Synthesis Of Plastic Zr-Based Bulk Metallic Glass Matrix Composites By The Copper-Mould Suction Casting And The Bridgman Solidification

Zr-based bulk metallic glass matrix composites with the composition of Zr56.2Ti13.8Nb5.0Cu6.9Ni5.6Be12.(5) were synthesized by the copper-mould suction casting and the Bridgman solidification. The composite, containing a well-developed flowery beta-Zr dendritic phase, was obtained by the Bridgman solidification with the withdrawal velocity of 0.8 mm/s and the temperature gradient of 45 K/mm, and the ultimate strength of 2050 MPa and fracture plastic strain of 14.6% of the composite were achieved, which was mainly interpreted by the homogeneous dispersion of bcc beta-Zr phase in the glass matrix. Crown Copyright (C) 2008 Published by Elsevier B.V. All rights reserved.

Electrocatalytic properties of Cu-Zr amorphous alloy towards the electrochemical hydrogenation of nitrobenzene

The Cu-Zr amorphous alloy was studied as an electrocatalyst towards the electrochemical hydrogenation of nitrobenzene. The electrocatalyst was activated by chemical etching in HF solution. Resulted changes in the morphology, chemical composition and crystalline structure of the electrocatalyst surface were characterised by scanning electron microscopy, X-ray diffraction and Auger electron spectroscopy. The electrocatalytic properties of the Cu-Zr amorphous alloy were assessed by voltammetric measurements. Due to the formation and aggregation of Zr residue modified Cu nanocrystals on the surface caused by the selective dissolution of Zr components in the chemical etching, the activated amorphous alloy is an effective electrocatalyst for the electrochemical reduction reaction of nitrobenzene with aniline as the main product. The positive shift of the peak potential and accompanying increase in the value of peak current in voltammograms with increasing Cu content and decreasing Zr content of the alloy surface in the chemical etching are indicative of improved electrocatalytic activity. (C) 2002 Elsevier Science B.V. All rights reserved.

Structure and electrochemical characteristics of melted composite Ti0.10Zr0.15V0.35Cr0.10Ni0.30-LaNi5 hydrogen storage alloys

The structure and electrochemical characteristics of melted composite Ti0.10Zr0.15V0.35Cr0.10Ni0.30+x% LaNi5 (x=0, 1, 5 and 10) hydrogen storage alloys have been investigated systematically. XRD shows that the matrix phase structure of V-based solid solution phase with a BCC structure and C14 Laves phase with hexagonal structure is not changed after adding LaNi5 alloy. However, the amount of the secondary phase increases with increasing LaNi5 content. Field emission scanning electron microscopy-energy dispersive spectroscopy (FESEM-EDS) shows that the C14 Laves phase contains more Zr and the white lard phase has a composition close to (Zr, Ti)(V, Cr, Ni, La)(2).

Electrochemical hydrogen storage in (Ti1-xVx)(2)Ni (x=0.05-0.3) alloys comprising icosahedral quasicrystalline phase

For (Ti1-xVx)(2)Ni (x = 0.05,0.1,0.15,0.2 and 0.3) ribbons, synthesized by arc-melting and subsequent melt-spinning techniques, an icosahedral quasicrystalline phase was present, either in the amorphous matrix or together with the stable Ti2Ni-type phase. With increasing x values, the maximum discharge capacity of the alloy electrodes increased until reached 271.3 mAh/g when x = 0.3. The cycling capacity retention rates for these electrodes were approximately 80% after a preliminary test of 30 consecutive cycles of charging and discharging.

Electrochemical Hydrogen Storage in Ti1.6V0.4Ni1-xCox Icosahedral Quasicrystalline Alloys

The discovery of the icosahedral phase (i-phase) in rapidly quenched Ti1.6V0.4Ni1-xCox (x=0.02-01) alloys is described herein. The i-phase occurs in a similar amount relative to the coexisting beta Ti phase. The electron diffraction patterns show the distinct spot anisotropy, indicating that the i-phase is metastable. The electrochemical hydrogen storage performance of these five alloy electrodes are also reported herein. The hydrogen desorption of nonelectrochemical recombination in the cyclic voltammetric (CV) response exhibits the demand for electrocatalytic activity improvement.

