed a continued release of both vancomycin and BMP-2 for 2–3 weeks. Furthermore, the developed meta-biomaterials exhibited a very strong antibacterial behavior with up to 8 orders of magnitude reduction in both planktonic and implant-adherent bacteria and no signs of biofilm formation. The osteogenic differentiation of mesenchymal stem cells was enhanced, as shown by two-fold increase in the alkaline phosphatase activity and up to four-fold increase in the mineralization of all experimental groups containing BMP-2. Eight-week subcutaneous implantation in vivo showed no signs of a foreign body response, while connective tissue ingrowth was promoted by the layer-by-layer coating. These results unequivocally confirm the superior multi-functional performance of the developed biomaterials.

  • 2. Dadbakhsh, S.
    et al.
    Hao, L.
    Kruth, J.-P.
    Selective laser melting towards manufacture of three dimensional in situ Al matrix composites: A review2013In: High Value Manufacturing: Advanced Research in Virtual and Rapid Prototyping - Proceedings of the 6th International Conference on Advanced Research and Rapid Prototyping, VR@P, 2013Conference paper (Refereed)
  • 3. Dadbakhsh, S.
    et al.
    Hao, L.
    Sewell, N.
    Jerrard, P.
    Direct fabrication of an in-situ Al composite using selective laser melting process2009In: Innovative developments in design and manufacturing advanced research in virtual and rapid prototyping: proceedings of the 4th International Conference on Advanced Research in Virtual and Rapid Prototyping, Leiria: CRC Press , 2009Conference paper (Refereed)
  • 4. Dadbakhsh, S.
    et al.
    Vrancken, B.
    Kruth, J. P.
    Luyten, J.
    Van Humbeeck, J.
    Texture and anisotropy in selective laser melting of NiTi alloy2016In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 650, p. 225-232Article in journal (Refereed)
  • 5. Dadbakhsh, Sasan
    et al.
    Hao, L.
    Effect of Al alloys on selective laser melting behaviour and microstructure of in situ formed particle reinforced composites2012In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 541, no 0, p. 328-334Article in journal (Refereed)
  • 6.
    Dadbakhsh, Sasan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Production engineering.
    Hao, L.
    Effect of Fe2O3 content on microstructure of Al powder consolidated parts via selective laser melting using various laser powers and speeds2014In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 73, no 9-12, p. 1453-1463Article in journal (Refereed)
  • 7. Dadbakhsh, Sasan
    et al.
    Hao, L.
    Effect of hot isostatic pressing (HIP) on Al composite parts made from laser consolidated Al/Fe2O3 powder mixtures2012In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 212, no 11, p. 2474-2483Article in journal (Refereed)
  • 8. Dadbakhsh, Sasan
    et al.
    Hao, L.
    In situ formation of particle reinforced Al matrix composite by selective laser melting of Al/Fe 2O 3 powder mixture2012In: Advanced Engineering Materials, ISSN 15272648, Vol. 14, no 1-2, p. 45-48Article in journal (Refereed)
    Abstract [en]

    This work presents a novel in situ reaction approach to produce Al matrix composites from a powder mixture of Al/5a wt% Fe 2O 3 by using selective laser melting (SLM). It is found that the SLM process not only is able to produce three-dimensional parts, but also is capable of activating an in situ reaction in the powder mixture, producing particles mainly from alumina (Al 2O 3) and iron combinations (such as Fe 2+Al 2O 4) in Al matrix. These particles (as reinforcements) can be distributed uniformly with a good particle/matrix interface under controlled conditions.

  • 9. Dadbakhsh, Sasan
    et al.
    Hao, L.
    Jerrard, P. G. E.
    Zhang, D. Z.
    Experimental investigation on selective laser melting behaviour and processing windows of in situ reacted Al/Fe2O3 powder mixture2012In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 231, no 0, p. 112-121Article in journal (Refereed)
  • 10. Dadbakhsh, Sasan
    et al.
    Hao, L.
    Kong, C. Y.
    Surface finish improvement of LMD samples using laser polishing2010In: Virtual and Physical Prototyping, ISSN 17452767, Vol. 5, no 4, p. 215-221Article in journal (Refereed)
    Abstract [en]

    Laser metal deposition (LMD) is an additive manufacturing (AM) process used for repairing and fabricating metallic parts. One of the major drawbacks of this process is the relatively rough surface of the manufactured parts. In this work, surface polishing using laser for LMD parts was studied. Using the LMD process, a series of block samples of Inconel 718 were produced. The top surface of the samples was then laser scanned using combinations of parameters. The surface roughness of the samples was evaluated and subsequently, optimum process parameters set for laser polishing were predicted using analytical experimental design (DoE) software. The results showed the capability of a laser to improve the finishing surface of the LMD parts to about 2 mm Ra, which can be acceptable for many industrial applications. The relation of laser energy to final surface roughness was also studied, showing the strong dependency of surface finish on laser energy. 

  • 11. Dadbakhsh, Sasan
    et al.
    Hao, L.
    Sewell, N.
    Effect of selective laser melting layout on the quality of stainless steel parts2012In: Rapid prototyping journal, ISSN 1355-2546, E-ISSN 1758-7670, Vol. 18, no 3, p. 241-249Article in journal (Refereed)
  • 12. Dadbakhsh, Sasan
    et al.
    Hao, Liang
    Effect of Layer Thickness in Selective Laser Melting on Microstructure of Al/5wt.%Fe2O3 Powder Consolidated Parts2014In: The Scientific World Journal, ISSN 1537744X, Vol. 2014, p. 10-Article in journal (Refereed)
  • 13. Dadbakhsh, Sasan
    et al.
    Karimi Taheri, A.
    Smith, C. W.
    Strengthening study on 6082 Al alloy after combination of aging treatment and ECAP process2010In: Materials Science and Engineering: A, ISSN 09215093, Vol. 527, no 18-19, p. 4758-4766Article in journal (Refereed)
    Abstract [en]

    Equal channel angular pressing (ECAP) was used before and after various aging treatments in order to strengthen a commercial 6082 Al alloy. Experiments were carried out to study the strengthening of the alloy due to pre and post-ECAP aging treatment. It was found that aging before and after ECAP processing is an effective method for strengthening of the alloy. An increase in both strength and ductility of the ECAPed specimen was achieved via appropriate post-aging treatment. This was in such a manner that for maximal strengthening, post-ECAP aging is best conducted at temperatures lower than those usually used for aging if prior work hardening is not undertaken. Pre-ECAP aging was also discussed in the light of dislocation density and work hardening.

