Iranian Journal of Materials Science and Engineering

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High energetic aluminum nanoparticles are mainly used as additive in solid rocket propellants. However, fabrication of these aluminized energetic materials is associated with decreasing the burning rate of propellants due to problems such as oxidation and agglomeration of nanoparticles. In this study, to improve combustion performance of aluminum nanoparticles, coating by metallic Ni shell was studied. Nickel coating of aluminum nanoparticles was performed through electroless deposition (ED) subsequently, morphology and chemical composition of Ni-coated nanoparticles were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). These studies show that a uniform Ni layer with a thickness of 10nm is coated on the surface of Al nanoparticles. Thermal analysis of uncoated and Ni-coated aluminum nanoparticles was done using differential thermal analysis (DTA) and thermo gravimetric analysis (TGA). The results of thermal analysis indicate that, coating the aluminum particles by Ni, leads to improvement in combustion performance of aluminum nanoparticles through decreasing critical ignition temperature, ignition delay time of the nanoparticles and promoting the ignition by exothermic chemical reactions between Al and Ni

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The aim of the present study is the prediction of critical conditions (including critical strain and flow stress) for the initiation of dynamic recrystallization during thermo-mechanical processing of plain carbon steels. For this propose, torsion tests were conducted at different temperature (1050, 1100 and 1150˚C) and strain rates (0.002, 0.02 and 0.2/s). All flow curves showed a peak stress indicating that dynamic recrystallization occurs during hot deformation. The critical stress and strain were then determined based on change in strain hardening rate as a function of flow stress. Finally, the effect of deformation conditions on these parameters was analyzed.

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In this work, TiN/TiCN & PN/TiCN multilayer films were deposited by plasma- assisted chemical vapour deposition (PACVD). Plasma nitriding (PN) and TiN intermediate layer prior to coating leads to appropriate hardness gradient and it can greatly improve the mechanical properties of the coating. The composition, crystalline structure and phase of the films were investigated by X-ray diffraction. Atomic force microscopy and scanning electron microscopy were employed to observe the morphology and structure of the films. The TiCN layer exhibited a columnar structure. The adhesion force between the film and the tool steel substrate was 30.8 MPa for TiN/TiCN and 25.4 MPa for PN/TiCN film determined by pull off tests. The hardness of TiN/TiCN film was 12.75 GPa while it was 5.4 GPa for PN/TiCN film, respectively. The improvement of the adhesion in TiN/TiCN was attributed to a less gradient hardness configuration. In addition, the mean friction coefficients of the films were about 0.2 for TiN/TiCN and 0.3 for PN/TiCN film determined by nanoindentation tests.

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trontium hexaferrite (SrFe 12 O 19 ) nanosized powders were synthesized by sol-gel auto-combustion method with and without cetyltrimethylammonium boromide (CTAB) addition in the sol with Fe/Sr ratio of 11 (using additional Sr). The resultant powders were investigated by X-ray Diffraction (XRD), Transmission Electron Microscope (TEM), Field Emission Scanning Electron Microscope (FESEM) and Vibration Sample Magnetometer (VSM) techniques. Phase constituents of the synthesized samples which were heat treated at temperatures in the range of 700- 900 ◦C were studied. XRD results revealed that CTAB addition facilitates the formation of single phase strontium hexaferrite at 800 ◦C. Microstructural evaluations with FESEM represented that CTAB addition causes formation of larger particles with a narrower size distribution. VSM results represented that the highest amount of intrinsic coercivity force ( i H C ) was obtained in the sample without CTAB addition and with additional Sr, calcined at 800 ◦C for 1 h which was equal to 5749.21 Oe, while the value of i H C was equal to 4950.89 Oe without additional Sr. The amount of maximum magnetization (M max ) was raised from 48.41 emu/g to 62.60 emu/g using CTAB and additional Sr. The microstructure and magnetic properties of the samples have been explained

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Aluminium base alloy (Al-Cu-Si) was reinforced with silicon carbide (SiC) particles, in various percentage compositions from 0-20 wt%. Silicon carbide particle size of 20µm was selected. The molten slurry of SiC reinforced base aluminium metal was casted through green and dry sand casting methods and solidification process was carried out under ambient conditions. A selected population of total casted samples were subjected to T6 heat treatment process, followed by evaluation of mechanical properties of hardness, tensile strength and impact loading. The micro sized SiC particles were preheated up to 300C prior pouring into the melted metal, for subsequent removal of residual gases and moisture content. A continuous manual stirring method was used for homogenous distribution of reinforced particle in molten slurry. The experimental results revealed that the highest parameters of hardness, impact energy and tensile strength were achieved in the T6 heat treated specimens having highest percentage composition (20%) of Silicon Carbide (SiC) particles

