A novel method to improve interfacial bonding of compound squeeze cast Al/Al-Cu macrocomposite bimetals:Simulation and experimental studies

A facile and innovative method to improve bonding between the two parts of compound squeeze cast Al/Al-4.5 wt.%Cu macrocomposite bimetals was developed and its effects on microstructure and mechanical properties of the bimetal were investigated.A special concentric groove pattern was machined on the top surface of the insert(squeeze cast Al-4.5 wt.%Cu) and its effects on heat transfer,solidification and distribution of generated stresses along the interface region of the bimetal components were simulated using ProCAST and ANSYS softwares and experimentally verified. Simulation results indicated complete melting of the tips of the surface grooves and local generation of large stress gradient fields along the interface. These are believed to result in rupture of the insert interfacial aluminum oxide layer facilitating diffusion bonding of the bimetal components. Microstructural evaluations confirmed formation of an evident transition zone along the interface region of the bimetal. Average thickness of the transition zone and tensile strength of the bimetal were significantly increased to about 375 μm and 54 MPa, respectively, by applying the surface pattern.The proposed method is an affordable and promising approach for compound squeeze casting of Al-Al macrocomposite bimetals without resort to any prior cost and time intensive chemical or coating treatments of the solid insert.

Simulation and experimental verification of interfacial interactions in compound squeeze cast Al/Al-Cu macrocomposite bimetal

The objective of this work was to investigate the thermal and mechanical interactions between the two components of a compound squeeze cast macrocomposite bimetal. First, an Al/Al-4.5wt.%Cu macrocomposite bimetal was fabricated by compound squeeze casting process. Then, heat transfer, solidification and distribution of the generated stresses along the interface region of the bimetal were analyzed using Thermo-Calc, ProCAST and ANSYS softwares, and structure, copper distribution and microhardness changes across the interface of the bimetal were studied. The results showed no noticeable change in the structure of the Al-4.5wt.%Cu insert and no obvious micromixing and diffusion of copper across the interface. Simulation results were in good agreement with the experimental ones only when an equivalent oxide layer at the interface was defined and its effect on heat transfer was considered. This layer caused up to 50% decrease in local liquid fraction formed on the surface of the insert. Simulation of the generated stresses showed a uniformly distributed stress along the interface which was significantly lower than the compressive strength of the oxide layer, resulting in its good stability during the fabrication process. It was postulated that this continuous oxide layer not only acted as a thermal barrier but prevented the direct metal-metal contact along the interface as well.

Micromechanical simulation and experimental investigation of aluminum-based nanocomposites

Ceramic reinforced metal matrix nanocomposites are widely used in aerospace and auto industries due to their enhanced mechanical and physical properties.In this research,we investigate the mechanical properties of aluminum/Nano-silica composites through experiments and simulations.Aluminum/Nanosilica composite samples with different weight percentages of silica nanoparticles are prepared via powder metallurgy.In this method,Nano-silica and aluminum powders are mixed and compressed in a mold,followed by sintering at high temperatures.Uniaxial tensile testing of the nanocomposite samples shows that adding one percent of Nano-silica causes a considerable increase in mechanical properties of nanocomposite compared to pure aluminum.A computational micromechanical model,based on a representative volume element of aluminum/silica nanocomposite,is developed in a commercial finite element software.The model employs an elastoplastic material model along with a ductile damage model for aluminum matrix and linear elastic model for nano-silica particles.Via careful determination of model parameters from the experimental results of pure aluminum samples prepared by powder metallurgy,the proposed computational model has shown satisfactory agreement with experiments.The validated computational model can be used to perform a parametric study to optimize the microstructure of nanocomposite for enhanced mechanical properties.

Metamaterial-based octave-wide terahertz bandpass filters

We present octave-wide bandpass filters in the terahertz(THz)region based on bilayer-metamaterial(BLMM)structures.The passband region has a super-Gaussian shape with a maximum transmittance approaching 70%and a typical stopband rejection of 20 dB.The design is based on a metasurface consisting of a metallic squarehole array deposited on a transparent polymer,which is stacked on top of an identical metasurface with a subwavelength separation.The superimposed metasurface structures were designed using finite-difference time-domain(FDTD)simulations and fabricated using a photolithography process.Experimental characterization of these structures between 0.3 and 5.8 THz is performed with a time-domain THz spectroscopy system.Good agreement between experiment and simulation results is observed.We also demonstrated that two superimposed BLMM(2BLMM)devices increase the steepness of the roll-offs to more than 85 dB/octave and enable a superior stopband rejection approaching 40 dB while the maximum transmittance remains above 65%.This work paves the way toward new THz applications,including the detection of THz pulses centered at specific frequencies,and an enhanced time-resolved detection sensitivity toward molecular vibrations that are noise dominated by a strong,off-resonant,driving field.

Synthesis and characterization of a new magnetic bromochromate hybrid nanomaterial with triethylamine surface modified iron oxide nanoparticles

We describe a novel method for the synthesis a new magnetic bromochromate hybrid nanomaterial, Fe3O4@SiO2@TEA@[CrO3Br], as a catalyst. The physical properties, morphology and magnetic investigations of magnetic bromochromate hybrid nanomaterials are identified by transmission electron microscopy （TEM）, scanning electron microscopy （SEM） and vibrating sample magnetometer （VSM） techniques. Fourier transform infrared （FT-IR）, elemental analysis, X-ray fluorescence （XRF）, X-ray diffraction （XRD） were also used for structural identification. The quantity of chromium is approximately 0.38%, which confirms to the immobilization amount of [CrO3Br]- and is equal to 0.007 mol/100 g.

Trihydrazinotrazine-grafting Fe_(3)O_(4)/SiO_(2) core-shell nanoparticles with expanded porous structure for organic reactions

This study focuses on the synthesis and characterization of a novel magnetic nanocomposite 2,4,6-trihydrazino-1,3,5-triazine(THDT)-fimctionalized with silica-coated iron oxide magnetic nanoparticles(MNPs).This nanocomposite has porous morphology decorated with the spherical MNPs.Through co-precipitation of iron salts,MNPs were obtained.The prepared THDT was placed on the chlorine surface-modified MNPs.The present environment-friendly nanocatalyst intensely accelerated the synthesis of highly functionalized tetra-hydrobenzo[b]pyran derivatives as well as reduced the reaction times and increased yields of the products.