  • 14.
    Dadbakhsh, Sasan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering. Katholieke Univ Leuven, PMA, Dept Mech Engn, B-3001 Leuven, Belgium ; Flanders Make, B-3001 Leuven, Belgium.
    Mertens, Raya
    Katholieke Univ Leuven, PMA, Dept Mech Engn, B-3001 Leuven, Belgium.;Flanders Make, B-3001 Leuven, Belgium..
    Hao, Liang
    China Univ Geosci, Gemol Inst, Wuhan 430074, Hubei, Peoples R China..
    Van Humbeeck, Jan
    Katholieke Univ Leuven, Dept Mat Engn, B-3001 Leuven, Belgium..
    Kruth, Jean-Pierre
    Katholieke Univ Leuven, PMA, Dept Mech Engn, B-3001 Leuven, Belgium.;Flanders Make, B-3001 Leuven, Belgium..
    Selective Laser Melting to Manufacture "In Situ" Metal Matrix Composites: A Review2019In: Advanced Engineering Materials, ISSN 1438-1656, Vol. 21, no 3, article id 1801244Article, review/survey (Refereed)
    Abstract [en]

    After a brief introduction on selective laser melting (SLM) and ex situ manufacture of metal matrix composites (MMCs), this paper reviews the capacities and benefits of SLM to activate and control various in situ reactions during fabrication of 3D parts. It introduces several systems (such as Al/Fe2O3, AlSi10Mg/SiC, Al/ZnO, Ti/C, Ti/SiC, Ti/Si3N4, Ti/Mo2C, Fe/SiC, etc.) used to manufacture Al-based, Ti-based, and steel-based in situ MMCs. Then, it illustrates the novel microstructural characteristics of these SLM-made in situ MMCs for different cases, as they may appear from nano-particles to nano-whiskers and dendritic reinforcements homogeneously distributed in a metal matrix. It also focuses on SLM associated in situ mechanisms, explaining how an in situ reaction propagates based on decomposition, diffusion, and reformation and how the growth mechanisms turn into different morphologies such as rounded particles, whiskers, or polygonal block shapes. The influence of various SLM parameters (such as energy density, laser power/speed, powder layer thickness, and the size of initial powder particles) and the SLM in situ challenges are also discussed.

  • 15.
    Dadbakhsh, Sasan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering. PMA/MaPS, Department of Mechanical Engineering, KU Leuven & Member of Flanders Make, Leuven, 3001, Belgium.
    Mertens, Raya
    Ji, Gang
    Vrancken, Bey
    Vanmeensel, Kim
    Fan, Haiyang
    Addad, Ahmed
    Kruth, Jean-Pierre
    Heat treatment possibilities for an in situ βTi-TiC composite made by laser powder bed fusion2020In: Additive Manufacturing, ISSN 2214-8604, E-ISSN 2214-7810, Vol. 36, article id 101577Article in journal (Refereed)
    Abstract [en]

    After laser powder bed fusion (LPBF) of an ultra-strong in situ TiC whisker reinforced β-Ti composite, this paper investigates the evolution of microstructure and mechanical properties in response to heat treatment at different temperatures. Using in depth nano-SEM and TEM analyses, it is shown that ageing at 400 °C rounds the whiskers, annihilates the strain fields and grows Mo segregated nano-cells, but without improving the ductility. In contrast, ageing at 600 °C enables the transformation of metastable β to a lamellar β + α, leading to a dual phase matrix embedding TiC particles. This is in such a manner that extra ageing at 600 °C coalesces the nano-lamellar α + β microstructure to form a coarser micro-lamellar α + β matrix. This microstructure achieves 66 % of the compressive deformation of Cp-Ti, and over 1400 MPa compressive strength after 1 h of ageing at 600 °C. Despite this success under compression, hard and stiff TiC particles may still cause large spherical fractured voids, severely limiting the plastic deformation under tension.

  • 16.
    Dadbakhsh, Sasan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Manufacturing and Metrology Systems.
    Mertens, Raya
    Vanmeensel, Kim
    Ji, Gang
    Kruth, Jean-Pierre
    In situ transformations during SLM of an ultra-strong TiC reinforced Ti composite2020In: Scientific Reports, E-ISSN 2045-2322, Vol. 10, no 1, article id 10523Article in journal (Refereed)
    Abstract [en]

    This work demonstrates a successful in situ method capable of producing an ultra-strong novel Ti composite without aluminium and vanadium. In this method, selective laser melting is used to conduct in situ alloying and reinforcing of a Ti/10.5 wt% Mo2C powder mixture. It is shown that this leads to a metastable β-Ti matrix homogeneously reinforced by high aspect ratio, 50–200 nm wide and up to several micrometre long TiC whiskers. The transformations of the phases are controlled by decomposition, dissolution, diffusion, and reformation of constituents. The whisker morphology of in situ formed TiC particles is associated with directional crystal growth along the TiC<110> direction. The developed TiC reinforced β-Ti alloy combines a hardness over 500 HV, a Young’s modulus of 126 GPa, and an ultimate compressive strength of 1642 MPa. Improving the ductility of this composite is the subject of another work.

  • 17. Dadbakhsh, Sasan
    et al.
    Mertens, Raya
    Vanmeensel, Kim
    Vleugels, Jef
    Humbeeck, Jan Van
    Kruth, Jean-Pierre
    In situ alloying and reinforcing of Al6061 during selective laser melting2018In: Procedia CIRP, ISSN 2212-8271, E-ISSN 2212-8271, Vol. 74, p. 39-43Article in journal (Refereed)
    Abstract [en]

    This work investigates the feasibility of a novel method to simultaneously alloy and reinforce a low alloyed Al alloy (i.e., Al6061) during selective laser melting (SLM) via in situ decomposition of zinc oxide (ZnO). Based on Gibbs free energy calculations, an Al6061+6wt%ZnO powder mixture is designed and prepared. The thermal decomposition of ZnO, resulting in the formation of Al oxide and free Zn, simultaneously alloys and reinforces the Al matrix. This also provides extra thermal energy that alters the dynamics of the melt pool and necessitates a completely different set of optimised SLM parameters compared to traditional Al alloys. After SLM, it is shown that this method can successfully reinforce the Al matrix with numerous nanometer sized oxide particles (typically ~ 50-120 nm). Despite this clear success to manufacture in situ reinforced Al composites by SLM, the applied method could not avoid partial Zn evaporation (limiting in situ alloying) and could not successfully suppress the cracking that also occurs after SLM of unreinforced Al6061.

