Theoretical study on behaviour of superplastic forming/diffusion bonding of bulk metallic glasses

Based on the behaviour of the superplastic deformation of metallic glasses and Pilling’s model, a diffusion bonding model suitable for metallic glasses is proposed in the present study. In the current model, the diffusion bonding processes consists of two stages: one is the plastic deformation stage and the other is the void shrinkage stage, in which, the atom diffusion and superplastic deformation are responsible for the void shrinkage. Applying this model to the diffusion bonding of a Zr based metallic glass, the predicted bonding time is in good agreement with the experimental result. A map for determining the bonding temperature and time to achieve high quality bonding in a Zr based metallic glass is suggested.

Compressive deformation and damage of Mg-based metallic glass interpenetrating phase composite containing 30-70 vol% titanium

Mg-based metallic glass interpenetrating phase composites (IPCs) containing 30-70 vol% titanium was fabricated in this study. The effects of reinforced phase volume fraction and interspace on the mechanical properties were investigated systematically. With increasing the volume fraction of titanium, the fracture strength and strain increased up to 1860 MPa and 44%, respectively. The results showed that the critical volume fraction (around 40%) of Ti metal should be required for significantly improving plasticity of IPC. Decreasing the interspace of the titanium phase could lead to enhancement of yield and fracture strength. The deformation behavior and strengthening mechanisms were discussed in detail.

Nanograin metals and metallic multilayers produced by severe plastic deformation

This research has developed an improved understanding of the structure-property relationships, fabrication technology and deformation mechanism of light bulk ultrafine grained materials and metallic multilayered structure.

Integrated fluid-thermal-structural numerical analysis for the quenching of metallic components

The quenching of a metal component with a channel section in a water tank is numerically simulated. Computational fluid dynamics (CFD) is used to model the multiphase flow and the heat transfer in film boiling, nucleate boiling and convective cooling processes to calculate the difference in heat transfer rate around the component and then combining with the thermal simulation and structure analysis of the component to study the effect of heat transfer rate on the distortion of the U-channel component. A model is also established to calculate the residual stress produced by quenching. The coupling fluid-thermal-structural simulation provides an insight into the deformation of the component and can be used to perform parameter analysis to reduce the distortion of the component. © 2011 Shanghai Jiaotong University and Springer-Verlag Berlin Heidelberg.

Effect of the degree of crystallinity on the electrochemical behavior of Mg65Cu25Y10 and Mg70Zn25Ca5 bulk metallic glasses

The effect of varying the percent crystallinity on the electrochemical behavior of Mg65Cu25Y10 and Mg70Zn25Ca5 bulk metallic glasses was studied. The alloys were heat-treated to achieve desired microstructures ranging from fully amorphous to fully crystalline, providing a systematic basis for subsequent testing. Potentiodynamic experiments in 0.01 M sodium chloride (NaCl) were used, whereby both the amorphous and partially crystallized samples were observed to have more noble corrosion potentials and lower anodic kinetics. However, this was accompanied by more rapid cathodic kinetics relative to their fully crystalline counterparts, meaning that corrosion rates were not significantly lower in the amorphous state. To describe the electrochemical response as a function of the degree of crystallinity, differential scanning calorimetry (DSC), scanning electron microscopy, x-ray diffraction (XRD), and electrical conductivity measurements were undertaken, where it was found that crystallinity alone is not necessarily the controlling factor and microchemistry that evolves upon devitrification, plays a key role in the electrochemical response of these materials.

Review of low actuation voltage RF MEMS electrostatic switches based on metallic and carbon alloys

Radio frequency micro electro mechanical systems (RF MEMS) have enabled a new generation of devices that bring many advantages due to their very high performances. There are many incentives for the integration of the RF MEMS switches and electronic devices on the same chip. However, the high actuation voltage of RF MEMS switches compared to electronic devices poses a major problem. By reducing the actuation voltage of the RF MEMS switch, it is possible to integrate it into current electronic devices. Lowering the actuation voltage will have an impact on RF parameters of the RF MEMS switches. This investigation focuses on recent progress in reducing the actuation voltage with an emphasis on a modular approach that gives acceptable design parameters. A number of rules that should be considered in design and fabrication of low actuation RF MEMS switches are suggested.

Mechanical behaviour of metallic thin films and multilayers at the micron/submicron scale

Mechanical behaviours of CuFe thin films and multilayers at micron scales were investigated by microcompression and nanoindentation tests. Experimental and modelling results provide essential understanding on the extrinsic size effects in polycrystalline metallic multilayers, which is critical for optimising mechanical properties of thin films and multilayers.

Mechanical Behavior of Nano-crystalline Metallic Thin Films and Multilayers Under Microcompression

Microcompression tests were performed to determine the mechanical behavior of nano-crystalline Cu/Fe and Fe/Cu multilayers, as well as monolithic Cu and Fe thin films. The results show that the micropillars of pure Cu thin film bulge out under large compressive strains without failure, while those of pure Fe thin film crack near the top at low compressive strains followed by shear failure. For Cu/Fe and Fe/Cu multilayers, the Cu layers accommodate the majority of plastic deformation, and the geometry constraints imposed by Fe layers exaggerates the bulging in the Cu layers. However, the existence of ductile Cu layers does not improve the overall ductility of Cu/Fe and Fe/Cu multilayers. Cracking in the Fe layers directly lead to the failure of the multilayer micropillars, although the Cu layers have very good ductility. The results imply that suppressing the cracking of brittle layers is more important than simply adding ductile layers for improving the overall ductility of metallic multilayers.

Finite element analysis of residual stresses in metallic coatings through a compound casting

Al and Mg alloys are widely used in industry as main lightweight alloys. They have excellent properties, such as low density, high ductility, and high specific strength, and so on. Generally speaking, Mg alloys are better than Al alloys. However the corrosion of Mg alloys is much more difficult to control compared Al alloys. Therefore to combine these two lightweight alloys, a composite-like structure is an ideal solution since Al alloys can be used as protective coatings for Mg alloys. Compound casting is a realistic technique to get this coating system. In the current study, we numerically study the compound casting using finite element method (FEM) to make these two alloys, a composite-like structure, satisfy requirements to resist corrosion required from industry, in which the aluminum layer is acting as a protective coating for the magnesium substrate. Several finite element models have been developed by using the birth and death element technique and we focus on compound casting-induced residual stresses in the compounded structure. The numerical results obtained from the proposed finite element models show the distribution profiles of thermal residual stresses. We found the major factors influencing the residual stresses are the temperature to pre-heating the Al substrate and the thickness of Mg deposits. © (2014) Trans Tech Publications, Switzerland.

Investigation of conformationally switchable biomolecular ligands at aqueous metallic interfaces.

An atomistic understanding was garnered through large scale molecular simulations, for the adsorption and interaction of reconfigurable hybrid biomolecule components at different aqueous metallic interfaces. This would allow for the development of future hybrid biomolecular ligands that could be used to synthesise novel and tuneable materials with unique electromagnetic properties.