Damage Tolerant Magnesium Metal Matrix Composites: Influence of Reinforcement and Processing

A growing impetus to enhance our understanding of the behavior of magnesium-based alloys for use in weight critical applications resulted as a consequence of the low density of magnesium. In an attempt to enhance the applicability of magnesium for a wide spectrum of performance-critical applications, the addition of reinforcement to the alloy was considered as an economically affordable and potentially viable scientific alternative. In this paper are reported the results of a study aimed at understanding the influence of saffil alumina short fiber reinforcement on microstructural development of a squeeze-cast magnesium alloy. Preliminary results confirm promise of the reinforced alloy, which retains hardness, strength, and stiffness better at elevated temperatures compared to the unreinforced counterpart. However, impact strength and toughness of the reinforced alloy are inferior. The importance of the matrix alloy in governing the overall mechanical response of the composite microstructure is discussed based on fractographic observations. The importance of volume fraction of the reinforcing phase on properties of the composite microstructure is highlighted.     

Nano-AlN particle reinforced Mg composites: microstructural and mechanical properties

In this study, nano-AlN particles were introduced into pure Mg matrix through the powder metallurgy technique incorporating microwave assisted two-directional sintering followed by hot extrusion. The effect of varying volume fraction of nano-AlN addition on the microstructural and mechanical properties of pure Mg was investigated. Microstructural characterisation revealed marginal grain refinement due to the fairly uniform distribution of AlN nano-particulates. X-ray diffraction results indicated basal texture weakening in Mg/0·2AlN composite. Tensile property measurements revealed an overall increase in strength properties and ductility. Among the developed composites, Mg/0·8AlN displayed superior strength (～30% improvement) and Mg/0·2AlN showed enhanced ductility (～80% enhancement). Under compressive loading, the developed Mg/AlN nanocomposite formulations exhibited improved strength properties without significant effect on compressibility.     

Influence of oxygen pressure on structural,optical and magnetic properties of pure ZnO films

In this paper, we study the influence of oxygen pressure on structural, optical and magnetic properties of pure ZnO films. The chemical compositions and thickness of the film were estimated by Rutherford backscattering spectrometry measurements. X-ray diffraction patterns show all the films are in single phase and preferred along (002) orientation. With an increase of oxygen pressure, grain growth and average root mean square roughness is found to be increased. It is found that the intensity of UV emission peak increases whereas visible emission peak decreases in intensity with an increase of oxygen pressure. From the magnetization measurements, it is observed that ZnO film grown without oxygen pressure shows an enhanced ferromagnetic behaviour than that of the films grown with oxygen pressure of 0.05 and 0.1 mbar.     

Properties of squeeze cast Mg-6Zn-3Cu alloy and its saffil alumina short fibre reinforced composites

In the present work, Mg-Zn-Cu alloy (ZC63) and its saffil alumina short fibre reinforced composites produced using the squeeze casting technique were evaluated for their properties. The unreinforced base alloys and their composites were characterized for their microstructure, hardness, yield strength, impact strength, wear resistance and corrosion resistance. The dependence of the properties of composites was studied as a function of fibre volume fraction. Results showed that the composites exhibited improved hardness, yield strength at elevated temperature and wear resistance in comparison to the monolithic alloy. However, ductility, impact strength and corrosion resistance of the composites were inferior to that of the base alloy. The nature of the base alloy matrix in determining the properties of the composites was discussed based on fractographic analysis.     

Highly potent and specific GSK-3beta inhibitors that block tau phosphorylation and decrease alpha-synuclein protein expression in a cellular model of Parkinson's disease

Research by Klein and co-workers suggests that the inhibition of GSK-3beta by small molecules may offer an important strategy in the treatment of a number of central nervous system (CNS) disorders including Alzheimer's disease, Parkinson's disease, and bipolar disorders. Based on results from kinase-screening assays that identified a staurosporine analogue as a modest inhibitor of GSK-3beta, a series of 3-indolyl-4-indazolylmaleimides was prepared for study in both enzymatic and cell-based assays. Most strikingly, whereas we identified ligands having poor to high potency for GSK-3beta inhibition, only ligands with a Ki value of less than 8 nM, namely maleimides 18 and 22, were found to inhibit Tau phosphorylation at a GSK-3beta-specific site (Ser 396/404). Accordingly, maleimides 18 and 22 may protect neuronal cells against cell death by decreasing the level of alpha-Syn protein expression. We conclude that the GSK-3beta inhibitors described herein offer promise in defending cells against MPP+-induced neurotoxicity and that such compounds will be valuable to explore in animal models of Parkinson's disease as well as in other Tau-related neurodegenerative disease states.     