  • 18. Dadbakhsh, Sasan
    et al.
    Speirs, Mathew
    Kruth, Jean-Pierre
    Schrooten, Jan
    Luyten, Jan
    Van Humbeeck, Jan
    Effect of SLM Parameters on Transformation Temperatures of Shape Memory Nickel Titanium Parts2014In: Advanced Engineering Materials, ISSN 1438-1656, E-ISSN 1527-2648, Vol. 16, no 9, p. 1140-1146Article in journal (Refereed)
  • 19. Dadbakhsh, Sasan
    et al.
    Speirs, Mathew
    Kruth, Jean-Pierre
    Van Humbeeck, Jan
    Influence of SLM on shape memory and compression behaviour of NiTi scaffolds2015In: CIRP annals, ISSN 0007-8506, E-ISSN 1726-0604, Vol. 64, no 1, p. 209-212Article in journal (Refereed)
  • 20. Dadbakhsh, Sasan
    et al.
    Speirs, Mathew
    Van Humbeeck, Jan
    Kruth, Jean-Pierre
    Laser additive manufacturing of bulk and porous shape-memory NiTi alloys: From processes to potential biomedical applications2016In: MRS bulletin, ISSN 0883-7694, E-ISSN 1938-1425, Vol. 41, no 10, p. 765-774Article in journal (Refereed)
    Abstract [en]

    NiTi alloys are well known not only due to their exceptional shape-memory ability to recover their primary shape, but also because they show high ductility, excellent corrosion and wear resistance, and good biological compatibility. They have received significant attention especially in the field of laser additive manufacturing (AM). Among laser AM techniques, selective laser melting and laser metal deposition are utilized to exploit the unique properties of NiTi for fabricating complex shapes. This article reviews the properties of bulk and porous laser-made NiTi alloys as influenced by both process and material parameters. The effects of processing parameters on density, shape-memory response, microstructure, mechanical properties, surface corrosion, and biological properties are discussed. The article also describes potential opportunities where laser AM processes can be applied to fabricate dedicated NiTi components for medical applications.

  • 21. Dadbakhsh, Sasan
    et al.
    Speirs, Mathew
    Yablokova, Ganna
    Kruth, Jean-Pierre
    Schrooten, Jan
    Luyten, Jan
    Van Humbeeck, Jan
    The Minerals, Metals
    Materials, Society
    Microstructural Analysis and Mechanical Evaluation of Ti-45Nb Produced by Selective Laser Melting towards Biomedical Applications2015In: TMS2015 Supplemental Proceedings, John Wiley & Sons, Inc. , 2015Conference paper (Refereed)
  • 22. Dadbakhsh, Sasan
    et al.
    Taheri, A. K.
    Study on static strain aging of 6082 aluminium alloy2010In: Materials Science and Technology, ISSN 0267-0836, E-ISSN 1743-2847, Vol. 26, no 2, p. 169-175Article in journal (Refereed)
  • 23. Dadbakhsh, Sasan
    et al.
    Verbelen, Leander
    Vandeputte, Tom
    Strobbe, Dieter
    Van Puyvelde, Peter
    Kruth, Jean-Pierre
    Effect of Powder Size and Shape on the SLS Processability and Mechanical Properties of a TPU Elastomer2016In: Physics Procedia, E-ISSN 1875-3892, Vol. 83, p. 971-980Article in journal (Refereed)
  • 24.
    Dadbakhsh, Sasan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Manufacturing and Metrology Systems.
    Zhao, Xiaoyu
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Manufacturing and Metrology Systems.
    Chinnappan, Prithiv Kumar
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Shanmugam, Vishal
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Zeyu, Lin
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Manufacturing and Metrology Systems.
    Hulme-Smith, Christopher
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Process and geometrical integrity optimization of electron beam melting for copper2022In: CIRP annals, ISSN 0007-8506, E-ISSN 1726-0604, Vol. 71, p. 201-204Article in journal (Refereed)
    Abstract [en]

    This work systematically analyzes and optimizes the process of electron beam melting for pure copper. It is shown that, for reliable manufacturing, the preheating temperature should be optimized to avoid porosity as well as part deformation. The electron beam should be fully focused to prevent shrinkage voids (correlated to negative defocusing) and material spattering (linked to positive defocusing). Smoother surfaces from lower hatch spacing (e.g., 100µm) can improve the density reliability, while longer overhangs are reached by a higher hatch spacing. A suitable starting contour strategy is also applied to mitigate border porosities, reduce side roughness and increase geometric precision.

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  • 25. Gorgin Karaji, Z.
    et al.
    Speirs, M.
    Dadbakhsh, S.
    Kruth, J. P.
    Weinans, H.
    Zadpoor, A. A.
    Amin Yavari, S.
    Additively Manufactured and Surface Biofunctionalized Porous Nitinol2016In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252Article in journal (Refereed)
  • 26. Hao, L.
    et al.
    Dadbakhsh, S.
    Materials and process aspects of selective laser melting of metals and metal matrix composites: A review2009In: Zhongguo Jiguang/Chinese Journal of Lasers, ISSN 0258-7025, Vol. 36, no 12, p. 3192-3203Article in journal (Refereed)
  • 27. Hao, L.
    et al.
    Dadbakhsh, S.
    Seaman, O.
    Felstead, M.
    Selective laser melting of a stainless steel and hydroxyapatite composite for load-bearing implant development2009In: Journal of Materials Processing Technology, Vol. 209, no 17, p. 5793-5801Article in journal (Refereed)
  • 28. Hao, L.
    et al.
    Raymond, D.
    Strano, G.
    Dadbakhsh, S.
    Enhancing the sustainability of additive manufacturing2010In: IET Conference Publications, 2010Conference paper (Refereed)
  • 29.
    Holmberg, Jonas
    et al.
    Department of Manufacturing Processes, RISE Research Institutes of Sweden AB, Argongatan 30, Mölndal, Sweden.
    Berglund, Johan
    Department of Manufacturing Processes, RISE Research Institutes of Sweden AB, Argongatan 30, Mölndal, Sweden.
    Brohede, Ulrika
    Department of Production Technology, Swerim AB, Isafjordsgatan 28A, Kista, Sweden.
    Åkerfeldt, Pia
    Division of Material Science, Luleå University of Technology, 971 87, Luleå, Sweden.
    Sandell, Viktor
    Division of Material Science, Luleå University of Technology, 971 87, Luleå, Sweden.
    Rashid, Amir
    KTH, School of Industrial Engineering and Management (ITM), Production engineering, Manufacturing and Metrology Systems.
    Zhao, Xiaoyu
    KTH, School of Industrial Engineering and Management (ITM), Production engineering, Manufacturing and Metrology Systems.
    Dadbakhsh, Sasan
    KTH, School of Industrial Engineering and Management (ITM), Production engineering, Manufacturing and Metrology Systems.
    Fischer, Marie
    Department of Industrial and Materials Science, Chalmers University of Technology, Hörsalsvägen 7B, Göteborg, Sweden.
    Hryha, Eduard
    Department of Industrial and Materials Science, Chalmers University of Technology, Hörsalsvägen 7B, Göteborg, Sweden.
    Wiklund, Urban
    Department of Material Science, Ångströmlaboratoriet, Uppsala University, Lägerhyddsvägen 1, Uppsala, Sweden.
    Hassila, Carl Johan Karlsson
    Department of Material Science, Ångströmlaboratoriet, Uppsala University, Lägerhyddsvägen 1, Uppsala, Sweden.
    Hosseini, Seyed
    Department of Manufacturing Processes, RISE Research Institutes of Sweden AB, Argongatan 30, Mölndal, Sweden.
    Machining of additively manufactured alloy 718 in as-built and heat-treated condition: surface integrity and cutting tool wear2023In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 130, no 3-4, p. 1823-1842Article in journal (Refereed)
    Abstract [en]

