Iranian Journal of Materials Science and Engineering

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Abstract: In this research work, crystallization kinetics of Fe55Cr18Mo7B16C4 alloy was evaluated by X-ray diffraction, TEM observations and differential scanning calorimetric tests. In practice, crystallization and growth mechanisms were investigated using DSC tests in four different heating rates. Results showed that a two -step crystallization process occurred in the alloy in which - Fe phase was crystallized in the first step after annealing treatments. Activation energy for the first step of crystallization i.e. - Fe was measured to be 276 (kj/mol) according to Kissinger model. Further, avrami exponent calculated from DSC curves was 2 and a three -dimensional diffusion controlled mechanism with decreasing nucleation rate was observed in the alloy. It is also known from the TEM observations that crystalline á – Fe phase nucleated in the structure of the alloy in an average size of 10 nm and completely mottled morphology.

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Abstract: The supersolidus liquid phase sintering characteristics of commercial 2024 pre-alloyed powder was studied at different sintering conditions. Pre-alloyed 2024 aluminum alloy powder was produced via air atomizing process with particle size of less than 100 µm. The solidus and liquidus temperatures of the produced alloy were determined using differential thermal analysis (DTA). The sintering process was performed at various temperatures ranging from the solidus to liquidus temperatures in dry N2 gas atmosphere for 30 min in a tube furnace. The maximum density of the 2024 aluminum alloy was obtained at 610ºC which yields parts with a relative density of 98.8% of the theoretical density. The density of the sintered samples increased to the maximum 99.3% of the theoretical density with the addition of 0.1 wt. %Sn powder to the 2024 pre-alloyed powder. The maximum density was obtained at 15% liquid volume fraction for both powder mixtures.

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TiO2/SiO2 nanocomposite with molar ratio 1:1 was synthesized by a free calcination sol-gel method using titanium tetra chloride and tetraethylorthosilicate as raw materials. In the composite, TiO2 nanocrystals are highly dispersed in the amorphous SiO2 matrix and the mater showed size quantization effect arising from the presence of extremely small titanium oxide species having a low coordination number. Thermal phase transformation studies of the as-prepared composite were carried out by means of X-ray diffraction (XRD) patterns and thermogravimetry–differential scanning calorimetry (TG–DSC) analyses. The studies showed existence of anatase phase in all the tested temperatures. When temperature exceeds 400°C, brookite phase was formed beside anatase phase. At 950°C amorphous silica matrix was transformed to crystobalite and brookite phase disappeared. Finally, small peaks of rutile phase were detectable at 1100°C.

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Abstract: Nickel was electrodeposited onto copper substrates with high {111} and {400} peak intensities. The grain size of coatings deposited onto the copper substrate with a higher {111} peak intensity was finer. Spheroidized pyramid morphology was obtained at low current densities on both copper substrates. By increasing the deposition current density, grain size of the coating was increased for both substrates and eventually a mixed morphology of pyramids and blocks was appeared without further increase in grain size. This decreased the anodic exchange current density probably due to the decrease of surface roughness and led to a lower corrosion rate.

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Abstract:Some types of glass and glass ceramics have a great potential for making bone tissue engineering scaffolds, drug carrier and bone cements as they can bond to host bone, stimulate bone cells toward osteogenesis, and resorb at the same time as the bone is repaired. Calcium phosphate glass ceramics have very attractive properties that allow them to use in bone tissue engineering. Calcium phosphate glasses could be used for the fabrication of resorbable constructs, with controlled biodegradability. This work was investigated crystallization and sinterability of biodegradable glass ceramics in the CaO–P2O5–Na2O–TiO2 system using differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Sinterability of the glasses also was investigated by measurement of sintering parameters. Different thermal treatments were applied to control the degree of devitrification of glasses. In the developed glass ceramics Ca2P2O7 were the first phase to precipitate in the mother glass structure, followed by Ca(PO3)2 and TiP2O7 at elevated temperature. Ca2P2O7 and Ca(PO3)2 seem to have a very positive effect in bone formation in vivo. It is therefore expected that glass ceramics understudy have good potential to be used for bone regeneration applications

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The probable reasons for evolution of weld porosity and solidification cracking and the structure- property relationship in aluminium welds were investigated. Aluminium plates (1xxx series) were welded by Tungsten Inert Gas (TIG) welding process, 5356 filler metal was used and heat input was controlled by varying welding current (145A, 175A and 195A). The welded samples were examined under optical and scanning electron microscopes and mechanical tests were performed to determine tensile and impact strengths. Secondary phase, identified as globules of Mg2Al3 precipitates, was found to be formed. Solidification cracking appeared in the heat affected zone (HAZ) and porosities were found at the weld portion. The tendency for the formation of solidification cracking and weld porosities decreased with increased welding current.

