| 1. |
- Safdar, Adnan, et al.
(författare)
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Effect of EBM processing parameters on surface roughness and microstructure of Ti-6Al-4V
- 2009
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Ingår i: Proceeding 22nd European Conference for Biomaterials. - : European Society for Biomaterials.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Titanium and its alloys especially Ti-6Al-4V is an attractive biomaterial due to their excellent biocompatibility. Electron Beam Melting (EBM) is one of the Solid Free Form Fabrication (SFFF) methods to build 3D solid and near-net shape objects for medical implants and aerospace industry. EBM system utilizes a high energy electron beam to selectively melt a powder layer according to CAD file in a vacuum chamber. EBM system can manufacture complex 3D geometries requiring no or very little machining before use. The EBM systems are energy and material efficient. The microstructures and surface properties of objects produced by EBM can be influenced by the setting of different processing parameters in the EBM system. In this study solid slabs of Ti-6Al-4V, approximately 5 x 5 cm with various thicknesses were produced with different sets of processing parameters such as beam current, offset focus, scan speed and scan direction. The effects of these parameters on surface roughness, surface morphology and microstructure of slabs have been evaluated by using confocal microscopy, SEM /EDX and optical microscopy. The samples for optical microscopy and SEM were prepared by using standard metallographic methods. Microstructures of Ti-6Al-4V alloy produced by EBM usually consist of columnar grains as shown in Figure 1. These grains always grow parallel to build direction. Layers of different contrasts were observed in the samples where the layer interface is perpendicular to the build direction as shown in figure 2. The growth of columnar grains and appearance of layers with different contrasts were observed irrespective of the parameter values. These two observed phenomena can be attributed to the partial reheating / re-melting of the solidified layer by the electron beam during the melting of subsequent layer. The diameter of individual grain and density of grains are not uniform and usually decreases with increase in build height. Upon cooling from the β-transus temperature, more or less continuous α-layers were found to form along the prior β grain boundaries. In the EBM produced Ti-6Al-4V alloy the β -phase was found to be in rod-like geometry, with a size of 0.05-0.1μm in diameter, imbedded in the α-plates. It was observed that the high value of off set focus can cause porosity in the sample. For example the resultant porosity could be up to 11%. On the other hand where the value of offset focus is relatively small no such phenomenon was observed. Reconstruction of 3D surface topography and roughness coefficient (Ra) were computed by using images taken from confocal microscope and novel computer program “COMSTAT’’ [A.Heydorn et al (2000)]. Figure 3 shows a 3D reconstructed surface of the EBM produced sample. The Ra is computed by using the equation below: Where Lfi is the thickness of ith point, Lf is the mean thickness and N is the number of measurements. It has been observed that the value of Ra is processing parameters dependent. A sample with bigger thickness or higher current values tends to have relatively higher values of Ra. The scan speed and scan direction can also influence the surface morphology and microstructures of the EBM produced alloys.
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| 2. |
- Adnan, Safdar, et al.
(författare)
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Effect of process parameters settings and thickness on surface roughness of EBM produced Ti-6Al-4V
- 2012
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Ingår i: Rapid prototyping journal. - : Emerald Group Publishing Limited. - 1355-2546 .- 1758-7670. ; 18:5, s. 401-408
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Tidskriftsartikel (refereegranskat)abstract
- Purpose – Ti-6Al-4V is one of the most attractive materials being used in aerospace, automotive and medical implant industries. Electron beam melting (EBM) is one of the direct digital manufacturing methods to produce complex geometries of fully dense and near net shape parts. The EBM system provides an opportunity to built metallic objects with different processing parameter settings like beam current, scan speed, probe size on powder, etc. The purpose of this paper is to determine and understand the effect of part's thickness and variation in process parameter settings of the EBM system on surface roughness/topography of EBM fabricated Ti-6Al-4V metallic parts. Design/methodology/approach – A mathematical model based upon response surface methodology (RSM) is developed to study the variation of surface roughness with changing process parameter settings. Surface roughness of the test slabs produced with different parameter settings and thickness has been studied under confocal microscope. Response surface methodology was used to develop a multiple regression model to correlate the effect of variation in EBM process parameters settings and thickness of parts on surface roughness of EBM produced Ti-6Al-4V. Findings – It has been observed that every part produced by EBM system has detectable surface roughness. The surface roughness parameter Ra varies between 1-20 µm for different samples depending upon the process parameter setting and thickness. The Ra value increases with increasing sample thickness and beam current, and decreases with increase in offset focus and scan speed. Originality/value – Surface roughness is related to wear and friction property of the material and hence is related to the life time and performance of the part. Surface roughness is an important property of any material to be considered as biomaterial. The surface roughness of the material depends upon the manufacturing method and environment and hence it is controllable either during fabrication or by post processing. From the 1st order regression model developed in this study, it is also evident that sample thickness, scan speed and beam current have relatively more effect on roughness value then the offset focus. With the model obtained equation, a designer can subsequently select the best combination of sample thickness and process parameter values to achieve desired surface roughness.
