ADVANCED MATERIALS IN ENGINEERING (ESTEGHLAL)
Year:2019 | Volume:38 | Issue:3 |Papers Count:8

One of the most effective ways to improve oxidation resistance of interconnects used in solid oxide fuel cells (SOFCs) is to apply a layer of conductive protective coating. In this study, Crofer 22APU ferritic steel was coated in a titanium-based powder mixture by pack cementation method. The powder composition for titanium coating was Ti 20 wt. %, NH4Cl 5 wt. % (activator) and Al2O3 75 wt. %. The optimum temperature and time to obtain the best coating quality in terms of adhesion and porosity were 800 ° C and 7 hours, respectivly. The obtained titanized coating consisted of TiFe, TiFe2 and TiCr2 phases. The results of isothermal and cyclic oxidation tests carried out at 900 ° C, showed that titanium-coated samples had better oxidation resistance than non-coated samples. Microstructural and phase studies of coated and oxidized samples were performed by scanning electron macroscopy (SEM) and X-ray diffraction analysis (XRD). During oxidation process, the coating layer was converted into TiFe, TiFe2, TiFe2O5, TiO2 and TiCr2O4 phases. The coated specimens had lower weight gains relative to uncoated samples showing that coating effectively protects the substrate against oxidation. Moreover, coated samples had higher electrical resistance than uncoated ones.

Due to their sensitivity to impact-induced delamination, woven fabric reinforced polymer composites have limited practical applications. Hybridization of polymer composites has been proposed as a solution to this problem. In this study, the effects of fiber reinforcement type, hybridization method, plies stacking sequence and loading rate on mode I delamination behavior of pure basalt, pure nylon, inter-ply and intra-ply hybrid (basalt/nylon) composites were investigated. Composites were prepared by the hand lay-up method (four layers for each sample) using basalt/nylon woven fabrics and epoxy resin. Crack length during its propagation in composite samples was measured by mode I delamination test. The inter-laminar fracture toughness of composite specimens was calculated using modified double-cantilever beam theory and the results were compared by statistical methods. A 30 to 80% improvement in the critical fracture toughness of intra-ply hybrid composite compared to pure ones was recorded. Moreover, the delamination initiation load decreased significantly by increasing the loading rate.

In this research, synthesis of lithium fluoride (LiF) nanoparticles by fluorolytic sol-gel method has been studied. Moreover, the effect of lithium ion to fluorine source molar ratio and calcination temperature on particle size and phase of LiF nanoparticles were investigated. Lithium acetate (C2H3LiO2), trifluoroacetic acid (TFA), ethylene glycol monobutyl ether and oleic acid were used as sources of Li + and F- ions, solvent and growth inhibitor, respectively. Thermal and X-ray diffraction (XRD) analyses as well as field emission scanning electron microscopy (FESEM) were used to investigate thermal behavior of the primary gel and to determine the phase and morphology of samples, respectively. The results showed that the 2: 1 molar ratio of Li + / TFA and the calcination temperature of 400 ° C result in LiF nanoparticles with a mean particle size of 80-100 nm.

In this paper, W-type SrCo2Fe16O27 hexaferrite nanostructures were synthesized by sol-gel auto-combustion method. Effect of annealing temperature on the structural, magnetic and optical properties of these SrCo2Fe16O27 nanostructures was investigated. In order to determine the annealing temperature of samples, the prepared gel was examined by thermo-gravimetric and differential-thermal analyses. Morphology and crystal structure of the prepared samples were characterized by field emission scanning electron microscopy and X-ray diffraction pattern. Based on X-ray diffraction results, at annealing temperature of 1000 ° C, the maximum amount of main phase formed. A planar morphology was spectroscopy for the synthesized samples through scanning electron microscope images. Fourier transform infrared analysis was used to confirm the synthesis of the main phase. Results confirmed the formation of tetrahedral and octahedral sites as the important characteristic of hexaferrites. Magnetic properties obtained of samples were measured by the vibrating sample magnetometer and the results showed that by increasing temperature, magnetic saturation increases. Moreover, optical properties of samples were investigated by ultraviolet– visible absorption and photoluminescence spectroscopies. The result of measurements of the energy gap approximately is same in the ultraviolet-visible and photoluminescence spectroscopes and also the energy gap is constant with increasing temperature.

