Journal of Advanced Materials in Engineering (Esteghlal)

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The soft magnetic nanocrystalline Fe73.5Si13.5B9Cu1Nb3 alloy (FINEMET®) is produced by heat treatment of amorphous precursor. Determining kinetic parameters of amorphous structure transformation to nanocrystalline allows the control of microstructure (e.g. size and volume fraction of nanocrystalline grains) in order to achieve desired soft magnetic properties by optimizing the heat treatment conditions. In this research, the nanocrystallization kinetics of amorphous FINEMET alloy were studied using isoconversional and isokinetic methods under non-isothermal conditions of various heating rates ranging from 5 to 20˚C/min. The changes in the microstructure and magnetic properties of amorphous ribbon during nanocrystallization process were studied using X-ray diffractometry and hysteresisgraph, respectively.

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Despite excellent bioactivity of bioactive ceramics such as hydroxyapatite, their clinical applications have been limited due to their poor mechanical properties. Using composite coatings with improved mechanical properties could be a solution to this problem. Therefore, the strength of metal substrate and the bioactivity of the improved composite coating combined could yield suitable results. The aim of this work was fabrication and characterization of hydroxyapatite-forsterite-bioactive glass nanocomposite coating. The sol-gel technique was used to prepare hydroxyapatite-forsterite-bioactive glass nanocomposite in order to coat on 316L stainless steel (SS) by deep coating technique. The X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and energy dispersive X-ray analysis (EDX) techniques were used to investigate the microstructure and morphology of the prepared coating. The results obtained from XRD analysis showed that the suitable temperature for calcination is 600 °C. At this temperature, the homogenous and crack-free coating could attach to the 316L SS substrate. The crystallite size of composite coatings determined via AFM was lower than 100 nm. Overall, the results obtained from this work indicate that hydroxyapatite-forsterite-bioactive glass nanocomposite coating can be a good candidate for biomedical applications.

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Although titanium has been recognized for its excellent bio-compatibility with human tissues and good corrosion resistance in some specific environments, little attention has been paid to the surface enrichment of the components by titanium. In this paper, titanium diffusion coating was formed on the surface of Ni-based alloy B-1900 via pack cementation technique and the microstructure of the coatings obtained was studied. Diffusion titanizing was carried out via pack cementation technique at 850 and 950 C for 3 hours in a mixture of commercially pure titanium, Al2O3 and NH4Cl powder. Microstructure, phase composition and concentration profile of the coatings were examined using optical and electron metallography, X-ray diffraction, and glow discharge optical spectroscopy. The results showed that Ti2Ni and AlNi2Ti were the main constituents of the coating. The formation mechanism of the coatings was also evaluated.

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Composite and nanocomposite Ni-Co/SiC coatings were synthesized by electro-codeposition of micro and nano-sized SiC particles with average diameter of 10m and 20nm using horizontal electrodes. Surface morphology, chemical composition, phase composition, hardness and corrosion resistance of the deposited coatings were studied using SEM observations and EDX, XRD, microhardness and polarization measurements as a function of the electrodeposition current density. The results indicated that the nanocomposite coatings exhibit higher hardness and corrosion resistance compared with the composite coatings containing micro-sized SiC particles despite their lower percentage of the SiC content. The maximum hardness values of 615HV and 490HV were obtained for nanocomposite and composite coatings deposited at current density of 3A/dm2. The observed properties were discussed based on the structural details.

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Coherency elastic strain between γ and  is one of the effective factors which affect the morphology, spatial re-arrangement and coarsening kinetics of  precipitates in nickel-base superalloys. In this investigation, using X-ray diffraction (XRD) technique, the - constrained and unconstrained lattice misfits were calculated for different morphologies of the  precipitates in Inconel 738LC nickel-base superalloy. The constrained and unconstrained misfits, hence the coherency elastic strains of different morphologies of the  precipitates were calculated from the XRD patterns of the bulk sample and electrolytically extracted  precipitates, respectively. According to the results, as the sizes of the  particles increased the - coherency as well as the compressive strain of the  precipitates was reduced and consequently their morphology changed from spherical to cubic, then flower-like, and finally dendritic shapes.

