Showing papers in "Advanced Engineering Materials in 2009"
TL;DR: In this article, the ultrasonic welding technique for joining carbon fiber reinforced thermoplastic composites (CFRP) with sheet metals like aluminium alloys or aluminium-plated steels is described.
Abstract: The ultrasonic welding technology is an innovative method to produce hybrid joints for multi-material components. The investigations described in this paper were carried out using the ultrasonic metal welding technique for joining carbon fibre reinforced thermoplastic composites (CFRP) with sheet metals like aluminium alloys or aluminium-plated steels. The achievable mechanical properties as a function of the process parameters are presented. Additionally, microscopic investigations of the bonding zone are discussed. One important advantage of ultrasonic metal welding is the possibility to realise a direct contact between the load bearing fibres of the reinforced composite and the metallic surface without destroying the carbon fibres.
200 citations
TL;DR: The most commonly used method is spark plasma sintering as mentioned in this paper, which has clear advantages over conventional Sintering methods, making it possible to sinter nanometric powders to near-full densication with little grain growth.
Abstract: Piezoelectric andferroelectric ceramicmaterialsarematureand ubiquitous materials for advanced technology. Theseceramics are the active elements in a range of piezoelectricdevices and perform functions such as sensing and actuation.The performance of these materials is closely related to theirmicrostructures and, for this reason, to the ways they havebeen processed. The first step in obtaining high-performanceceramics with a homogeneous microstructure and controlledgrain size that meet the requirements of industry isto preparepowderswithcontrolledstoichiometryandsmallparticlesize.However, even if a small-size powder is used, conventionalsintering is often unable to provide dense, very fine-grainedceramics, due to the high temperatures still required fordensification,andthefactthatthelowestgrainsizeachievableby classical techniques remains about 0.5mm or even higher,depending on the system. To solve this problem, the masstransport during the sintering step must be enhanced, sincethe temperature and time needed for consolidation must bereduced in order to achieve smaller grain sizes. Among themethods reported for activation of the mass transportduring the sintering process, the application of an electricalcurrent through the sample during heating represents apromising technique for rapid densification of ceramics atrelatively low temperatures. The most novel and increas-ingly used method is spark plasma sintering, which hasclear advantages over conventional sintering methods,making it possible to sinter nanometric powders to nearfull densification with little grain growth. This has becomeincreasingly important recently, with the miniaturization ofelectronic devices and the need to investigate size effects onthe properties in the sub-micrometer range and approach-ing the nanometer scale ( 100nm).In many material applications there is a need for densematerials, often being very close to their theoretical density.Unfortunately, taking account the fragility and refractoryproperties of ceramic materials and several difficultiesinherent in the sintering process, the compaction withoutany additives becomes a real challenge from both practicaland theoretical aspects.The final electromechanical properties of piezoelectricceramic components greatly depend upon the history of theceramic. Each step in the preparation of the material has to becarefully monitored and controlled toobtain the best product.The primary steps of the preparation of the ceramic materialaresynthesisoftheprecursor,fabricationofgreenbodiesand,last but not least, sintering of the pellet to achieve properdensification. This third step, which follows powder prepara-tion, consists of thermal treatment with the aim of strengthen-ing the desired piece. It occurs via bonding of the compactgrains without melting. Such ‘‘welding’’ may be followed
180 citations
TL;DR: In this paper, the modulated structure of the AlCrFeCoNiCu high-entropy alloy consists of NiAl intermetallics (β') and a (α-Fe, Cr) solid solution (β).
Abstract: The modulated structure of the AlCrFeCoNiCu high-entropy alloy consists of NiAl intermetallics (β') and a (α-Fe, Cr) solid solution (β). The formation of the NiAl intermetallics greatly affects the strengths and magnetic properties of the A1 x CrFeCoNiCu alloys. Evidently, the AlCrFeCoNiCu alloy cannot be treated as a solid-solution alloy.
180 citations
TL;DR: In this paper, a nominally new Fe-Mn-Si based shape memory alloy with a small amount of VC was designed, and a shape recovery of more than 90% after an elongation of 4% could be achieved when the alloys were heated up to 225°C.
