Effects of caliber rolling on microstructure and room temperature tensile properties of Mge3Ale1Zn alloy

Mge3Ale1Zn(AZ31)alloy was caliber rolled isothermally in the temperature range of 250e450
C to develop fine grains of 3.6e12.5 mm.The stressestrain curves obtained from tensile tests at room temperature were found to vary with the temperature employed in caliber rolling.Maximum tensile strength of 290 MPa and ductility of 13.5%were obtained upon caliber rolling at 300
C as compared to 188 MPa and 15.2%,respectively,in the mill-rolled condition.The variations in tensile properties are explained by the concomitant grain size,texture and twins obtained as a function of caliber rolling temperature.

Microstructure, properties and hot workability of M300 grade maraging steel

This paper presents isothermal uniaxial compression test results of M300 grade maraging steel over a wide range of temperatures(900 e1200℃) and strain rates(0.001 e100 s^(-1)) to examine hot deformability and concurrent microstructural evolution. Processing map is generated and indicated the optimum processing parameters in the temperature range of 1125℃-1200℃ and strain rate range of 0.001 e0.1 s^(-1). High values of the efficiency of power dissipation, microstructural observations and EBSD results indicate softening mechanism to be the occurrence of dynamic recrystallisation. Material constants in a constitutive relation are evaluated from the flow stress data useful in computer modelling.

Enhanced Ferroelectric and Converse Piezoelectric Properties of Dense Lead-Free Na_0.4K_0.1Bi_0.5TiO₃Ceramics for Actuator Applications

In this work, lead-free Na0.4Bi0.5 TiO3-K0.1Bi0.5TiO3 (NKBT) piezoelectric ceramics were prepared by the solid-state reaction method and their structural, ferroelectric and dielectric properties were systematically studied. NKBT sintered at 1150℃ for 4 h exhibited highly dense (96% - 98% of the theoretical density) and uniform grains of size 1.1 μm. The coexistence of tetragonal (P4bm) and rhombohedral (R3c) phases due to the presence of morphotrophic phase boundary for the chosen composition has been confirmed by the Rietveld refinement studies. Enhanced ferroelectric properties such as remnant polarization (Pr) and coercive field (EC) are found to be 37 μC/cm2 and 30 kV/cm, respectively. The optimized synthesis procedure for NKBT ceramics resulted in enhanced strain (%) and converse piezoelectric coefficient (d33*) of 0.3 % and 554 pm/V which is attributed to smaller grain size and switching of non 180o domains. NKBT ceramics with such excellent piezoelectric properties can be considered as a promising candidate for actuator applications.

Interlaminar Fracture Toughness of Epoxy Glass Fiber Fly Ash Laminate Composite

Epoxy glass fiber laminate composite (PMCs) are finding ever increasing applications in aerospace and automobile industries due to its high strength to weight ratio and resistance to aqueous environment. Additions of particulate reinforcements in the polymer matrix are reported to improve the Interlaminar Shear Strength and Interlaminar Fracture Toughness of the composites. In the present investigation, epoxy glass fiber laminate composites were processed using hand layup and vacuum bagging technique. The particulate reinforcement precipitator fly ash (25 - 45 μm) was added in the epoxy matrix by mechanical mixing up to 10 wt%. The effects of fly ash reinforcement on the mechanical properties and Interlaminar Fracture Toughness were studied before and after exposure to aqueous fog in a salt fog chamber at 45°C. In unexposed condition Mode I interlaminar fracture toughness of epoxy glass fiber laminate composite improved by the addition of fly ash reinforcement 10% (By weight) by 49.43% and when it was subjected to aqueous fog for 10 days the interlaminar fracture toughness improved 58.42%. Exposure to aqueous fog for 10 days causes plasticization of resin matrix and weakening of fiber/matrix interface results in improvement in interlaminar fracture toughness. The fracture surfaces were analyzed using scanning electron microscopy.

