علی شکوه فر

This study aims to compare the effect of graphite content (0–5 wt.%) on the mechanical and ‎tribological properties of aluminum matrix nanocomposites. The bulk samples were prepared ‎by the mechanical milling/hot pressing (temperature 420 °C/ pressure 400 MPa/ time 1h) ‎process. According to the obtained results in this work, the addition of graphite to an ‎aluminum matrix significantly improves the wear properties of aluminum (wear rate and ‎coefficient of friction). The best wear performance was obtained with the sample containing ‎‎5wt.% graphite, which showed a 62% reduction in the wear rate and a 2.5-fold reduction in ‎coefficient of friction compared to the unreinforced aluminum sample. Although increasing ‎the amount of graphite in the range of 0-5 wt.% leads to a continuous improvement in the ‎wear behavior of the composite material, it results in a simultaneous deterioration of the ‎mechanical properties (hardness and compressive strength) and the density of the Aluminum- ‎Graphite composites.‎

Polymer matrix composites are one of the most widely used types of composites due to their lightness, and special strength and stiffness. Fibers-reinforced composites are the most important composites, and basalt fibers are one of the important types of mineral fibers that are used in the matrix of polymers. In this research, the effect of addition of silica fume particles (which has not been used in fibers reinforced polymer composites) on the mechanical properties of basalt fibers-epoxy composites under bending and tensile loadings was studied. The silica fume particles are surface modified with silane and then with different percentages (2, 4 and 6 wt.%) were distributed inside the epoxy matrix using a mechanical stirrer and ultrasonic waves. Hand lay-up method was used to make composite samples. The results of this research showed that with the addition of silica fume particles, the greatest improvement in the properties of the tensile strength and modulus, as well as the bending strength and modulus of the sample containing 4 wt.% silica fume is 22, 34, 27 and 40% respectively in compared to the sample without silica fume. On the other hand, the results of mechanical tests and microstructural examination after failure showed that the improvement of the interface between the fibers and the matrix as a result of the proper distribution of these particles inside the matrix has a significant effect on improving the mechanical properties. Also, the unfavorable distribution of these particles leads to the loss of mechanical properties under different loadings.

The purpose of this research is synthesis of nanocomposite with high photocatalyst property and magnetic separation ability in order to degradation of organic pollutants and reusability, respectively. Therefore, Eu doped ZnS - Fe3O4 nanocomposite is synthesized via sonochemical method which this method is easy and low cost. The synthesized photocatalyst is investigated with X-ray Diffraction Pattern (XRD), Energy Dispersive X-ray Spectroscopy (EDS), Photoluminescence Spectroscopy (PL), UV-Vis Spectrophotometry. As a consequence of testing the capability of magnetic separation, the high amount of photocatalyst attracted by the magnet guarantees the property of recyclability. Photocatalytic application in presence of synthesized nanocomposite for degradation of Rhodamine-B dye under UV-C and visible lamp is studied and results showed 81% and 78% degradation efficiency under UV-C lamp for 3 hours and visible lamp for 1 hour, respectively. In addition, stability and reuse investigation showed that the nanocomposite still remains its photocatalytic capacity after 3 cycles test.

In this research, a hybrid aluminum matrix nanocomposite was made using tungsten disulfide nanoparticles and carbon nanotube. Ultrasonic was used for mixing powders in acetone. Then hybrid particles and aluminum powder were mixed by mmechanical stirrer for 2 h and ball mill for 5h. The final mixed powder were compressed by hot pressing. Microstructural analysis of the specimens was performed by Optical Microscopy (OM) and Field Emission Scanning Electron Microscopy (FESEM). The results showed that the reinforcement phases were properly adsorbed on aluminum particles, there was a good distribution of the reinforcement particles in the aluminum matrix, and nanoparticles maintained their structure. The density of samples was measured by Archimedes method and the relative density of hybrid samples was found to be 96 to 98%. Micro hardness test showed that hybridization had a positive effect on the hardness and the hybrid nanocomposite micro hardness increased with increasing carbon nanotube content up to 20% that of Al/ WS2 nanocomposite. Compressive strength measurements showed that hybridization increased the final compressive strength up to 17%. Wear test showed the friction coefficient of the hybrid nanocomposite decreased up to 50% compared to the pure aluminum.