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| 3. |
- Adnan, Safdar, et al.
(författare)
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Evaluation of microstructural development in electron beam melted Ti-6Al-4V
- 2012
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Ingår i: Materials Characterization. - : Elsevier BV. - 1044-5803 .- 1873-4189. ; 65, s. 8-15
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Tidskriftsartikel (refereegranskat)abstract
- In the current work an investigation of the microstructures of EBM built Ti-6Al-4V test bars has been performed using OM, SEM, TEM and XRD. It has been found that the prior beta phase, that formed during the initial solidification, possesses a column shaped morphology with growing direction parallel to built direction. Typical (alpha+beta) structures namely Widmanstatten alpha platelets with rod-like beta phase formed on the interfaces of the fine alpha grains, have been observed in the columnar prior beta grains. Grain boundary alpha phase was found to be formed around the boundaries of the columnar prior beta grains. Different phases present in the parts, especially the BCC beta phases have been characterized. The TEWEDX results indicate very high V composition in the beta phase. Results of TEWSAED and XRD also revealed that a superlattice structure could be present in the beta phase. Phase transformation sequence is discussed according to the processing history and the microstructures observed.
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| 4. |
- de Peppo, Giuseppe Maria, 1981, et al.
(författare)
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Free-form-fabricated commercially-pure Ti and Ti6Al4V porous scaffolds support the growth of human embryonic stem cell-derived medsodermal progenitors
- 2012
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Ingår i: The Scientific World Journal. - : Hindawi Limited. - 2356-6140 .- 1537-744X. ; 2012
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Tidskriftsartikel (refereegranskat)abstract
- Commercially-pure titanium (cp-Ti) and the titanium-aluminum-vanadium alloy (Ti6Al4V) are widely used as reconstructive implants for skeletal engineering applications, due to their good mechanical properties, biocompatibility and ability to integrate with the surrounding bone. Electron beam melting technology (EBM) allows the fabrication of customized implants with tailored mechanical properties and high potential in the clinical practice. In order to augment the interaction with the biological tissue, stem cells have recently been combined with metallic scaffolds for skeletal engineering applications. We previously demonstrated that human embryonic stem cell-derived mesodermal progenitors (hES-MPs) hold a great potential to provide a homogeneous and unlimited supply of cells for bone engineering applications. This study demonstrates the effect of EBM-fabricated cp-Ti and Ti6Al4V porous scaffolds on hES-MPs behavior, in terms of cell attachment, growth and osteogenic differentiation. Displaying different chemical composition but similar surface properties, EBM-fabricated cp-Ti and Ti6Al4V scaffolds supported cell attachment and growth, and did not seem to alter the expression of genes involved in osteogenic differentiation and affect the alkaline phosphatase activity. In conclusion, interfacing hES-MPs to EBM-fabricated scaffolds may represent an interesting strategy for design of third-generation biomaterials, with the potential to promote implant integration in clinical conditions characterized by poor bone quality. Copyright 2012 G. M. de Peppo et al.
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| 5. |
- Forslund, Robert, et al.
(författare)
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A greedy algorithm for optimal heating in powder-bed-based additive manufacturing
- 2021
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Ingår i: Journal of Mathematics in Industry. - : Springer Science and Business Media LLC. - 2190-5983. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- Powder-bed-based additive manufacturing involves melting of a powder bed using a moving laser or electron beam as a heat source. In this paper, we formulate an optimization scheme that aims to control this type of melting. The goal consists of tracking maximum temperatures on lines that run along the beam path. Time-dependent beam parameters (more specifically, beam power, spot size, and speed) act as control functions. The scheme is greedy in the sense that it exploits local properties of the melt pool in order to divide a large optimization problem into several small ones. As illustrated by numerical examples, the scheme can resolve heat conduction issues such as concentrated heat accumulation at turning points and non-uniform melt depths.
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| 6. |
- Lindahl, Carl, et al.
