Iranian Journal of Materials Science and Engineering

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Mechanical properties of metals are substantially dependent on the microstructure, which can be controlled by thermo-mechanical parameters such as the temperature, strain and strain rate. Hence, understanding the microstructural evolution of alloys during the hot deformation is crucial for engineering the metal forming processes. The main objective of this work is to present an overview of Cellular Automaton (CA) modeling for predicting the microstructure of alloys during the dynamic recrystallization (DRX) phenomenon. In this review paper, first, overall descriptions about the DRX phenomenon and CA modeling were presented. Then, the CA modeling procedure was compared with similar methods. Meanwhile, related studies in the field of the DRX simulation by using the CA modeling were evaluated. Four main stages of the model were analyzed in terms of the “nucleation”, “growth”, “topological changes” and “texture evaluation” steps. Most important limitations including the calibration sensitivity, limitations in continuous DRX modeling, ignoring microstructural effects on the deformation behavior, limited applications and database as well as repeated results were discussed and then objective suggestions for the further development were provided. Finally, future prospects in CA modeling of DRX were presented in the last section.
 

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Modification of MnFe₂O₄@SiO₂ core-shell nanoparticles with (3-aminopropyl) triethoxysilane (APTES) was investigated. The magnetite MnFe₂O₄ nanoparticles with an average size of ~33 nm were synthesized through a simple co-precipitation method followed by coating with silica shell using tetraethoxysilane (TEOS); that has resulted in a high density of hydroxyl groups loaded on nanoparticles. The prepared MnFe₂O₄@SiO₂ nanoparticles were further functionalized with APTES via silanization reaction. For having suitable surface coverage of APTES, controlled hydrodynamic size of nanoparticles with a high density of amine groups on the outer surface, the APTES silanization reaction was investigated under different reaction temperatures and reaction times. Based on dynamic light scattering (DLS) and zeta potential results, the best conditions for the formation of APTES-functionalized MnFe₂O₄@SiO₂ nanoparticles were defined at a reaction temperature of 70 °C and the reaction time of 90 min. The effectiveness of our surface modification was established by X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), Fourier transforms infrared spectroscopy (FTIR), and vibrating sample magnetometer (VSM). The prepared magnetite nanostructure can be utilized as precursors for synthesizing multilayered core-shell nanocomposite particles for numerous applications such as medical diagnostics, drug, and enzyme immobilization, as well as molecular and cell separation.

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In this work, the facile synthesis and identification of hexylmethylimidazolium bis(trifluoromethyl­sulfonyl)­amide ([HMIM]­TFSA) and hexylmethylimidazolium triethyltrifluorophosphate ([HMIM]FAP) ionic liquids (ILs), as multifunctional and multipurpose gear oil additives, is introduced. The tribological tests indicated that both ([HMIM]TFSA) and ([HMIM]FAP) ILs demonstrate antiwear/extreme pressure properties (AW/EP) to the gear oils by preventing wear and scar of the lubricated system at low and high temperatures. [HMIM]TFSA provided superior performance in comparison to [HMIM]FAP. Because of the presence of heteroaromatic imidazole moiety in the ILs structure, the prepared ILs also imparted anticorrosion, antioxidant, and anti-rust properties to the lubricant. All these observations confirmed that the ILs are single component multifunctional and multipurpose oil additives. In addition, due to avoiding the use of toxic and harmful elements in the preparation of ILs make the fabricated oils potential candidates for green lubricants.

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Sago hampas was chemically modified through esterification process to adsorb both laboratory and commercial synthesized ZnO nanoparticles from water in a batch adsorption studies. The esterified sago hampas (ECSH) as a biosorbent w:as char:acterized using Energy dispersive X-ray spectroscopy (EDX), Fourier-transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET) technique s. Investigating the effect of pH, contact time, initial sorbate ion concentration, temperature and sorbent mass were carried out where adsorption parameters were analyzed using Langmuir, Freundlich and Temkin models. The correlation between kinetics of adsorption and tgr rate order of ZnO nanoparticles on ECSH were also determined. The adsorption of the ZnO nanoparticles was found to increase with increasing contact time with the attainment of equilibrium at 100th minutes with maximum removal efficiency of 85.5% (0.036 mg/g) and 89.6% (0.106 mg/g)  ZnO nanoparticles for laboratory and commercial synthesized ZnO from aqueous solution. An optimum pH of 8 with adsorbent dose of 2.0 g at a temperature of 50 oC gave good results of  ZnO nanoparticles removal. The equilibrium data for both sorbate solution fitted well for both Langmuir and Freundlich isotherm models. From the Langmuir model, ECSH recorded greater sorption capacity of 0.2 mg/g and 0.6 mg/g for both laboratory and commercial synthesized ZnO nanoparticles respectively. The kinetic studies showed pseudo-second order model as the best fitted for the sorption of ZnO nanoparticles for both synthesized samples.