In the present study, mesoporous silica/iron oxide nanocomposite (MCM-41/γ-Fe2O3) was prepared with hydrothermal method and then the application of the nanocomposite as an adsorbent for the removal of Ni(II), Cd(II), Cr(III), Pb(II) and Zn(II) ions from aqueous solution was investigated. Furthermore, the effects of the solution pH, contact time and adsorbent dosages on removal percentage were studied. The results indicated that the adsorption of these ions on the surface of the adsorbent increase with increasing of solution pH, contact time and adsorbent dosage. The maximum percent removal (in the condition of: pH=5, t=50min, w=0.16g) of Ni(II), Zn(II), Cd(II), Cr(III) and Pb(II) ions was reached 53, 79, 61, 89 and 99.5%, respectively. The synthesized mesoporous silica/iron oxide nanocomposite was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), vibrating sample magnetometer (VSM), nitrogen adsorption-desorption (BET) and Field Emission Scanning electron microscopy (FE-SEM). The concentrations of metal ions of the solutions were measured by atomic absorption spectroscopy (AAS). According to the results, MCM-41/γ-Fe2O3 nanocomposite exhibited a large surface area 461.19m2/g, a total pore volume 0.4128cm3/g, a mean pore diameter 3.58nm, a narrow pore size distribution and the superparamagnetic behavior.

In this research, WS2 nanoparticles were synthesized using hydrothermal method and then added to aluminum matrix as reinforcement. Nanocomposites were fabricated by powder metallurgy processing followed by Spark Plasma Sintering (SPS) consolidation. Transmission electron microscopy (TEM) and XRD of synthesized powder showed WS2 nanoparticles were synthesized successfully. Microstructural properties of nanocomposites were investigated using optical microscopy (OM), field emission scanning electron microscopy (FESEM) and energy dispersive spectroscopy (EDS). Nanoparticles were well distributed in the aluminum matrix and have a good dispersion. The presence of nanoparticles in the matrix reduces the size of the grain less than 20 µm so that the size of the grain becomes smaller by increasing the amount of nanoparticles .The density of the sample showed that the nanocomposite had a very good compressibility and relative density reach to near 99% in 4wt. %WS2. Hardness and compressive strength of nanocomposites were evaluated. Mechanical evaluations indicated that, the increase in weight fraction of WS2 nanoparticles, resulted in improvement of hardness and compressive strength of aluminum. Concentration of tungsten disulfide nanoparticles has a direct effect on increasing the mechanical properties of nanocomposite. The compressive strength increased up to 120 MPa, about twice the base metal, and the hardness raised up to 30%.

In this study, friction stir butt welding of Mg and Al alloys with applying Zn interlayer was performed. To obtain optimum condition, a combination of two travel and three rotation speeds were selected. Mg-Zn and Mg-Al-Zn IMCs, Al solid solution and residual Zn, were the most common phases in the stirred zone, which eliminated the formation of Al-Mg intermetallics. The maximum mechanical properties were achieved for the joint fabricated at 35 mm/min and 600 rpm, caused to 24% improvement in tensile strength and around 3 times enhancement of elongation compared with Zn free sample FSWed at the same conditions. The fracture micrographs were consistent with corresponding ductility results. Fracture surfaces of Zn-added samples presented a fine texture with a mixture of brittle and ductile fracture feature, which was different from the coarse cleavage plane and fully brittle fracture of the joint without Zn interlayer.

In this paper, the sensing properties of SnO2-PdPt nanohybrid to methane gas and effect of reduced graphene oxide (rGO) on improving its sensing performance was investigated. For this reason, first SnO2 was synthesized by hydrothermal method and then hybridized by Pd, Pt and PdPt catalysts. For investigating the effect of rGO, by the in-situ hydrothermal method, SnO2-rGO was synthesized instead of SnO2. Results showed that the nanohybrid sensor with bimetallic alloy catalyst, had higher response t lower temperature compared with monometallic catalysts and on the other hand, adding rGO, reduced the optimum sensing temperature of SnO2-PdPt and enhanced its response to methane. The SnO2-PdPt nanosensor showed 52.22% response to 1000ppm CH4 at 200oC. The sensing response and recovery times for this hybrid were 94s and 3.5min respectively, whilst the SnO2-rGO-PdPt showed 69.5% response at 150oC to the same concentration of methane. The response and recovery times for this hybrid were 50s and 4.5min respectively.

