The article investigates the development of a manufacturing route for highly porous titanium foams suitable for craniofacial surgery applications, particularly in cranioplasties. The study focuses on ...the polyurethane replication method for foam production and emphasizes reducing residual gas content, as it significantly affects the mechanical properties and suitability for approval of the foams. Various factors such as starting materials, solvent debinding, heating schedules, and hydrogen atmosphere are analyzed for their impact on residual gas content. It is shown that significant reductions in residual gas content can only be achieved by reworking each step of the process. A combination of initial solvent debinding of the PU template with dimethyl sulphoxide, reduction of suspension additives, use of coarser Gd. 1 powders, and an integrated debinding and sintering process under partial hydrogen atmosphere achieves a significant reduction in residual gas content. This way, the potential for producing titanium foams that comply with relevant standards for craniofacial implants is demonstrated.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Characterising the structure of cellular metals is a difficult task. The internal structure of cellular metals can be determined using micro-computed tomography (mCT). However, mCT scanning provides ...digital images in greyscale with various problematic artefacts. In addition, the grey intensity of cellular metals usually varies greatly due to the internal porosity of the material. Therefore, binary image segmentation to extract material segments from digital images is quite difficult. Our contribution can be summarised as follows. A comprehensive evaluation of various mixture models that have been shown in the literature to be useful for tomography, but for the purpose of binary image segmentation of cellular metals and internal porosity assessment. We propose a novel merging technique to merge different components of the mixture model for the purpose of binary image segmentation of cellular metals. Finally, to enforce spatial regularisation and further improve the binary image segmentation, we combine the obtained two-segment mixture model (material-void mixture model) with Markov random fields and evaluate the effects of different strengths of spatial regularisation. Our proposals are thoroughly investigated using five different types of cellular metals. The reported results are promising and competitive and speak in favour of the relevance of our proposals.
•Improvements in unsupervised image segmentation of mCT-scanned cellular metals for structure quantification are proposed.•The improvements are based on the merging of the components in the mixture model and the spatial regularisation.•The merging of the mixture components is based on the target volume of the scanned cellular metal.•Optimal mixture model should be selected based on the criteria for an optimal model and the target material volume.•Increasing spatial regularisation can lead to a deterioration in performance in cellular metal with thin and broken walls.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
A three-dimensional fully auxetic cellular structure with negative Poisson's ratio is presented. Samples are fabricated from Ti6Al4V powder via selective electron beam melting. The influence of the ...strut thickness and the amplitude of the strut on the mechanical properties and the deformation behaviour of cellular structures is studied.
NiTi foams are unique among biocompatible porous metals because of their high recovery strain (due to the shape-memory or superelastic effects) and their low stiffness facilitating integration with ...bone structures. To optimize NiTi foams for bone implant applications, two key areas are under active study: synthesis of foams with optimal architectures, microstructure and mechanical properties; and tailoring of biological interactions through modifications of pore surfaces. This article reviews recent research on NiTi foams for bone replacement, focusing on three specific topics: (i) surface modifications designed to create bio-inert porous NiTi surfaces with low Ni release and corrosion, as well as bioactive surfaces to enhance and accelerate biological activity; (ii)
in vitro and
in vivo biocompatibility studies to confirm the long-term safety of porous NiTi implants; and (iii) biological evaluations for specific applications, such as in intervertebral fusion devices and bone tissue scaffolds. Possible future directions for bio-performance and processing studies are discussed that could lead to optimized porous NiTi implants.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Porous metals and metallic foams are presently the focus of very active research and development activities. There are currently around 150 institutions working on metallic foams worldwide, most of ...them focussing on their manufacture and characterisation. Various companies are developing and producing these materials which are now being used in numerous industrial applications such as lightweight structures, biomedical implants, filters, electrodes, catalysts, and heat exchangers. This review summarizes recent developments on these materials, with particular emphasis on research presented at the latest International Conference on Porous Metals and Metallic Foams (MetFoam 2007).
Porous metals and metallic foams are presently the focus of very active research and development activities. There are currently around 150 institutions working on metallic foams worldwide, most of them focussing on their manufacture and characterisation. Various companies are developing and producing these materials which are now being used in numerous industrial applications such as lightweight structures, biomedical implants, filters, electrodes, catalysts, and heat exchangers. This review summarizes recent developments on these materials, with particular emphasis on research presented at the latest International Conference on Porous Metals and Metallic Foams (MetFoam 2007).
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Processing of Titanium Foams Dunand, D. C.
Advanced engineering materials,
June, 2004, Volume:
6, Issue:
6
Journal Article
Peer reviewed
Because of their excellent mechanical properties, low density and biocompatibility, titanium foams are attractive for structural and biomedical applications. This paper reviews current techniques for ...titanium foam processing, which are all based on powder‐metallurgy because of the extreme reactivity of liquid titanium. A first group of processes is based on powder sintering with or without place‐holder or scaffolds. A second group relies on expansion of pressurized pores created during prior powder densification.
Because of their excellent mechanical properties, low density and biocompatibility, titanium foams are attractive for structural and biomedical applications. This paper reviews current techniques for titanium foam processing, which are all based on powder‐metallurgy because of the extreme reactivity of liquid titanium. A first group of processes is based on powder sintering with or without place‐holder or scaffolds. A second group relies on expansion of pressurized pores created during prior powder densification.