    Additive manufacturing (AM) using powder bed fusion is becoming a mature technology that offers great possibilities and design freedom for manufacturing of near net shape components. However, for many gas turbine and aerospace applications, machining is still required, which motivates further research on the machinability and work piece integrity of additive-manufactured superalloys. In this work, turning tests have been performed on components made with both Powder Bed Fusion for Laser Beam (PBF-LB) and Electron Beam (PBF-EB) in as-built and heat-treated conditions. The two AM processes and the respective heat-treatments have generated different microstructural features that have a great impact on both the tool wear and the work piece surface integrity. The results show that the PBF-EB components have relatively lower geometrical accuracy, a rough surface topography, a coarse microstructure with hard precipitates and low residual stresses after printing. Turning of the PBF-EB material results in high cutting tool wear, which induces moderate tensile surface stresses that are balanced by deep compressive stresses and a superficial deformed surface that is greater for the heat-treated material. In comparison, the PBF-LB components have a higher geometrical accuracy, a relatively smooth topography and a fine microstructure, but with high tensile stresses after printing. Machining of PBF-LB material resulted in higher tool wear for the heat-treated material, increase of 49%, and significantly higher tensile surface stresses followed by shallower compressive stresses below the surface compared to the PBF-EB materials, but with no superficially deformed surface. It is further observed an 87% higher tool wear for PBF-EB in as-built condition and 43% in the heat-treated condition compared to the PBF-LB material. These results show that the selection of cutting tools and cutting settings are critical, which requires the development of suitable machining parameters that are designed for the microstructure of the material.

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  • 30. Jadhav, S. D.
    et al.
    Dadbakhsh, S.
    Goossens, L.
    Kruth, J. P.
    Van Humbeeck, J.
    Vanmeensel, K.
    Influence of selective laser melting process parameters on texture evolution in pure copper2019In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 270, p. 47-58Article in journal (Refereed)
    Abstract [en]

    In the present work, Crack-Free pure copper parts with relative densities exceeding 98% are processed by selective laser melting (SLM) using a high-power fiber laser. The influence of different laser scan parameters such as hatch spacing, laser power and scan speed on the texture evolution in the manufactured parts is determined. On the top surfaces, a clear interrelationship between laser scan parameters and crystallographic texture is established. This shows that the texture at the top surface can be very strong especially when a high laser power and a low scanning speed is used. However, a random texture exists in the core of the sample due to successive re-melting and altered heat gradients induced by the application of a 90° scan rotation between subsequent layers. A maximum electrical conductivity of 88% of the International Annealed Copper Standard (IACS) is achieved in the as-built state. Damage to the optical mirror of the SLM machine is observed and recommendations for sustainable up-scalability are proposed.

  • 31. Jadhav, Suraj Dinkar
    et al.
    Dadbakhsh, Sasan
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Chen, Rong
    Shabadi, Rajashekhara
    Kruth, Jean-Pierre
    Van Humbeeck, Jan
    Vanmeensel, Kim
    Modification of Electrical and Mechanical Properties of Selective Laser-Melted CuCr0.3 Alloy Using Carbon Nanoparticles2019In: Advanced Engineering Materials, ISSN 1438-1656, E-ISSN 1527-2648, Vol. n/a, no n/a, article id 1900946Article in journal (Refereed)
    Abstract [en]

    Herein, the influence of carbon nanoparticle addition on the selective laser melting (SLM) behavior and the resultant properties of gas-atomized CuCr0.3 powder are investigated. The carbon addition neither affects the powder flowability, nor its packing density, but it significantly enhances the optical absorption for infrared radiation. Despite the improved optical absorption of the powder bed after carbon addition, a comparable SLM behavior is observed for both virgin and carbon-mixed CuCr0.3 powders. Furthermore, the addition of carbon nanoparticles facilitates in situ deoxidation of copper and chromium oxides present in the CuCr0.3 powder. Accordingly, a larger fraction of chromium is obtained in its metallic form in the as-built carbon-mixed CuCr0.3 part. The presence of metallic chromium allows tailoring of the mechanical and electrical properties by postheat treatments (HTs). The best combination of mechanical (tensile strength of 298?±?19?MPa, yield strength of 208?±?18?MPa, ductility of 21?±?4%) and electrical (87?±?1% international annealed copper standards [% IACS]) properties is realized for the carbon-mixed CuCr0.3 alloy after a direct age hardening HT. The improvement in mechanical properties is attributed to the precipitation of nanometer-sized, coherent, and metallic chromium precipitates in the copper matrix.