Crystallographic and electrochemical characteristics of Ti45Zr35Ni13Pd7 melt-spun alloys

Ti45Zr35Ni13Pd7 alloys are prepared by melt spinning at different cooling rates (v). The phase structure and electrochemical hydrogen storage performance are investigated. When U is 10 m/s, the alloy consists of icosahedral quasicrystalline phase (I-phase), C14 Laves phase and a little amorphous phase. When v increases to 20 or 30 m/s, a mixed structure of I-phase and amorphous phase is formed. Maximum discharge capacity of alloy electrode decreases from 156 mAh/g (v = 10 m/s) to 139 mAh/g (v = 30 m/s) with increasing v. High-rate discharge ability at the discharge current density of 240 mA/g decreases monotonically from 61.2% (v = 10 m/s) to 56.8% (v = 30 m/s).

Catalytic oxidation of cyclohexane over Ti-Zr-Co catalysts

Ti-Zr-Co alloys have been fabricated and characterized, and their catalytic performance was discussed for the oxidation of cyclohexane with oxygen under solvent-free condition. The icosahedral quasicrystalline phase (I-phase)-forming ability of Ti-Zr-Co alloys with different compositions was discussed, and it was confirmed that I-phase could be formed as a dominating phase at the Ti-rich composition region from Ti53Zr27Co20 to Ti75Zr5Co20 in as-cast alloys. The composition and microstructure of Ti-Zr-Co alloys present crucial influences on its catalytic activity and selectivity in the oxidation of cyclohexane. The influences of some reaction parameters such as temperature, reaction time, and catalyst amounts were also investigated. Ti70Zr10Co20 alloy containing quasicrystal microstructure showed good catalytic performance with a 6.8% conversion of cyclohexane and 90.4% selectivity of cyclohexanol and cyclohexanone. It behaves as an efficient heterogeneous catalyst for the oxidation of cyclohexane and could be recycled five times without loss in activity and selectivity.

Microstructure and some dynamic performances of Ti0.17Zr0.08V0.34RE0.01Cr0.1Ni0.3 (RE = Ce, Dy) hydrogen storage electrode alloys

Microstructure and some dynamic performances of Ti0.17Zr0.08V0.34RE0.01Cr0.1Ni0.3 (RE=Ce, Dy) hydrogen storage electrode alloys have been investigated using XRD, FESEM-EDS, ICP-MS and EIS measurements. The alloy is composed of V-based solid solution phase with a dendritic shape and a continuous C14 Laves phase with a network shape surrounding the dendrite. Pressure-composition isotherm curves indicate that the alloy with Dy addition has a lower equilibrium hydrogen pressure and a wider plateau region. The alloy electrode with Dy addition has higher discharge capacity, while the alloy electrode with Ce addition has better activation and higher cycle stability. The alloy electrode with Ce addition has better electrochemical activity with higher exchange current density (127.5 mA g(-1)), lower charge transfer resistance (1.37 Omega) and lower apparent activation energy (30.5 kJ mol(-1)). The capacity degradation behavior for the alloy electrode is attributed to two main factors: one is the dissolutions of V and Zr element to KOH solution, and another is the larger charge transfer resistance which increases with increasing cycle number.

The diffusion of Co⠶溩 Zrâ â Tiâ â alloy /|nS. Kumar. -- 260 St Catharines [Ont.] : Dept. of Physics, Brock University,

The diffusion of Co60 in the body centered cubic beta phase of a ZrSOTi SO alloy has been studied at 900°, 1200°, and 1440°C. The results confirm earlier unpublished data obtained by Kidson17 • The temperature dependence of the diffusion coefficient is unusual and suggests that at least two and possibly three mechanisms may be operative Annealing of the specimen in the high B.C.C. region prior to the deposition of the tracer results in a large reduction in the diffusion coefficient. The possible significance of this effect is discussed in terms of rapid transport along dislocation network.

Effects of alloying elements on the cytotoxic response of titanium alloys

Titanium alloys, alloys, especially beta-type alloys containing beta-stabilizing elements, constitute a highly versatile category of metallic materials that have been under constant development for application in orthopedics and dentistry. This type of alloy generally presents a high mechanical strength-to-weight ratio, excellent corrosion resistance and low elastic modulus. The purpose of this study is to evaluate the cytotoxicity and adhesion of fibroblast cells on titanium alloy substrates containing Nb, Ta, Zr, Cu, Sn and Mo alloying elements. Cells cultured on polystyrene were used as controls. In vitro results with Vero cells demonstrated that the tested materials, except Cu-based alloy, presented high viability in short-term testing. Adhesion of cells cultured on disks showed no differences between the materials and reference except for the Ti-Cu alloy, which showed reduced adhesion attributed to poor metabolic activity. Titanium alloys with the addition of Nb, Ta, Zr, Sn and Mo elements show a promising potential for biomedical applications. (C) 2011 Elsevier B.V. All rights reserved.