Abstract: In this work, a nominally new Fe-Mn-Si based shape memory alloy with a small amount of VC was designed. After an optimized thermo-mechanical treatment, a shape recovery of more than 90% after an elongation of 4% could be achieved when the alloys were heated up to 225°C. In addition, high recovery stresses of up to 380 MPa could be obtained after heating to 225°C, whereas 330 MPa were obtained after heating to 160°C.
135 citations
TL;DR: In this paper, the microstructure of conventional and auxetic foams produced through the traditional thermo-mechanical process and the novel chemo-machinery process are compared.
Abstract: Images showing the microstructure of conventional and auxetic foams produced through the traditional thermo-mechanical process and the novel chemo-mechanical process. Auxetic foams exhibit the unusual property of becoming fatter which when stretched a property which makes them superior to conventional foams in various applications ranging from smart tunable filters to vibration-proofing materials.
124 citations
TL;DR: In this article, a review of high-k ALD processes potentially applicable to the production of capacitors, concentrating on very recent developments, is presented, including possible ALD routes to materials not previously grown.
Abstract: This paper reviews several high-k ALD processes potentially applicable to the production of capacitors, concentrating on very recent developments. A list of the dielectric materials under investigation consists of the oxides of several metals, including the Group 4 (Ti, Zr, Hf) elements. The binary oxides of Group 4 metals, as well as their mixtures with other oxides, doped hosts, or multi-layers in the form of nano-laminates are of interest.Several examples of our recent results are shown, including possible ALD routes to materials not previously grown, as well as advances in process development.
123 citations
TL;DR: In this paper, a novel design approach for precipitation hardened ductile high strength martensitic and austenitic-martensitic steels (up to 1.5 GPa strength) is reported.
Abstract: In this work, we report about a novel design approach for precipitation hardened ductile high strength martensitic and austenitic-martensitic steels (up to 1.5 GPa strength). The alloys are characterized by a low carbon content (0.01 wt% C), 9–15 wt% Mn to obtain different levels of austenite stability, and minor additions of Ni, Ti, and Mo (1–2 wt%). The latter are required for creating precipitates during aging heat treatment. Hardening in these materials is realized by combining the TRIP effect with a maraging treatment [transformationinduced plasticity (TRIP); maraging: martensite aging through thermally stimulated precipitation of particles]. The TRIP mechanism is based on the deformation-stimulated athermal transformation of metastable austenite (face centered cubic Fe–Mn phase) into martensite (metastable body centered cubic or orthorhombic Fe–Mn phase) and the resulting matrix and martensite plasticity required to accommodate the transformation misfit. [3–11] The maraging treatment is based on hardening the heavily strained martensite through the formation of small intermetallic precipitates (of the order of several nanometers). These particles act as highly efficient obstacles against dislocation motion through the Orowan and Fine-Kelly mechanisms enhancing the strength of the material. [12–17] While both types of alloys, i.e., TRIP steels [3–11] and maraging steels [12–17] have been well investigated, the combination of the two mechanisms in the form of a set of simple Fe–Mn alloys as suggested in this work, namely, the precipitation hardening of transformation-induced martensite by intermetallic nanoparticles, opens a novel and lean alloy path to the development of ultrahigh strength steels that has not been much explored in the past. [18,19] We refer to these
105 citations
86 citations
TL;DR: In situ growth of highly porous metal-organic frameworks (MOFs) in the presence of pulp fibers results in high surface area MOF/textile composites as mentioned in this paper, which is indispensable for any industrial application of MOFs.
Abstract: In situ growth of highly porous metal-organic frameworks (MOFs) in the presence of pulp fibers results in high surface area MOF/textile composites. Such a carrier concept is indispensable for any industrial application of MOFs.
84 citations
TL;DR: In this article, a new method was developed for producing highly porous NiTi for use as an implant material, which combined the space-holder technique with the metal injection molding process.