  • 32. Jadhav, Suraj Dinkar
    et al.
    Dadbakhsh, Sasan
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering. PMA, Department of Mechanical Engineering, Belgium.
    Vleugels, Jozef
    Hofkens, Johan
    Puyvelde, Peter Van
    Yang, Shoufeng
    Kruth, Jean-Pierre
    Humbeeck, Jan Van
    Vanmeensel, Kim
    Influence of Carbon Nanoparticle Addition (and Impurities) on Selective Laser Melting of Pure Copper2019In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 12, no 15Article in journal (Refereed)
    Abstract [en]

    The addition of 0.1 wt % carbon nanoparticles significantly improved the optical absorption and flowability of gas-atomized copper powder. This facilitated selective laser melting (SLM) by reducing the required laser energy density to obtain 98% dense parts. Moreover, the carbon addition led to an in situ de-oxidation of the copper parts during the SLM process. The properties of the as-built copper parts were limited to a tensile strength of 125 MPa, a ductility of 3%, and an electrical conductivity of 22.7 &times; 106 S/m, despite the advantageous effect of carbon on the powder characteristics and SLM behavior. The modest mechanical properties were associated with the segregation of carbon nanoparticles and other impurities, such as phosphorus and oxygen along grain boundaries of epitaxially grown grains. Whereas, the low electrical conductivity was mainly attributed to the phosphorus impurity in solid-solution with copper.

  • 33. Jadhav, Suraj Dinkar
    et al.
    Dhekne, Pushkar Prakash
    Brodu, Etienne
    Van Hooreweder, Brecht
    Dadbakhsh, Sasan
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Manufacturing and Metrology Systems. KU Leuven, Department of Mechanical Engineering, & Member of Flanders Make, Celestijnenlaan 300, B-3001 Heverlee, Belgium.
    Kruth, Jean-Pierre
    Van Humbeeck, Jan
    Vanmeensel, Kim
    Laser powder bed fusion additive manufacturing of highly conductive parts made of optically absorptive carburized CuCr1 powder2021In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 198Article in journal (Refereed)
    Abstract [en]

    Fabrication of fully dense and highly conductive copper alloy parts via laser-based additive manufacturing (L-AM) is challenging due to the high optical reflectivity of copper at λ = 1060 – 1080 nm and high thermal conductivity. To overcome this, the use of optically absorptive surface-modified copper powders is being evaluated in the laser powder bed fusion (LPBF) process. Although the surface-modified powders exhibit high optical absorption at room temperature, not all of them allow the fabrication of fully dense parts at a laser power below 500 W. Accordingly, this article proposes the use of optically absorptive carburized CuCr1 powder for the consistent fabrication of copper parts. Moreover, a densification mechanism of parts is discussed to explain the distinct LPBF processing behavior of different surface-modified powders, such as carburized CuCr1 and carbon mixed CuCr1 powders, albeit having similar room temperature optical absorption. This investigation clearly outlines the advantage of a firmly bonded modified layer present on the surface of the carburized CuCr1 powder over a loosely attached carbon nanoparticle layer present in the carbon-mixed CuCr1 powder. Apart from the successful fabrication of CuCr1 parts, fabricated parts are subjected to two different post-heat treatments, and it is shown that the final properties can be customized by applying tailored post-heat treatments.

  • 34. Jadhav, Suraj Dinkar
    et al.
    Dhekne, Pushkar Prakash
    Dadbakhsh, Sasan
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Manufacturing and Metrology Systems.
    Kruth, Jean-Pierre
    Van Humbeeck, Jan
    Vanmeensel, Kim
    Surface Modified Copper Alloy Powder for Reliable Laser-based Additive Manufacturing2020In: Additive Manufacturing, ISSN 2214-8604, E-ISSN 2214-7810, Vol. 35, article id 101418Article in journal (Refereed)
    Abstract [en]

    Owing to the high optical reflectivity of copper, silver, and gold in the infrared region, high laser power is required for laser-based additive manufacturing (L-AM). This increases the risk of damaging the laser optics due to sustained back-reflections and renders L-AM of reflective metals an unsustainable technology. To tackle this issue, a novel, industrially upscalable powder surface modification method is proposed and validated using a CuCr1 alloy. The surface of CuCr1 powder is modified by the outward diffusion of chromium in a nitrogen atmosphere, forming a rim around the powder particles. This doubled the optical absorption of the powder. Consequently, a mere 20% of the laser energy is required to process the surface-modified powder by laser powder bed fusion compared to the virgin CuCr1 powder. The fabricated parts demonstrate a very high thermal conductivity of 370 ± 15 W/(m·K) and tensile strength of 439 ± 19 MPa, after applying a suitable post-heat treatment.

  • 35. Jadhav, Suraj Dinkar
    et al.
    Van Cauwenbergh, Pierre
    Lietaert, Karel
    Van Humbeeck, Jan
    Kruth, Jean-Pierre
    Dadbakhsh, Sasan
    Ivekovic, Aljaz
    Vanmeensel, Kim
    SLM of CuNi10 alloy using gas atomized powder2017In: Materials Science and Technology, Pittsburgh, Pennsylvania, USA, 2017Conference paper (Refereed)
  • 36. Jean-Pierre, Kruth
    et al.
    Sasan, Dadbakhsh
    Bey, Vrancken
    Karolien, Kempen
    Jef, Vleugels
    Jan Van, Humbeeck
    Additive Manufacturing of Metals via Selective Laser Melting: Process Aspects and Material Developments2015In: Additive Manufacturing, CRC Press, 2015Chapter in book (Refereed)
  • 37. Jerrard, P. G. E.
    et al.
    Hao, L.
    Dadbakhsh, S.
    Evans, K. E.
    Consolidation behaviour and microstructural characteristics of Al and a mixture of Al-Cu alloy powders following selective laser melting processing2011In: Lasers in engineering (Print), ISSN 0898-1507, E-ISSN 1029-029X, Vol. 22, no 5-6, p. 371-381Article in journal (Refereed)
  • 38.
    Lin, Zeyu
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Production engineering.
    Surreddi, Kumar Babu
    Materials Technology School of Information and Technology Dalarna University SE‐791 88 Falun Sweden.
    Hulme-Smith, Christopher
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Dadbakhsh, Sasan
    KTH, School of Industrial Engineering and Management (ITM), Production engineering.
    Rashid, Amir
    KTH, School of Industrial Engineering and Management (ITM), Production engineering.
    Influence of Electron Beam Powder Bed Fusion Process Parameters on Transformation Temperatures and Pseudoelasticity of Shape Memory Nickel Titanium2023In: Advanced Engineering Materials, ISSN 1438-1656, E-ISSN 1527-2648Article in journal (Refereed)
    Abstract [en]

    Electron beam powder bed fusion (PBF-EB) is used to manufacture dense nickel titanium parts using various parameter sets, including the beam current, scan speed and post cooling condition. The density of manufactured NiTi parts are investigated with relation to the linear energy input. The results implies the part density increases with increasing linear energy density to over 98% of the bulk density. With a constant energy input, a combination of low power and low scan speed leads to denser parts. This is attributed to lower electrostatic repulsive forces from lower number density of the impacting electrons. After manufacturing, densest parts with distinct parameter sets are categorized into three groups: i) high power with high scan speed and vacuum slow cooling, ii) low power with low scan speed and vacuum slow cooling and iii) low power with low scan speed and medium cooling rate in helium gas. Among these, a faster cooling rate suppresses phase transformation temperatures, while vacuum cooling combinations do not affect the phase transformation temperatures significantly. All the printed parts in this study exhibit almost 8% pseudoelasticity regardless of the process parameters, while the parts cooled in helium have a higher energy dissipation efficiency ( ), which implies faster damping of oscillations. 