Twinning and the ductility of magnesium alloys Part I: “Tension” twins

Magnesium and its alloys do not in general undergo the same extended range of plasticity as their competitor structural metals. The present work is part I of a study that examines some of the roles deformation twinning might play in the phenomenon. A series of tensile test results are reported for the common wrought alloy AZ31. These data are employed in conjunction with a simple constitutive model to argue that View the MathML source twinning (which gives extension along the c-axis) can increase the uniform elongation in tensile tests. This effect appears to be similar to that seen in Ti, Zr and Cu–Si and in the so called TWIP phenomenon in steel.

Effect of solidification grain refinement on the development of wrought Mg alloys

A recent trial investigated the effect of solidification grain refinement of billet on the grain refinement and properties of alloy ZM20. It was found that even at levels of 0.4Mn, significant grain refinement could be obtained when 0.7Zr was added. At 0.2Mn grain sizes as low as 60μm were
obtained. Billets of Mg-2Zn-0.2Mn with four different grain sizes, due to different Zr and cooling rates were then cast via vertical direct chill casting and extruded conventionally. Benefits of grain refinement of the billet on extrusion were found to be a slight increase in the size of the operating
window, and a reduction of the grain size in the extrudate. However, the effect of the reduction in extrudate grain size due to refinement of the billet was small compared with the amount of grain refinement obtained due to recrystallisation on extrusion.

Effect of surface roughness of Ti, Zr, and TiZr on apatite precipitation from simulated body fluid

Some of the critical properties for a successful orthopedic or dental implant material are its biocompatibility and bioactivity. Pure titanium (Ti) and zirconium (Zr) are widely accepted as biocompatible metals, due to their non-toxicity. While the bioactivity of Ti and some Ti alloys has been extensively investigated, there is still insufficient data for Zr and titanium-zirconium (TiZr) alloys. In the present study, the bioactivity, that is, the apatite forming ability on the alkali and heat treated surfaces of Ti, Zr, and TiZr alloy in simulated body fluid (SBF), was studied. In particular, the effect of the surface roughness characteristics on the bioactivity was evaluated for the first time. The results indicate that the pretreated Ti, Zr and TiZr alloy could form apatite coating on their surfaces. It should be noted that the surface roughness also critically affected the bioactivity of these pretreated metallic samples. A surface morphology with an average roughness of approximately 0.6 microm led to the fastest apatite formation on the metal surfaces. This apatite layer on the metal surface is expected to bond to the surrounding bones directly after implantation.

Plastic deformation in a partially crystallized Zr-based BMG under Vickers indenter

Vickers indentations were carried out on an anneal-introduced partially crystallized Zr₄₁Ti₁₄Cu_12.5 Ni₁₀Be_22.5 bulk metallic glass (BMG), and the evolution of the shear bands in this samplewas investigated and compared to the as-cast, aswell as the structurally relaxed counterparts. The results indicate that the plastic deformation in the partially crystallized BMG was accommodated by the semi-circular (primary) and radial (secondary) shear bands. A full crack or flake that was produced due to the spring back during the load removal was observed. The shear band density in the annealed alloy which was dispersed with crystalliteswas significantly lower than that of the as-cast alloy. The difference of the shear band features among the three kinds of alloy status, i.e., partially crystallized, structurally relaxed and as-cast alloys was discussed in terms of the free volume in the BMGs and the characteristics of nano-composites. It has been demonstrated that the plasticity for the three statuses of alloys queues in the descending order as the as-cast, annealed with partial crystallization, and annealed without crystallization.

Effects of alloying elements on the corrosion behavior and biocompatibility of biodegradable magnesium alloys: a review

Magnesium (Mg) based alloys have been extensively considered for their use as biodegradable implant materials. However, controlling their corrosion rate in the physiological environment of the human body is still a significant challenge. One of the most effective approaches to address this challenge is to carefully select alloying compositions with enhanced corrosion resistance and mechanical properties when designing the Mg alloys. This paper comprehensively reviews research progress on the development of Mg alloys as biodegradable implant materials, highlighting the effects of alloying elements including aluminum (Al), calcium (Ca), lithium (Li), manganese (Mn), zinc (Zn), zirconium (Zr), strontium (Sr) and rare earth elements (REEs) on the corrosion resistance and biocompatibility of Mg alloys, from the viewpoint of the design and utilization of Mg biomaterials. The REEs covered in this review include cerium (Ce), erbium (Er), lanthanum (La), gadolinium (Gd), neodymium (Nd) and yttrium (Y). The effects of alloying elements on the microstructure, corrosion behavior and biocompatibility of Mg alloys have been critically summarized based on specific aspects of the physiological environment, namely the electrochemical effect and the biological behavior. This journal is © the Partner Organisations 2014.