Department of Metallurgical & Materials Engineering

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Ni-Co-nano SiC composite coatings were electrodeposited from a modified Watt's bath containing CTAB or SDS by pulse electrodeposition at four different peak current densities. The synergistic effect of the pulse peak current density and surfactant results in distinct morphological characteristics (characterized by SEM &amp; TEM) and structural properties (characterized by XRD) producing nanocomposites with different mechanical (microhardness testing and nanoindentation testing) and electrochemical properties which can be traced to a multitude of factors such as nano SiC content and distribution, Cobalt content, grain refinement and texture. CTAB acts as a better dispersing agent for stabilising SiC nanoparticles compared to SDS, producing non-agglomerated SiC nanoparticles with a narrow size distribution. Increasing current density changes microstructure from spherical aggregates of polyhedral crystals (at 0.2 Acm−2) to uniform globular morphology (at 0.3 Acm−2) and finally to spherical aggregates (at 0.4 and 0.5 Acm−2), decreases cobalt content, increases SiC incorporation (up to a peak current density of 0.4Acm−2) and decreases coating thickness. Peak current density of the pulse electrodeposition is a vital factor in determining the crystallite size whereas both peak current density and nature of surfactant used are important factors in determining the texture. Electrodeposits with CTAB as surfactant provided higher values of hardness compared to SDS as surfactant, with C3 having the maximum hardness of 582 VHN because of nanosized grains and uniform dispersion of nano sized SiC. Nanocomposite electrodeposited using SDS as surfactant at a peak current density of 0.3Acm−2 has the highest corrosion resistance with a corrosion current density of 0.47 μAcm−2 and polarization resistance of 120.37 KOhm cm−2 in 3.5 wt% NaCl solution. © 2017 Elsevier B.V.

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Journal of Alloys and Compounds

Synergistic effect of peak current density and nature of surfactant on microstructure, mechanical and electrochemical properties of pulsed electrodeposited Ni-Co-SiC nanocomposites

Organic compounds evolve as a promising alternative to currently used inorganic materials in rechargeable batteries due to their low-cost, environmental friendliness and flexibility. One of the strategies to reach acceptable energy densities and to deal with the high solubility of known organic compounds is to combine small redox active molecules, acting as capacity carrying centres, with conducting polymers. Following this strategy, it is important to achieve redox matching between the chosen molecule and the polymer backbone. Here, a synergetic approach combining theory and experiment has been employed to investigate this strategy. The framework of the density functional theory connected with the reaction field method has been applied to predict the formal potential of 137 molecules and identify promising candidates for the referent application. The effects of including different ring types, e.g. fused rings or bonded rings, heteroatoms, and π bonds, as well as carboxyl groups on the formal potential, have been rationalized. Finally, we have identified a number of molecules with acceptable theoretical capacities that show redox matching with thiophene-based conducting polymers which, hence, are suggested as pendent groups for the development of conducting redox polymer based electrode materials. © The Royal Society of Chemistry.

Journal of Materials Chemistry A

Designing strategies to tune reduction potential of organic molecules for sustainable high capacity battery application

An experimental setup was designed, fabricated and used to form radial hydrides in Zr-2.5%Nb alloy pressure tube spool. The design of setup was based on ensuring a hoop stress in the spool greater than threshold stress for reorientation of hydrides in this alloy, which was achieved by manipulating the thermal expansion coefficient of the plunger and pressure tube material and diametral interference between them. The experimental setup was loaded on a universal testing machine (UTM) fitted with an environmental chamber and subjected to a temperature cycle for the stress reorientation treatment. The metallographic examination of the hydrogen charged spools subjected to stress re-orientation treatment using this set up revealed formation of predominantly radial hydrides. The variation of fracture toughness of material containing radial hydride with test temperature showed typical ‘S’ curve behavior with transition temperatures more than that of the material containing circumferential hydride. © 2017 Elsevier B.V.