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In the present study NiCrAlY bond coating layer was produced by electroplating against common atmospheric plasma spraying (APS). Both types of the bond coats were applied on IN738LC base metal then, the YSZ (ZrO2-8% Y2O3) thermal barrier top layer was coated by atmospheric plasma spray technique. Hot corrosion is one of the main destructive factors in thermal barrier coatings (TBCs) which come as a result of molten salt effect on the coating–gas interface. In this investigation the hot corrosion behavior of coatings was tested in the furnace which was contain Na2SO4-55% V2O5 and mixed salts environment at 900°C up to 15 hr. dwell time. Optical microscopy, scanning electron microscopy (SEM / EDS) and X-ray diffraction analysis (XRD) was used to determine the crystallographic structure and phase transformation of the coatings before and after the hot corrosion tests. The transformation of tetragonal Zirconia to monoclinic ZrO2 and formation of YVO4 crystals as hot corrosion products caused the degradation of mentioned TBCs. The results showed NiCrAlY coated by economical electroplating method a viable alternative for common thermals sprayed bond coats in hot corrosive environments with same corrosion behavior

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Crystallization kinetics of Fe52Cr18Mo7B16C4Nb3 alloy was evaluated using X-ray diffraction, differential scanning calorimetric (DSC) tests and TEM observations in this research work. In effect, crystallization and growth mechanisms were investigated using DSC tests in four different heating rates (10, 20, 30, 40 K/min) and kinetic models (i.e. Kissinger- Starink, Ozawa, and Matusita methods). Results showed that a two -step crystallization process occurred in the alloy in which α - Fe and Fe3B phases were crystallized respectively in the structure after heat treatment. Activation energy for the first step of crystallization i.e., α - Fe was measured to be 421 (kj/mol) and 442 (kj/mol) according to both Kissinger- Starink and Ozawa models respectively. Further, Avrami exponent calculated from DSC curves was 1.6 and a two -dimensional diffusion controlled mechanism with decreasing nucleation rate was observed in the alloy. TEM observations reveal that crystalline α – Fe phase nucleated in the structure of the alloy in an average size of 10 nm and completely mottled morphology

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The conical nanostructure improves the applications of alumina membranes and provides three dimensional nanometer scale systems to study the chemical and physical properties. In this study, the nano cone structure is produced in porous anodic alumina (PAA) by two-step anodizing. This conical nanostructure will improve the application of PAA membranes. This approach is novel generation of the so-called "gradually decreased voltage" technique, in which the voltage- time curve is divided into three stages and the effect of each step is investigated for different electrolytes. The effect of the decreasing voltage is examined in two types of electrolytes oxalic and phosphoric acid with a constant decrease in voltage rate. The results of SEM, FE-SEM images show the slope of the inner cone layer in the oxalic acid to be considerably larger compared with phosphoric acid.

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The rapidly solidified prealloyed alpha brass powder with a size range of 40 to 100 μm produced by water atomization process was consolidated using liquid phase sintering process. The relationships between sintering temperature, physic-mechanical properties and microstructural characteristics were investigated. Maximum densification was obtained at 930 °C, under 600 MPa compacting pressure, with 60 min holding time. The microstructure of the sintered brass was influenced by dezincification and structural coarsening during supersolidus liquid phase sintering. As a consequence of Kirkendall effect atomic motion between Cu and Zn atoms caused to dezincification at the grain boundaries and formation of ZnO particles on the pore surfaces. It was concluded that microstructural analysis is in a well agreement with obtained physical and mechanical properties. Also, the amount of liquid phase, which depends on sintering temperature, results in different load bearing cross section areas, and it affects the type of fracture morphologies.

