مجله مواد نوین
سال ششم شماره 3 (پیاپی 23، بهار 1395)

Electrolytic plasma galvanization is one of the newest methods for corrosion protection of steels. In this research, Plasma electrolytic (PE) method were used for zinc deposition on st12 steel. Work-Pieces were connected to the cathode of high voltage direct current source and were placed inside electrolyte. Sodium hydroxide alkaline solution including 3 wt% zinc dissolved in saturated HCl acid and 30 wt% ZnSO4 solution were used as electrolytes and NaCl were added to increase the electrical conductivity. Surface morphology and composition of coatings was analyzed by SEM and EDAX. Corrosion behavior was also evaluated by DC polarization in 3.5 wt% NaCl.Results showed that zinc deposition formed broccoli type morphology coating because of the plasma spark actions. Corrosion resistance of steel increased by zinc coating to the more active potential and changing of electrolyte type from ZnSO4 to alkaline (zinc ion saturated) solution increased electric conductivity and so PE process current increases to 3A and initial spark generation voltage decreases to 50 V.

A suitable bond coat to control the spallation is recommended for increasing service life of the coatings. Using modified aluminide coatings as a bound coat has become a common approach nowadays. In this work, a zirconium modified nickel aluminide coating was formed by pack cementation process and the effect of the percentage of aluminum in Al-Cr alloy, which was used as the source of aluminum in coating process, was studied. ZrOCl2.8H2O and alumina were also used as activator and filler material, respectively. Cyclic high-temperature oxidation test was carried out at 1100 °C. Each cycle was consisted of one hour heating in furnace and 10 minutes cooling in the air. Microstructures of the coatings were investigated by means of SEM. EDS analyses were carried out to specify chemical composition of different layers of the coating. Phase analysis was examined by XRD. The results confirmed that the coatings produced by high activity of aluminum source, showed higher resistance to cyclic high-temperature oxidation.

The effect of strain rate on the hot tensile behavior of Invar alloy was studied and determination of fundamental equations by hot tensile tests over temperature range of 850- 1150 °C and at strain rates of 0.01, 0.1, 1 s-1 were carried out. The stress-strain curves and structure of sample after fracture was investigated. It was found that grain boundary sliding was the major mode of intergranular failure in the Invar alloy. In this alloy, increasing the strain rate is found to improve ductility. The experimental data of flow stress were constitutively analyzed and the apparent activation energy of deformation was estimated to be 411.5 kJ/mol.

The precipitation behavior and the hardness evolution of AA2024 under severe plastic deformation (SPD) and natural ageing have been studied. During SPD process, GPB zones/Cu-Mg co-clusters are dynamically precipitated. This is confirmed by elimination of GPB zones/Cu-Mg co-clusters formation effect in differential scanning calorimetery (DSC) study of deformed and undeformed samples. The occurrence of GPB zones or Cu-Mg co-clusters formation during SPD process reduces natural ageing kinetics of deformed samples. The formation of metastable phases at strain ~ 1 has been privileged in comparison with that of stable phases.

Flexural properties of milled E-glass, S-glass, and high strength carbon fiber reinforced epoxy composites have been studied. As received fibers were chopped and milled by an attrition mill, and their morphologies were evaluated by Scanning Electron Microscope (SEM). The epoxy composites were prepared simply by mixing and stirring 1wt.% of the milled fibers with a conventional hot-cure epoxy resin. The effects of resin system degassing and employing a coupling agent (γ-aminopropyltriethoxysilane or γ-APS) were evaluated based on the flexural properties of the epoxy composites. The SEM micrographs of the fracture surfaces were used to investigate the active toughening mechanisms. The most appropriate flexural properties were obtained for the degassed and modified milled E-glass fiber reinforced epoxy. Its bending strength and tangent modulus of elasticity were enhanced up to 1.22 and 1.20 times in comparison to the pristine one. The current study shows that the composite not only is cost effective, but also offers higher flexural strength and tangent modulus of elasticity

In this study the electrochemical behavior of the imidazole as a self -assembled inhibitor on hybrid coating prepared by sol - gel with immersion method on carbon steel deposition was studied. It was observed that corrosion resistance of coating based on hybrid 3-methacryloxy propyltrimethoxysilane significantly increased in the presence of imidazole inhibitor. In order to prepare hybrid coatings 3-methacryloxy propyltrimethoxysilane specified ratios were combined with ethanol and distilled water. Mild carbon steel before applying the hybrid coating was immersed in different concentrations solutions of 0.001, 0.01 and 0.1 M of imidazole inhibitor. Self-assembled film of imidazole was formed on the surface of the substrate. The morphology of the coating was studied by scanning electron microscopy. The impact of the self-assembled film of inhibitor was examined on anti-corrosion properties of coating for different concentration of inhibitor in hydrochloric acid as well as corrosive environment. Potentiodynamic polarization test and SEM technique characterization were compared by original carbon steel samples. It Was determined that adding the corrosion inhibitor to protect system of the carbon steel, the inhibition efficiency improved corrosion resistance up to 97% in 0.5 M of hydrochloric acid.

