نشریه فرآیندهای نوین در مهندسی مواد
پیاپی 36 (بهار 1395)

In the current research, within purification of apatite stone of Bafg investigated its using in the formulation of white glaze of Single firing of fast fired Wall Tile (Monoporosa Tile). The results of the investigations done on the purificated apatite of Bafg determined that this matter showing good thermal stability under the temperature of 1400 degress centigerate and isn’t any unfavorabale element in its compositon for using in ceramic glaze formulations exception of iron. Nevereless the problem of low Thermal Expansion Coefficient of the white glazes of Monoporosa, The Dilatometry results of the glaze containing Apatite dictated higher Thermal Expansion Coefficient. The images of SEM showed both the safe adhering of glaze to engobe and increment of amount of insoluble fine particles of zircon in the base phase of glaze that with the safe results of colourimetry was the explanatory of increment of the whitness of current glaze. Also by considering the low price of this matter, it wills reduce the final price of glaze.

In this research, welding of Incoloy 925 nickel-iron based superalloy was examined in order to investigate the effect of chemical composition of used filler metals on the microstructure, mechanical properties and corrosion resistance of welded zones. For this purpose, shielding gas tungsten arc welding process and two nickel-base filler metals including ERNiCrMo-3 and ERNiCr-3 were used. Morphological observations showed that at the end of solidification, microstructure of weld metals were stabilized in the form of austenitic with dendritic morphology. In addition, in tensile test although tensile strength of weld metals were lower than Incoloy 925 base alloy but rupture in specimens occurred in heat-affected zone of base metal. In charpy impact test, ERNiCr-3 weld metal was broken by more attracting fracture energy compared to Incoloy 925 base metal and ERNiCrMo-3 weld metal. By performing potentiodynamic polarization test also determined that the corrosion potential difference between base metal and ERNiCrMo-3 weld metal can persuade occurrence of galvanic corrosion in the joint. Finally, with regard to the achieved results, ERNiCr-3 filler metal was diagnosed better selection for welding of Incoloy 925 superalloy.

In the present work, Alumina coating with an approximate thickness of 240 µm was applied via high velocity oxy-fuel (HVOF) method on a 4340 hot-work tool steel substrate. The morphology of the coating and the influences of the corrosive medium which contained hydro-chloric acid (5-15 vol.%) were studied using scanning electron microscope (SEM). Afterwards, the wear behavior of the coatings in dry and acidic wet environments were studied using a pin-on-disk wear apparatus and the wear mechanism was analyzed through SEM studies. The results of the wear tests showed that the wear rate in the 5% acidic medium was approximately the same as that of the dry test. Furthermore, the results showed that increasing the concentration of acid in the wear medium (up to 15%), leads to a continuous increase of the wear rate which was ascribed to increased corrosion rate. The dominant wear mechanism in all the tested situations was determined as sticking wear. As the wear rate increased, the wear surfaces showed increased roughness. Finally, hot corrosion experiments were carried on the coated specimens at the temperature of 880 ˚C. At this condition, the coating lasted for about 460 hours.

In the present study, the HA-TiO2 nanostructured composite coatings with 0, 10 and 20 wt% TiO2 were fabricated by electrophoretic deposition at 20 V for 3 min. Electrochemical corrosion behavior of the samples was conducted in SBF solution at 37oC by potentiodynamic polarization tests. For the effect of titania on apatite formation, electrochemical impedance spectroscopy after in-vitro tests were conducted on coatings. The variation of electrochemical parameters in equivalent circuit with different times of apatite formation was discussed for each sample. The lowest corrosion current density (icorr) and the highest corrosion potential (Ecorr) and linear polarization resistance (Rp) were obtained for HA-20 wt% TiO2 sample. The EIS analysis revealed that the total resistance of HA-20 wt% TiO2 sample is higher than that of other samples. The ICP analysis of Ca2 concentration of SBF solution showed that the highest dissolution rate was achieved for HA sample. The concentration of Ca2 of HA-20 wt% TiO2 sample remained almost constant after 15 days immersion which indicated the accelerated apatite formation. Moreover, the bonding strength of coating was increased by a factor of 2 with the addition of titania in HA-20 wt% TiO2 sample.

The graphite has been generally used as a high-temperature structural material. However, graphite can easily react with oxygen even at temperatures as low as 400 °C. The graded silicon carbide (SiC) characterized by compositional gradation over microscopic distances, is considered to be the most promising coating material in order to prevent the oxidation of graphite. In this paper, SiC coating has been created on five kinds of graphite substrates using a pack cementation method. The relationship between the microstructure and property of graphite substrates and SiC coating was investigated experimentally and theoretically. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis demonstrate that the coating obtained by the pack cementation is a dense structure comprising Si, C and β-SiC. It was found that the kind of graphite has marked effect on the microstructure of SiC coating. SiC gradient coating is expected to form on the surface of graphite with high density, good graphitized, appropriate porosity and the pore radius mainly over the range of 600–710 nm.