(författare)
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Biomimetic calcium phosphate coating of additively manufactured porous CoCr implants
- 2015
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 353, s. 40-47
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this work was to study the feasibility to use a biomimetic method to prepare biomimetic hydroxyapatite (HA) coatings on CoCr substrates with short soaking times and to characterize the properties of such coatings. A second objective was to investigate if the coatings could be applied to porous CoCr implants manufactured by electron beam melting (EBM). The coating was prepared by immersing the pretreated CoCr substrates and EBM implants into the phosphate-buffered solution with Ca2+ in sealed plastic bottles, kept at 60 degrees C for 3 days. The formed coating was partially crystalline, slightly calcium deficient and composed of plate-like crystallites forming roundish flowers in the size range of 300-500 nm. Cross-section imaging showed a thickness of 300-500 nm. In addition, dissolution tests in Tris-HCl up to 28 days showed that a substantial amount of the coating had dissolved, however, undergoing only minor morphological changes. A uniform coating was formed within the porous network of the additive manufactured implants having similar thickness and morphology as for the flat samples. In conclusion, the present coating procedure allows coatings to be formed on CoCr and could be used for complex shaped, porous implants made by additive manufacturing.
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| 7. |
- Lundh Snis, Ulrika, 1970-, et al.
(författare)
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Nordic Innovation Networks in Education : Dealing with Educational Challenges with Cross Boarder Collaboration and User Driven Design
- 2012
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Ingår i: Uddevalla Symposium 2012<em> </em>. - 9789197794343 ; , s. 553-571
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Konferensbidrag (refereegranskat)abstract
- This is an EU-funded project related to cross boarder collaboration for educational purposes supported by information and communication technologies between Danish, Norwegian and Swedish schools. The project started in 2011 and extends to 2014 so this empirically dominated paper reports on early findings related to cross-border collaboration challenges. The aim of the project is to develop innovative cross-border teaching models by the means of user-driven, practice-based co-design processes between practitioners and researchers. In the first year, 18 classes from 13 schools in Denmark, Norway and Sweden in the Öresund-Kattegatt-Skagerack region participated. Organized in so called Nordic class-match groups (consisting of students and teachers from one class in each country) new cross-border teaching models are co-created, tested and evaluated in an iterative process. Since teaching models are subject dependent, the project develop teaching models in several subject domains, i.e. math, language, science and social studies / history. Heretofore findings show, however, that organizational and technical issues have superseded and squeezed out subject-oriented discussions due to surprisingly many practical issues that needed to be handled first. We have identified three major thresholds to overcome. The first is related to technical difficulties in schools when diverse IT systems are to be synchronized. The second threshold concerns scheduling coordination difficulties in order to allow synchronous cross boarder collaboration. The third threshold concerns linguistic and communication difficulties rooted in participants communicating in their respective Nordic language. Being able to communicate within Nordic languages are explicit learning goals in all three schools systems, and therefore part of the project aim and consequently all participants are expected to use their native languages when communicating. The next phase of the project is therefore to find solutions to these technical, organizational and linguistic barriers, and already now we see some barrier breaking models taking shape in the active network of Nordic teachers, students, school leaders, IT support teams and researchers.
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| 8. |
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| 9. |
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| 10. |
- Palmquist, Anders, 1977, et al.
(författare)
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Long-term biocompatibility and osseointegration of electron beam melted, free-form-fabricated solid and porous titanium alloy: Experimental studies in sheep.
- 2013
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Ingår i: Journal of biomaterials applications. - : SAGE Publications. - 1530-8022 .- 0885-3282. ; 27:8, s. 1003-1016
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of the present study was to evaluate the long-term osseointegration and biocompatibility of electron beam melted (EBM) free-form-fabricated (FFF titanium grade 5 (Ti6Al4V) implants. Porous and solid machined cylindrical and disk-shaped implants were prepared by EBM and implanted bilaterally in the femur and subcutaneously in the dorsum of the sheep. After 26 weeks, the implants and surrounding tissue were retrieved. The tissue response was examined qualitatively and quantitatively using histology and light microscopic (LM) morphometry. Selected bone implants specimens were evaluated by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and micro-computed tomography (mCT). The results showed that both porous and solid implants were osseointegrated and high bone-implant contact was observed throughout the porous implant. In the soft tissue, the porous implants showed thinner fibrous encapsulation while no signs of intolerance were observed for either implant type. Taken together, the present experimental results show that FFF Ti6Al4V with and without porous structures demonstrate excellent long-term soft tissue biocompatibility and a high degree of osseointegration. The present findings extend earlier, short-term experimental observations in bone and suggest that EBM, FFF Ti6Al4V implants possess valuable properties in bone and soft tissue applications.
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