Depending on the casting conditions and alloy composition, microstructure and properties of the aluminium alloys will be different. Generally Al–Ti and Al–5Ti–1B master alloys are added to the aluminium alloys for grain refinement. In recent years computer-aided cooling curve analysis (CA-CCA) has been used extensively in metal casting industry to predict microstructure constituents, grain refinement and to calculate the latent heat of solidification. The aim of this study is to investigate the effect of cooling rate and grain refinement on the microsructural characteristics of Al-Cu alloys by cooling curve analysis. To do this, Al-Cu alloys containing 2.2, 3.7, and 4.8 wt.% Cu were melted and solidified with 0.04, 0.19, 0.42, and 1.08 K/s cooling rates. The temperature of the samples was recorded using a K thermocouple and a data acquisition system connected to a PC. Some samples were Grain refined by Al-5Ti-1B to see the effect of grain refinement on the aforementioned properties. The stractural results show that grain size and secondary dendrite arm spacing decreased by increasing of cooling rate and grain refinement. Thermal analysis results showed that, in a well refined alloy, nucleation will occur in a shorter time, and a undercooling approximately decreases to zero.

Permalloy (80%wt. Ni, 20%wt Fe) coatings were electroplated in 25°C by applying current density of 100 mA/cm2 in a bath with the pH of 3.8. A mechanical stirrer (160 RPM) was used during 8 hours electroplating. Saccharin was used as a stress reducing agent and a grain refiner to gain nanocrystalline coatings. The pH of plating was controlled by boric acid as a buffer. The SEM images of surface of coatings indicated the different processes of forming the cauliflower structure including nucleation, three dimension growth and integration of crystals. To study the effects of different parameters on the roughness of coatings, various temperatures (25, 45, 75°C), different times (3, 8 hours), different amounts of saccharin in the bath (10, 5, 3, 1g/L) and two different types of agitation (magnetic and mechanic stirrer) were investigated. The results of roughness test showed that decreasing the plating time and the amount of saccharin in the bath decrease the surface roughness. In addition, increasing the temperature and using magnetic stirrer caused a decline in the surface roughness. Increasing the temperature would also change the alloy composition.

In this research friction stir processing (FSP) was used to produce surface composite layer with zirconia reinforcement particles on aluminum AA5086 alloy. The effect of the combination ratio of ZrO2/Graphite powders on microstructure and hardness of surface hybrid composite layer fabricated by friction stir processing on aluminum alloy was investigated. A H13 work steel tool with taper cylindrical pin geometry was used to produce hybrid composite layer. The FSP parameters were 1250 RPM in rotational speed and 50 mm/min in traverse speed of tool. Microstructures of produced samples were evaluated by means of optical microscopy and distribution of particles was evaluated by scanning electron microscopy. The hardness of surface composite layer was characterized using vickers hardness test. The results revealed that FSP caused to grain refinement and by increasing the passes of process to three passes on fabricating surface composite, distribution of zirconia particles on matrix has improved. The maximum of hardness value was achieved by producing surface hybrid composite (15%ZrO2/15%Gr). X-ray diffraction studies were carried out in order to identify the phases present in the stir zone of the specimens. The results showed that no reaction occurred between the aluminum matrix and the reinforcement particles during three FSP passes.

The high strength micro alloyed steels befor welding are prepare with hot or cold rolling. After welding, the weld metal region heat-treated to provide good mechanical properties. The heat treatment is annealing and reheating to different peak temperatures then cooling down very slowly in the furnace to achieve the best fracture strength. In this research, the Charpy impact were used to evaluate the fracture resistance of the weld of metals. The optical microscopy and scanning electron microscopy were used for study of the microstructure before and after apply of thermal cycles. According to results the optimum resistance to fracture was shown in the cycle of annealing to peak temperature of 950 °C and reheating in the second cycle to temperature peak of 650 °C. The thermal cycle of the final microstructure consists of pearlite/ bainite and polygonal ferrite along with a large number of metal oxide impurities. Evaluation of fracture surfaces indicate that the microstructure of pearlite/bainite and polygonal ferrite as compared with only ferritic/pearlitic has shown more ductile fracture. The samples with the highest fracture resistance has shown low hardness in comparison with other samples that were heat treated.

With increasing sintering temperature, liquid is pulled down by gravity and it causes porosity elimination at this area. The difference in liquid volume fraction makes microstructural gradient from up to bottom of sintered compacts. In this paper the influence of gravity on shape and also microstructure evolution of compacts was studied. Cu-10Sn-10Pb samples were sintered at the range of 890-970°C for 20 min. The in situ images from samples were taken at various sintering conditions. It is concluded that distortion increases from top to bottom sections of samples due to viscosity reduction and the weight of upper sections. Liquid volume fraction at the bottom increases with increasing sintering temperature and finally elephant foot profile is appeared. Lead plays an important role in fragmentation and rearrangement of bronze particles and this affects on shape and microstructure during sintering.

In the present research , synthesis of nano structure SiC in presence of high surface area of mesoporous carbon(CMK-1) were investigated. To synthesis SiC ,leached and cation exchanged zeolite were used with sucrose and mesoporous carbon. Samples with carbon ,type of carbon and processed zeolite ,fired at 700-750oc under argon diffrents of amount atmosphere with 50C/min heating rate and soaking time about 3hrs were prepered. XRD and XRF analysis were carried out on natural zeolite. To characterize the CMK-1 XRD,SEM/EDX with BET were used. Moreover to characterize ,leached and cation exchanged zeolite SEM/EDS and XRD analysis were used. XRD results showed that the amount of mesoporous carbon as well as the type of processing of zeolite had the main role in synthesis of high purrity SiCs. XRD and SEM/TEM studies showed that Nano structure of SiC was produced in the process.