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A schematic representation of the surface modification process of Mg-based foams by DPNS (directed plasma nanosynthesis). Irradiation (left): The transformation of the surface under Ar+ ions ...bombardment is presented. Initial oxide layers are removed, and the MgO layer is nanostructured. Then, an Al supply from the interior of the alloy can be accelerated via irradiation-enhanced Gibbsian segregation to the layer adjacent to the oxide. Immersion (right): The transformation of the surface after immersion in DMEM is illustrated; various combinations of DPNS parameters, including incident energy, fluence, and incident angle with respect to the surface normal, led to varied surface chemistry topography.
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•Porous AZ31 was modified at the nanoscale via directed plasma nanosynthesis (DPNS).•Ar+ irradiation modified the nanotopography and chemistry of the outer surface.•Al segregation on porous AZ31 surfaces was dependent on the DPNS parameters.•DPNS allowed the tunability of the hydrogen release of porous AZ31.•DPNS improved the apatite formation ability in porous AZ31.
Directed plasma nanosynthesis (DPNS) is a plasma-based surface modification process used to provide high-fidelity bioactive and bioresorbable interfaces for Mg-based foams having an average 500-μm pore size and containing main components of Al, Zn and Ca at bal., 3.3%, 1.11%, and 0.21%, respectively. Correlations of incident particle energies of 400–700 eV and room temperature, normal and off-normal incidence angles of 0° and 60°, respectively, and high-ion fluence conditions are combined to elicit a bioreactive Mg-foam surface. H2 evolution and pH levels of irradiated and non-irradiated Mg-foams were examined and correlated to the DPNS parameters. In situ X-ray photoelectron spectroscopy and focused ion-beam results have shown that energies of ~ 400–700 eV can control surface topography and composition, which, in turn, controls the foam-corrosion mechanism. Samples are immersed in Dulbecco’s modified eagle media, and a synergistic reaction is found in which the irradiated samples enhance the formation of calcium–phosphate (CaP) phases to CaP ratios close to the hydroxylapatite phase that enhances bone-tissue regeneration. These results lead to a surface modification strategy that adjusts the interaction of the material and the environment without using a coating that could affect the geometry and the bulk properties of the porous material.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
A device with a controllable atmosphere has been designed and fabricated to sinter metal particles in the manufacturing processes of metallic components (porous or non-porous parts). The device ...avoids the employment of an expensive controlled atmosphere furnace (a furnace in which it is possible to produce a vacuum or through which a constant flow of highly pure inert gas is maintained to protect the specimen). Metallic powders of pure metals or alloys with sintering temperatures (Ts) up to 1300°C and different forms and particle sizes can be used. The device consists of two chambers (an upper chamber for the atmosphere control and a lower chamber for the sintering processes) which are coupled by a sealed system composed of an O–ring and a clamp. The device is designed to be utilized with any conventional vertical electrical furnace (a furnace without the possibility of producing a vacuum inside or maintaining a constant flow of inert gas inside) and can be operated in three different ways: i) with a vacuum inside, ii) with a static atmosphere of inert gas inside, and iii) with a dynamic atmosphere of inert gas inside.
Open cell, stochastic nickel foams are widely used for the electrodes and current collectors of metal – metal hydride batteries. Closed cell, periodic aluminum honeycomb is extensively used for the ...cores of light, stiff sandwich panel structures. Interest is now growing in other cell topologies and potential applications are expanding. For example cellular metals are being evaluated for impact energy absorption, for noise and vibration damping and for novel approaches to thermal management. Numerous methods for manufacturing cellular metals are being developed. As a basic understanding of the relationships between cell topology and the performance of cellular metals in each application area begins to emerge, interest is growing in processes that enable an optimized topology to be reproducibly created. For some applications, such as acoustic attenuation, stochastic metal foams are likely to be preferred over their periodically structured counterparts. Nonetheless, the average cell s
ize, the cell size standard deviation, the relative density and the microstructure of the ligaments are all important to control. The invention of more stable processes and improved methods for on‐line control of the cellular structure via in‐situ sensing and more sophisticated control algorithms are likely to lead to significant improvements in foam topology. For load supporting applications, sandwich panels containing honeycomb cores are much superior to those utilizing stochastic foams, but they are more costly than stochastic foam core materials. Recently, processes have begun to emerge for making open cell periodic cell materials with triangular or pyramidal truss topologies. These have been shown to match the stiffness and strength of honeycomb in sandwich panels. New cellular metals manufacturing processes that use metal textiles and deformed sheet metal are being explored as potentially low cost manufacturing processes for these applications. These topologically optimized systems are opening up new multifunctional applications for cellular metals.
Open cell, stochastic nickel foams are widely used for the electrodes and current collectors of metal–metal hydride batteries. Closed cell, periodic aluminum honeycomb is extensively used for the cores of light, stiff sandwich panel structures. Interest is now growing in other cell topologies and potential applications are expanding. For example cellular metals are being evaluated for impact energy absorption, for noise and vibration damping and for novel approaches to thermal management. Interest is growing in processes that enable an optimized topology to be reproducibly created. Recently, processes have begun to emerge for making open cell periodic cell materials with triangular or pyramidal truss topologies, matching the stiffness and strength of honeycomb in sandwich panels. These topologically optimized systems are opening up new multifunctional applications for cellular metals.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
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