In this research, 3 layer composite weld containing Titanium diboride (TiB2) on low carbon steel (ST37) was carried out through flux cored arc welding via flux cored electrodes containing 100% TiB2 and 50-50 TiB2-Fe. Then, wear and microhardness tests were used for surviving hardness and wear behavior of samples. The obtained results showed that by increasing volume percent of TiB2 in microstructure, the hardness of layers increased. Also, the highest wear resistance belonged to third layer of sample with 50% TiB2 and thereafter, belonged to first layer of sample with 100% TiB2. The scanning electron microscopic investigation of samples wear surfaces indicated that by increasing volume fraction of TiB2 into layers, the depth wear scratches in the third and second layers decreased and segregation of wear debris in these layers increased, compared with first layer. Also, it was found that by increasing the layers, wear mechanism changed from ploughing to cutting.

In this study, the friction stir welding process was used for simultaneously joining of AZ31 magnesium alloy and production of Mg/Sic nanocomposite in the stir zone. All combinations of three rotational speeds i.e, 600, 800, and 1000 rpm and four traveling speeds i.e, 25, 75, 125 and 175 mm/min were tested and then the mechanical properties were examined. The joint fabricated with rotational speed of 800 rpm and traveling speeds of 75 mm/min, exhibited the highest mechanical properties, So that the yield strength, tensile strength and percent elongation improved by 11%, 39% and 88%, respectively. The results show that the proper distribution of nanoparticles in the stir zone can reduce the average grain size and improve mechanical properties. The main reason for this change is related to pinning effect and increased nucleation sites associated with SiC nano-particles. Moreover, reinforcement particles resulted in breaking of primary grains in stir zone of friction stir welding.

Nano-composite coating of Ni-Co/SiO2 is produced by the direct current electrochemical deposition method on the steel substrate. The analyze of X-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM) are prepared by a nickel-cobalt alloy coatings and Nano-composite coating of Ni-Co / SiO2 that the electrochemical condition were the same in all of them and their grain size and their surface morphology were compared and analyzed. The grain size of Nano-composite coating was less than the alloy coating and surface morphology of the Nano-composite coating was finer and smoother than the alloy coating. The hardness of Nano-composite coating was more than alloy coating. If the electrolyte temperature be 50 degrees Celsius, then the Nano-composite coating of Ni-Co/SiO2 will have the maximum hardness. Adding surfactant to the electrolyte prevents agglomeration of nanoparticles and thus, increases the amount of particles in the coating and the micro-hardness of the Nano-composite coating of Ni-Co/SiO2.The effect of SDS was more than CTAB for the produced coating and the most optimal value for the SDS concentration in the electrolyte was 0.3 grams per liter.

The most successful ‘‘top–down’’ approach to produce bulk ultra-fine grained or nanostructured materials involves the use of severe plastic deformation (SPD) processing. The amount of higher effective plastic strain per pass plays a key role on the final microstructure of SPD processed samples. In the present study the numerical experiments of the combination of the equal channel angular pressing (ECAP) and simple shear extrusion (SSE) as a new process entitled “planar twist channel angular extrusion (PTCAE)” was performed based on the Response Surface Methodology (RSM), as a statistical design of experiment approach, in order to investigate the effect of parameters on the response variations, achieving the mathematical equations, predicting the results to impose higher effective plastic strain values. Α and ϕ angles, radius and friction coefficient was imposed as the input parameters while average, minimum and maximum effective strain and maximum load was imposed as the output parameters. Governing regression equations obtained after analysis of the simulation data by Minitab software. Optimum process parameters are: α=450, Φ =450, r=2 mm and µ=0.1. Verification of the optimum results using simulation experiment was done. Good agreement between simulation, experimental and optimization was occurred.