Abstract: A new method was developed for producing highly porous NiTi for use as an implant material. The combination of the space-holder technique with the metal injection molding process allows a net-shape fabrication of geometrically complex samples and the possibility of mass production for porous NiTi. Further, the porosity can be easily adjusted with respect to pore size, pore shape, and total porosity. The influence of the surface properties of powder metallurgical NiTi on the biocompatibility was first examined using human mesenchymal stem cells (hMSCs). It was found that pre-alloyed NiTi powders with an average particle size smaller than 45 μm led to the surface properties most suitable for the adhesion and proliferation of hMSCs. For the production of highly porous NiTi, different space-holder materials were investigated regarding low C- and O-impurity contents and the reproducibility of the process. NaCl was the most promising space-holder material compared to PMMA and saccharose and was used in subsequent studies. In these studies, the influence of the total porosity on the mechanical properties of NiTi is investigated in detail. As a result, bone-like mechanical properties were achieved by the choice of Ni-rich NiTi powder and a space-holder content of 50 vol% with a particle size fraction of 355–500 μm. Pseudoelasticity of up to 6% was achieved in compression tests at 37 °C as well as a bone-like loading stiffness of 6.5 GPa, a sufficient plateau stress σ25 of 261 MPa and a value for σ50 of 415 MPa. The first biological tests of the porous NiTi samples produced by this method showed promising results regarding proliferation and ingrowth of mesenchymal stem cells, also in the pores of the implant material.
78 citations
TL;DR: In this article, it was shown that high solidification rates prevented coarsening of dispersion strengthened particle diameters, which usually occurs during melting and compromises the high temperature creep strength of these alloys.
Abstract: This paper was the first to show that melt-sensitive oxide dispersion strengthened powder metallurgy alloys such as Fe-Cr-Al PM2000 alloy could be successfully processed into solid components using Selective Laser Melting (SLM). The key finding of the work was that high solidification rates prevented coarsening of dispersion strengthened particle diameters, which usually occurs during melting and compromises the high temperature creep strength of these alloys. The work has been internationally cited and was the foundation for inspiring further work which aimed to produce novel heat exchangers for space applications using this rapid prototyping technique.
TL;DR: In this paper, the authors summarize recent results on resistive switching effects in inorganic materials obtained in the research groups of the authors and discuss the implications of these results for the suitability of the investigated material systems as well as for the direction of further research.
Abstract: Solid state memories play an important role for the electronic systems used in today's information society. The classical approach of charge storage is expected to reach its physical scaling limits very soon. New storage effects are therefore receiving significant interest from industry and academia. In the paper we summarize recent results on resistive switching effects in inorganic materials obtained in the research groups of the authors. We discuss the implications of these results for the suitability of the investigated material systems as well as for the direction of further research.
TL;DR: In this article, a low current density preconditioning process is used to produce an improved lithium transport mechanism by the action of charge flow through a plastic crystal electrolyte (figure).
Abstract: A low current density preconditioning process, which produces an improved lithium transport mechanism is created by the action of charge flow through a plastic crystal electrolyte (figure). A reduction in cell polarisation at high applied current density is demonstrated which approaches the rates required for these electrolytes to be used in practical devices.
TL;DR: In this article, the influence of layer thickness and sample orientation within the building chamber of the 3D-printer on microstructure, porosity, and mechanical properties of the preforms and final composites was investigated.
Abstract: Alumina/glass composites were fabricated by three-dimensional printing (3DP™) and pressureless infiltration of lanthanum-alumino-silicate glass into sintered porous alumina preforms. The preforms were printed using an alumina/dextrin powder blend as a precursor material. They were sintered at 1600 °C for 2 h prior to glass infiltration at 1100 °C for 2 h. The influence of layer thickness and sample orientation within the building chamber of the 3D-printer on microstructure, porosity, and mechanical properties of the preforms and final composites was investigated. The increase of the layer thickness from 90 to 150 µm resulted in an increase of the total porosity from ∼19 to ∼39 vol% and thus, in a decrease of the mechanical properties of the sintered preforms. Bending strength and elastic modulus of sintered preforms were found to attain significantly higher values for samples orientated along the Y-axis of the 3D-printer compared to those orientated along the X- or the Z-axis, respectively. Fabricated Al2O3/glass composites exhibit improved fracture toughness, bending strength, Young's modulus, and Vickers hardness up to 3.6 MPa m1/2, 175 MPa, 228 GPa, and 12 GPa, respectively. Prototypes were fabricated on the basis of computer tomography data and computer aided design data to show geometric capability of the process.