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The effect of cooling rate after annealing at 900 °C on the microstructure and hardness of high entropy alloys was investigated using two typical samples with the chemical composition of Co₁₆Cr_14.5Fe₂₉Mn_11.5Ni₂₉ and Co_11.5Cr₇Fe₂₇Mn₂₇Ni₂₇(Nb_0.08C_0.5) (at%). The microstructural characterisation and hardness measurements were carried out by optical microscopy, scanning electron microscopy, wavelength-dispersive X-ray spectroscopy, electron back scattered diffraction, X-ray diffraction technique and Vickers hardness testing. A face centred cubic crystal structure matrix was observed in both alloys before and after annealing and regardless of cooling conditions. SEM analyses revealed an extensive precipitation in Co_11.5Cr₇Fe₂₇Mn₂₇Ni₂₇(Nb_0.08C_0.5) alloy after annealing. It was also found that air/furnace cooling can enhance grain growth-coarsening just in Co₁₆Cr_14.5Fe₂₉Mn_11.5Ni₂₉. However, the hardness results generally showed insignificant hardness variations in both alloys after water-quenching, air-cooling and furnace-cooling. The results suggested that the hardness is mainly controlled by solid solution strengthening.

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Graphene oxide (GO) and reduced graphene oxide (rGO) is a semiconductor device which finds its many applications in the various electronic devices. In the present study GO and rGO thin sheets have been grown over Si wafers using Hummer’s and modified Hummer’s method and a comparison in the properties of the coatings have been carried out. The morphology of the sheets characterized by SEM revealed similar transparent sheet like structure for both the chemical synthesis. The diffraction pattern of GO and rGO prepared with modified Hummer’s method showed peak shift to lower diffraction angle from 9.96 ^o to 9.63 ^o and 26.4 ^o to 26.3 ^o respectively. The diffraction peaks were observed at diffraction phase of 001 and 002 crystal plane. FTIR spectra revealed presence of oxygen functional groups in GO thin sheets whereas peaks for oxygen functionalities are absent in rGO. The polarization curve indicated similar corrosion resistance of GO and rGO thin sheets grown under Hummer’s and modified Hummer’s. Capacitive property of rGO is better than GO as observed by the electrochemical analysis of GO and rGO..Graphene oxide (GO) and reduced graphene oxide (rGO) is a semiconductor device which finds its many applications in the various electronic devices. In the present study GO and rGO thin sheets have been grown over Si wafers using Hummer’s and modified Hummer’s method and a comparison in the properties of the coatings have been carried out. The morphology of the sheets characterized by SEM revealed similar transparent sheet like structure for both the chemical synthesis. The diffraction pattern of GO and rGO prepared with modified Hummer’s method showed peak shift to lower diffraction angle from 9.96 ^o to 9.63 ^o and 26.4 ^o to 26.3 ^o respectively. The diffraction peaks were observed at diffraction phase of 001 and 002 crystal plane. FTIR spectra revealed presence of oxygen functional groups in GO thin sheets whereas peaks for oxygen functionalities are absent in rGO. The polarization curve indicated similar corrosion resistance of GO and rGO thin sheets grown under Hummer’s and modified Hummer’s. Capacitive property of rGO is better than GO as observed by the electrochemical analysis of GO and rGO.

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The graphene oxide -TiO₂ (GO-TiO₂) and pre-reduced graphene oxide -TiO₂ (rGO-TiO₂) nanocomposites were fabricated successfully by hydrothermal method. The microstructure of synthesized nanocomposites was investigated using field emission scanning electron microscopy (FESEM) equipped with energy dispersive spectroscopy (EDS) analysis. Moreover, galvanostatic charge/discharge (GCD), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) methods in three electrode system were applied to evaluate electrochemical properties. The results revealed that nanoparticles distributed more uniformly on graphene sheets, at lower concentrations of TiO₂. The rGO-TiO₂ and GO-TiO₂ nanocomposites showed 224 and 32 F/g specific capacitance at 5 mV s^-1 scan rate in 1 M KOH aqueous electrolyte, respectively. The pre-reduction of graphene oxide is the main reason for the better electrochemical performance of rGO-TiO₂ nanocomposite compared to GO-TiO₂ nanocomposite.