Combined shear extrusion (CSE) is a new severe plastic deformation (SPD) technique to produce bulk ultra-fine grained materials. CSE is obtained by the combination of simple and pure shear extrusion. This technique is based on definitions of pure and simple shear. In the present work, the nonlinear (large) deformation elasticity theory is used for obtaining the shear strain applied to the sample under pure shear extrusion with various angles of distortion. Also plastic deformation characteristics of CSE method were analyzed with finite element analysis using commercial Deform 3D software. Shear strain and effective strain applied to the sample, the load required to carry out the process and the final shape of the cross-sectional area were studied for different angles of distortion. Analytical results and finite element analysis shows by increasing the angles of distortion, shear strain and increased rate of shear strain applied to the sample increased so the effective strain and load required to carry out the process increases. Analysis of finite element and geometry of the die shows that distribution of shear strain and effective strain is inhomogeneously and symmetrical in specimen’s cross section which increases from the center to the corners and by increasing the angles of distortion, distribution of strain becomes more inhomogeneously, also the final shape of the cross-sectional area deforms more.

Multi-pass welding process is one of the most applicative methods of welding in various industries. In this paper، temperature and residual stress distribution due to three pass welding of two plates made of AISI 321 stainless steel having different thicknesses is studied. Welding process consists of three welding passes of two Shielded Metal Arc Welding (SMAW) process and one Gas Tungsten Arc Welding (GTAW) process. First، the benchmark plates are manufactured and welding process is performed. The transient temperature distribution during the welding process is recorded using thermocouples attached to the welding plates. First this process simulated experimentally and temperature distribution during to welding process was measured using thermocouples. Furthermore، the final residual stress distribution after welding process is measured using incremental center hole drilling technique (ICHD). The three pass welding process was then simulated using ABAQUS finite element (FE) code. The finite element model consists of temperature-dependent properties of base metal and weld metal. Furthermore، moving heat source and the element-birth technique is implemented in FE model. Experimentally measured temperature and residual stresses provide an in-depth knowledge insight the complicated welding process.. Comparing between the results shows that the numerical predictions and experimental measurements have good agreement and therefore the FE developed model can be employed in designing and evaluating of welded structures.

Recently، great attention has been focused on epoxy polymers in different industrial and scientific activities، owing to superior mechanical properties and their stability in different environmental conditions. In this study، the molecular dynamics method was used to study the structure of cross-linked epoxy polymers and predict glass their transition temperature (Tg). The epoxy polymer with a certain degree of cross linking was constructed through the previously proposed cross linking procedure. A temperature cycle (300-600 K) with a constant rate was then applied to the cross-linked epoxy، and a rough estimate of the glass transition region was obtained through mean squared displacement curves. Thereafter، variation of density in terms of temperature was utilized to precisely calculate Tg. The estimated Tg was found to be in good agreement with experimental observations. Radial distribution function was finally used to investigate the effects of temperature and cross linking on the local structure of simulated polymer.

In this study a feed forward back propagation artificial neural network (ANN) model was established to predict Vickers microhardness in aluminum-alumina nanocomposites which have been synthesized by mechanical alloying and hot pressing. Volume percent of reinforcement، size of nanoparticles، force in microhardness test; and mechanical alloying parameters، such as time، ball to powder ratio (BPR) and speed of ball mill were used as the inputs and Vickers microhardness as the output of the model. Effective parameters in training such as learning rate، hidden layers and number of neurons، were determined by trail and error due to amount and percentage of errors. Regression analysis in train، validation and test stages; and mean squared error were used to verify the performance of neural network. Average error of predicted results was 2. 67% or 2. 25 Vickers. Also mean squared error for validation data was 7. 76. As can be expected، ANN methods reduce the expenses of experimental investigations، by predicting the optimum parameters.

NiTiCu intermetallic compound with nanocrystalline structure was successfully synthesized through mechanical alloying and subsequent annealing process. The X-ray diffraction (XRD) analysis revealed that after 60 h milling of high purity elemental powders mixture of Ni، Ti and Cu via a planetary high energy ball milling، the Cu dissolved into B2 structure and NiTiCu phase was obtained. Annealing of as-milled powders at 1173 K for 15 min leads to formation of nanometric NiTiCu (B19'') phase، grain growth and release of internal strain. Structural characterization was examined by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The results demonstrated that this route result in preparation compounds with suitable morphology and homogeneous structure. Formation of nanometric structure enhances thermoelasticity and shape memory behavior in this compound by narrowing the thermal hysteresis.