TL;DR: In this article, a general quantitative model has been developed that provides fundamental understanding of the metal-induced crystallization (MIC) of amorphous semiconductors, and it has been employed to predict the MIC temperature for various metal/amorphous-semiconductor systems.
Abstract: A general, quantitative model has been developed that provides fundamental understanding of the metal-induced crystallization (MIC) of amorphous semiconductors. Interface thermodynamics has been shown to play a decisive role for the whether or not occurrence of MIC. The model has been employed to predict the MIC temperature for various metal/amorphous-semiconductor systems. A consequence of the model is the prediction that the thickness of an ultrathin, pure Al film put on the top of an amorphous Si layer can be used as a very accurate tool to tune the crystallization temperature of amorphous Si. These theoretical predictions have been confirmed experimentally. The fundamental understanding reached may lead to pronounced technological progress in the low-temperature manufacturing of crystalline-Si-based devices deposited on cheap and flexible substrates such as glasses, plastics, and possibly even papers.
TL;DR: In this paper, a novel composites on the basis of austenitic stainless TRIP-steel as matrix with reinforcements of Mg-PSZ are presented, which are characterized by optical and scanning electron microscopy before and after deformation, showing the microstructure and the deformation induced martensite formation.
Abstract: Novel composites on basis of austenitic stainless TRIP-steel as matrix with reinforcements of Mg-PSZ are presented. Compact rods were produced by cold isostatic pressing and sintering, square honeycomb samples by the ceramic extrusion technique. The samples are characterized by optical and scanning electron microscopy before and after deformation, showing the microstructure and the deformation- induced martensite formation. The mechanical properties of samples with 5 vol% zirconia are superior compared to zirconia-free samples and composites with higher zirconia contents in terms of bending and compression tests. The honeycomb samples exhibit extraordinary high specific energy absorption in compression.
TL;DR: At concentrations ranging up to 80 × 10−3 M, cells exposed to the PVA‐coated nanoparticles demonstrate high cell viability without necrosis and apoptosis, in contrast, significant apoptosis is observed in Cells exposed to bare SPIONs at a concentration of 80×103M.
Abstract: Super-paramagnetic iron oxide nanoparticles (SPIONs) are recognized as powerful biocompatible materials for use in various biomedical applications, such as drug delivery, magnetic-resonance imaging, cell/protein separation, hyperthermia and transfection. This study investigates the impact of high concentrations of SPIONs on cytotoxicity and cell-cycle effects. The interactions of surface-saturated (via interactions with cell medium) bare SPIONs and those coated with poly(vinyl alcohol) (PVA) with adhesive mouse fibroblast cells (L929) are investigated using an MTT assay. The two SPION formulations are synthesized using a co-precipitation method. The bare and coated magnetic nanoparticles with passivated surfaces both result in changes in cell morphology, possibly due to clustering through their magnetostatic effect. At concentrations ranging up to 80 × 10−3 M, cells exposed to the PVA-coated nanoparticles demonstrate high cell viability without necrosis and apoptosis. In contrast, significant apoptosis is observed in cells exposed to bare SPIONs at a concentration of 80 × 10−3 M. Nanoparticle exposure (20–80 × 10−3 M) leads to variations in both apoptosis and cell cycle, possibly due to irreversible DNA damage and repair of oxidative DNA lesions, respectively. Additionally, the formation of vacuoles within the cells and granular cells indicates autophagy cell death rather than either apoptosis or necrosis.
TL;DR: An analysis on the influence of solid phase thermal conductivity and cellular structure on the heat transfer mechanisms (HTM) by means of studding diverse case studies combining theoretical and experimental data is presented in this article.
Abstract: An analysis on the influence of solid phase thermal conductivity and cellular structure on the heat transfer mechanisms (HTMs) by means of studding diverse case studies combining theoretical and experimental data. The radiation and conduction mechanisms have been analyzed for cellular materials based on insulating and conductive matrixes using similar concepts and models for both types of materials.