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  • 39.
    Lin, Zeyu
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Manufacturing and Metrology Systems.
    Zhao, Xiaoyun
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Manufacturing and Metrology Systems.
    Dadbakhsh, Sasan
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Manufacturing and Metrology Systems.
    Rashid, Amir
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Manufacturing and Metrology Systems.
    Evaluating the electron beam spot size in electron beam melting machines2021Conference paper (Refereed)
    Abstract [en]

    Since electron beam (EB) is the main additive manufacturing (AM) tool in electron beam melting (EBM), EB spot size plays a significant role in the parts quality, surface roughness as well as the microstructure and corresponding properties. So far, the research on the relationship between the machine parameters and the EB spot size has been mainly based on the single track and powderless single track printing on a metal plate such as stainless steel. However, this method, due to material thermal properties as well as the melting phenomena, cannot reveal the actual value for the EB spot size. This research is carried out to establish a simple methodology on measuring the EB spot size in a more accurate way with a low cost. To do so, a ceramic surface coating was applied to the surface of a metal copper starting plate and stainless steel plate. Afterwards, the EB applied the tracks onto the coatings and regular metal plate. The analysis showed that the EB tracks on ceramic coated stainless steel plates could be the best replica for the electron beam among those materials tested in this work.  

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  • 40. Malakizadi, Amir
    et al.
    Mallipeddi, Dinesh
    Dadbakhsh, Sasan
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Manufacturing and Metrology Systems.
    M'Saoubi, Rachid
    Krajnik, Peter
    Post-processing of additively manufactured metallic alloys – A review2022In: International journal of machine tools & manufacture, ISSN 0890-6955, E-ISSN 1879-2170, ISSN 0890-6955, Vol. 179, no 103908Article in journal (Refereed)
    Abstract [en]

    Additive manufacturing (AM) is characterised by several unique advantages, such as (freedom of) design, capability of fusing dissimilar materials, near-net-shape, and achieving a more sustainable production. While the increased precision of metal AM in recent years reduced the needed amount of post-processing to meet dimensional tolerance, the requirements for functional surfaces necessitate a well-understood post-processing, ranging from heat treatment to machining and finishing. The inherently rough initial (as-built) surface topography next to complex material microstructure affects the capability of post-processing/finishing operations to smooth the surface texture and obtain a favourable surface integrity. In this respect, a more fundamental understanding of the effects of material properties on post-processing/finishing is needed. Therefore, this review paper aims to establish the relationship between the characteristics of different AM technologies, microstructural properties of materials in as-built and heat-treated conditions, and the physical properties influencing the response of additively manufactured materials during post-processing/finishing operations. In particular, emphasis is placed on the physics-based understanding of how the microstructural characteristics of 316L, Ti6Al4V and Alloy 718 produced using the two principal technologies, Powder Bed Fusion (PBF) and Direct Energy Deposition (DED), influence their mechanical properties like tensile strengths, hardness and ductility. These properties are among the key factors influencing the response of material during post-processing/finishing operations involving material removal by shear deformation. This review paper also discusses the role of post-processing/finishing on fatigue performance, tribological behaviour and corrosion resistance of investigated AM materials. The paper summarises the state-of the art of post-processing/finishing operations and future research trends are highlighted.

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  • 41.
    Mansour, Rami
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Gillgren, Sara
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Dadbakhsh, Sasan
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Manufacturing and Metrology Systems.
    Topology Optimization for Additive Manufacturing – A Numerical Study of Current Design Framework Capabilities and Limitations2022In: Advances in Transdisciplinary Engineering / [ed] A.H.C. Ng et al., IOS Press , 2022, Vol. 21, p. 592-603Conference paper (Refereed)
    Abstract [en]

    Topology optimization (TO) is commonly used to minimize the weight of a structural component subject to a constraint on the maximum equivalent stress. In TO for additive manufacturing (AM), constraints on the build direction as well as the overhang angle are also included in the optimization. However, current design framework generally doesn’t include the residual stresses and distortions that result from the AM process directly into the TO. In this work, it is shown that this limitation can result in components that may fail during the Selective Laser Melting (SLM) due to high stresses and distortion that were not accounted for in the TO. For the studied demonstrative bracket design from Ti-6Al-4V, it is shown that the spatial stress distribution, including both the location and magnitude of the maximum stress, is strongly altered after SLM compared to the stresses used in the TO, even after heat treatment. This work highlights the importance of integrating AM process simulation with residual stress and distortion prediction directly in the TO, which is currently a difficult and computationally inefficient task.

  • 42.
    Matija, Milenovic
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Mao, Huina
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Dadbakhsh, Sasan
    KTH, School of Industrial Engineering and Management (ITM), Production engineering.
    Design and Development of Damping SandwichPanels for Satellite Housing Using AdditiveManufacturing2022Conference paper (Refereed)
    Abstract [en]

    The present work investigates the performance of additively-manufactured sandwich structures with the goal of reducing the effect of vibrations on a spacecraft during launch, whilst minimizing mass. Additive manufacturing allows designers to implement custom and complex geometries, such as the sheet gyroid structures, inside sandwich panels. Accordingly, this work details the development of gyroid-based sandwich structures for damping. Several test specimens are designed, additively manufactured using ABS plastic, and their damping performances are evaluated based on both simulation and experiments. Damping values are identified using frequency response transfer functions. The results show that as theory predicts, adding more mass, through the added thickness of the gyroid reduces the amplitude of vibrations. However, on a damping-per-unit-mass basis, the experimental results are inconclusive mainly due to the measurements of vibrations in the center of the sandwich panels instead of the sides where the vibrations can be maximum. Therefore, simulations better illustrate the changes of the damping behavior at different applied frequencies. Lessons and experiences are summarized for future work, particularly in exploring the effects of varying other 3D printed composite meta-lattice sandwich structures for satellites. 