Ferrite features in simulated transition zone of EH36 shipbuilding steel submerged arc welded by CaF_(2)-SiO_(2)-MnO fluxes

Ferrite features in the simulated transition zone welded with CaF_(2)-SiO_(2)-MnO fluxes containing various MnO contents have been investigated.Confocal laser scanning microscopy has been applied to simulate the thermal cycling of the transition zone and the phase transformations during cooling have been in-situ observed.It has been found that the appearance temperature for ferrite side plate decreases with increasing Mn content in the weld metals caused by MnO content increasing.Meanwhile,growth rates for both ferrite side plate and acicular ferrite are significantly enhanced with a higher Mn content of weld metal.Furthermore,from the statistical fractions of salient microstructures,for all samples,the acicular ferrite,grain boundary ferrite,and polygonal ferrite take over more than 90%.It has also been demonstrated that with the increase in Mn content,the ferrite side plate fraction increases slightly from 5%to 10%and the acicular ferrite fraction shows a tendency of first increasing and then decreasing,which experiences the maximum with the flux containing 30 wt.%MnO.This phenomenon is believed to be controlled by the O and Mn contents in weld metals synergistically.

Microstructure and texture evolution in AZ31 magnesium alloy during caliber rolling at different temperatures

Magnesium alloy AZ31 was caliber rolled at different temperatures viz.523K,573K,623K,673K and 723K imposing a total cumulative reduction of 92%and a cumulative strain of 2.6.The associated microstructure and texture evolution were studied using Electron Back Scattered Diffraction(EBSD)and X-ray macro-texture observations respectively.Grain refinement was observed in all the caliber rolled bars indicating the occurrence of dynamic recrystallization.Asymmetry parameter and texture index were used to study the evolution of texture.Near doubling of the yield strength at room temperature was observed by caliber rolling at a temperature of 573K.The improvement in mechanical properties was explained on the basis of the fine grain microstructures and suitable development of crystallographic texture.Based on the present study,warm caliber rolling can be used as a good production method for obtaining long bars of high strength magnesium alloy AZ31.

Grain growth in calibre rolled Mg-3Al-1Zn alloy and its effect on hardness

Calibre rolling of Mg-3Al-1Zn alloy at 300℃ led to development of fine grain size of 3μm.Subsequent annealing,from 5 to 6000 minutes at 300-450℃,revealed faster grain growth initially up to 60 minutes,which became sluggish on prolonged annealing.The time exponent for grain growth kinetics(n)suggests bi-linear behaviour with n=0.11 and 0.008 over these time scales.The activation energy,based on various n values,varied over wide ranges that made the understanding of the mechanisms for grain growth difficult.This problem is explained by concurrent evolution of texture and grain boundary structure.The effect of grain growth on hardness at ambient temperature was found to follow the H-P type relationship.

Simulating molten pool features of shipbuilding steel subjected to submerged arc welding

Submerged arc welding process has been simulated to investigate the molten pool features of EH36 shipbuilding steel.One case only involved the surface tension model,and another one involved both the surface tension model and the interface tension model.The role of interface tension during welding is revealed,and the evolution of molten pool morphology is understood by comparing the surface temperature distribution,surface tension and interface tension distribution,and the streamline of the molten pool for the two cases.When the interface tension model is disregarded,a flow conducive to the outward expansion is formed in the surface area of the molten pool,resulting in a small weld depth-to-width ratio.After applying the interface tension model,the expanding outward flow is restrained,which leads to a deep penetration morphology with a large weld depth-to-width ratio due to the inward flow governed by the Marangoni forces.The simulation results involving the interface tension model have been verified with satisfactory predictability.

Impact toughness variations of EH36 weld metal treated by CaF_(2)–SiO_(2)–MnO submerged arc welding flux

Fused ternary CaF_(2)–SiO_(2)–MnO fluxes have been manufactured and applied to join EH36 shipbuilding steel under high heat input submerged arc welding.Five fluxes have been designed to clarify the effect of MnO content in CaF_(2)–SiO_(2)–MnO flux on the impact toughness of the weld metal,with the added amount of MnO from 10 to 50 wt.%at the expense of CaF_(2).With the increase in MnO content,the Charpy impact energy increases first and then decreases,experiencing a maximum value at 30 wt.%MnO.Microstructure of the weld metals has also been studied to account for impact toughness variations.It has been demonstrated that the highest acicular ferrite volume fraction in the weld metal is achieved at 30 wt.%MnO,which is concurrent to the maximum value of Charpy impact energy.It is believed that the Mn and O content variations in the weld metal contribute synergistically to such an interesting phenomenon.

