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- ItemSurface effects and challenges for application of piezoelectric langasite substrates in surface acoustic wave devices caused by high temperature annealing under high vacuum(Basel : MDPI, 2015) Seifert, Marietta; Rane, Gayatri K.; Kirbus, Benjamin; Menzel, Siegfried B.; Gemming, ThomasSubstrate materials that are high-temperature stable are essential for sensor devices which are applied at high temperatures. Although langasite is suggested as such a material, severe O and Ga diffusion into an O-affine deposited film was observed during annealing at high temperatures under vacuum conditions, leading to a damage of the metallization as well as a change of the properties of the substrate and finally to a failure of the device. Therefore, annealing of bare LGS (La 3 Ga 5 SiO 14 ) substrates at 800 ∘ C under high vacuum conditions is performed to analyze whether this pretreatment improves the suitability and stability of this material for high temperature applications in vacuum. To reveal the influence of the pretreatment on the subsequently deposited metallization, RuAl thin films are used as they are known to oxidize on LGS at high temperatures. A local study of the pretreated and metallized substrates using transmission electron microscopy reveals strong modification of the substrate surface. Micro cracks are visible. The composition of the substrate is strongly altered at those regions. Severe challenges for the application of LGS substrates under high-temperature vacuum conditions arise from these substrate damages, revealing that the pretreatment does not improve the applicability.
- ItemDeformation-induced martensitic transformation in Cu-Zr-Zn bulk metallic glass composites(Basel : MDPI, 2015) Wu, Dianyu; Song, Kaikai; Cao, Chongde; Li, Ran; Wang, Gang; Wu, Yuan; Wan, Feng; Ding, Fuli; Shi, Yue; Bai, Xiaojun; Kaban, Ivan; Eckert, JürgenThe microstructures and mechanical properties of (Cu0.5Zr0.5)100−xZnx (x = 0, 1.5, 2.5, 4.5, 7, 10, and 14 at. %) bulk metallic glass (BMG) composites were studied. CuZr martensitic crystals together with minor B2 CuZr and amorphous phases dominate the microstructures of the as-quenched samples with low Zn additions (x = 0, 1.5, and 2.5 at. %), while B2 CuZr and amorphous phases being accompanied with minor martensitic crystals form at a higher Zn content (x = 4.5, 7, 10, and 14 at. %). The fabricated Cu-Zr-Zn BMG composites exhibit macroscopically appreciable compressive plastic strain and obvious work-hardening due to the formation of multiple shear bands and the deformation-induced martensitic transformation (MT) within B2 crystals. The present BMG composites could be a good candidate as high-performance structural materials.
- ItemSelective laser melting of Ti-45Nb alloy(Basel : MDPI, 2015) Schwab, Holger; Prashanth, Konda Gokuldoss; Löber, Lukas; Kühn, Uta; Eckert, JürgenTi-45Nb is one of the potential alloys that can be applied for biomedical applications as implants due to its low Young’s modulus. Ti-45Nb (wt.%) gas atomized powders were used to produce bulk samples by selective laser melting with three different parameter sets (energy inputs). A β-phase microstructure consisting of elliptical grains with an enriched edge of titanium was observed by scanning electron microscopy and X-ray diffraction studies. The mechanical properties of these samples were evaluated using hardness and compression tests, which suggested that the strength of the samples increases with increasing energy input within the range considered.
- ItemStress-corrosion interactions in Zr-based bulk metallic glasses(Basel : MDPI, 2015) Schwab, Holger; Prashanth, Konda Gokuldoss; Löber, Lukas; Kühn, Uta; Eckert, JürgenStress-corrosion interactions in materials may lead to early unpredictable catastrophic failure of structural parts, which can have dramatic effects. In Zr-based bulk metallic glasses, such interactions are particularly important as these have very high yield strength, limited ductility, and are relatively susceptible to localized corrosion in halide-containing aqueous environments. Relevant features of the mechanical and corrosion behavior of Zr-based bulk metallic glasses are described, and an account of knowledge regarding corrosion-deformation interactions gathered from ex situ experimental procedures is provided. Subsequently the literature on key phenomena including hydrogen damage, stress corrosion cracking, and corrosion fatigue is reviewed. Critical factors for such phenomena will be highlighted. The review also presents an outlook for the topic.
- ItemMechanical and structural investigation of porous bulk metallic glasses(Basel : MDPI, 2015) Wu, Dianyu; Song, Kaikai; Cao, Chongde; Li, Ran; Wang, Gang; Wu, Yuan; Wan, Feng; Ding, Fuli; Shi, Yue; Bai, Xiaojun; Kaban, Ivan; Eckert, JürgenThe intrinsic properties of advanced alloy systems can be altered by changing their microstructural features. Here, we present a highly efficient method to produce and characterize structures with systematically-designed pores embedded inside. The fabrication stage involves a combination of photolithography and deep reactive ion etching of a Si template replicated using the concept of thermoplastic forming. Pt- and Zr-based bulk metallic glasses (BMGs) were evaluated through uniaxial tensile test, followed by scanning electron microscope (SEM) fractographic and shear band analysis. Compositional investigation of the fracture surface performed via energy dispersive X-ray spectroscopy (EDX), as well as Auger spectroscopy (AES) shows a moderate amount of interdiffusion (5 at.% maximum) of the constituent elements between the deformed and undeformed regions. Furthermore, length-scale effects on the mechanical behavior of porous BMGs were explored through molecular dynamics (MD) simulations, where shear band formation is observed for a material width of 18 nm.
- ItemPhonon spectrum engineering in rolled-up micro- and nano-architectures(Basel : MDPI, 2015) Fomin, Vladimir M.; Balandin, Alexander A.We report on a possibility of efficient engineering of the acoustic phonon energy spectrum in multishell tubular structures produced by a novel high-tech method of self-organization of micro- and nano-architectures. The strain-driven roll-up procedure paved the way for novel classes of metamaterials such as single semiconductor radial micro- and nano-crystals and multi-layer spiral micro- and nano-superlattices. The acoustic phonon dispersion is determined by solving the equations of elastodynamics for InAs and GaAs material systems. It is shown that the number of shells is an important control parameter of the phonon dispersion together with the structure dimensions and acoustic impedance mismatch between the superlattice layers. The obtained results suggest that rolled up nano-architectures are promising for thermoelectric applications owing to a possibility of significant reduction of the thermal conductivity without degradation of the electronic transport.
- ItemRecent advances in the synthesis and biomedical applications of nanocomposite hydrogels(Basel : MDPI, 2015) Spizzirri, Umile Gianfranco; Curcio, Manuela; Cirillo, Giuseppe; Spataro, Tania; Vittorio, Orazio; Picci, Nevio; Hampel, Silke; Iemma, Francesca; Nicoletta, Fiore PasqualeHydrogels sensitive to electric current are usually made of polyelectrolytes and undergo erosion, swelling, de-swelling or bending in the presence of an applied electric field. The electrical conductivity of many polymeric materials used for the fabrication of biomedical devices is not high enough to achieve an effective modulation of the functional properties, and thus, the incorporation of conducting materials (e.g., carbon nanotubes and nanographene oxide) was proposed as a valuable approach to overcome this limitation. By coupling the biological and chemical features of both natural and synthetic polymers with the favourable properties of carbon nanostructures (e.g., cellular uptake, electromagnetic and magnetic behaviour), it is possible to produce highly versatile and effective nanocomposite materials. In the present review, the recent advances in the synthesis and biomedical applications of electro-responsive nanocomposite hydrogels are discussed.