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    Design_and_Development_of_Damping_Sandwich_Panels_for_Satellite_Housing_Using_Additive_Manufacturing
  • 43. Mertens, R.
    et al.
    Dadbakhsh, S.
    Humbeeck, J. Van
    Kruth, J.-P.
    Application of base plate preheating during selective laser melting2018In: Procedia CIRP, ISSN 2212-8271, E-ISSN 2212-8271, Vol. 74, p. 5-11Article in journal (Refereed)
    Abstract [en]

    Base plate preheating is one of the recent enhancing tools added to the process of Selective Laser Melting (SLM). This tool aims at a reduction of thermal stresses in SLM parts, achieved by decreasing the thermal gradients during SLM processing. In the current study, base plate preheating up to a temperature of 400°C is applied during SLM of 4 different materials, including aluminum 7075 alloy, nickel alloy Hastelloy X, H13 tool steel and CoCr. General trends, as well as material specific effects are discussed regarding part density, crack formation, internal stresses, microstructure and mechanical properties. These show how base plate preheating can induce different influences according to each particular material category.

  • 44. Paraskevas, Dimos
    et al.
    Dadbakhsh, Sasan
    KU Leuven, Department of Mechanical Engineering, Celestijnenlaan 300A, Heverlee, B-3001, Belgium.
    Vleugels, Jef
    Vanmeensel, Kim
    Dewulf, Wim
    Duflou, Joost R.
    Solid state recycling of pure Mg and AZ31 Mg machining chips via spark plasma sintering2016In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 109, p. 520-529Article in journal (Refereed)
    Abstract [en]

    This work investigates the applicability of spark plasma sintering (SPS) as a solid state recycling technique for magnesium alloy scrap. In this respect, machining chips from pure Mg and AZ31 Mg alloy ingots are chemically cleaned, cold compacted and SPSed directly into bulk specimens. It is found that SPS can successfully establish full densification and effective metallurgical bonding between chips without altering compositional constituents. This is attributed to the dynamic compaction during sintering as well as to the disruption of the chips' surface oxide film due to SPS electric current based joule heating. Apart from the successful consolidation, microstructural analysis of the initial Mg ingots, chips and SPS recycled material reveals that the SPS microstructure was finer than that of the original ingots due to significant deformation induced grain refinement during machining. As a result, the recycled materials had a higher compression and shear strength than that of the starting ingot material. The findings indicate that SPS is an effective alternative method for solid state recycling of magnesium alloy scrap.

  • 45. Shi, Qimin
    et al.
    Mertens, Raya
    Dadbakhsh, Sasan
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Li, Guichuan
    Yang, Shoufeng
    In-situ formation of particle reinforced Aluminium matrix composites by laser powder bed fusion of Fe2O3/AlSi12 powder mixture using laser melting/remelting strategy2022In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 299, article id 117357Article in journal (Refereed)
    Abstract [en]

    In-situ preparation of particle reinforced Al matrix composites (PRAMCs) by laser powder bed fusion (LPBF) is a promising strategy to strengthen Al-based alloys. The laser-driven thermite reaction can be a practical mechanism to in-situ synthesise PRAMCs. However, the introduction of elements oxygen by adding Fe2O3 makes the powder mixture highly sensitive to form porosity and Al2O3 film during LPBF, bringing challenges to prepare dense materials. This work develops an LPBF processing strategy combined with consecutive high-energy laser melting scanning and low-energy laser remelting scanning to prepare dense PRAMCs from Fe2O3/AlSi12 powder mixture. A high relative density (98.2 ± 0.55 %) was successfully obtained by optimising laser melting (Emelting) and remelting energy density (Eremelting) to Emelting = 35 J/mm2 and Eremelting = 5 J/mm2. Results reveal the necessity to increase Emelting to improve metal liquid’s spreading/wetting by breaking up Al2O3 films surrounding molten pools; however, the high-energy laser melting produced much porosity. Low-energy laser remelting could close the resulting internal pores, backfill open gaps and smoothen solidified surfaces. Although with two-times laser scanning, the microstructure still shows fine cellular Si networks with Al grains inside (grain size 370 nm) and in-situ nano-precipitates (Al2O3, Si and Al-Fe(-Si) intermetallics). Finally, the fine microstructure, nano-structured dispersion strengthening and high-level densification strengthen the prepared in-situ PRAMCs, reaching yield strength of 426 ± 4 MPa and tensile strength of 473 ± 6 MPa. Furthermore, the results can provide valuable information to process other powder mixtures with severe porosity/oxide-film formation potential considering the evidenced contribution of laser melting/remelting strategy to densify material and obtain good mechanical properties during LPBF.

  • 46. Speirs, Mathew
    et al.
    Dadbakhsh, Sasan
    KU Leuven, Belgium.
    Buls, S
    Kruth, JP
    Van Humbeeck, J
    Schrooten, J
    Luyten, Jan
    The effect of SLM parameters on geometrical characteristics of open porous NiTi scaffolds2013In: High Value Manufacturing: Advanced Research in Virtual and Rapid Prototyping - Proceedings of the 6th International Conference on Advanced Research and Rapid Prototyping, VR@P 2013, Leiria, Portugal: CRC Press , 2013, p. 309-314Conference paper (Refereed)
    Abstract [en]

    Selective Laser Melting (SLM) is a promising technique for the production of biometallic scaffolds for orthopaedic applications. To produce successful scaffolds, the laser parameters should be carefully selected in order to achieve open porosity especially when pores are <1000 μm. In this study, we investigate the effect of different laser parameters (capable to produce dense bulk NiTi samples) on production of scaffolds with open porosities of 1000 μm and varying strut thicknesses 100-300 μm. Two different sets of laser parameters were used: 40W laser power with 160 mm/s scanning velocity and 250W with 1000 mm/s, corresponding to low and high laser parameters respectively. Micro-CT scanning experiments were carried out to illustrate the limitations of laser parameters in production of open porous scaffolds. Volume fraction and closed porosity were assessed. It was found that a large CAD mismatch was observed in the building (XZ) direction and internal porosity appears within struts of the samples produced with high laser processing parameters. The residual particles on struts were also shown to increase as strut thickness increases.