Electrical and magnetic properties of 0-3 Ba(Fe_(1/2)Nb_(1/2))O_(3)/PVDF composites

Lead-free Ba(Fe_(1/2)Nb_(1/2))O_(3)/PVDF O_(3) composites were fabricated using melt.mixing technique.X-ray diffraction,scanning electron microscopy,dielectric,impedance,ac conductivity,magnetic force microscopy(MFM)and vibrating sample magne-tometer studies were undertaken to characterize the samples.Average crstallite size of the Ba(Fe_(1/2)Nb_(1/2))O_(3) powder,estimated using Williamson-Hall approach,was found to be~42 nm.The fller particles of~0.5-1 pum were found to disperse in the polymer matrix of all the composites.Filler concentration dependent values of real and imaginary parts of complex permittivity showed increasing trend and were seen to follow Bruggeman and Furukawa equations.The data for ac conductivity exhibited negative temperature coeficient of resistance character of the test materials and were found to obey Jonscher's power law.The correlated barier hopping model was found to explain satisfactorily the mechanism of charge transport occurring in the system.MFM confirmed the presence of magnetic phases in the composites.Typical magnetization versus applied field curves indicated the possibility of magnetoelectric coupling in the system.Hence,the present composites have shown themselves as potential multi-functional candidate materials for use in high density data storage applications.

Improved photocatalytic degradation of organic dye using Ag3PO4/MoS2 nanocomposite

Highly efficient Ag3PO4/MoS2 nanocomposite photocatalyst was synthe- sized using a wet chemical route with a low weight percentage of highly exfoliated MoS2 （0.1 wt.%） and monodispersed Ag3PO4 nanoparticles （-5.4 nm）. The structural and optical properties of the nanocomposite were studied using various characterization techniques, such as XRD, TEM, Raman and absorption spectroscopy. The composite exhibits markedly enhanced photocatalytic activity with a low lamp power （60 W）. Using this composite, a high kinetic rate constant （k） value of 0.244 min^-1 was found. It was observed that -97.6% of dye degrade over the surface of nanocomposite catalyst within 15 min of illumination. The improved photocatalytic activity of Ag3PO4/MoS2 nanocomposite is attributed to the efficient interfacial charge separation, which was supported by the PL results. Large surface area of MoS2 nanosheets incorporated with well dispersed Ag3PO4 nanoparticles further increases charge separation, contributing to enhanced degradation efficiency. A possible mechanism for charge separation is also discussed.

Rationally engineered 3D-dendritic cell-like morphologies of LDH nanostructures using graphene-based core-shell structures

Functionalization of graphene-based materials using chemical moieties not only modify the electronic structure of the underlying graphene but also enable in limited enhancement of targeted properties.Surface modification of graphene-based materials using other nanostructures enhances the effective properties by minimally modifying the properties of pristine graphene backbone.In this pursuit,we have synthesized bio-inspired hierarchical nanostructures based on Ni–Co layered double hydroxide on reduced graphene oxide core–shells using template based wet chemical approach.The material synthesized have been characterized structurally and electrochemically.The fabricated dendritic morphology of the composite delivers a high specific capacity of 1056 Cg^(−1).A cost effective solid state hybrid supercapacitor device was also fabricated using the synthesized electrode material which shows excellent performance with high energy density and fast charging capability.