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Mechanically Activated Self-propagating High temperature Synthesis (MASHS) is the method which is used to promote self-propagating synthesis by increasing activity of reactants and increase the purity of products. In this study Ti 2 AlC and Ti3AlC2 max phases were synthesized by using mechanically activated self-propagating high temperature synthesis (MASHS) and samples reactivity and phase structure of samples was studied. This process was performed by combination of short duration ball milling (MA) of reactants (Ti, Al and C as raw materials) and selfpropagating high temperature synthesis (SHS) by microwave or furnace. Mixtures of Ti/Al/C by mole ratio of 2:1:1 and 3:1:2 were milled for 2h., then exothermic reaction was initiated in microwave or high temperature furnace and their reaction behavior and structure have been investigated by DTA and XRD. Results revealed that it’s possible to fabricate these materials by MASHS method but purity of them depends on type of reaction condition. DTA and XRD analyses proved that increasing of soaking time did not improve purity of compounds and some impurities such as TiC would be formed in non-optimized reaction routes.

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Pure cobalt coatings were electrodeposited on copper substrate by means of direct electric current in a chloride solution at different current densities in the range of 10-70 mA cm -2 . The surface morphology and microstructure were investigated via X-ray diffraction analysis and scanning electron microscopy. Corrosion behavior of cobalt coatings was also studied in a 3.5 wt% NaCl solution using potentiodynamic polarization and impedance spectroscopy techniques. The results showed that corrosion resistance of deposits was strongly influenced by the coating’s morphology. Co deposit obtained in lower current densities exhibited the highest corrosion resistance, due to their lower grain boundaries and so the least density of active sites for preferential corrosion attacks

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In the present study, CrN, TiN and (Ti, Cr)N coatings were deposited on D6 tool steel substrates. Physical and mechanical properties of coatings such as microstructure, thickness, phase composition, and hardness were evaluated. Phase compositions were studies by X-ray diffraction method. Mechanical properties were determined by nano-indentation technique. The friction and wear behaviour of the coatings were investigated using ball-on-disc tests under normal loads of 5, 7 and 9 N at sliding distance of 500 m, at room temperature. Scanning electron microscope equipped with energy dispersive spectroscopy, optical microscope, and 2D/3D profilometry were utilized to investigate the microstructures and wear mechanisms. Wear test results clarified that the wear resistance of (Ti, Cr)N and TiN coatings was better than that of CrN coating. The wear resistance of the (Ti, Cr)N coatings was related to the Ti content in the coatings and reduced by decreasing the Ti content. The dominant wear mechanisms were characterized to be abrasive and tribochemical wear

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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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Lead zirconate titanate (PZT) as a piezoelectric ceramic has been used widely in the fields of electronics, biomedical engineering, mechatronics and thermoelectric. Although, the electrical properties of PZT ceramics is a major considerable, but the mechanical properties such as fracture strength and toughness should be improved for many applications. In this study, lead monoxide, zirconium dioxide and titanium dioxide were used to synthesize PZT compound with chemical formula Pb(Zr 0.52 ,Ti 0.48 )O 3 by calcination heat treatment. Planetary mill with zirconia balls were used for homogenization of materials. Two-stage calcination was performed at temperatures of 600˚C and 850˚C for holding time of 2h. In order to improve the mechanical properties of PZT, various amount of ZnO and/or Al 2 O 3 particles were added to calcined materials and so PZT/ZnO, PZT/Al 2 O 3 and PZT/ZnO+Al 2 O 3 composites were fabricated. Composites samples were sintered at 1100˚C for 2 h in the normal atmosphere. Microstructural component and phase composition were analyzed by XRD and SEM. The density, fracture strength, toughness and hardness were measured by Archimedes method, three-point bending, direct measurement length crack and Vickers method, respectively. Dielectric and piezoelectric properties of the samples were also measured by LCR meter and d33metet tester, respectively. The results showed that by addition of ZnO and Al 2 O 3 to composite materials, the relative density of PZT based composites was increased in conjunction with a signification improvement of mechanical properties such as flexural strength, toughness and hardness. Moreover, the dielectric and piezoelectric properties of PZT such as dielectric constant, piezoelectric coefficient and coupling factor were decreased while the loss tangent was also increased.