TL;DR: In this paper, in-situ neutron studies were performed for the detection of atomic disorder in the ordered phases of the bcc β-phase of titanium aluminides, where complementary laser scanning confocal microscopy was employed for in-Situ microstructural investigations.
Abstract: In recent times, novel titanium aluminides containing the bcc β-phase at high temperatures are being developed for improved hot-working capabilities, however, predictions of the phase diagrams are merely uncertain. Here we present in-situ neutron studies, which are particularly sensitive to the atomic disorder in the ordered phases. Complementary laser scanning confocal microscopy is employed for in-situ microstructural investigations.
TL;DR: In this article, an Al85.5Ni9.5La5 cylindrical rod with a diameter of 1 mm has been produced and its thermal and mechanical properties are explored for the first time.
Abstract: More attention has been paid to bulk metallic glasses (BMGs) in recent years due to their superior properties, and they have already been developed successfully in many systems such as Zr-, Fe-, Mg-, Cu-, Ti-, Ni- and La-based alloys. [1–6] In the meantime, Al-based metallic glass has also received particular interest because of its low density and potential aerospace applications. [7] However, an Al-based metallic glassy rod with a diameter of 1 mm has not yet been produced. Mechanical properties of these materials are usually measured by examining wires and ribbons. [8,9] Therefore, the research and application of Al-based metallic glasses are limited to a large extent due to the sample size. It is important and significant to develop Al-based BMGs. Different methods, such as alloying for example, which are popular and effective in other alloy systems, [10] have been employed to improve the glass-forming ability (GFA) of Al-based metallic glasses. They have little effect on the GFA of Al-based alloy systems. [11,12] The low GFA of Al-based alloys results from the existence of local-ordering clusters and high-melting-temperature phases in the alloy melt, which usually act as nucleation sites. This further promotes crystallization: the precipitation of fcc-Al, and intermetallics, which deteriorate the GFA. In this paper, the successful preparation of an Al-based BMG with a diameter of 1 mm in the Al85.5Ni9.5La5 (in atomic percentage) alloy by a melt-treatment technique is described. The treatment is adapted to not only remove the pre-existing nuclei but also to realize a high cooling rate. The thermal and mechanical properties of the Al85.5Ni9.5La5 BMG, along with its compressive-fracture behavior are explored for the first time. This work will greatly promote the development and application of Al-based BMGs. Figure 1a shows a photograph of an Al85.5Ni9.5La5 BMG cylindrical rod with a diameter of 1 mm. The surface is smooth and lustrous, like other as-cast BMGs. Figure 1b shows X-ray diffraction (XRD) patterns of as-cast ribbons, sheets and rods. It can be seen that only one broad diffraction peak in the 2u range from 358 to 458, characteristic of an amorphous structure, is detected, without any crystalline peaks. Figure 2 shows differential scanning calorimetry (DSC) curves of the as-cast ribbons, sheets and rods. The three traces display similar glass-transition and crystallization behaviors and indicate similar amounts of exothermic heat, which is consistent with the XRD results. In comparison to the GFA of Al86Ni9La5 reported in ref. [13], we found that a larger size of amorphous alloy is obtained with our casting strategy than with the ordinary wedge-casting method. COMMUNICATION
TL;DR: This experimental study provides the first evidence in vitro that bioactive glass-ceramic scaffolds made from both 45S5 Bioglass and boron containingBioactive glass as well as their ionic dissolution products do no exhibit antibacterial effect against several strains of S. aureus.
Abstract: Staphylococcus aureus is an opportunistic pathogen of major clinical interest for its high prevalence in biomaterial-related infections. This experimental study provides the first evidence in vitro that bioactive glass-ceramic scaffolds made from both 45S5 Bioglass ® and from boron containing bioactive glass (45S5.2B) as well as their ionic dissolution products do no exhibit antibacterial effect against several strains of S. aureus.
TL;DR: In this article, the changes of the three dimensional architecture of a eutectic AlSi12 alloy during heat treatment are revealed by means of synchrotron holotomography.