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Graphene oxide thin layers, graphene oxide:silver nano-composite, graphene oxide:zinc oxide nano-composite and graphene oxide:zinc oxide/graphene oxide:silver bilayer were deposited by spray pyrolysis method. The synthesized thin layers were characterized using X-ray diffraction spectroscopy, field emission scanning electron microscope, energy dispersive x-ray spectroscopy and Raman spectroscopy. The optical properties and the band gap of the thin layers were also studied and calculated using the Tauc equation. Gram-negative bacterium of Escherichia coli was used to study the antibacterial properties of thin layers. The results showed that among the thin layers investigated, GO:ZnO/GO:Ag bilayer had the greatest effect on the inhibition of E. coli growth and was able to control the growth of bacterium after 2 hours.

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Flash sintering of 8 mol% yttria-stabilized zirconia (8YSZ) as solid oxide fuel cell (SOFC) electrolyte is studied. The relation between relative density, shrinkage, sample temperature during the flash, and incubation time, with the electric field strength, current density, as well as contact paste, are modeled by response surface methodology (RSM). The electric field strength and current density varied from 50 to 400V.cm^-1 and 50 to 200mA.mm^-2, respectively. Also, platinum (Pt) and lanthanum strontium manganite (LSM) used as contact paste. Results show that using LSM paste lead to higher density and more shrinkage compare with Pt paste. Contrary, the electric field strength has no significant effect on density and shrinkage. However, a minimum electric field strength equal to 80 V.cm^-1 is necessary for flash onset. As the field increases, the incubation time decreases dramatically. Compare with samples with LSM paste, samples with Pt contact paste reach to a higher temperature during the flash. Flash sintered 8YSZ shows the mean grain size of 0.3μm, which is about half of the conventionally sintered 8YSZ. Electrochemical Impedance Spectroscopy reveals despite lower mean grain size, the resistivity of flash sintered 8YSZ is lower than conventionally sintered 8YSZ.

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Microscopic studies has shown that adjacent to the interface between cement paste and aggregate, there exists an area with high porosity and low binding compounds that is referred to as interfacial transition zone (ITZ). ITZ in concrete and mortar imposes a number of negative effects, including flexural and compressive strengths reduction and permeability enhancement. That’s why many research attempts have been devoted to limit ITZ and its negative effects. The present study investigates the possibility of utilizing fine Portland cement (PC) clinker as a reactive aggregate in mortar for the same purpose. For this, natural quartz sand in normal mortar (NM) was totally replaced with PC clinker of the same particle size distribution and the most important engineering properties of the new mortar referred to as Reactive Aggregate Mortar (RAM) were measured and compared with NM as control. The results of compressive strengths measurements represented 65% and 21% increases at curing ages of 7 and 90 days, respectively, for RAM compared to NM. Chloride penetration depth in RAM displayed reductions by about 33% and 26% after 14 and 28 days of exposure, respectively. The effect of PC clinker reactivity on the microstructure and size of ITZ was studied by using scanning electron microscopy.

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Finite element analysis has been carried out to investigate the effect of various parameters on axisymmetric hot extrusion process using aluminum alloy. The objective of the present work is to investigate the effect of friction coefficient, die angle, die-profile radius and predefined temperature of workpiece through FEM simulation of extrusion process. Nodal temperature distribution, heat flux, peak temperature at nodes and peak flux induced are identified as the output variables to assess the thermo-mechanical deformation behavior of aluminum alloy. Mesh sensitivity analysis is performed for the evaluation of mesh convergence as well as depicts the accuracy of present FEM model. Higher will be the coefficient of friction between interacting surfaces of die-billet assembly, more will be the increment in nodal temperature in billet. Higher will be the coefficient of friction, higher will be the generation of heat flux within billet, as this is achieved for highest coefficient of friction. Peak nodal temperature diminishes with increase in die profile radius nearly by 17 %.Maximum heat flux diminishes non-linearly by 30% with increase in die profile radius. Maximum nodal temperature increases nearly linearly by 14% with increment in predefined temperature of billet. Maximum heat flux decreases non-linearly by 5 % with increment in the initial temperature of workpiece. Validation of present numerical model is established on the basis of deformation behavior in terms of evolution of nodal temperature distribution upon comparison with previous studies available in literature.