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In this study, magnetite (Fe3O4) nanoparticles were synthesized by chemical co-precipitation from the solution containing iron salts in alkaline medium under N2 gas and room temperature. Magnetite nanoparticles were characterized by X- ray diffraction (XRD), Fourier transform infrared spectrometer (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA), differential thermal analysis (DTA), Brunauer-Emmet-Teller (BET), and vibrating-sample magnetometer (VSM). The rheological properties of magnetite ferrofluid were examined by rheology apparatus. The biocompatibility and cytotoxity of magnetite nanoparticles were evaluated by 3T3 and fibroblast cells. The results showed that the Fe3O4 magnetite nanoparticles coated by polyvinyl alcohol (PVA) could be an appropriate candidate for biomedical applications.

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Carbon fiber composite is one of the most important materials in aerospace engineering applications. For fabrication of this composite, optimum polymerization and carbonization cycles of phenolic resin were obtained [1]. Then, carbon/phenolic composite was fabricated by mixing different weight percentages of T700 carbon fiber with phenolic resin, and the flexural strength of specimens was examined.The samples were pyrolyzed at 1100°C to form high temperature phenolic matrix. Because of high porosity of samples, the composite was impregnated to increase the density and reduce porosity. The maximum flexural strength of samples was obtained with 40 wt. % of fiber. With addition of TiO2 and ZrO2 nanoparticles to carbon/phenolic composite, thermal and mechanical improvement was measured. The samples were examined by ablation test and microstructures of composites were analyzed by SEM.

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This study aims to characterize and evaluate the applicability of Polyhedral OligomericSilsesquioxane (POSS)/ Poly (carbonate-urea) Urethane (PCU) nanocomposite films as a temporary skin substitute by means of FTIR, MTT assay, cell proliferation assay and SEM studies. FTIR spectra showed all the characteristic peaks of POSS/PCU nanocomposite. The indirect cytotoxicity of membranes was investigated by MTT assay. In MTT test, L929 mouse fibroblasts were exposed to the extract of the films for 24 h. MTT results showed no sign of cell cytotoxicity for the extracts at the extraction times up to14 days. Menwhile, it was found that POSS nanocages have a stimulating effect on L929s. In cell proliferation assay, L929s were cultured on the films for 3, 7 and 14 days. The cells showed a high rate of proliferation in direct contact with the biomaterial after 7 and 14 days. Morphology and density of the cells on the nancomposite surface was investigated through SEM observations. SEM micrographs showed that the cells adhered well on the surface after 3 days of culture. Moreover, after 7 days, cell density increased so substantially that a cell layer was formed on the membranes.

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Short life of current total hip replacement metallic implants is generally dependent on the aseptic loosening of the implant, which occurs due to mismatch of elastic modulus between bone and metallic implant materials. Decreasing in elasticmodulus of implant could be successful. Forsterite is biocompatible and bioactive ceramic which has suitable mechanical properties. In presented research the composite materials based on Co-Cr-Mo alloy with 10, 15 and 20wt% of forsteritenanopowder as reinforcement were fabricated and mechanical behavior of the composites were evaluated. Composites were fabricated by ball milling, cold pressing and sintering. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used for characterization and evaluation phase composition and microstructure of the composites. Density, microhardness, compressive strength and elastic modulus of fabricated composites were evaluated. Obtained results showed elastic modulus of composite materials based on Co-Cr-Mo alloy reinforced with 10, 15 and 20wt% of forsteritenanopowder decreased significantly. Results also showed that the compressive strength of Co-base alloy composites reinforced with 10, 15 and 20 wt% forsterite were lower than cast Co-Cr-Mo alloy. With increasing in the content of reinforcement, compressive strength of the composites were decreased. Microhardness of prepared composites were higher than cast Co-Cr-Mo alloy. With increasing in content of bioceramic reinforcement, microhardness of the composites were increased.