Finite element (FE) simulations in conjunction with experimental analysis were carried out to characterize the deformation behavior of an AISI 321 austenitic stainless steel (ASS) during cold pilgering process. The effect of process parameters including feed rate (4 and 8 mm) and turn angle (15, 30 and 60° ) on damage build-up were also evaluated. The Johnson-cook model was used to simulate the flow behavior of material. By considering compressive stresses, a new revised Latham-Cockcraft damage was calculated and used to determine the optimum process parameters. It was found that the radial and hoop strains in all friction conditions were compressive, while the axial strains were observed to be tensile. The amount of strain (whether it is compressive or tensile strain) was also higher on the outside of the tube compared to its inside. By considering fatigue cycles of a tube element during the process, the feed rate of 8mm, turn angle of 60° and the lowest coefficient of friction were determined as optimum parameters.

In this study, polycaprolactone/chitosan/1% baghdadite composite coating was applied on anodized AZ91 alloy to improve the corrosion rate of AZ91 alloy in simulated body fluid (SBF) solution for long immersion times, control its degradability and enhance its bioactivity. By applying the composite coating and after seven days of immersion in a phosphate buffer solution, the corrosion rate decreased from 0. 21 mg/h. cm 2 (for AZ91 sample) to 0. 1 mg/h. cm 2 (for anodized AZ91 sample). Formation of apatite layer on the surface of specimens is considered a criterion for bioactivity. In order to evaluate the ability of specimens to get covered by an apatite, the SBF test was used. Application of the composite coating yielded the highest ability for apatite formation, controlled release of ions, and the lowest corrosion rate in the SBF so that it could be considered a good choice for bone implants.

The aim of this study was to fabricate the Mg-1Al-Cu alloys with various amounts of Cu content (0, 0. 25, 0. 5 and 1 wt. %) using spark plasma sintering (SPS) approach and evaluation of their degradation rate and biological properties. The results indicated that Cu incorporation (0. 25 wt. %) significantly diminish degradation rate from 0. 039 cm/h in pure Mg to 0. 00584 cm/h in Mg-1Al-0. 25Cu alloy. In addition, Mg-1Al-0. 25Cu alloy could noticeably (1. 25 times) promote viability of MG63 cells compared to pure Mg, owing to the optimized ion release. Moreover, the antibacterial activity of Mg-1Al-0. 25Cu was considerable. In summary, Mg-1Al-0. 25Cu alloy with appropriate degradation rate, good biocompatibility and antibacterial properties can be introduced as a biodegradable orthopedic implant.

The outer surface of heat exchanger tubes that work under fluidized bed waste or biomass incineration is exposed to severe high-temperature erosion-corrosion (E-C). To evaluate the behavior and enhance the service life of the tubes, the real service conditions ought to be simulated in the laboratory. In this study a test rig with a fluidized bed of hot sand was designed and manufactured to expose nickel-based SFNi4 alloy to high-temperature E-C. In order to increase the corrosiveness of the environment, the silicon oxide sand was mixed with 0, 0. 5 and 1 wt. % of a mixture of NaCl and KCl salts with 1: 1 molar ratio. The erosive conditions of the environment were changed by altering air flow rate from 20 to 25 L/min and changing the sand incident angle from 45 to 90 degrees. The rate of material removal was calculated by measuring the thickness of each sample before and after the test. After each experiment, the surface and cross-section of specimens were studied using SEM and EDS analysis. Finally, the optimum E-C parameters to ensure actual industrial conditions were obtained.