Journal of Nuclear Materials

Influence of hydride orientation on fracture toughness of CWSR Zr-2.5%Nb pressure tube material between RT and 300 °C

Friction stir processing (FSP) has been shown to be effective in the microstructural modification. In this study, 2507 super duplex stainless steel was subjected to multipass FSP and the processed samples were investigated. Refinement in grain size of both ferrite and austenite was observed in the stir zone of the processed samples. Increased number of passes led to further reduction in grain size. Anodic polarization studies in 3.5 wt% NaCl solution showed that the processed samples possessed improved corrosion resistance. The Mott-Schottky analysis confirmed that the charge carrier density in the passive oxide layer is decreased with decreasing grain size. © 2017, The Minerals, Metals & Materials Society.

Minerals, Metals and Materials Series

Friction Stir Processing of 2507 Super Duplex Stainless Steel: Microstructure and Corrosion Behaviour

Corrosion behaviour of polymer coated Mg alloy screw is compared with a laboratory coupon with emphasis on the adhesion of coating to surface features such as threads. The corrosion behaviour of poly (ε-caprolactone) (PCL) coated commercial pure Mg (CP Mg) and Mg-4Zn-0.2Ca alloy in simulated body fluid (SBF) is investigated. CP Mg with a high corrosion rate (8.426 mmyr− 1) formed large amount of corrosion products on the surface which pushed out the PCL layer. In contrast the Mg-4Zn-0.2Ca alloy with a corrosion rate of 2.481 mmyr− 1 held the PCL coating intact for up to 72 h. Fully and partially threaded screws of the Mg-4Zn-0.2Ca alloy were fabricated and coated with PCL. It was found that pH variation of the medium depends on PCL adhesion to screw, which was better in the threaded regions than in smoother areas. As a result, the fully threaded screws showed slower pH rise than partial threaded ones. The crests and troughs of the threads act as anchoring points for the polymer. It was found in the current study that the increased adhesion of PCL coating to threaded Mg alloy substrate dominates over the increased corrosion rates of threaded surface. © 2017 Elsevier Ltd

Materials and Design

Coatings on implants: Study on similarities and differences between the PCL coatings for Mg based lab coupons and final components

In this article, we investigate into the ternary tin based alloy, thin film anodes for lithium ion batteries, specifically into Sn-Sb-Cu system, synthesized via electrodeposition. The alloy electrodes show a stable discharge capacity of ∼600 mAh g−1 discharged at a rate of 200 mA g−1 (∼0.3C) for 50 cycles. FESEM images show a nano-dendritic, porous microstructure which can help in accommodating high volume expansion during lithiation and prevent the problem of pulverization. The phases present in the prepared anodes are Sn, SnSb and Cu6 Sn5 which are all active towards lithium insertion and extraction. The behavior of this multi-phase alloy system is examined using X-ray diffraction measurements. At extremely slow discharge rates, the phases take up lithium at distinct potentials with reactions with SnSb, Cu6Sn5 and Sn occurring at 0.86 V, 0.65 V and 0.45 V, respectively. A mechanism, where a lithiated phase decomposes and internally supplies lithium to the reacting phase, is observed and thereby lowering the total specific capacity of the anode as a whole when discharged. EIS measurements further reveal that there is degradation in the reaction kinetics with increasing cycles. Finally, failure of the anode is investigated and the cause is identified as the delamination of active material from the current collector. The problem is successfully removed by replacing Copper current collector with Silver current collector, where the intermetallic composition reacts at a lower voltage than Tin. Cycling the anode above this cutoff voltage removes the problem of delamination. However, it is identified that the existing electrolyte composition in the market, used for graphite anodes, is incompatible with Tin based anodes. © 2017

Investigation on lithium conversion behavior and degradation mechanisms in Tin based ternary component alloy anodes for lithium ion batteries