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In this research, two different carbonaceous materials (Graphite:G and Petrocoke:P) were separately compared in terms of the carbothermic reduction of hematite and anatase in order to synthesize Fe-TiC nanocrystalline composite by mechanically activated sintering method. Powders were activated in a planetary high-energy ball mill under argon atmosphere for 0, 2, 5, 10,and 20 h. Then, the activated powders were analyzed by XRD and SEM to investigate phase constituents and microstructure of the mixtures. Results proved that Fe 2 O 3 and TiO 2 were not reduced by carbonaceous materials even after 20h of milling. SEM investigations showed that G-mixture was more homogenous than P-mixture after 20h of milling, meaning that graphite-anatase-hematite was mixed satisfactorily. Thermogravimetry analysis was done on 0 and 20h milled powders. TG and DTG curves showed that mechanical activation led to almost 300°C decrease in the reduction temperature of hematite and anatase in both mixtures. In the next step, the powders were sintered in a tube furnace under argon atmosphere. In the G-mixture, anatase was reduced to titanium carbide at 1100°C but, in the P-mixture, temperature of 1200°C was essential for completely reducing anatase to titanium carbide.Results of phase identification of the sintered powders showed that anano-crystalline ironbased composite with titanium carbide, as the reinforcement was successfully synthesized after 20 h high-energy milling of the initial powders and subsequent sintering occurred at 1200˚C for 1h

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In the present study, the feasibility of α-Fe ferromagnetic phase formation in glass and glass-ceramic by reduction in hydrogen atmosphere have been investigated. The glass with the composition of 35Na 2 O–24Fe2O3–20B 2O3 – 20SiO 2 –1ZnO (mol %) was melted and quenched by using a twin roller technique. As quenched glass flakes were heat treated in the range of 400-675 °C for 1-2 h in hydrogen atmosphere, which resulted in reduction of iron cations to α-Fe and FeO. The reduction of iron cations in glass was not completely occurred. Saturation magnetization of these samples was 8-37 emu g -1 . For the formation of glass ceramic, As quenched glass flakes heat treated at 590 °C for 1 h. Heat treatment of glass ceramic containing magnetite at 675°C in hydrogen atmosphere for 1 h led to reduction of almost all of the iron cations to α-Fe. Saturation magnetization of this sample increased from 19.8 emu g -1 for glass ceramic to 67 emu g -1

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In this paper, the effect of MgO, BaO, Na 2 O and SrO addition to a pre-melted CaO-Al2O3 -Si 2 O synthetic slag on sulfur removal from plain carbon steel was studied under the same experimental conditions. The slags were pre-melted at 1400°C in an electric resistant furnace and desulfurization experiments were carried out in a high frequency induction furnace. The results showed that the optimum reaction time for desulfurization was 15 min. It was found that while SrO addition to the ternary slag enhances the sulfur removal capability, MgO, Na 2O and BaO additions reduce desulfurization efficiency of the ternary slag. Moreover, it was observed that restricting access to oxygen from the atmosphere by using a covered crucible, could increase desulfurization efficiency of the slag by more than two fold

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MgAl2O4/Ti(C,N) composites were synthesized through aluminothermic reaction between Al,TiO 2,MgO powders and phenolic resin in coke bed condition. Effect of addition of carbon black and sugar into the mixture at different temperatures were investigated. The phases and microstructures of samples were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). MgAl 2O4 /Ti(C,N) composites without additive were obtained after heat treatment at 1600˚C. With addition of carbon black TiC, TiN and Ti(C,N) were appeared after firing at 1400˚C and formation of spinel/Ti(C,N) composites were completed at 1600˚C. In sample containing sugar, MgAl2O4 -Ti(C,N) composite were completely synthesized at 1400˚C. In this sample crystallite size of Ti(C,N) were 32 nm and carbon content of titanium carbonitride (Ti(C,N)) reached to 0.442 value.

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 Microsegregation is one of the most important phenomena occurs during solidification. It usually results in formation of some unexpected second phases which generally affect the mechanical properties and specially reduce the workability of casting products. The aim of this research is to study the effect of cooling rate and grain refinement on the microsegregation in Al-4.8 wt.% Cu. For this purpose two series of experiments were designed. In the first set of experiments, the alloy was melted and cooled in three different rates, i.e. 0.04, 0.42, and 1.08 K/s in a DTA furnace. In the second series of experiments, the effect of grain refinement on the microsegregation at a constant cooling rate of 0.19 K/s was investigated. Al-5Ti-1B master alloy was used as grain refiner. Results showed that by increasing the cooling rate the amount of non-equilibrium eutectic phase increases from 5.1 to 7.4 wt.%, and the minimum concentration of solute element in primary phase decreases from 1.51 to 1.05 wt.% Cu. By grain refinement of the alloy, the amount of non-equilibrium eutectic phase decreases from 5.5 to 4.7 wt.%, and the minimum concentration of solute element in the primary phase increases from 0.98 to 1.07 wt.% Cu. So it is concluded that increasing cooling rate in the range of 0.04 to 1.08 K/s, increases and grain refinement reduces the microsegregation 