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Crystallization of α – Fe phase during annealing process of Fe55Cr18Mo7B16C4 bulk amorphous alloy has been evaluated by X- ray diffraction, differential scanning calorimetric tests and TEM observations in this research. In effect, crystallization mechanism and activation energy of crystallization were evaluated using DSC tests in four different heating rates (10, 20, 30, 40 K/min). A two -step crystallization process was observed in the alloy in which α–Fe phases was crystallized in the first step after annealing process. Activation energy for the first step of crystallization process (i.e. α – Fe phase) was measured to be 276 (Kj/mole) according to Kissinger kinetic model. Furthermore, Avrami exponent calculated from DSC curves was two and a three -dimensional diffusion controlled mechanism with decreasing nucleation rate was observed in the alloy. It is also known from the TEM observations that crystalline α – Fe phase nucleated in the structure of the alloy in an average size of 10 nm and completely mottled morphology

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The purpose of this research is to achieve the optimal parameters for producing forged aluminium alloy 7075 aircraft door bracket by using finite element modelling (FEM) with commercial DEFORM-3D V6.1 and physical simulations with plasticine and Plexiglas dies. Also, forging speed has been examined as the main factor for controlling to produce a part without any defects. The results of Physical Simulation showed that the flow pattern has good agreement with the results of FEM that based on the use of hydraulic presses with initial billet and dies temperatures 410 and 400 ° C, respectively, and different forging speeds 5, 10 and 15 mm/sec. Distribution of effective strain rate, effective strain, effective stress, temperature , forging force and dies­ wear showed improvement the results in forging speed of 5 mm/sec. Processing map of Aluminium alloy 7075 also checked out at constant strain 0.5, indicated that the specified area of the forged part is located in a safe area. Forging force in optimized forging speed 5 mm/sec showed that the forging process using a 1000-ton press can be done easily

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Al2O3/TiC composites are used as cutting tools for machining gray cast iron and steels. The addition of iron improves the toughness of Al2O3/TiC composites. Ilmenite, aluminum and graphite can be used to produce in-situ Al2O3/TiC–Fe composites. However, the formation mechanism and reaction sequences of this system are not clear enough. Therefore, the present research is designed to determine the reactions mechanism of the first step of reactions that may be occurred between raw materials. In this research, pure ilmenite was synthesized to eliminate the effects of impurities available in the natural ilmenite in the system. The milled and pressed samples, prepared from the synthesized ilmenite, aluminum and graphite mixture with a molar ratio of 1:2:1, were heat treated at 720°C for 48h. In addition, two samples one containing ilmenite and aluminum with a molar ratio of 1:2 and ilmenite and graphite with a molar ratio of 1:1 were heat treated at 720°C for 48h. The final products were analyzed with XRD. It was found that at 720°C, aluminum reacts with FeTiO3, forming Fe, TiO2 and Al2O3. Since the aluminum content used in the mixture was more than the stoichiometry for reaction of ilmenite and aluminum, some unreacted aluminum remains. Therefore, the residual aluminum reacts with the reduced Fe to form Fe2Al5.

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The epoxy coatings containing multi-walled carbon nanotube/ poly ortho aminophenol nanocomposite were prepared and used as anticorrosive coatings. The nanocomposites with different contents of carbon nanotube were synthesized in a solution of sodium dodecyl sulfate and ammonium peroxy disulfate as a surfactant and an oxidant, respectively. The morphology and structural properties were confirmed by Fourier transform infrared spectroscopy and scanning electron microscopy methods. The mean size of nanocomposite particles was 20-35 nm determined by scanning electron microscopy. The epoxy coatings containing the nanocomposites were applied over mild steel panels and their corrosion performance was investigated using electrochemical impedance spectroscopy and potentiodynamic polarization measurements in a 3.5 % sodium chloride solution. The results showed that epoxy coatings consisting of nanocomposite with 1 wt.% multi-walled carbon nanotube exhibited higher anticorrosive properties than other prepared coatings of different carbon nanotube contents, which could be due to the strong interaction between the mild steel surface and the conjugated nanocomposite.

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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.