مجله مواد نوین
سال هفتم شماره 1 (پیاپی 25، پاییز 1395)

Zirconium carbide Nano particle was synthesized through sol-gel method. Although sol-gel process is usually used to producing oxide compounds, in this study it was successfully employed to produce a carbide powder. For this purpose, zirconium propoxide and saccharose were initially used as zirconium and carbon sources, respectively. The starting sol was produced in 5 different pH, in order to examine its effects on the properties of the obtained powder. Heat-treatment of the gel, in a range of 700-1400 °C, resulted in the formation of mixed zirconia-carbon powder, and subsequently, zirconium carbide. Then, differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to investigate heat performance of the gel, structure and micro-structures of the synthesized powder, respectively. Results showed that increasing the pH could not only affect the reaction process and efficiency of the zirconium carbide synthesis, but it also decreased the particles size of the powder. Therefore, at pH 4.2, 5.2 and 6.2, the size ranges of 130-190, 90-150 and 50-100 nm were obtained, respectively. It was also noted that changes in pH had no effects on the morphology of the spherical particles.

In the present study, it was attempted to perform the residual stress analysis in the aluminum sheets A.A5083 via experimental results of hot metal forming process by gas.Then the accuracy of simulations was evaluated by the Finite Element Method and its comparison with experimental tests. The aim of the present study was to apply an efficient approach to determine the stresses caused during the forming process. Thus, the inductive stress in the imperfect conical sheets produced by gas blow process was measured method via hole drilling. In the experimental test, the stress equal to 44.5 Mpa was obtained. Then, The temperature dependant residual stresses of hot metal forming process were evaluated by the Finite Element Analysis Method. To simulate the forming process, ABAQUS/Explicit finite element software was used. The maximum of deviation in the results of finite element calculations and experimental tests for the maximum stress in the piece was 7%. Thus, it was concluded that via finite element calculations more accurate study on hot metal forming method by gas can be done.

In the current research, samples of thermoset polyurethane were fabricated through the solution casting method. In order to investigate the effect of strain rate on the mechanical properties of polyurethane, a tensile test was done on standard samples, at ambient temperature and different strain rates (2×10-5 to 2×10-2); and activation enthalpy was obtained by using tensile test results and Eyring model equations. Chemical and thermal characterizations were done by fourier transform infrared spectroscopy, dynamical-mechanical analysis and thermogravimetry. Fracture surface of samples were also studied by scanning electron microscopy. Tensile test results showed that by increasing strain rate, tensile strength and elastic modulus were improved by 80 and 300% respectively, while fracture strain was reduced by more than 50%. It was also evident by investigation of SEM micrographs that the fracture surface of samples was changed to brittle fracture by increasing strain rate. Finally, the amount of activation enthalpy obtained was 45.49 kJ/mol, which is a new result for thermoset polyurethane.

In this research, nanocrystalline FeCoW alloy coatings were electrodeposited on copper substrate. The results showed that current density and bath composition can affect structural and magnetic properties. However, surface morphology changed due to bath composition. Furthermore, by increasing current density, the amount of fcc phase decreased in fcc淇 double phase structure. It was observed that deposition parameters didn’t change the grain size of the coatings efficiently, and this parameter was lower than 20 nm for all the cases. Due to the diffusional phenomenon that take places at higher current densities, the amount of deposited tungsten decreased, and thus lower microhardness values were reported. By comparing XRD and VSM data, it was assumed that the extensive change in the coercivity is related to the phase structure in these alloys.

To investigate the influence of primary texture and thermomechanical parameters on hot working behavior of AZ63 magnesium alloy, the flow behavior and deformation texture of hot compression test was compared for both cast and extruded samples. The extruded samples were machined in two extruded and normal directions. Compression tests were carried out at 250 °C and the strain rate of 1 s-1 and 0.01 s-1 and various strains. Microstructural observations and texture investigation in various conditions reveal that the presence of extensive twins and contraction twins in extruded samples and extensive twinning in cast samples at primary deformation strains and recrystallization at final strains of extruded samples have a significant influence on texture evolutions.

In the present study, 5083 aluminium alloy sheets by tungsten inert gas welding­-­brazing were joined to galvanized steel sheets with 4043 and 4047 filler wires. The amount of the weld heat and filler metal type influence the­ mechanical and microstructural properties of the resultant joint. The results obtained from microstructural observation showed that with equal weld heat input the thickness of brittle intermetallic compound layer for the joint produced with 4047 filler metal was approximately half of that for joint produced with 4043 filler metal. Energy­ dispersive x-­ray spectrometry analysis results­ showed that the IMCs layer formed in interface of steel-weld seam consisted of Fe­(Al, Si)3 phase­ in side of steel and Al7.3Fe1.7 Si phase in side of welded seam. ­It was found that the joint produced with 4047­ filler metal exhibit­ed higher mechanical resistance of 170 MPa than that produced with 4043­ of 120 MPa. The results of­ x-ray diffraction analysis conducted on the fracture plane showed the presence of Al0.5Fe3Si0.5 phase. Moreover, for joints produced with 4047 filler metal, the FeSi2 phase­­ created from enriching of Si atoms in IMCs layer was seen.

In this research elements of the raw materials used to form MoSi2-TiC nanocomposite. The plan in this Research procedure was based on combustion synthesis, mechanical activation mechanism (MASHS). Initially Mo, Si, Ti and C elemental powder were weighed by stoichiometry ratio and were milled with weight ratio of ball to powder 5 to 1, 10 to 1 & 15 to 1, milling time 4, 8, 12 hours with 250 and 300 rpm by the planetary mill. After wards the milled powders were compacted to pellet form by uniaxial press and synthesized samples were done in an atmospheric argon controlled tubular furnace with a temperature between 700 - 1100 °C. To identify phases, XRD analysis was used and to evaluate morphology, SEM and TEM images were used. XRD patterns from synthesized samples with (MASHS) method show a successful composite molybdenum disilicide - titanium carbide synthesis. Results show the best process conditions for synthesis MoSi2-TiC nanocomposite with MASHS method was: milling duration about 4 hours, ball to powder weight ratio 15 to 1, mill rotation speed 300 rpm, constant pressure press 300MPa and temperature 850°C. The grain size calculation by reitveld method showed the size of titanium carbide crystallite and molybdenum disilicide in optimum condition of approximately 28 nm and above 100 nm respectively. The images of SEM and TEM proved that a nanostructure composite has been synthesized.

In this study, UPVC (Unplasticized polyvinyl Chloride) and SAN (Styrene Acrylonitrile) were mixed in the absence and presence of silver and titanium dioxide nanoparticals to prepare UPVC/SAN and UPVC/SAN/Ag-TiO2 blends by solution casting method. The results of FTIR confirmed the blending and compatibility of the mentioned polymers.The mechanical properties of the prepared blends in different weight percentages were studied. Results showed the increasing of the parameters of the tension strength (maximum 25.9% in respect to UPVC), young's modulus (maximum 21.5% in respect to SAN), and breaking length (maximum 75% in respect to UPVC) of blends with respect to pure polymers. Also, the addition of 0.2%wt of silver and titanium dioxide nanoparticals to UPVC-SAN blends caused a decrease in the parameters of young's modulus (maximum 53%), the tension strength (maximum 70%), and an increase in breaking length (maximum 300%) with respect to the blends. In addition, TGA technique confirmed that the addition of nanoparticles improve the thermal stability of blend. Also, scanning electron microscopy (SEM) technique was used to characterize the morphology of the prepared nanocomposite film.