Electrical properties of 0-30.5(Ba_(0.7)Ca_(0.3))TiO_(3)-0.5Ba(Zr_(0.2)Ti_(0.8))O_(3)/PVDF nanocomposites

Lead-free x(0.50(Ba_(0.7)Ca_(0.3)TiO_(3)-0.50Ba(Zr_(0.2)Ti_(0.8)O_(3)-(1-x)PVDF ceramic–polymer nanocomposites with x=0.025,0.05,0.10,0.15,0.20,0.25 were prepared using melt-mixing technique.The distribution of nanoceramic filler particles(0.50(Ba_(0.7)Ca_(0.3)TiO_(3)-0.50Ba(Zr_(0.2)Ti_(0.8)O_(3)in the PVDF matrix were examined using scanning electron microscope.Impedance analysis indicated the negative temperature coefficient of resistance character of all the test specimens.Filler concentrationdependent piezoelectric coefficient(d33Þdata followed exponential growth types of variation.The data for ac conductivity were found to obey Jonscher’s power law.The correlated barrier hopping(CBH)model was found to explain the mechanism of charge transport occurring in the system.The low value of loss tangent(-10^(-2))along with the high value of d_(33) foreshadowing the prospect of present nanocomposite is a better nonlead option for piezo-sensing/detection applications,especially in bio-medical area.

Mimosine functionalized gold nanoparticles (Mimo-AuNPs) suppress β-amyloid aggregation and neuronal toxicity

Evidence suggests that increased level/aggregation of beta-amyloid(Aβ)peptides initiate neurodegeneration and subsequent development of Alzheimer’s disease(AD).At present,there is no effective treatment for AD.In this study,we reported the effects of gold nanoparticles surface-functionalized with a plant-based amino acid mimosine(Mimo-AuNPs),which is found to cross the blood-brain barrier,on the Aβfibrillization process and toxicity.Thioflavin T kinetic assays,fluorescence imaging and electron microscopy data showed that Mimo-AuNPs were able to suppress the spontaneous and seed-induced A_(1-42) aggregation.Spectroscopic studies,molecular docking and biochemical analyses further revealed that Mimo-AuNPs stabilize A_(1-42) to remain in its monomeric state by interacting with the hydrophobic domain of A_(1-42)(i.e.,Lys16 to Ala21)there by preventing a conformational shift towards theβ-sheet structure.Additionally,Mimo-AuNPs were found to trigger the disassembly of matured A_(1-42) fibers and increased neuronal viability by reducing phosphorylation of tau protein and the production of oxyradicals.Collectively,these results reveal that the surface-functionalization of gold nanoparticles with mimosine can attenuate Aβfibrillization and neuronal toxicity.Thus,we propose Mimo-AuNPs may be used as a potential treatment strategy towards AD-related pathologies.

On the high temperature phase transition in Ba(Zr_(0.20)Ti_(0.80))O_(3) ceramic

Temperature dependent X-ray diffraction(XRD)and dielectric properties of perovskite Ba(Zr_(0.2)Ti_(0.8))O_(3) ceramic prepared using a standard solid-state reaction process is presented.Along with phase transitions at low temperature,a new phase transition at high temperature(873℃ at 20 Hz),diffusive in character has been found where the lattice structure changes from monoclinic(space group:P2=m) to hexagonal(space group:P6=mmm).This result places present ceramic in the list of potential candidate for intended high temperature applications.The AC conductivity data followed hopping type charge conduction and supports jump relaxation model.The experimental value of d_(33)=98 pC/N was found.The dependence of polarization and strain on electric field at room temperature suggested that lead-free Ba(Zr_(0.2)Ti_(0.8))O_(3) is a promising material for electrostrictive applications.

Graphene-Based Coronal Hybrids for Enhanced Energy Storage

Functional materials with designer morphologies are anticipated to be the next generation materials for energy storage applications.In this manuscript,we have developed a holistic approach to enhance the surface area and hence the properties of nanostructures by synthesizing coronal nanohybrids of graphene.These nanohybrids provide distinctive advantages in terms of performance and stability over vertically stacked nanocomposites reported in literature.Various double hydroxide materials self-assembled as coronal lamellae on graphene shells have been synthesized and systematically studied.These coronal nanohybrids result in about a threefold increase in energy storage capacity as compared to their traditionally synthesized nanocomposite counterparts.The 3D graphene-based nanofibrils in the synthesized coronal nanohybrids provide mechanical support and connect the nodes of the double hydroxide lattices to inhibit restacking.Complex morphologies such as coronal nanostructures increase the interaction surface of the nanostructure significantly.Such an approach is also expected to bring a paradigm shift in development of functional materials for various applications such as sensors,energy storage,and catalysis.