In this paper, core - shell nanofibers were synthesized by single stage electrospinning. To achieve on this aim, a coaxial needle was used, and oxides precursor were solved in polyvinyl alcohol (PVA) solution, and injected by separate syringes which connected to one pump. Calcination was done on synthsised core – shell nanofibers. The morphology and microstructure of nanofibers were examined by field emission scanning electron microscope (FE-SEM), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The final structure is ZnO as shell and SnO2 as core. The core diameter and the shell thickness nanofiber from TEM image are approximately 45 nm and 25 nm, respectively. The average diameters of as-electrospun and calcined core - shell nanofibers are about 175 and 79 nm, respectively.

Uses of by product refractories, with quality ulmost look like product with pure material are important. In this project, make different composition with use of phosphate and borate additivies with by product magnesite base, and then do physical experiments and berezil strength. For indicates phase and microstructure use x-rey diffraction (XRD) and scaning electron microscopy(SEM). Conclusions show that composition with 5% Boric acid and 5% borax, are the best composition. Then look like that Boric acid with borax create a amurphos phase that cause to increase strength and physical properties too, already use of pure material is better but refractories mass that get from by product cause to decrease product price and is good for factory. Then all of this properties near project to until prupose for example use in gunning mass.

One of the advanced routes for manufacturing the magnesium-matrix composites is infiltration casting into ceramic foams. In this research, magnesium-matrix composite AZ91-Al2O3 production has been investigated. Therefore, AZ91 alloy molten is prepared by usage of torch furnace under protection of MAGREX flux, then, poured in preheated mold at 250°C with preheated alumina foam at 800 °C. For investigating the effect of pressure, pressures at 50, 75 and 100 MPa in 1 minute applied until solidification was completed. For comparison, similar experiments were done without applying pressure. The results showed that solidification under pressure reduced porosity noticeably in comparison with gravity casting to 60%. By addition the ceramic reinforcement to the base alloy, mechanical strength reduced due to formation of MgAl2O4 spinel phase at interface and formation of residual compression stresses because of thermal mismatch between matrix and reinforcement. The mechanical strength and ductility of the samples are increased by rising of applied pressure to (0-100 MPa) due to decrease grain size and better strength interface of alumina and alloy. Additionally, wear rate due of composite decreased in comparison to base alloy declined markedly (about 53%). This may be due to higher intrinsic alumina strength. Also, by applying pressure on molten metal during solidification, wear rate is noticeably lesser than similar gravity sample due to decreasing the grain size and markedly declining the porosity. The dominant mechanism for base alloy is adhesive wear and for composite is abrasive wear and delamination.

In this study, the new method of via friction stir processing (FSP) was used to create a composite surface layer of Al / Al2O3-TiB2. The microstructural variation, distribution of reinforcement particles and adhesion of the composite layer to the substrate, were investigated via optical and scanning electron microscope. Hardness results showed that the nanocomposite layer hardness was increased for 70% as compared with the primary aluminum and reaches the hardness of 95 in Vickers method due to the grain refinement as a consequence of the dynamic recrystallization and existence of the hard ceramic particles of Al2O3-TiB2. To study the wear behavior of nanocomposite samples, primary aluminum and friction stirred possessed aluminum wear investigated via the reciprocating wear testing machine and the predominant wear mechanisms and wear rate of the samples were compared with each other. The results show a significant increase in wear resistance of nanocomposite layer of Al / Al2O3-TiB2 due to the higher hardness and grain refinement due to the recrystallization in the stirred areas.

This study attempts to investigate the micro structure and wear behavior done on the surface of carbon steel. In doing so, specimens of carbon steel were filled through gas tungsten arc welding (GTAW) applying pulse and continuous currents by filler metal. The cross-section samples were examined by light microscopy and electron microscopy. The hardness test, the hardness of the samples was determined. Pin on disc wear test to evaluate the wear resistance of plain carbon steel specimens coated and welded something done. The wear surfaces were examined by scanning electron microscopy. Therefore, a sample with pulse configuration the lowest wear rate is the highest surface hardness. In order to optimize the welding conditions and the impact of each of the factors used to determine the degree of difficulty in pulsed mode, the Taguchi experimental design technique and the use of S / N ratio have been used. Finally, the overall results of the analysis revealed that the variable factors, peak flow and low flow, respectively, are considered the most influential factors on the response.

In this research, the effect of sodium additive on silicon nitride synthesis has been investigated via carbothermal reduction and nitridation procedures, by using MCM-48 silicate precursor, and saccharose as a carbon agent. In this study, at first mesoporouse silicate has been synthesised, and then binary mixture was prepared by solving MCM-48 and saccharose in deyonized water. In order to investigate the effect of sodium additives, triple systems were prepared by sodium additive (in 1, 2 or 3 weight percent range) in the same time with binary mixtures. Then in temperature of 1400°C nitridation were performed under nitrogen gas atmosphere. Characterization of physical and microstructural properties of mesoporouse silicate and silicon nitride samples performed by various techniques likely X- Ray Diffraction, Scanning Electron Microscopy and Transmission Electron Microscopy. Results shows adding sodium cause to decreasing of liquid phases creating temperature and covering MCM-48 surfaces with this phases and will be prevent the formation of silicon nitride. Also filling the pores with liquid phases cause to prevent the formation of porouse structure.