Abstract: The changes of the three dimensional architecture of a eutectic AlSi12 alloy during heat treatment are revealed by means of synchrotron holotomography. The non-destructive nature of the holotomography technique allows to analyze the same volumes in different thermal conditions. The results show a disintegration of the interconnected eutectic Si-lamellae into isolated elongated particles. The load carrying capacity of both types of Si morphologies is studied by in situ neutron diffraction during compression tests. The experimental results are compared to those obtained using a micromechanical model developed for metal matrix composites based on a homogenization approach. The correlation between experiments and calculations shows that the interconnectivity of Si must be considered to account for the strength exhibited by the eutectic alloy. The present study bridges the gap between the already available two-dimensional studies of architecture and properties of the binary AlSi12 alloy and new three-dimensional studies of more complex systems based on this alloy.
TL;DR: In this paper, the representative volume element (RVE) plays a central role in efforts to predict the effective thermo-physical and transport properties of heterogeneous materials and a quantitative definition of its size is proposed.
Abstract: The representative volume element (RVE) plays a central role in efforts to predict the effective thermo-physical and transport properties of heterogeneous materials. A quantitative definition of its size is proposed in this work. It is shown that RVE depends on the morphological or physical property being investigated. The methodology is applied to real samples of open-celled materials (such as metallic foam) whose structure is obtained from X-Ray microtomography.
TL;DR: In this article, internal load transfer under external compressive loading in metal/ceramic composites has been studied for the first time using energy dispersive synchrotron X-ray diffraction.
Abstract: Freeze casting offers a new technique to fabricate ceramic preforms for metal/ceramic composites. Internal load transfer under external compressive loading in such composites has been studied for the first time using energy dispersive synchrotron X-ray diffraction. The results show that load transfer takes place from the soft metallic alloy to the hard ceramic which has been explained in the light of generalized Hooke's law and classical laminate theory.
TL;DR: The grain microstructure is strongly bimodal due to the mixture of large dendritic grains that solidify in the shot sleeve and are subsequently injected into the die cavity, and the small grains that nucleate inside the cavity and grow to a size dictated by the solute content and the solidification rate.
Abstract: The grain microstructure is strongly bimodal due to the mixture of large dendritic grains that solidify in the shot sleeve and are subsequently injected into the die cavity, and the small grains that nucleate inside the cavity and grow to a size dictated by the solute content and the solidification rate. The large grains form only in concentrated alloys; their size is also partially controlled by the growth restriction factor.
TL;DR: In this paper, the impact of surface roughness of pure Hydroxyapatite (HA) and the influence of Si0 2 introduction during freeze casting on adhesion, proliferation, and differentiation of human osteoblast-like cells (MG-63) was investigated.
Abstract: Freeze casting is a fabrication method that allows producing near-net-shaped ceramics with variable porosity. Hydroxyapatite (HA) was modified by the addition of different amounts of SiO 2 nanoparticles during freeze cast preparation. The addition of SiO 2 introduced a partial phase transformation of HA to β-tricalcium phosphate and improved the form stability due to less shrinkage after sintering. The impact of surface roughness of pure HA ceramics and the influence of Si0 2 introduction during freeze casting on adhesion, proliferation, and differentiation of human osteoblast-like cells (MG-63) was investigated. While both cell attachment and proliferation of smooth pressed HA was significantly enhanced compared to rough freeze cast HA, the addition of SiO 2 improved the cell numbers of the latter. The expression of cell differentiation markers osteocalcin and collagen I was found to be supported by rough surfaces (R a = 5-6 μm) in particular on ceramics containing Si0 2 .
TL;DR: In this article, the compression behavior of a Ca 65 Mg 15 Zn 20 bulk-metallic glass (BMG) was studied and the fracture strength was inversely proportional to the fracture time.
Abstract: The compression behavior of a Ca 65 Mg 15 Zn 20 bulk-metallic glass (BMG) was studied. The specimens showed no macroscopic plasticity. They fractured by exploding into many very small pieces. The Vickers hardness of the Ca 65 Mg 15 Zn 20 BMG was about 1.42 GPa. The fatigue limit for compression-compression fatigue was found to be about 140 MPa after 10 6 cycles. The fracture strength was inversely proportional to the fracture time. The proposed mechanism of the splitting and shear fracture modes clearly explained these properties.