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In this research, using impregnation method, spinel cobalt and copper ferrites nanoparticles are synthesized on the surface of hematite. Synthesized powders were characterized and examined by FTIR, XRF, XRD, FESEM, BET and EDS analysis and the dye degradation were investigated by UV-vis and AAS methods. Specific surface area increased especially in the sample containing cobalt, which indicates the precise of synthesis and the creation of high surface nano particles at hematite surface. The size of particles was in the nano scale and a good uniformity observed in the structure. The results indicated a significant increase in the catalytic ability of hematite nano composite after synthesis. Their catalytic capability investigated by the Fenton reaction with complete removal of methylene blue from the solution via UV-vis irradiation. The samples stability discovered to be excellent by the AAS method.

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This study deals with the effects of erbium (Er) addition on the microstructural evolution and tensile properties of Al-Mg₂Si in-situ metal matrix composites. The morphology of primary Mg₂Si and eutectic phases were observed in details using optical microscope and scanning electron microscopy (SEM). The results showed that the increase of Er content has a slight effect on the size and morphology of primary Mg₂Si phases, but the eutectic structure evolves from the coarse structure into the fine one. Also, with Er addition the eutectic mixtures of Al and Mg₂Si with fibrous morphology has been developed instead of the flake like Al-Mg2Si eutectic microstructure. Meanwhile, Al₃Er phase was observed in the samples containing Er. The ultimate tensile strength (UTS) of the composite changes under the various content of Er. The maximum strength was found at the 0.6 wt% Er with the fine eutectic microstructure. The study of SEM micrographs from the fracture surface of composites revealed that Er addition changes the fracture mode from brittle to ductile one with fine dimples. The mechanism of microstructural evolution was discussed in details.

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Niobium addition is an appropriate approach for improvement of superalloy’s operation. The purpose of this study is twofold: (1) to investigate on the η and γ^/ phase precipitations along with (2) to identify the high-temperature tensile properties in A286 and Nb-A286, as a modified type. The heat treatment of both alloys was carried out in a two-stage aging procedure at 760°C for 16 h and 820°C for 2 to 30 hours, following characterized by optical and Scanning electron (SEM-EDS) microscopies, differential thermal analysis (DTA) and high temperature tensile tests. The results showed that niobium addition was increased the volume fraction of γ^/ phase, from 10.7% to 12%, decreased its size, from 94 to 71 nm, and rising the γ^/-dissolution temperature from 987°C to 1007°C. Moreover, the γ^/ to η phase transformation was sluggishly occurred in Nb-A286 due to more stable of γ^/ precipitations. Furthermore, the Nb-A286 alloy demonstrates higher mechanical properties than A286 one, approximately 100MPa improvement, which it was contributed to the much large volume fraction and finer size of more stabilized γ^/ phase.
 

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  As an alternative to conventional fertilizers, e.g. NPK (the Nitrogen-Phosphorous-Potassium containing chemical fertilizers) which release their nutrients in a short period of time, due to high solubility in irrigation water, glass fertilizers are ideal as they release macro- and micronutrients for crops and plant nourishment. Also, despite conventional ones, they have no ground-water pollution. In the present study, glass fertilizers were synthesized via Polymer-Derived Ceramics (PDC) method. Despite the melt-casting procedure, PDC needs lower temperatures in heat treatment. The precursors consist of poly-siloxane and active fillers. Thus, thanks to gaseous release during heat treatment of the present active fillers, i.e. Ca(OH)₂, MgCO₃, and Al(OH)₃, a porous microstructure can be generated. In order to manipulate the pore size and specific surface area, fractions of active fillers were used as calcined. The experiments showed that upon increase of non-calcined active fillers, the specific surface area and the amount of porosity was increased due to more gaseous release during heat treatment. Thus, affected by microstructure, the release rate of macro and micro-elements was higher in the sample containing non-calcined active fillers, in comparison to other samples. Additionally, the porous samples were able to be loaded by extra nutrients containing Nitrogen, like KNO₃.