  • 47. Speirs, Mathew
    et al.
    Wang, X.
    Van Baelen, S.
    Ahadi, A.
    Dadbakhsh, Sasan
    Department of Mechanical Engineering, KU Leuven, Louvain, Belgium.
    Kruth, J. -P
    Van Humbeeck, J.
    On the Transformation Behavior of NiTi Shape-Memory Alloy Produced by SLM2016In: Shape Memory and Superelasticity, ISSN 2199-3858, Vol. 2, no 4, p. 310-316Article in journal (Refereed)
    Abstract [en]

    Selective laser melting has been applied as a production technique of nickel titanium (NiTi) parts. In this study, the scanning parameters and atmosphere control used during production were varied to assess the effects on the final component transformation criteria. Two production runs were completed: one in a high (~1800 ppm O2) and one in a low-oxygen (~220 ppm O2) environment. Further solution treatment was applied to analyze precipitation effects. It was found that the transformation temperature varies greatly even at identical energy densities highlighting the need for further in-depth investigations. In this respect, it was observed that oxidation was the dominating factor, increased with higher laser power adapted to higher scanning velocity. Once the atmospheric oxygen content was lowered from 1800 to about 220 ppm, a much smaller variation of transformation temperatures was obtained. In addition to oxidation, other contributing factors, such as nickel depletion (via evaporation during processing) as well as thermal stresses and textures, are further discussed and/or postulated. These results demonstrated the importance of processing and material conditions such as O2 content, powder composition, and laser scanning parameters. These parameters should be precisely controlled to reach desired transformation criteria for functional components made by SLM.

  • 48. Strobbe, Dieter
    et al.
    Dadbakhsh, Sasan
    Department of Mechanical Engineering, KU Leuven, Division Production Engineering, Machine Design and Automation, Heverlee, Belgium.
    Verbelen, Leander
    Van Puyvelde, Peter
    Kruth, Jean-Pierre
    Selective laser sintering of polystyrene: a single-layer approach2018In: Plastics, rubber and composites, ISSN 1465-8011, E-ISSN 1743-2898, Vol. 47, no 1, p. 2-8Article in journal (Refereed)
    Abstract [en]

    Selective laser sintering (SLS) is a powder bed-based additive manufacturing technique to produce complex three-dimensional parts. Although every thermoplastic polymer theoretically can be processed via this technique, variable material behaviour complicates the optimisation of the processing parameters. This study investigates the processability of polystyrene by SLS by evaluating bed temperatures and laser parameters. The morphology of single-layer parts is examined through scanning electron microscopy and roughness measurements to find an indication for the optimal processing parameters. Additionally, the effect of carbon black (CB) (as a colouring additive) on the processability of polystyrene is studied. It is found that polystyrene without CB is processable at a bed temperature just below the glass transition temperature. The addition of CB reduces the consolidation of single layers. The single-layer investigation is extended to, and shown to correlate with, a preliminary investigation of the relative density of multilayer parts.

  • 49.
    Subasic, Mustafa
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Olsson, Mårten
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Dadbakhsh, Sasan
    KTH, School of Industrial Engineering and Management (ITM), Production engineering, Manufacturing and Metrology Systems.
    Zhao, Xiaoyu
    KTH, School of Industrial Engineering and Management (ITM), Production engineering, Manufacturing and Metrology Systems.
    Krakhmalev, Pavel
    Department of Engineering and Physics, Karlstad University, 651 88 Karlstad, Sweden.
    Mansour, Rami
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics. Department of Mechanical and Production Engineering, Aarhus University, 8200 Aarhus N, Denmark; DIGIT Center, 8200 Aarhus N, Denmark.
    Fatigue strength improvement of additively manufactured 316L stainless steel with high porosity through preloading2024In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 180, article id 108077Article in journal (Refereed)
    Abstract [en]

    This work investigates the influence of a single tensile preload, applied prior to fatigue testing, on the fatigue strength of 316L stainless steel parts manufactured using laser-based powder bed fusion (PBF-LB) with a porosity of up to 4 %. The specimens were produced in both the horizontal and vertical build directions and were optionally preloaded to 85 % and 110 % of the yield strength before conducting the fatigue tests. The results indicate a clear tendency of improved fatigue life and fatigue limit with increasing overload in both cases. The fatigue limits increased by 25.8 % and 24.6 % for the horizontally and vertically built specimens, respectively. Extensive modelling and experiments confirmed that there was no significant alteration in the shape and size of the porosity before and after preloading. Therefore, the observed enhancement in fatigue performance was primarily attributed to the imposed local compressive residual stresses around the defects.

  • 50.
    Tang, Danna
    et al.
    China Univ Geosci, Gemol Inst, Wuhan 430074, Hubei, Peoples R China.;Hubei Jewelry Engn Technol Res Ctr, Wuhan 430074, Hubei, Peoples R China..
    Hao, Liang
    China Univ Geosci, Gemol Inst, Wuhan 430074, Hubei, Peoples R China.;Hubei Jewelry Engn Technol Res Ctr, Wuhan 430074, Hubei, Peoples R China..
    Li, Yan
    China Univ Geosci, Gemol Inst, Wuhan 430074, Hubei, Peoples R China.;Hubei Jewelry Engn Technol Res Ctr, Wuhan 430074, Hubei, Peoples R China..
    Li, Zheng
    China Univ Geosci, Gemol Inst, Wuhan 430074, Hubei, Peoples R China.;Hubei Jewelry Engn Technol Res Ctr, Wuhan 430074, Hubei, Peoples R China..
    Dadbakhsh, Sasan
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Dual gradient direct ink writing for formation of kaolinite ceramic functionally graded materials2020In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 814, article id UNSP 152275Article in journal (Refereed)
    Abstract [en]

    Direct ink writing (DIW) technique has emerged as a powerful tool to create specific functionally graded materials (FGMs) products with macroscopic and microscopic porous architectures and mechanical properties. In order to explore the DIW process control method of ceramic composite FGMs, several additives (e.g., polysorbate, liquid paraffin and water) were mixed with kaolinite and barite powders to print the gradient materials with difference in both material compositions and structures. A stable ceramic slurry with a viscosity of 2.66-3.66 GP s at 5 MPa atmospheric pressure has been formulated by uniformly mixing 2 mm and 10 mm particles. Besides, the optimized flow rate of 150 mml/s and thickness of 0.5 mm were well proved to obtain good stacking of the slurry, whereas, the change of velocity shows little effect on the forming quality. The meso/macro pores of the gradient component can be achieved by adjusting the printing and sintering processes. The dual-extrusion DIW method presented here is versatile to be adapted to a wide range of biomimetic ceramic materials for the fabrication of FGMs objects with unprecedented properties.

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