This study aims to synthesis of a thin coating of nano-crystalline copper reinforced with MWCNT through pulse electrodeposition from a highly basic bath. Copper ion was complexed with ammonia to stabilize Cu2+ at pH&gt; 10, at which functionalized MWCNT also able to well disperse and stabilize in aqueous solution. This technique enables co-deposition of Cu-MWCNT. The depositions were carried out galvanostatically at 10, 50 and 100 mA/cm2 current densities. At 10 mA/cm2 current density, both pure copper and copper oxide depositions take place with {110} and {111} planes parallel to the surface of the substrate, respectively. Whereas, at higher current densities, cauliflower type of grain growth is observed for pure copper deposition and no trace of copper oxide is evident. Crystallite size is in the range of 39 to 98 nm. This composite coating can serve as one of the potential candidate in the area of thin current collector for micro electrical contact. © 2017 Elsevier B.V.

Surfaces and Interfaces

Synthesis and characterization of MWCNT reinforced nano-crystalline copper coating from a highly basic bath through pulsed electrodeposition

A general three-dimensional continuum model of phonons in two-dimensional materials is developed. Our first-principles derivation includes full consideration of the lattice anisotropy and flexural modes perpendicular to the layers and can thus be applied to any two-dimensional material. In this paper, we use the model to not only compare the phonon spectra among the group-IV materials but also to study whether these phonons differ from those of a compound material such as molybdenum disulfide. The origin of quadratic modes is clarified. Mode coupling for both graphene and silicene is obtained, contrary to previous works. Our model allows us to predict the existence of confined optical phonon modes for the group-IV materials but not for molybdenum disulfide. A comparison of the long-wavelength modes to density-functional results is included. © 2017 Willatzen et al.

Fulltext

Beilstein Journal of Nanotechnology

3D continuum phonon model for group-IV 2D materials

Deformation and failure behaviors of E-form magnesium (Mg) alloy sheets were investigated using a mini-V-bending test. The evolution of the microstructure and microtexture of the deformed E-form Mg alloy sheets (before and after failure) was analyzed via an electron back-scattered diffraction (EBSD) technique. Finite element analysis (FEA) was used to capture the heterogeneous distribution of longitudinal-strain components through the thickness direction under mini-V-bending at different punch strokes. The relationships between punch stroke, bending radius and longitudinal-strain at the tension and compression zones were established. EBSD analysis revealed that shear localization by dislocation slip along with compression and double twins were the main deformation mechanisms in the tension zone while tensile twins were a main deformation mechanism in the compression zone in E-form Mg alloy sheets during mini-V-bending. The effect that deformation twinning had on the crack propagation sites in E-form Mg alloy sheets was also investigated. The networks of compression {101¯1} and double {101¯1}−{101¯2} twins in the tension zone of E-form Mg alloy sheets were closely related to the crack propagation during mini-V-bending at near room temperature (RT). © 2017 Elsevier B.V.

The effect of strain heterogeneity on the deformation and failure behaviors of E-form Mg alloy sheets during a mini-V-bending test

The dissimilar weld joints between 316L austenitic stainless steel and SS400 ferritic steel were used to investigate the effect that microstructure exerts on hardness heterogeneity in weld joints. In order to identify the constituent phases and deformation mechanisms in the dissimilar weld joints, microstructure characterization of undeformed and deformed specimens was conducted via optical microscope (OM), electron back-scattered diffraction (EBSD), and transmission electron microscopy (TEM) techniques. Micro-hardness measurements across the different weld regions and mini-tension testing combined with digital image correlation (DIC) were conducted to evaluate the mechanical properties of the base metals (BMs), the weld zone (WZ), and the heat-affected zone (HAZ). Local strain heterogeneity on deformed specimens was also explained by microstructure heterogeneity in terms of grain morphology and constituent phases. Non-uniform enhancements of the strain distributions were distinct in the WZ, which consisted of a dendritic structure with a irregular morphologies. Uneven patterns of a martensite transformation from γ to α′ in the 316L contributed to localized heterogeneity in the strain distribution. © 2017 Elsevier B.V.