bulk metallic glasses were prepared by cooling the melt with a rate of about 10 K/s and investigated with respect to their chemical and structural homogeneity by atom probe field ion microscopy and transmission electron microscopy. The measurements on these slowly cooled samples reveal that the alloy exhibits phase separation in the undercooled liquid state. Significant composition fluctuations are found in the Be and Zr concentration but not in the Ti, Cu, and Ni concentration. The decomposed microstructure is compared with the microstructure obtained upon primary crystallization, suggesting that the nucleation during primary crystallization of this bulk glass former is triggered by the preceding diffusion controlled decomposition in the undercooled liquid state. © 1995 American Institute of Physics.In the last decade, phase separation in the amorphous or undercooled liquid state has been studied in a large variety of metallic glasses. Decomposition was, for example, reported in the Ti-Zr-Be system, 1,2 in Zr-Cu, 3,4 , Zr-Co, 5,6 and lately in the La-Al-Ni 7 and the Zr-Y-Ni-Al 8 bulk metallic glass ͑BMG͒ forming systems. In BMG forming alloys, phase separation becomes an important factor in understanding the crystallization process and the glass forming ability.The novel multicomponent BMG formers that, for example, additionally include Zr-Al-Ni, 9 Zr-Al-Cu-Ni, 10and Zr-Ti-Cu-Ni-Be, 11 exhibit an extremely high glass forming ability. For the Zr 41.2 Ti 13.8 Cu 12.5 Ni 10.0 Be 22.5 alloy, a cooling rate of only 1 K/s is required to suppress crystallization and to form a metallic glass.12 If one assumes classical nucleation from a homogeneous undercooled liquid state below the melting point or a supercooled liquid state above the glass transition, this implies very small nucleation rates for crystallization at relatively high diffusion constants 13 and should result in a rather coarse microstructure upon crystallization. However, in contradiction to this, there are indications in several BMG forming alloy systems that primary crystallization results in a microstructure consisting of nanocrystals with a very high number density embedded in an amorphous matrix. 14 -16 In this letter we will show that the Zr 4.12 Ti 13.8 Cu 12.5 Ni 10.0 Be 22.5 alloy decomposes during undercooling in the liquid state. This decomposition appears to be a necessary precursor for the nucleation of crystals and further results in a uniform distribution of crystals on a very fine length scale during primary crystallization. Results of atom probe field ion microscopy ͑AP/FIM͒ and transmission electron microscopy ͑TEM͒ will be shown to support this description.Amorphous alloy ingots with a nominal composition of Zr 41.2 Ti 13.8 Cu 12.5 Ni 10.0 Be 22.5 were prepared from a mixture of the elements of purity ranging from 99.5% to 99.9% by induction melting on a water-cooled silver boat under a Ti gettered argon atmosphere. Several pieces were remelted together in a 1 2 inch inner diameter silica tube and then water quenched, resulting in a 4 ...

Ti-6Al-4V alloy has been widely used in restorative surgery due to its high corrosion resistance and biocompatibility. Nevertheless, some studies showed that V and Al release in the organism might induce cytotoxic effects and neurological disorders, which led to the development of V-free alloys and both V-and Al-free alloys containing Nb, Zr, Ta, or Mo. Among these alloys, Ti-13Nb-13Zr alloy is promising due to its better biomechanical compatibility than Ti-6Al-4V. In this work, the corrosion behavior of Ti, Ti-6Al-4V, and Ti-xNb-13Zr alloys (x ¼ 5, 13, and 20) was evaluated in Ringer's solution (pH 7.5) at 37 8C through open-circuit potential measurements, potentiodynamic polarization, and electrochemical impedance spectroscopy. Spontaneous passivity was observed for all materials in this medium. Low corrosion current densities (in the order of 10 À7 A/cm 2 ) and high impedance values (in the order of 10 5 Vcm 2 at low frequencies) indicated their high corrosion resistance. EIS results showed that the passivating films were constituted of an outer porous layer (very low resistance) and an inner compact layer (high resistance), the latter providing the corrosion resistance of the materials. There was evidence that the Ti-xNb-13Zr alloys were more corrosion resistant than both Ti and Ti-6Al-4V in Ringer's solution.

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New perspectives have been developed to understand the processes of modeling heterogeneous membranes. These are crucial steps prior to applying advanced techniques like molecular dynamic simulations of whole membrane systems. Lipid, protein, and membrane packing problems are addressed based on biochemical properties in combination with computational optimization techniques. The CELLmicrocosmos 2.2 MembraneEditor (CmME) is introduced as an appropriate framework to handle such problems by offering diverse algorithmic approaches. Its algorithm plug-in-interface enables modelers to generate problem-specific algorithms. Good solutions concerning runtime and lipid density are realized by focusing on the outer shapes of the PDB-based molecules. Application cases are presented like the publication-based modeling of inner and outer mitochondrial membrane-fragments, semiautomatic incorporation of proteins, and the assembly of rafts. Concerning geometrical aspects of the lipids, the achieved results are consistent with experimental observations related to lipid densities and distributions. Finally, two membranes simulated with GROMACS are analyzed and compared: the first is generated with conventional scripting techniques, the second with the CmME Distributor algorithm. The examples prove that CmME is a valuable and versatile tool for a broad set of applications in analysis and visualization of biomembranes.

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