In this study, Tantalum carbide (TaC) nanoparticles was synthesized through the gas - solid reaction by chemical vapor deposition (CVD) method using carbon nanotubes as the carbon source. The structure of samples were studied by Transmission Electron Microscopy (TEM), Field Emission-Scanning Electron Microscopy (FE-SEM), X-Ray Diffraction (XRD) and Raman Spectroscopy. The thermal behavior of the nanoparticles were examined by TG-DTA thermal analysis. Studies indicated that during the reaction, TaC nanoparticles was formed with quasi-spherical morphology and grain size range of 30-40nm. Also, using phase and thermal analysis, the formation mechanism of Tantalum carbide nanoparticles were discussed with regarding to the role of carbon nanotubes.

Welding of power plant shafts have many problems like، martensite formation، remained Austenite، sensitivity to cold crack and residual stress. Accurate selection of welding process and variable، determination of suitable filler metals and appropriate post weld heat treatment will decrease this kind of problems. Because of existence of carbon and alloying elements in steel shaft 26 NiCrMoV 11-5، low hydrogen Cr-Mo fillers for overlaying welding on steel shaft surface was selected. Normalizing and Annealing heat treatments were selected and compared with as-welded specimen. The purpose of this work was specifying desirable post weld heat treatment and evolution of microstructure in weld and HAZ zones with micro hardness، LOM، SEM and XRD. According to metallographic and XRD results it was concluded that in welded specimen with Cr-Mo filler rod and normalized heat treatment، the amount of carbide phases were decreased، and hardness variation in weld zone and base metal was low when compare with other process. As a result، welded specimen with Cr-Mo filler rod and normalized heat treatment had appropriate microstructure and uniform hardness distribution.

Mechanical alloying process has been utilized to synthesis immiscible systems، nanostructured materials، and nanocomposites for decades. In this paper، synthesis and characterization of Al-4. 5wt%Cu alloy and its composite، reinforced with TiC، through mechanical milling process are studied. X-ray diffraction technique، scanning electron microscopy and transmission electron microscopy were utilized to characterize the mechanically milled powders. XRD and SEM results indicate the fact that supersaturated solution of Cu in Al occurred during mechanical milling process as a result of mutual diffusion of Al and Cu. In addition، TEM results illustrate the fact that not only mechanically milled powders are nanostructured but also TiC particles had been nanosized after milling process.

In this paper، titanium dioxide (TiO2) nanoparticles were synthesized by sonochemical method in temperature 20ºC، 35ºC and 50ºC. For examination of the effect of synthesis temperature on TiO2 nanoparticles prepared this method، C12H28O4Ti (Tetraisopropyl titanate)، sodium hydroxide (NaOH) and ethanol (C2H5OH) on ground solvent were used as initial materials. Appropriate solvents were applied to prepare of samples. The process parameters such as temperature device play the most important role in the size and morphology of the final products. Sonochemical process at different temperature was carried out at sonication power (9W) for 1. 5h and then the obtained materials washed and dried at room temperature for 48h. For determining particle size and also evaluation of morphological properties، X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used. The thermogravimetric and differential thermal analysis (TG/DTA) for determining temperature and time of crystallization was used. From TEM observations the size of titanium dioxide nanoparticles is estimated to be significantly smaller than ~12 to ~25 nm.

Researches show that properties of semiconductor materials such as electrical، optical and sensor properties can be improved in the nano scale. Among the semiconductor materials، zinc oxide with excellent electronic properties has been considered extremely. The application and properties of zinc oxide nanoparticles relate to their size and morphology. Therefore، many researches have been made on the synthesis of zinc oxide nanoparticles with different morphologies. In this paper، zinc oxide nanoparticles have been synthesized at different temperatures from 2- Methoxy Ethanol via chemical bath deposition. The results show that the average size of the nanoparticles is 30- 50 nm and changing the synthesis temperature causes to morphological transformation.

In this paper، SNO/ZNO nano-composites have been synthesized via chemical bath deposition، CBD and the effect of synthesize temperature on the particles size and their morphology has been studied. The obtained results show that with increasing the synthesize temperature، the particles size of nano-composite decreases and their morphology changes from plate with width and length median of 58 to 260nm for samples synthesized at 25˚C to sphere with doiameter median of 58 and 50nm for samples synthesized at 50 and 75˚C، respectively. Also، at low temperature the content of SNO nano-particles is lower than that of ZNO. In this research، the type of obtained phases، phase''s percent، particles size، morphology and specific surface area were determined by XRD، XRF، Tem، SEM and BET، respectively.