In current investigation, after SiC coating being applied on carbon-carbon composite by chemical vapor deposition method (CVD), the effect of different parameters on deposition kinetic has been studied. In order to investigate the phases of SiC coating, XRD analysis has been used. Moreover, SEM analysis has been carried out to study the morphology of Carbon-Carbon composite before and after SiC coating being applied. Furthermore, in order to study process exhaust, EDS analysis has been performed. In this regard, the effect of following parameters on deposition rate has been studied: temperature, entrance gas composition, time, and position of sample in reactor. The result of the research shows that, regarding to deposition mechanism; changes of deposition parameter affect the deposition rate. In addition, SEM images demonstrate that the crystal size of SiC and coating thickness in optimum condition of deposition are almost 300 nm and 3 μm consecutively. Finally, through the SEM images, the surface of Carbon-Carbon composite before and after SiC coating has been compared.

In this research, chlorination of chalcopyrite in a low-energy mill was carried out in order to convert chalcopyrite to copper chloride. Chalcopyrite milling was performed at ambient temperature and in different times and dry chlorine gas atmosphere. Also, chlorination process was combined by mechanoleaching using different solvents at different times. X-ray diffraction analysis was used to identify the phases formed in the samples. X-ray diffraction pattern of milled chalcopyrite powders showed that in the low-energy milling, after a specified time, chalcopyrite is converted to chloride of iron, copper and sulfur. Scanning electron microscope images were obtained to evaluate the products morphology and reaction kinetics. Eventually, after 20 hours milling, about 60 percent of chalcopyrite were converted into chlorides.

Boron carbide because of properties such as high hardness, high Young's modulus and low density is highly regarded, however due to difficulties in sintering ability, low fracture toughness and low oxidation resistance at temperatures greater than 1000 ° C, its application is limited relatively. Obtaining a high-density boron carbide by conventional methods is very difficult and costly because of the high melting point, covalently bonded, its low self-diffusion and high vapor pressure. Many of researches have been done to improve the sintering condition by different methods and using various kinds of sintering aids. It is often observed that small amounts of oxides have been more effective on sintering improvement of non-oxidizing ceramics. In this paper, the effect of different oxidizing sintering aids has been reported on sintering behavior and mechanical properties of boron carbide.

In the present study, Ni-P coatings were successfully deposited on mild steel surface via electroless plating. The optimization of heat treatment parameters (i.e., temperature and time) based on response surface methodology has been systematically studied in order to obtain the simultaneously improvement in corrosion resistance and hardness. X ray diffraction analysis (XRD), scanning electron microscopy (SEM) and EDS analysis were used to characterize the coatings. The corrosion behavior of the coatings was evaluated using Tafel polarization method in 3.5 wt.% NaCl aqueous solution. It has been found that the as-plate coating has an amorphous structure and heat treatment caused to precipitate Ni3P phase as well as to form crystalline nickel phase. The corrosion resistance and hardness are strongly affected by heat treatment. By increasing the time and temperature corrosion resistance and hardness firstly increased and then decreased. The results showed that low corrosion rate less than 2 mpy and high hardness value more than 900 vickers were achieved by heat treatment at 450° C for 75 min.

The samples wear tempered at 520-720 °C for 3-10 h and air cooling to investigate the effect of tempering treatment on microstructural evolution and mechanical properties of13%Cr SuperMartensitic Stainless Steel. After heat treatment, hardness and tensile strength tests were performed for investigation of mechanical properties. Moreover, optical microscopy and scanning electron microscopy (SEM) were performed for investigation of microstructure observations. X-Ray diffraction (XRD) was carried out to measure of austenite retained in the samples. The results indicated that the optimization of mechanical properties were achieved by austenitizing treatment at 1050 °C for 1 h and water quenching and then tempering treatment at 600 °C for 3 h with air cooling.The results indicated that the optimization of mechanical properties were achieved by austenitizing treatment at 1050 °C for 1 h and water quenching and then tempering treatment at 600 °C for 3 h with air cooling.The results indicated that the optimization of mechanical properties were achieved by austenitizing treatment at 1050 °C for 1 h and water quenching and then tempering treatment at 600 °C for 3 h with air cooling.

In this paper cement/carbon nanotube mechanical properties were predicted by micromechanical model. The effects of CNT properties such as internal, external diameters and its length as well as its volume percent on Young's modulus were investigated by this model. In addition, the effect of representative volume element (RVE) element shape (cylindrical, cubic and hexagonal) on Young's Modulus (E) was studied systematically. Finally, the predicted results were compared with cement /CNT experimental results. The predicted results showed that by increasing external CNT diameters, CNT Volume percent and its length, Young's Modulus (E) was increased. However, the internal diameter of CNT didnt have significant effect on E. These data indicated that hexagonal element shape resulted higher E rather than square and cylindrical RVE shape. Comparison of predicated E and experimental E showed that the proposed model could predict young modules with high accuracy. These results showed that micro mechanical modeling is a valuable method for predication of cement/CNT mechanical properties in nanoscale.