Preparation and performance evaluation of poly (ether-imide) incorporated polysulfone hemodialysis membranes

Biocompatible Polysulfone (PSf) hemodialysis membranes were prepared by phase inversion technique using poly (ether-imide) (PEI) as the modification agent and Polyethylene glycol (PEG-200) as the pore former. The effect of PSf/PEI blend ratio on the morphology, hydrophilicity, water content, porosity, glass transition temperature, mechanical strength, biocompatibility and permeation rate of the prepared membranes were studied and were found to be improved significantly by the incorporation of PEI in the dope solution. The scanning electron microscopy (SEM) studies revealed that, incorporation of PEI resulted in the formation of spongy sub-layer and increased the connectivity of pores between sub-layer and bottom layer. The water content and permeation rate of the membranes of PSf/PEI blend membranes were increased considerably indicating the enhancement of hydrophilicity and it was supported by lower contact angle values of the blend membranes. The existence of single well defined Tg over entire composition established the compatibility between the components in blend membranes. The biocompatibility of membranes was investigated through protein adsorption, platelet adhesion and thrombus formation on the membrane surface. Anticoagulant activity of PSf/PEI blend membranes was evaluated by measuring the activated partial thrombin time (APTT), prothrombin time (PT), thrombin time (TT) and fibrinogen time (FT). The results revealed that antithrombogenicity of PSf/PEI blend membranes was increased significantly. The efficiency of these membranes in removal of urea, creatinine and vitamin B₁₂ were studied and found to be improved for blend membranes. Thus, it is worth mentioning to note that, the biocompatible PSf/PEI blend membranes prepared in this study would offer immense potential in hemodialysis.     

Effect of ball milling the hybrid reinforcements on the microstructure and mechanical properties of Mg-(Ti + n-Al2O3) composites

In this study, composites containing pure magnesium and hybrid reinforcements (5.6 wt.% titanium (Ti) particulates and 2.5 wt.% nanoscale alumina (n-Al₂O₃) particles) were synthesized using the disintegrated melt deposition technique followed by hot extrusion. The hybrid reinforcement addition into the Mg matrix was carried out in two ways: (i) by direct addition of the reinforcements into the Mg-matrix, Mg-(5.6Ti + 2.5n-Al₂O₃) and (ii) by pre-synthesizing the composite reinforcement by ball milling and its subsequent addition into the Mg-matrix, Mg-(5.6Ti + 2.5n-Al₂O₃)_BM. Microstructural characterization revealed significant grain refinement due to reinforcement addition. The evaluation of mechanical properties indicated a significant improvement in microhardness, tensile and compressive properties of the composites when compared to monolithic magnesium. For the Mg-(5.6Ti + 2.5n-Al₂O₃) composite, wherein the reinforcements were directly added into the matrix, the improvement in strength properties occurred at the expense of ductility. For the Mg-(5.6Ti + 2.5n-Al₂O₃)_BM composites with pre-synthesized ball-milled reinforcements, the increase in strength properties was accompanied by an increase/retention of ductility. The observed difference in behaviour of the composites is primarily attributed to the morphology and distribution of the reinforcements obtained due to the ball-milling process, thereby resulting in composites with enhanced toughness.     

A Hybrid Artificial Bee Colony and Harmony Search Algorithm-Based Metahueristic Approach for Efficient Routing in WSNs

Wireless Personal Communications - The replacement of sensor node battery in wireless sensor network (WSN) is considered to be the highly crucial task in hostile environments. The process of...     

Properties of squeeze cast Mg-10Al-Mn alloy and its alumina short fibre composites

Magnesium alloys are very suitable for applications that require materials with high strength-to-weight ratio. However, the use of magnesium alloys is limited due to their low elevated temperature properties. Magnesium matrix composites are the possible alternatives. The present work involved the production and subsequent property evaluation of AM100 magnesium alloy and its alumina short fibre reinforced composites. Studies on microstructure, hardness, density, stiffness, tensile properties, impact strength, wear resistance and corrosion resistance were carried out. Results indicate the significant improvement in the properties achieved by making composites. The findings also highlight the dominant roles of the base alloy matrix and the fibre volume fraction in determining the above properties.