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Nano-sized NiFe2O4 powders were synthesized by sol–gel auto-combustion method using pH values from 7 to 9 in the sol. The effect of pH variations on complexing behavior of the species in the sol has been explained. Changes in phase constituents, microstructure and magnetic properties by changes in pH values were evaluated by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and vibration sample magnetometer (VSM) techniques. Changes in pH value from 7 to 9 changes the amounts of NiFe2O4, FeNi3 and α-Fe2O3 phases. Calculated mean crystallite sizes are in the range of 44 to 51nm. FESEM micrographs revealed that increasing the pH value to 9 causes formation of coarse particles with higher crystallinity. Saturation magnetization was increased from 36.96emu/g to 39.35emu/g by increasing pH value from 7 to 8 which is the result of increased FeNi3 content. Using higher pH values in the sol reduces the Ms value.

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The inherent reactivity of the Al–Cu alloys is such that their use for structural, marine, and aerospace components and structures would not be possible without prior application of a corrosion resistance system. Historically these corrosion resistance coatings were based on the use of chemicals containing Cr (VI) compounds. Silane coatings are of increasing interest in industry due to their potential application for the replacement of current toxic hexavalent chromate based treatments. In this study, hydrophobic coating sol was prepared with methyltriethoxysilane (MTES), methanol (MeOH), and water (as 7M NH4OH) at a molar ratio of 1:25:4.31 respectively. The coatings were applied by a dip-technique to 2024-T3 Al alloy, and subsequently cured at room temperature and there after heat treated in an oven at 150°C. The anticorrosion properties of the coatings within 3.5 wt% NaCl solution were studied by Tafel polarization technique. The sol–gel coating exhibited good anticorrosion properties providing an adherent protection film on the Al 2024-T3 substrate. The surface properties were characterized by water contact angle measurement, scanning electron microscopy (SEM), and the composition was studied by Fourier transform infrared spectroscopy (FTIR).

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High speed and absence of a precise control over pressure distribution confine sheet Electromagnetic Forming into a die to simple shapes having shallow depth. It is possible to reach a higher depth by using a convex punch instead of a concave die. In this study, sheet Electromagnetic Forming on a punch and sheet Electromagnetic Forming into a die are investigated. The electromagnetic part of the study is investigated analytically and its mechanical part is studied numerically. In order to couple electromagnetic with mechanical parts, no-coupling method is used. The obtained results are verified by comparing the obtained results with previous experimental ones in literature. Rate-dependent and rate-independent hardenings are taken into consideration for the mechanical behavior for material of AAl1050. Using appropriate hardening model for material yields acceptable results. Moreover, a convex punch instead of a concave die is used to reach to a higher depth in sheet Electromagnetic Forming.

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A homogenous TiO₂ / multi-walled carbon nanotubes(MWCNTs) composite film were prepared by electrophoretic co-deposition from organic suspension on a stainless steel substrate.  In this study, MWCNTs was incorporated to the coating because of their long structure and their capability to be functionalized by different inorganic groups on the surface. FTIR spectroscopy showed the existence of carboxylic groups on the modified carbon nanotubes surface. The effect of applied electrical fields, deposition time and concentration of nanoparticulates on coatings morphology were investigated by scanning electron microscopy. It was found that combination of MWCNTs within TiO₂ matrix eliminating micro cracks presented on TiO₂ coating. Also, by increasing the deposition voltages, micro cracks were increased. SEM observation of the coatings revealed that TiO₂/multi-walled carbon nanotubes coatings produced from optimized electric field was uniform and had good adhesive to the substrate.

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In the present work, iron recovery from a low-grade hematite ore (containing less than 40% iron), which is not applicable in common methods of ironmaking, was studied. Non-coking coal was used as reducing agent. Reduction experiments were performed under various coal to hematite ratios and temperatures. Reduction degree was calculated using the gravimetric method. Reduced samples were subjected to magnetic separation followed by X-ray diffraction analysis. Total iron content, degree of metallization and recovery efficiency in magnetic part were determined by quantitative chemical analysis, which were obtained about 82%, 95% and 64% respectively under optimal conditions. CaO as an additive improved ore reducibility and separation efficiency. The microstructure of reduced samples and final products were analyzed by scanning electron microscopy. Final product with a high degree of metallization can be used in steel making furnaces and charging of blast furnaces which can improve production efficiency and decrease coke usage.

