Volume 112, Issue 5

Multiscale modeling of macroscopic elastic properties of pearlitic hypereutectoid steel using the Eshelby matrix–inclusion approach is possible. The model works through successive homogenization steps, based on the elastic properties of cementite and ferrite. Globular pearlite is homogenized using α Mori–Tanaka approach. Lamellar pearlite and pearlite colonies with fragmented proeutectoid cementite are homogenized by α classical self-consistent scheme. In the case of pearlite colonies surrounded by α continuous cementite film, α generalized self-consistent scheme is used. The influence of microstructural parameters such as the pearlite colony size or the thickness of the proeutectoid cementite on Young’s and shear moduli and on coefficients of the stiffness tensor is simulated. Proof of concept is obtained by comparison between predicted elastic behavior and experimental results from the literature.

Al–TiO 2 –C–La 2 O 3 refiners were synthesized by the in-situ exothermic dispersion method using TiO 2 , C, Al and La 2 O 3 powders as raw materials. Scanning electron microscopy equipped with energy dispersive X-ray spectrometry and X-ray diffraction were used to investigate the microstructures of the Al–TiO 2 –C–La 2 O 3 refiners. Commercial pure aluminum was refined by the Al–TiO 2 –C–La 2 O 3 refiners, aimed at investigating refining performance and the resistance to recession. The results show that the Al–TiO 2 – C–La 2 O 3 refiner with 0.2% La 2 O 3 is composed of α-Al, blocky Al 3 Ti, dispersive Al 2 O 3 and TiC, which has a better refining effect on commercial pure aluminum than the Al– TiO 2 –C refiner. The average grain size refined by the above refiner is about 80 μm and it performs better and has a longer refining effect. The grain structure refined by Al–TiO 2 – C–La 2 O 3 becomes finer within 5 min and remains the same after 120 min, while refined by the Al–TiO 2 –C refiner the equivalent times are 10 min and 30 min respectively.

The effects of friction heat and friction coefficient on the abrasive wear response of Al-7.5Si–SiCp composite against low-cost hypereutectic (Al-17.5Si) alloy were investigated as functions of the abrasive size and applied load in both as-cast and after heat-treatment conditions. Experiments were performed on pin-on-disc apparatus at 38 –80 μm abrasive size, 5 – 20 N applied load, 100 –400 m abrading (sliding) distances and 1 m s –1 constant sliding speed. The frictional heating of as-cast and heat-treated composite was superior compared to the matrix alloy and hypereutectic alloy, whereas the trend reversed for the friction coefficient. The frictional heating and friction coefficient of the materials increased with the abrasive size and applied load in both as-cast and after heat-treatment. The worn surface and wear debris particles were examined by using field emission scanning electron microscopy to understand the wear mechanism.

The Sb–S and In–S binary systems were assessed thermodynamically using the CALculation of PHase Diagrams (CAL-PHAD) approach based on the experiment data in the literature. Both phase diagrams revealed a congruent melting compound and liquid immiscibility. Therefore, associate species, Sb 2 S 3 and In 2 S 3 , were introduced into the associate model to describe the liquid phase during optimization. The binary intermediate compounds, Sb 2 S 3 , InS(α, β), and In 6 S 7 , were treated as stoichiometric phases. Considering the wide composition range, In 2 S 3 (α, β, γ), were modeled using the sublattice model. A set of self-consistent thermodynamic parameters representing most of the reliable thermodynamic properties and phase diagram information were derived.

In this research, mixtures of barium ferrite and graphite were milled in a high-energy mechanical milling machine. The effect of recalcination on the magnetic properties of the milled samples was studied. Phase analysis, phase transformations at high temperatures, particle size distribution, magnetic properties, and particle morphology were characterized by means of X-ray diffraction, hot stage X-ray diffraction, dynamic light scattering, vibrating sample magnetometry, high-resolution transmission electron microscopy, and field-emission scanning electron microscopy, respectively. A magnetic nanocomposite of BaFe 12 O 19 /Fe 3 O 4 formed after 20 and 40 h milling. The average particle size for the 20 and 40 h milled samples reached 106 and 68 nm, respectively. Recalcination of the milled samples resulted in barium ferrite structure recovery. The decreased particle size due to the milling and subsequent recalcination results in increased coercivity values. The coercivity for the milled and calcined sample could increase more than 40% compared to as-received barium ferrite and reaches 3935 Oe for the sample calcined at 1050 °C.