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In this study, mullite– irconia composite samples were prepared by reaction sintering of alumina and zircon powder via gel casting process. Gel casting is a new ceramic forming technique. This process is based on the casting of slurry, containing ceramic powder, dispersant and premix monomer solution. To achieve stabilized, high solid loading (80 wt%) and castable slurry, the rheological properties of slurry were optimized. The monomers polymerized the slurry to form gelled specimens. After gelation, the specimens were unmolded, then dried out under controlled condition. Burning out and sintering of the specimens was carried out in the range of 1400-1700°C. Apparent porosity and bulk density of the sintered samples were measured by soaking in water. Crystalline phase evolution and microstructure were determined by XRD and SEM techniques. Results showed that the reaction sintering and mullite formation was completed at 1700°C due to very slow diffusion of Al3+ ions within amorphous silica formed at the decomposition of zircon. The sintered samples at this temperature also showed the lowest apparent porosity (≈ 4%) and the highest bulk density (≈3.40 gr/cm-3).

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In this project, we prepared biomimetic nanocomposite scaffolds from gelatin and chitosan and hydroxyapatite and subsequently the scaffolds were evaluated by common used bulk technique. For this purpose, the nanocomposite hydrogel/apatite bone tissue engineering scaffolds were fabricated using applied biomimetic method accompanied with freeze drying technique. The apatite was precipitated using double diffusion mechanism within gelatin hydrogel in similar pH and temperature to the human body. Chitosan initial percentage (20, 30 and 40%) was set as variables. Nanocomposites were soaked in glutaraldehyde solution in order to enhance mechanical properties and make them insoluble in water. Diffusion of calcium and phosphate from lateral hydrogel into the middle hydrogel caused formation of parallel white layer-formed precipitate. Analysis of precipitates formed within middle hydrogel for the samples, showed that detected materials are composed of carbonated hydroxyapatite and dicalcium phosphate dihydrate (DCPD, brushite). Also, mechanical behavior obtained for the scaffolds were comparable with spongy bone. With increasing chitosan in the composite scaffold, the water up-take was increased from 379 to 661%. Phase composition, microstructure and structural groups in the composite samples were also characterized by X-Ray Diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infra-red (FTIR) analyses. Eventually, the obtained results showed that the composite contains 20% chitosan had appropriate properties for fabricating bone scaffold.

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In the present work, molecular dynamics simulation method was used for determining Young's modulus, Shear modulus and Poisson’s ratio of Al-SiC nanocomposites, with different volume fractions of the reinforcements. For simulation, the open source package, LAMMPS, was used. After putting Aluminum and Silicon Carbide atoms in their initial positions, interatomic potentials between them were defined. EAM potential was used for Aluminum atoms, Morse potential was used for Al-C and Al-Si, and for C-C, Si-C, and Si-Si Tersoff potential was used. According to the elastic bounding principal, and the comparison between the simulations results and Voigt, Ruess and Halpin-Tsai micromechanical models showed that the results were close to the upper bound Voigt model.

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Application of ceramic reinforcements is one of the effective and well-known ways to refine the microstructure of brittle metals such as magnesium. In this research, the influence of nano/micro particles of zirconia on the microstructure of cast AZ91 alloy was studied. At the first stage, nano and micro ZrO2 powders were blended through mechanical alloying procedure. In five specimens, the total amount of nano and micro reinforcements in the final mixture was fixed at 5 wt%, whereas their ratio was varied. Two other composites were also produced using 5wt% of nano or micro particles of zirconia. These powder mixtures were then stirred in the molten AZ91 at 650C by vortex method and finally cast in a sand mold at 615C. For comparison, two monolithic castings including a conventionally cast specimen and a super heat-treated sample were also cast. The average grain sizes for all composites were decreased with respect to both monolithic castings. The best results in terms of grain size and microstructure improvement were obtained for AZ91/5wt% nano ZrO2 composite with remarkable improvement in comparison with monolithic castings.

