مجله مواد نوین
سال چهارم شماره 4 (پیاپی 16، تابستان 1393)

In this study، aluminum matrix nanocomposite reinforced with silicon dioxide nanoparticles (SiO2) were produced using ultrasonic technique and then using TiH2 foaming agent fabrication of aluminum nanocomposite foams by melt rout process was carried out. Furthermore، microstructural analysis using optical microscope and scanning electron microscope to ensure the production of nanocomposite foam and evaluation the role of nanoparticles on morphology and cell wall thickness. Liquid drainage during foaming process was studied with computer softwares. The results revealed multifaceted structures of cells and appropriate distribution of nanoparticles in cell walls using microscopic evaluations. Also، it was observed that the thickness of cell walls and plateau borders area changes from foam surface.

Composites constitute a new class of materials، which are mostly used for mechanical and tribological applications. Among these materials، copper deposits with incorporation of hard ceramic particles such as boron carbide (B4C)، combine good mechanical properties (due to the presence of B4C)، with high electrical and thermal conductivity (due to the presence of Copper). The purpose of this study is to apply the copper coating on boron carbide particles by electroless method and study the effect of time of sensitization and activation processes and also electroless bath temperature on the amount and uniformity of the Cu Coating. Times 30، 60 and 80 minute to evaluate the effect of time of sensitization and activation processes has been considered، also temperatures 25،50 and 75 degree centigrade were selected to evaluate the effect of electroless bath temperature on copper deposition of ceramic particles. The effect of time of sensitization and activation processes has been studied using SEM، and the effect of electroless bath temperature has been investigated by XRD، SEM and Atomic Absorbtion analysis. The results showed that the optimum time of activation and sensitization was 80 minutes and the optimum bath deposition temperature at pH 12 and time of deposition 60 minute، was 75 degrees centigrade.

In the current investigation a Ni-B-Al2O3composite coating was fabricated through electroless method and the effects of heat treatment on microstructure، hardness and tribological properties was studied. Electroless Ni-B-Al2O3 coating of 30 µm thickness was applied on the surface of Ck45 steel. Following that، the coated samples went through heat treatment for 1 h at 400 ˚C. X-ray diffraction and scanning electron microscopy were utilized in order to characterize the coating. Tribological behavior and hardness of the samples were studied by means of pin on disk and Vickers microhardness measurement device. The results revealed that the addition of Al2O3 particles leads to grain refinement and consequent microhardness elevation. Moreover، heat treatment resulted in nanocrystalline structure، therefore، hardness and wear resistance of the coating improved due to transformation of amorphous phase to crystalline structure and production of Ni3B phase.

One of the main problems with stainless steels is their sensitization during fabrication or conditions under which they are utilized. Thus determining the degree of sensitization (DOS) is very crucial. To change the DOS of the specimens، heat treatment was conducted at 500-800 for 24 h. In this paper the Double loop electrochemical potentiokinetic reactivation test (DLEPR) and anodic polarization tests were first conducted at 25 in a 0. 5 molar sulphuric acid containing 0. 01 molar KSCN for AISI 316 sensitized specimens، the potential range related to transpassive region of each specimen was determined. The electrochemical impedance test in the potentials related to this region and in the frequency range 0. 01-100000Hz was performed. The results were indicative of the presence of three different regions namely the anodic dissolution of the passive layer، dissolution of the grain boundaries and the occurrence of pitting corrosion due to the variations in the anodic potential. The healing effect was observed at the temperatures above 600 for this alloy. By performing the Electrochemical Impedance Spectroscopy (EIS) tests in the potentials related to the dissolution of the passive layer at the grain boundaries، the sensitization of the alloys was determined.

Marine structures in addition to sustain water hydrostatic pressure should be as far as possible resistant against the loads resulting from underwater explosions. The ratio of strength to weight of these structures should be high as far as possible، so the designed structure in terms of materials، energy and the cost would be optimized. In this paper at first a method for simulation of underwater explosion phenomena in the ABAQUS software environment is presented and by using available experimental results، this method is verified. Then، by using this method the dynamic behavior of the composite structure subjected to underwater explosion is investigated. In following، an algorithm is presented by which the weight of plate can be optimized by using genetic algorithm through change of the angle and thickness of composite plate، in conditions that structure against underwater explosion load would not be fractured. Results show that the presented algorithm can optimize the composite structure weight. Upon to 38% weight reduction، the structure is still resistant against the explosive load. According to low weight to strength ratio of composite structures، they have many applications in military and marine industries. The presented method can be used to optimize the weight and strength of marine structures subjected to underwater load.

In this paper، the cordierite bonded porous SiC composites were prepared by a reaction bonding method. For this reason، SiC، talc and kaolin as raw materials، using graphite and poly urethane sponge as the pore-forming agents were used for the preparation of these composites. The effects of raw materials type and content، silicon carbide content and type and content of pore-forming agent on the properties of these composites after firing at 1250 °C were investigated. Hence، the physical and mechanical properties، thermal shock resistance، refractoriness under load، phase composition and microstructure of these composites were evaluated. The results showed that raw materials type and composition have effects on the formation of cordierite phase drastically. The cristobalite، corundum، primary and secondary mullite phases can form in composite besides of cordierite which their contents depend on raw materials and silicon carbide content. Besides، type and content of pore-forming agent have a great effect on the mechanical strength of these composites. The best results were obtained with composition containing 30 wt. % graphite and 60 wt. % silicon carbide. The microstructural investigations showed that a proper cordierite-mullite bonding was formed between silicon carbide particles.

Titanium alloys are widely used in many fields such as the automotive، aerospace and chemical industries. In some applications، titanium alloys are needed for use with particular welding methods. These are GTAW، GMAW and laser welding. In this study، titanium Grade- 2 (Cp-Ti) plates were welded using Laser welding and GTAW. Tensile and flexural tests were applied to the welded samples. The microstructure and SEM images of main material and welded regions were studied and micro hardness measurements were performed. Tensile and flexural strengths of laser welded samples were higher than GTA welded samples. The micro hardness values of the weld-zone of laser welded samples were lower than the GTA welded samples welding zone. In microstructure and SEM investigations، oxide structures and the splashes of molten metal appearing like drops were identified. The width of the weld- zone in laser welding was in a narrow range.

In this paper removal of methylene blue dye from wastewater was studied. Separation was studied by adsorption batch method. Adsorbent is tassel that is an agricultural waste. The effect of temperature، time، pH and solution volume on adsorption was investigated. This adsorbent was eluted and treated by Ethylenediamine 1M for 60 min. The best fitted isotherm model was Langmuir and maximum capacity was obtained 166 mg dye on 1g adsorbent. The best kinetic model was pseudo second order model.