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- ItemTi/Al multi-layered sheets: Accumulative roll bonding (Part A)(Basel : MDPI, 2016) Romberg, Jan; Freudenberger, Jens; Bauder, Hansjörg; Plattner, Georg; Krug, Hans; Holländer, Frank; Scharnweber, Juliane; Eschke, Andy; Kühn, Uta; Klauß, Hansjörg; Oertel, Carl-Georg; Skrotzki, Werner; Eckert, Jürgen; Schultz, LudwigCo-deformation of Al and Ti by accumulative roll bonding (ARB) with intermediate heat treatments is utilized to prepare multi-layered Ti/Al sheets. These sheets show a high specific strength due to the activation of various hardening mechanisms imposed during deformation, such as: hardening by grain refinement, work hardening and phase boundary hardening. The latter is even enhanced by the confinement of the layers during deformation. The evolution of the microstructure with a special focus on grain refinement and structural integrity is traced, and the correlation to the mechanical properties is shown.
- ItemNon-isothermal kinetic analysis of the crystallization of metallic glasses using the master curve method(Basel : MDPI, 2011) Torrens-Serra, Joan; Venkataraman, Shankar; Stoica, Mihai; Kuehn, Uta; Roth, Stefan; Eckert, JürgenThe non-isothermal transformation rate curves of metallic glasses are analyzed with the Master Curve method grounded in the Kolmogorov-Johnson-Mehl-Avrami theory. The method is applied to the study of two different metallic glasses determining the activation energy of the transformation and the experimental kinetic function that is analyzed using Avrami kinetics. The analysis of the crystallization of Cu47Ti33Zr11Ni8Si1 metallic glassy powders gives Ea = 3.8 eV, in good agreement with the calculation by other methods, and a transformation initiated by an accelerating nucleation and diffusion-controlled growth. The other studied alloy is a Nanoperm-type Fe77Nb7B15Cu1 metallic glass with a primary crystallization of bcc-Fe. An activation energy of Ea = 5.7 eV is obtained from the Master Curve analysis. It is shown that the use of Avrami kinetics is not able to explain the crystallization mechanisms in this alloy giving an Avrami exponent of n = 1.
- 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.
- ItemStructural and mechanical characterization of Zr58.5Ti8.2Cu14.2Ni11.4Al7.7 bulk metallic glass(Basel : MDPI, 2011) Prashanth, Konda G.; Scudino, Sergio; Khoshkhoo, Mohsen Samadi; Surreddi, Kumar B.; Stoica, Mihai; Vaughan, Gavin; Eckert, JürgenThermal stability, structure and mechanical properties of the multi-component Zr58.5Ti8.2Cu14.2Ni11.4Al7.7 bulk metallic glass have been studied in detail. The glassy material displays good thermal stability against crystallization and a fairly large supercooled liquid region of 52 K. During heating, the alloy transforms into a metastable icosahedral quasicrystalline phase in the first stage of crystallization. At high temperatures, the quasicrystalline phase undergoes a transformation to form tetragonal and cubic NiZr2-type phases. Room-temperature compression tests of the as-cast sample show good mechanical properties, namely, high compressive strength of about 1,630 MPa and fracture strain of 3.3%. This is combined with a density of 6.32 g/cm3 and values of Poisson’s ratio and Young’s modulus of 0.377 and 77 GPa, respectively. The mechanical properties of the glass can be further improved by cold rolling. The compressive strength rises to 1,780 MPa and the fracture strain increases to 8.3% for the material cold-rolled to a diameter reduction of 10%.
- ItemTungsten as a chemically-stable electrode material on Ga-containing piezoelectric substrates langasite and catangasite for high-temperature saw devices(Basel : MDPI, 2016) Rane, Gayatri K.; Seifert, Marietta; Menzel, Siegfried; Gemming, Thomas; Eckert, JürgenThin films of tungsten on piezoelectric substrates La3Ga5SiO14 (LGS) and Ca3TaGa3Si2O14 (CTGS) have been investigated as a potential new electrode material for interdigital transducers for surface acoustic wave-based sensor devices operating at high temperatures up to 800 °C under vacuum conditions. Although LGS is considered to be suitable for high-temperature applications, it undergoes chemical and structural transformation upon vacuum annealing due to diffusion of gallium and oxygen. This can alter the device properties depending on the electrode nature, the annealing temperature, and the duration of the application. Our studies present evidence for the chemical stability of W on these substrates against the diffusion of Ga/O from the substrate into the film, even upon annealing up to 800 °C under vacuum conditions using Auger electron spectroscopy and energy-dispersive X-ray spectroscopy, along with local studies using transmission electron microscopy. Additionally, the use of CTGS as a more stable substrate for such applications is indicated.
- ItemProduction of porous β-Type Ti–40Nb alloy for biomedical applications: Comparison of selective laser melting and hot pressing(Basel : MDPI, 2013) Zhuravleva, Ksenia; Bönisch, Matthias; Prashanth, Konda Gokuldoss; Hempel, Ute; Helth, Arne; Gemming, Thomas; Calin, Mariana; Scudino, Sergio; Schultz, Ludwig; Eckert, Jürgen; Gebert, AnnettWe used selective laser melting (SLM) and hot pressing of mechanically-alloyed β-type Ti–40Nb powder to fabricate macroporous bulk specimens (solid cylinders). The total porosity, compressive strength, and compressive elastic modulus of the SLM-fabricated material were determined as 17% ± 1%, 968 ± 8 MPa, and 33 ± 2 GPa, respectively. The alloy’s elastic modulus is comparable to that of healthy cancellous bone. The comparable results for the hot-pressed material were 3% ± 2%, 1400 ± 19 MPa, and 77 ± 3 GPa. This difference in mechanical properties results from different porosity and phase composition of the two alloys. Both SLM-fabricated and hot-pressed cylinders demonstrated good in vitro biocompatibility. The presented results suggest that the SLM-fabricated alloy may be preferable to the hot-pressed alloy for biomedical applications, such as the manufacture of load-bearing metallic components for total joint replacements.
- 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.
- 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.
- ItemTi/Al multi-layered sheets: Differential speed rolling (Part B)(Basel : MDPI, 2016) Romberg, Jan; Freudenberger, Jens; Watanabe, Hiroyuki; Scharnweber, Juliane; Eschke, Andy; Kühn, Uta; Klauß, Hansjörg; Oertel, Carl-Georg; Skrotzki, Werner; Eckert, Jürgen; Schultz, LudwigDifferential speed rolling has been applied to multi-layered Ti/Al composite sheets, obtained from accumulative roll bonding with intermediate heat treatments being applied. In comparison to conventional rolling, differential speed rolling is more efficient in strengthening the composite due to the more pronounced grain refinement. Severe plastic deformation by means of rolling becomes feasible if the evolution of common rolling textures in the Ti layers is retarded. In this condition, a maximum strength level of the composites is achieved, i.e., an ultimate tensile strength of 464 MPa, while the strain to failure amounts to 6.8%. The deformation has been observed for multi-layered composites. In combination with the analysis of the microstructure, this has been correlated to the mechanical properties.
- 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.