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A powder mixtures of 18.72% wt, 17.67% wt Al2O3 and 63.6% wt zircon were prepared and milled in a planetary ball milled for one up to 10 hours in presence of air. After removal Iron impurity from as-milled samples, they were isothermally heated in temperature range of 1300-1450 0C for one hour in an air atmosphere. After cooling the samples, they were studied using XRD analyses. The XRD and PSA analyses were showed that the size of particles in the mixtures decreased with increasing of milling time and the mixtures became amorphous nature. The isothermal runs observed that pre-milling on the mixtures has great effect, wherever the zircon decomposition temperature and mullite formation temperature decreased to about 1300 0C in a one-hour-milled sample. The amount of tetragonal zirconia increased with increasing in milling time at 1300 0C, however the amount of tetragonal zirconia decreased with increasing of temperature up to 1450 0C. The amount of tetragonal zirconia at 1300 0C in the three hours milled samples was the highest value among all samples.

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In this study, effect of potential on composition and depth profiles of passive films formed on 316L stainless steel in 0.05 M sulfuric acid has been examined using X-ray photoelectron spectroscopy (XPS). For passive film formation within the passive region, four potentials -0.2, 0.2, 0.5, and 0.8 VSCE were chosen and films were gown at each potential for 60 min. XPS analysis results showed that atomic concentration of Cr and Fe initially increase (E < 0.5 VSCE) and then decrease with potential. This decrease is due to surface dissolution of the Fe and Cr oxides. For both alloying elements, Ni and Mo, no obvious change in atomic concentration was showed. Results indicated that at higher potentials, before entering transpassive region, oxidation of Cr3+ to Cr6+ is happened.

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In plasma sprayed nanostructured composite coatings with ceramic matrix, the feedstock must consist of nanoparticles of appropriate specifications. In this research, the procedure for production of Cr2O3-Ag agglomerated nanostructured composite powder to produce comosite coatings has been investigated. Nanopowders of Cr2O3 with 0, 2, 5, and 10 volume percentages of silver were dispersed to obtain a homogeneous aqueous dispersion appropriate for spray drying process. In the second stage, Cr2O3-Ag composite powders were produced by agglomeration process. The nanostructured composite powders were, then, used in the atmospheric plasma spray (APS) process to deposit a series of composite coatings for evaluation. The composite powders, with a granulated morphology, had uniform distribution of silver in a ceramic matrix and the coatings were composed of nanoparticles and particles of nano-sized crystallites. Experimental results indicated that presence of nanoparticle zones within the microstructure led to non-uniform porosities formed between splats and these zones. Furthermore, use of nanopowders in the feedstock caused a reduction in lamellae thickness of plasma sprayed coatings.

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Mechanical alloying technique is used for production of nanostructured soft magnetic alloys. In this work the back propagation (BP) artificial neural adopted to model the effect of various mechanical alloying parameters i.e. milling time and chemical composition, on the properties of Fe-Ni powders. Lattice parameter, grain size, lattice strain, coersivity and saturation intrinsic flux density are considered as the output of five BP neural networks. The results obtained show the efficiency of designed networks for the prediction of the properties of Fe-Ni powders.

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An important parameter in composite materials is mechanical behavior and matrix-reinforcement interface interaction under applied stresses. In this investigation, bending strength of carbon-carbon composites synthesized from wood was analyzed as a measure of the composite mechanical properties. Also, densification efficiency of the products was determined by measuring the bulk density and open porosity percentage. Using scanning electron microscopy, optical microscopy, X-Ray diffraction, and Raman spectroscopy, the final product was examined to evaluate and interpret the morphology and internal texture and results of mechanical test. The results showed that we are able to use an ordinary material such as wood for production of a unique product with great properties called two-dimensional carbon-carbon composites.

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In this study, pure powders such as molybdenum, silicon, aluminum and titanium carbide were utilized to produce MoSi2 compound, MoSi2 /20 Vol % TiC composite, MoSi2-x Al alloyed compound and MoSi2-x Al/20 Vol % TiC alloyed composite. The initial powders were mixed in specified ratios, and then, were activated by mechanical milling. Milled powders were compacted, synthesized and sintered in the temperature range of 1100 -1400 oC. SEM was used to investigate the microstructural change and XRD for identification of phases. Effect of aluminum addition on phase formation was investigated. Addition of aluminum by over 9 atomic percent resulted in the formation of Mo(Si,Al)2 in alloyed matrix.