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Nowadays, Ni-free austenitic stainless steels are being developed rapidly and high price of nickel is one of the most important motivations for this development. At present research a new FeCrMn steel was designed and produced based on Fe-Cr-Mn-C system. Comparative studies on microstructure and high temperature mechanical properties of  new steel and AISI 316 steel were done. The results showed that new FeCrMn developed steel has single austenite phase microstructure, and its tensile strength and toughness were higher than those of 316 steel at 25, 200,350 and 500°C. In contrast with 316 steel, the new FeCrMn steel did not show strain induced transformation and dynamic strain aging phenomena during tensile tests that represented higher austenite stability of new developed steel. Lower density and higher strength of the new steel caused higher specific strength in comparison with the 316 one that can be considered as an important advantage in structural applications but in less corrosive environment

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In this work, the effects of co-precipitation temperature and post calcination on the magnetic properties and photocatalytic activities of ZnFe₂O₄ nanoparticles were investigated. The structure, magnetic and optical properties of zinc ferrite nanoparticles were characterized by X-ray diffraction (XRD), vibrating sample magnetometry and UV–Vis spectrophotometry techniques.  The XRD results showed that the coprecipitated as well as calcined nanoparticles are single phase with partially inverse spinel structures. The magnetization and band gap decreased with the increasing of co-precipitation temperature through the increasing of the crystallite size. However, the post calcination at 500 °C was more effective on the decreasing of magnetization and band gap. Furthermore, photocatalytic activity of zinc ferrite nanoparticles was studied by the degradation of methyl orange under UV-light irradiation. Compare with the coprecipitated ZnFe₂O₄ nanoparticles with 5% degradation of methyl orange after 5 h UV-light light radiation, the calcined ZnFe₂O₄ nanoparticles exhibited a better photocatalytic activity with 20% degradation.

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In this paper the feasibility of fabricating controlled porous skeleton of pure tungsten at low temperature by addition of submicron particles to tungsten powder (surface activated sintering) has been studied and the best parameters for subsequent infiltration of Cu were acquired. The effects of addition of submicron particles and sintering temperature on porous as well as infiltrated samples were studied. The samples were examined by scanning electron microscopy (SEM), Vickers hardness measurements and tensile test. The composites made have been investigated and revealed the making W-Cu composite with good density, penetrability, hardness and microstructure. Consequently, the sintering temperature was reduced considerably (Ts≤1650^oC) and a homogeneous porous tungsten was obtained. Also, composite prepared by this method exhibited elongation about 28% that is much more than conventional W-15%wt Cu composites. This method of production for W–Cu composites has not been reported elsewhere

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In this work the procedure to the synthesis of Ba₂GdSbO₆ complex perovskite by the solid-state reaction method is reported. Theoretically a study of the crystalline and electronic structure was performed into the framework of the Density Functional Theory (DFT). The most stable structure is obtained to be a rhombohedral perovskite with a lattice constant a=6,0840 Å.  Due the occurrence of a mean energy gap of 2,84 eV close to the Fermi level for both up and down spin polarizations this material is classifies as insulator.  The effective magnetic moment of material obtained from the calculations was 7,0 m_B. The crystalline structure was analyzed through the X-ray diffraction technique and Rietveld refinement of the experimental data. Results are strongly in agreement with those theoretically predicted. Magnetic response was studied from measurements of magnetic susceptibility as a function of temperature. Results reveal the paramagnetic feature of this material in the temperature regime from 50 K up to 300 K. From the fitting with the Curie law the effective magnetic moment was obtained to be 8,1 m_B, which is slightly higher that the theoretical value for the Gd³⁺ isolated cation predicted by the theory of paramagnetism. The energy gap obtained from experiments of diffuse reflectance is relatively in agreement with the theoretical predictions. The dielectric constant as a function of applied frequencies at room temperature was measured. Results reveal a decreasing behavior with a high value of dielectric constant at low applied frequencies

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In this paper, cyclic flaring and sinking (CFS) as a new severe plastic deformation (SPD) method was employed to produce the ultrafine grain (UFG) copper tubes. The extra friction has eliminated in the CFS method that provided the possibility for production of longer UFG tubes compared to the other SPD methods. This process was done periodically to apply more strain and consequently finer grain size and better mechanical properties. The CFS was performed successfully on pure copper tubes up to eleven cycles. Mechanical properties of the initial and processed tubes were extracted from tensile tests in the different cycles. The remarkable increase in strength and decrease in ductility take placed in the CFS-ed tubes. The material flow behavior during CFS processing was analyzed by optical microscopy (OM), and a model was presented for grain refinement mechanism of pure copper based on multiplication and migration of dislocations (MMD). This mechanism caused that the initial grains converts to elongated dislocation cells (subgrains) and then to equiaxed ultrafine grains in the higher cycles. The CFS method refined the microstructure to fine grains with the mean grain size of 1200nm from initial coarse grain size of 40µm