Cobalt ferrite nanoparticles (CFNs) were synthesized using cobalt nitrate hexahydrate and ferric nitrate nonahydrate through a wet chemical method. Various characterization techniques were used to confirm the synthesis of CFNs. The thermal stability, structure, morphology and crystallinity of the synthesized CFNs were determined by thermogravimetric analysis, field emission scanning electron microscopy, Fourier transform infrared spectroscopy and X-ray diffraction. The results show that the synthesized nanoparticles are stable and crystalline with fine homogenized structure. Vibrating sample magnetometry was used to determine the magnetic properties of the synthesized material. The coercivity was noted to be decreased and the hysteresis loop gradually flattens as the temperature increases toward the Curie temperature.

Monoclinic BiVO 4 photocatalyst films decorated on glass substrates were successfully fabricated via a dip-coating technique with different annealing temperatures of 400 ° C, 450 ° C, 500°C, and 550 ° C. All of the physical and chemical properties of as-prepared BiVO 4 photocatalyst film samples were investigated using X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and UV–vis diffuse reflectance spectra techniques. The results revealed that the as-prepared BiVO 4 photocatalyst film samples retained a monoclinic phase with an average particle size of about 50 – 100 nm. Moreover, the BiVO 4 photocatalyst film samples showed a strong photoabsorption edge in the range of visible light with the band gap energy of 2.46 eV. The photocatalytic activities of all the film samples were tested by the degradation of model acid orange 7 under visible light irradiation. The BiVO 4 photocatalyst film sample annealed at a temperature of 500 ° C showed the highest photoactivity efficiency compared with other film samples, reaching up to 51%within 180 min. In addition, the stability and reusability of BiVO 4 photocatalyst film sample made with an annealing temperature of 500 ° C did not show loss of photodegradation efficiency of acid orange 7 after ten recycles. A likely mechanism of the photocatalytic process was established by trapping experiments, indicating that the hydroxyl radical scavenger species can be considered to play a key role for acid orange 7 degradation under visible light irradiation.

In this study, chitosan/perlite nanocomposites were synthesized using the solvent casting method and then characterized using Fourier transform infrared spectroscopy, X-ray diffraction, optical contact angle, differential thermal analysis/thermogravimetry, differential scanning calorimetry, atomic force microscopy, transmission electron microscopy and Zetasizer NanoS devices. Perlite was determined to be dispersed in nano size and homogeneously in the chitosan matrix. Chitosan/perlite nanocomposite was generally more thermally stable compared to pure chitosan polymer. The fact that the amount of perlite in the nanocomposite increased showed that the hydrophilic properties of nanocomposites increased. In addition, antibacterial activities of the samples were investigated using the agar-disk diffusion method and hemocompatibility testing was also performed.

Aluminum alloys have a strong tendency to form alumina layers on their surfaces when exposed to atmospheric air, even at room temperature. This is a severe challenge for brazing aluminum alloys as the alumina layer acts as a diffusion barrier and hinders the interactions between the filler metal and the base material. In order to achieve a good metallurgical bond between the filler metal and the aluminum alloy, it is of crucial importance to remove the alumina layer as well as to simultaneously prevent further oxidation of the aluminum alloy. The current investigation focuses on the detailed micro-structural changes that occur during in-situ brazing of liquid filler metal, 95Sn-5Cu (wt.%) on an aluminum alloy, Al-7Si-0.3Mg. These in-situ studies were performed in a large chamber scanning electron microscope in order to monitor the interactions of the filler metal and the base material, particularly the role of Cu on alumina detachment. After the in-situ experiments, the local surface and cross-sectional regions were analyzed by scanning electron microscopy in conjunction with energy dispersive X-ray spectroscopy to understand the variation in chemistry across the wetted region, which includes the interfacial region between filler metal and the base material. As the alumina scale present on the aluminum alloy is very thin (<50 nm), nanoscale characterization techniques such as transmission electron microscopy in scanning mode, including selected area electron diffraction for crystal structure determination, were performed. From this investigation, it was found that the Cu in liquid filler metal diffuses into the base material via the oxide layer, resulting in the formation of Al 2 Cu intermetallic precipitates.

In this work, TA2/T2 was used as a composite interlayer to prevent the formation of brittle Ti-Fe intermetallics when joining TC4 Ti alloy to 304 stainless steel. The TA2/T2 (commercially pure Ti and Cu) composite interlayer was prepared by explosive welding. The laser was focused on the TC4-TA2 interface, which joined the TC4 and TA2 by fusion welding. At the TC4-TA2 interface, a weld zone was formed due to the mixing of molten TC4 and TA2. The laser was also focused on the T2-304 stainless steel interface, a weld zone was formed due to the mixing of molten T2 and 304 stainless steel. Composite interlayer TA/T2 was used not only to prevent the formation of Ti-Fe intermetallics during welding but also to improve microstructure and properties of the stainless steel–Ti alloy joint. The joint fractured at the TA2/T2 explosive welding interface with a maximum tensile strength of 428 MPa.